Radio Frequency and Infrared Drying of Sized Textile Wrap ...infohouse.p2ric.org/ref/39/38698.pdf · Technology utilization End ... and finishing of the cloth can help keep the U.S

EPRl Electric Power Research Institute

Topics: Textile processing Electrotechnology Technology utilization End use Energy efficiency

EPRl CU-7006 Projects 2893-6, -8 Final Report November 1990

Radio Frequency and Infrared Drying of Sized Textile Warp Yarns-

Prepared by West Point Foundry and Machine Company West Point, Georgia and Auburn University Auburn, Alabama

R E P O R T S U M M A R Y SUBJECT Industrial

TOPICS Textile processing End use Electrotechnology Energy efficiency Technology utilization

Customer service and marketing managers I

AUDIENCE

Radio Frequency and Infrared Drying of Sized Textile Warp Yarns Drying sized textile warp yarns without contacting the warp is easily accomplished by either radio frequency or infrared techniques. Although the process is more expensive than conventional drying, the substantial savings accrued during subsequent weaving and finishing of the cloth can help keep the U.S. textile industry competitive and support electrical load.

BACKGROUND The key to high productivity in the manufacture of textiles is to maximize the efficiency of the weaving looms. To speed operation of the looms, warp threads are coated with starch or polyvinyl alcohol, which act as stiffening solutions (or size) to reduce yarn hairiness and provide added strength. In conventional practice, warp threads are dipped in liquid size and dried over Teflon-coated cylinders heated internally by steam. Disadvantages of contact drying with steam cans include (1) overheating and subsequent weakening of the threads during the slowdowns necessary to repair thread breaks and (2) the need to add waxes to the size to prevent threads from sticking to the cylinders. Weakened threads cause loom stops, whereas wax additions increase the cost of the size formulation, the quantity of size required, and the expense of a downstream finishing operation to remove the wax.

OBJECTIVES

APPROACH

RESULTS

To demonstrate the ability of radio frequency (RF) and infrared (IR) technology to dry warp size in a noncontact mode and to evaluate the economic benefits of such processes.

The project team modified two Calloway slashers (laboratory sizing machines) to dry 6-in. warp, first with a 12.5-kW RF dryer and then with a 20-kW IR dryer. Based on results of the laboratory investigation, they calculated the overall economic benefits of the new technologies.

Both RF and IR heaters in the laboratory tests dried the warp size. The RF dryer, however, was much easier to control because of its self-limiting action, and the IR system required careful application of power to prevent burning the threads during changes in speed. The properties of the thread,

EPRl CU-7006s Electric Power Research Institute

such as strength and hairiness, remained the same during both contact and noncontact drying.

A subsequent economic analysis demonstrated that capital and operating costs of RF and IR dryers were six to seven times greater than those associated with conventional steam can drying. Savings come from the reduction of size and elimination of both the wax and the wax removal process. Overall, simple payback for RF equipment occurred in one and a half years; simple payback for IR equipment took just half a year.

EPRl PERSPECTIVE The textile industry is a major employer in some parts of the United States and is under considerable competitive pressure from overseas manufacturers. This study provides the industry with good bottom-line information on new electrotechnologies that may increase productivity and reduce costs. The next step is to demonstrate the savings in a mill by adding an RF or IR heater in parallel with a full-scale steam can dryer so that either system may be operated individually and the results compared.

PROJECTS RP2893-6, RP2893-8 EPRl Project Manager: K. R. Amarnath Customer Systems Division Contractors: West Point Foundry and Machine Company; Auburn U n ive rsi ty

For further information on EPRl research programs, call EPRl Technical Information Specialists (415) 855-2411.

Radio Frequency and Infrared Drying of Sized Textile Warp Yarns

CU-7006 Research Projects 2893-6, -8

Final Report, November 1990

Prepared by

WEST POINT FOUNDRY AND MACHINE COMPANY 301 West Tenth Street

West Point, Georgia 31833

Principal Investigator H. G. Ruddick

AUBURN UNIVERSITY Auburn, Alabama 36830

Contributors W. S. Perkins M. W. Reed

R. M. Broughton, Jr.

Prepared for

Electric Power Research Institute 3412 Hillview Avenue

Palo Alto, California 94304

EPRl Project Manager K. R. Amarnath

Industrial Program Customer Systems Division

ORDER I N G I N FORM AT1 0 N

Requests for copies of this report should be directed to Research Reports Center (RRC), Box 50490, Palo Alto, CA 94303, (415) 965-4081 There IS no charge for reports requested by EPRl member utilities and affiliates, U S utility associations, U S government agencies (federal, state, and local), media, and foreign organizations with which EPRl has an information exchange agreement On request , RRC will send a catalog of EPRl reports

Electric Power Research Institute and EPRl are registered service marks of Electric Power Research Institute. Inc

Copyright 0 1990 Electric Power Research Institute. Inc All rights reserved

NOTICE This report was prepared by the organization(s) named below as an account of work sponsored by the Electric Power Research Institute Inc (EPRI) Neither EPRl members of EPRl the organization(s) named below nor any person acting on behalf of any of them (a) makes any warranty express or implied with respect lo the use of any information apparatus method or process disclosed in this report or that such use may not infringe privately owned rights or (b) assumes any liabilities with respect to the use of or for damages resulting from the use of any information apparatus method or process disclosed in this report

Prepared by West Point Foundry and Machine Company West Point Georgia and Auburn University Auburn Alabama

ABSTRACT

As the speed of textile looms increases, improved methods of preparing warp yarns for weaving are

required. In this report, laboratory studies of RF and IR drying of slasher sized warp yarns made by

Auburn University were analyzed to determine the application of this technology to production equip-

ment. Yarn qualities, production capacities, energy consumptions, and economic considerations are

discussed. Inputs for this study included information from academic institutions, chemical suppliers, equipment suppliers, electric utilities, textile machinery manufacturers, and fabric manufacturers.

Analysis indicated that when the entire cost of fabric formation is included, RF and IR technology

may be of benefit in drying sized textile warp yarns.

... 111

FOREWORD

This project was undertaken to determine whether new electrotechnology could offer any benefits to

the traditional process of drying sized warp over steam cylinders. Laboratory studies of radio frequency and infrared heating proved that both of these processes would dry the size without degrad-

ing the yarn. Unfortunately, non-contact processes did not iinprove yarn properties as was hoped for

at the outset. The electrical processes were considerably more expensive than the conventional

steam cylinders, but they offered the promise of even greater savings in downstream processes

because they were non-contact dryers that could start and stop quickly. If these downstream sav-

ings can be achieved in actual operations, the radio frequency equipment would pay for itself in 1112

years and the infrared equipment would pay for itself in year. The next step in the program is to develop additional laboratory confirmation that projected savings are, in fact, obtainable. After this

confirmation, a program can be considered to demonstrate the new technology in a full-scale mill

application to evaluate the process and to confirm the downstream savings.

To provide meaningful "bottom line" information to prospective users of the new technology, EPRl

utilized a team effort between the Auburn University researchers, who generated the technical data

in their laboratories, and an experienced manufacturer of sizing equipment, West Point Foundry and

Machine Company, who provided the overall interpretation of those data.

K. R. Amarnath, Project Manager

Customer Systems Division

V

b

ACKNOWLEDGMENTS

The principal investigators are grateful to those members of industry who contributed their time to

provide the information which is the foundation of this study.

Mr. Lee Lemere

Dr. Roy Broughton Dr. Yehia El Mogahzy

Prof. Warren Perkins

Dr. Morton Reed

Mr. James Parker Mr. Wm. Sibley

Mr. Donald L. Nehrenberg Mr. John Trembley

Mr. Gary Birdwell

Mr. Bill Studstill

Mr. Sterling Pitts

Mr. Stephen L. Salaun

Mr. Marty Ellis

Mr. Mitch Strause

Mr. James Farrington

Mr. Roger Benjamin

Mr. George White

Mr. Coen Hupkes

Mr. John Zimmerly

Mr. Robert W. Singleton

Mr. Clint Caban

Mr. Clint Moody

Mr. Jim Spann

Mr. John Strandberg

Mr. Tony Koral

Mr. George M. Thorn

Mr. Barrie Tweedle

Mr. Robert McCullough

Air Products and Chemicals, Inc.

Auburn University Auburn University

Auburn University

Auburn University

Carolina Power and Light Co.

Computer Control + Integration, Inc.

E. I. DuPont de Nemours & Company Entron Technologies, Inc.

Georgia Power Company Georgia Power Company

Glenro, Inc. Impact Systems

Institute of Textile Technology

Institute of Textile Technology

J. P. Stevens Company

Kell Chemicals

Ntronix, Inc.

Panel Technology

PSC, Inc. Radiant Heat, !nc.

Radio Frequency Corp.

Russell Corp.

Russell Corp.

Strandberg Engineering Laboratories, Inc.

Strayfield International Ltd.



Textile Consultant

vii

Mr. Robert Dachert

Dr. Richard Smith

Mr. Ronald Lutz Mr. M. R. Sanio

Mr. Frank Smith Mr. Gayron Davis

Mr. Carl Summers

Thermex Thermatron

Thermo Energy Company

Tennessee Valley Authority University of Texas at Austin

W. T. LaRose & Associates, Inc.

WestPoint Pepperell, Inc.

WestPoint Pepperell, Inc.

We would also like to express our appreciation to TVA for permission to report on the RF experiments at Auburn (Appendix A) which were sponsored by them under TVA Contract No. 68097.

viii

c

CONTENTS

Section

Summary

Introduction

Results and Discussion

Recommendations for Further Study

References

APPENDIX A - Report Radio Frequency Drying of Textile Yarns in Sizing

APPENDIX B - Infrared Drying of Textile Yarns in Sizing

!?iXl!2

1-1

2-1

3-1

4-1

5-1

A- 1

B-1

ix

ILLUSTRATIONS

Fiaure !me 3-1

3-2

3-3

3-4

3-5

3-6

3-7

3-8

Callaway Laboratory Slasher Equipped for Radio Frequency Drying

RF Dryer and Generator Installation on Callaway Laboratory Slasher

3-1

3 -2

Detail of RF Applicator 3-3

Fringefield Electrode Assembly Detail 3-3

Callaway Laboratory Slasher Equipped for Infrared Drying 3-5

IR Dryer Installation on Callaway Laboratory Slasher 3-6

Detail of IR Dryer 3-6

3-7 West Point Production Cylinder Slasher

xi

TABLES

Table

3-1

3-2

3-3

3 -4

3-5

3-6

3-7

3-8

3-9

3-1 0

3-1 1

3-12

3-13

3-14

Production and Drying Requirements for a Typical Sheeting Mill

Estimate of Energy to Dry 1 Ib Warp

Dryer Energy Comparison

Dryer Cost Comparison

Dryer Energy Cost Comparison

RF and IR Maintenance Cost Comparison

Operating Cost Comparison

Estimate of Potential Size Savings

Estimate of Savings in Finishing Resulting from Removal of Wax

Calculation of Possible Savings through Elimination of Overdrying

Investigation on the Effects of Overdrying on Weaving

Calculation of Possible Savings through Elimination of Overdrying

Overall Cost of RF and IR Drying Compared to Cylinder Drying

Potential Annual Savings of RF and IR to Cylinder Drying

!!!%E

3-8

3-9

3-10

3-1 1

3-1 1

3-12

3-13

3-14

3-14

3-15

3-16

3-18

3-20

3-20

xiii

Section 1

SUMMARY

Historically, sheets of warp yarn are prepared for weaving by the application of an abrasion resistant

coating of size material. Such a coating is applied as a liquid and dried with cylinder dryers in a

slasher. The very best preparation of warp yarns for weaving is required for today’s high speed

rapier, projectile, and air jet looms.

In an effort to improve the quality of sized warp yarns, the Textile Engineering Department at Auburn

University investigated in their laboratory the use of RF and IR slasher drying. These Auburn studies

determined there is no significant physical differences between sized yarns dried by RF, IR, or

conventional heated cylinders.

When only the sizing or slashing process is considered, this study did not show an economic

justification for direct replacement of cylinder dryers with either RF or IR drying methods. It was felt,

however, use of the unique properties of RF and IR drying in slashing could possibly provide savings in other areas of fabric formation and finishing.

For some time, it has been felt yarn degradation due to overdrying occurs at slasher creep speed

with subsequent additional loom stops during weaving.(l ) When used as supplemental heating

sources to less expensive conventional cylinder dryers, the low thermal inertia of RF and IR drying

systems may minimize the effects of warp yarn overdrying at creep speed. It had also been proposed that RF and IR noncontact drying may eliminate the need for wax additives to size

formulas.(l) These additives prevent sticking of sized warp yarns to heated drying cylinders. The

removal of wax additives could also have an impact on finishing costs since scouring to remove

waxes from finished fabric would no longer be necessary.(2)

This study shows that when RF and IR drying is considered from an overall fabric formation and

finishing point of view, the potential savings in weaving, sizing chemicals, and fabric finishing more

than offset the higher costs of drying using RF and IR. If the projected savings can be realized,

payback for the RF and IR equipment is estimated to be 11/2 years and 1/2 years, respectively. If

further study confirms the promise of cost benefits, a full scale mill trial can be considered to deter-

mine downstream benefits.

1-1

Section 2

INTRODUCTION

As the speed of weaving increases with the introduction of newer and faster weaving machines,

increased stresses placed upon the yarn ends require superior yarn preparation for weaving. One of

the most common stoppages during weaving is when one or more of the warp yarn ends break as

they are shifted to allow insertion of filling yarn. Another common stoppage of air jet weaving ma-

chines is when filaments or hairs protruding from the warp yarns prevent the filling being inserted by

a jet of air from reaching across the fabric being woven. These stops are called “warp related filling

stops”. These warp and warp related filling stops directly affect weaving efficiency and fabric quality

and therefore the cost of weaving. As a result, the textile industry and manufacturers of sizing

machines have focused on improving the uniformity and quality of the abrasion resistant size material

coating applied to the yarns with a sizing machine or “slasher”.

It has been anticipated that improved methods of drying sized warp yarns after immersion in liquid

size baths would produce warp yarns with a better encapsulation of size material and less hairiness.

A warp yarn with such properties, it was reasoned, would weave better if all other properties re-

mained unchanged.

Although it is anticipated that substantial savings can be realized in weaving by the presentation of better prepared warp yarns to the weave room, it is also obvious that the introduction of RF and IR

drying technology will cause changes in size application costs before weaving and fabric finishing costs after weaving.

It is a common practice to mix wax additives into liquid size formulas containing polyvinyl alcohol

(PVA) as a film former. These additives are said to provide a release agent to prevent sized yarn

being dried from sticking to the entering Teflon-coated drying cylinder.(l) It has been proposed that

warp yarns partially dried without contact to drying cylinders will not need a wax release agent added

to the size formula to prevent sticking during subsequent cylinder drying. Although wax additives do

provide lubrication for weaving, synthetic substitutes are available for this purpose. As the addition

of wax reduces the tensile strength of the size film, it has been proposed that 25 percent less size

material will be required if waxes are eliminated.(l) It is also possible the removal of wax additives

from size formulas can reduce the cost of finishing by eliminating the need for scouring the wax from the fabric.(2)

2-1

It has been suggested that RF and IR drying might yield improved quality or “hand” of the woven

fabric. In search for the answers to many of the above questions, the Department of Textile Engi-

neering at Auburn University, under contract to the Tennessee Valley Authority, investigated thc use

of RF drying of sized warp yarns.(3) An additional study was conducted on the use of IR and RF

slasher drying under contract with EPR1.(4) Both studies involved the use of laboratory scale slash-

ers and the evaluation of properties of sized w x p yarns dried with RF, IR, and conventional heated cylirlder methods. The strength, elongation, abrasion resistance, and hairiness of the RF and IR

dried yarns were measured by Auburn University and compared to control samples of warp yarns

dried by conventional contact cylinder dryers. These two studies are included as Appendices A and

€3 to this report.

The above studies were analyzed by West Point Foundry and Machine Company to determine if

reductions in the overall cost of fabric formation could be realized by applying RF or IR drying in

slashing. The impact of RF and IR dryers on slasher capital expenditures, energy requirements, and

slasher dryer maintenance costs were calculated and sompared to conventional sizing processes.

In addition, the impact of RF and IR drying to weaving, chemical usage, and fabric finishing costs

were investigated.

2-2

Section 3

RESULTS AND DISCUSSIONS

Two separate laboratory investigations were conducted at Auburn Universit: to stud! new methods

of drying sized textile warp yarns. The initial study was made to evaluate RF slasher drying.(3) A

second study investigated IR slasher drying.(4)

RF Drying Study

The RF dryer study involved retrofitting a Callaway slasher with an RF dryer powered by a 12.5 kW

RF generator. A diagram of the Callaway slasher is shown in Figure 3-1. The RF dryer and genera-

tor installation is illustrated in Figure 3-2.

TAKE up

0 0 0

3 0 0 0

RADUNT H A T SECTION

L i 01

3 c o I

i 0 0 0

W T H A T KCTK)N

SCWEZE ROUS

Figure 3-1 Callaway Laboratory Slasher Equipped for Radio Frequency Drying

3-1

RF Applicator

Power Supply q E I e c t m d e s r 12.5 kw, 22MHz

-Yarn Path

Figure 3-2 RF Dryer and Generator Installation on Callaway Laboratory Slasher

The RF applicator illustrated in Figure 3-3 contains two sets of oppositely charged electrical ele-

ments. These elements are supported by rails in a vertical ladder like configuration. The positive

elements are insulated from the applicator enclosure. RF power supplied from an adjoining genera-

tor (not shown) produces a fringefield effect as seen in Figure 3-4. The yarn drying paths are ar-

ranged with movable rollers so the distance between the moving yarn and elements can be varied.

3-2

NULATOR-

W O R T FORT UECTROMS

- . / V Z ' MA.

A L W RODS 25 PLACES

NEGATIVE ELECTRODES

Figure 3-3 Detail of RF Applicator

I I : + /

Figure 3-4 Fringefield Electrode Assembly Detail

3-3

-

In an RF applicator the elements act like a condenser or capacitor with a dielectric between them.

As the voltage alternates, the charge alternates. In the RF applicator used in the Auburn study, the

voltage and charge alternated at 22 MHZ. As molecules within the dielectric try to align themselves

with the alternzting field their motion generate heat. Molecules of water carried by the yarn into the

fringefield are likewise excited generating heat for their evaporation.

For this study, a cotton polyester yarn was chosen of the type typically used in textile mills to weave

large quantities of bed sheeting. Laboratory conditions were adjusted to best approximate mill conditions.

The Auburn study revealed no significant differences in strength, abrasion resistance, and hairiness

between yarns dried by RF and conventional methods. There was, however, a desirable increase of

residual elongation noted in yarns dried by RF. Auburn was not able to ascertain whether these

changes were a result of RF drying or laboraiory procedures.

Other findings by Auburn included:

1.

2.

3.

4.

5.

Radio frequency drying of warp yarns is a self-limiting process whereby the heating due to the RF

essentially ceases whr n the yarn reaches approximately 2% moisture content.

Prolonged stopping of the yarn in the RF field did not seem to have a measurable affect on yarn

strength or abrasion resistance. (However, it was noted that prolonged exposure to drying by

either RF or conventional cylinder drying caused an undesirable reduction in residual elongation

of sized yarn.)

The relationship between warp yarn drying and steady state power utilization became nearly

linear as the air gap between the yarn and RF drying elements was decreased. An air gap of

approximately .2 cm (5 /a inch) gave good drying results.

Increasing the electrical conductivity of the size solution by the nddition of an electrolyte improved

the coupling of RF energy to the warp yarns.

Laboratory RF drying of sized warp yarns was found to be approximately 40% energy efficient.

RF dryers now available have operating efficiencies of 60%.

Independent Analysis of the RF Drying Study

As Auburn identified that there are no significant improvements in yarn properties when using RF

drying, justification for this technology must be realized by employing RF’s ease of control and self-

3-4

c t

stop. This overdrying has long been suspected of causing undocumented increases in warp and

warp related filling stops during weaving. Later analysis in this report focuses on the cost savings

that may be realized in weaving by reduction or elimination of overdrying.

It is felt an air gap of .2 cm (.078 in), as determined by Auburn, may be difficult to consistently

achieve in production machines due to fluttering of unsupported yarn during drying. It is clear that vertical drying paths are preferable to horizontal paths as they eliminate sagging of the warp yarns

against horizontal RF elements.

A problem encountered by Auburn was moisture condensation on the RF elements. Heating of the elements to temperatures above the dew point may eliminate this condensation. In the Auburn

study, condensation caused arcing that burned the warp yarns and caused unacceptable black

spots.

IR Drying Study

The IR drying study involved installing a 60 kW infrared dryer on a Callaway slasher. A diagram of the Callaway slasher equipped for Infrared Drying is shown in Figure 3-5. A view of the iR dryer

installation is shown in Figure 3-6.

0 0

I O C

S M E Z E DETECTOR ROLLER - -? eg TE" ROLLS

I TME up

I RADIANT H A T

SfCW

(L-J 0

COWUClWN HAWG OW

0

RADIANT H A T SECTION

Figure 3-5 Callaway Laboratory Slasher Equipped for Infrared Drying

3-5

Yarn Path

Upper If? Panel

Lower Retlectnr

Figure 3-6 IR Dryer Installation on Callaway Laboratory Slasher

Details of the IR dryer used in this investigation are shown in Figure 3-7. The tungsten lamps employed are capable of providing operating temperatures to 4000°F (2200°C). Reflecting tiles similar

to those used on the-heat shield of the NASA space shuttle are located behind the lamps to redirect

essentially all of the energy thru quartz windows to the work area. A reflector frame returns any

energy that passes thru the yarn sheet. Internal cooling air reduces housing temperatures, protects

internal components, and enables a rapid cool down when power is removed. The IR is not emitted

at a single wavelength but is a range of wavelengths with the majority of the radiation occurring

between 1.3 to 1.9 microns depending the voltage applied to the unit.

1 R. EMITTER ASSEMBLY

YARN. PATH

TUNGSTEN EMTTER

WARTZ WELD

REFLECTOR ASSEMBLY

Figure 3-7 Detail of IR Dryer

3-6

The yarn samples, size formulations, and running conditions were similar to those used in the RF

drying study. This study determined that the quality of warp yarn dried by IR is not significantly different from warp yarns dried by RF or conventional heated cylinders. Additional findings included:

1. The drying efficiency of the laboratory IR dryer was found to be 30% when corrected to utilize the

full dryer width.

2. Start-up and shutdown of the laboratory slasher was found to be very difficult due to the initial

required starting power level of the IR power supply and thermal lag of the IR heating elements

during shutdown. Excessive energy being transferred to the warp during start-up and shutdown was

found to cause burn-through of warp yarns.

Independent Analysis of the Auburn IR Study

Since there was no significant difference in the quality of sized yarn dried by IR or cylinder drying,

any justification for IR drying must, like RF drying, be derived from savings in other areas such as the elimination of warp yarn overdrying during sizing or removal of wax additives from size formulas.

These eliminations directly impact the chemical, weaving, and finishing costs.

Required Production Capacities for Warp Drying

In order to project the Auburn RF and IR results to full-scale slashing environments, a typical slasher

production and drying requirement was established. Conditions for this requirement were similar to those actually being used in a large textile mill weaving fabrics for bed sheeting.

The yarn and sizing conditions obtained from the sheeting mill, together with typical slasher run and

creep speeds, allow calculation of production and drying load requirements. These requirements are shown in Table 3-1.

3-7

Table 3-1

Production and Drying Requirements for a Typical Sheeting Mill

Yarn and Si7- . . . .

Yarn -34/1 Ne Ends - 11,000 Fiber - 50P/50C Speed

Wet Pickup - 100% Size Add-on - 14% Regain - 6%

- 100 YPM Water to be Evaporated - 80%

100 YPM - Run 5 YPM - Creep

Production 8, nryhghad Run Creep (100 YPM) (5 YPM)

Warp Prod., Ibhr

Drying Load Total, Ib, water/hr

231 1 115.6

1849 92.5

3-8

To provide maximum separation of the yarn ends during drying, the total drying load is divided in

today's sizing machines into four separate drying paths. An illustration of such a machine is shown

in Figure 3-8.

Direction of warp movmmmnt - S t m m heeled drying cyllnder (typ(cai)

1 and 2 3 and 4

Figure 3-8 West Point Production Cylinder Slasher

Required Drying Energy For Production Slashing

The total amount of energy required to heat and dry 1 ib of representative wet warp yarn was calcu-

lated and is shown in Table 3-2. An energy comparison was then formulated for RF, IR and cylinder

drying using information contributed by suppliers of RF and IR equipment along with Auburn study

results. Table 3-3 compares the resulting energy requirements of RF, IR, and cylinder drying.

Table 3-2

Estimate of Energy to Dry 1 Ib Warp

Energy to heat 1 .O Ib yarn Heat .14 Ib size

Heat .86 Ib water

Evaporate .80 Ib waterb

Calcu1ations:a

Heat Yarn

Heat Size Heat Water

Evaporate Water

- 9.3 Btu

- 1.3

- 31.8

-776.2 81 8.6 Btu/lb

(1.0)(.25)(212-175) = 9.3

(.14)(.25)(212-175) = 1.3

(.86)(1)(212-175) = 31.8

(.80)(970.3) =776.2 81 8.6

Notes:

aoperating temperature of Size Applicator bath assumed at 175'F.

b6% moisture left in yarn after drying.

3-9

Table 3-3

Dryer Energy Comparison

Warp Ib per hr 231 1 231 1 231 1

Lb water evaporated per hr

1849 1849 1849

- Power Req’d, kW (Theoretical) 555 555

- Efficiency, % 58.3a 30b

Inbut Power, kW 952 1850 -

- 2773 Steam, Ib per hr -

Notes:

aAverage of estimates by 3 manufacturers of RF equipment. bEstimate by IR manufacturer based on openness of yarn sheet.

Economlc Analysis

The conditions shown in Table 3-1 for a typical sheeting mill were used in preparing an economic

analysis of RF, IR, and cylinder drying. This analysis included considerations of sizing, chemical,

weaving, and finishing costs.

Inputs from RF and IR suppliers, as well as experience by West Point Foundry and Machine Com-

pany in cylinder dryer operation, were used to estimate capital costs for the three drying methods

given in Table 3-4. On a capital basis, both RF and IR dryers are more expensive than cylinder

dryers.

3-1 0

Table 3-4

Dryer Cost Comparlson

Equipment Costs $1,564,000 $467,652 $1 40,000

Amortization, $/IN (1 5 year life)

.015 .005 .001

Notes:

aRF capital cost average of 3 suppliers of RF equipment.

blR'capita1 cost average of 2 suppliers of IR equipment.

Cylinder dryer cost based on 20 cylinder dryer.

dAmortization based on 3000 operating hours per year at 231 1 Ib/hr

Using previously derived energy requirements, it was then possible to project energy costs for the

three drying methods. The results shown in Table 3-5 indicate that RF and IR dryers are five to ten

times more costly to operate on an energy basis than cylinder dryers.

Table 3-5

Dryer Energy Cost Comparlson

BE" l R b w Energy Cost $/lb .021 .040 .005

Notes:

Assume 3000 operating hours per year

Energy costs used: Electricity - $ .05/kWh

Steam - $4.25/1000 Ib

aAverage of estimates by 3 suppliers of RF equipment.

bEstimate by IR supplier based on openness of yarn sheet.

3-1 1

C

A comparison of maintenance costs for RF, IR and cylinder drying was made and tabulated in Table

3-6. Inputs for this analysis were received from suppliers of RF and IR equipment.

Table 3-6

RF 81 IR Maintenance Cost Comparison

E a BtJ wc Maintenance Parts, $/lb .007 .001 .0005

Notes:

Based on 3000 operating hours per year at 231 1 Ib/hr.

alncludes tube and replaceable parts costs. Maintenance based on average estimate of multiple suppliers.

blncludes replacement lamps.

clncludes bearings, belts, rotary joints, steam traps, parts and Teflon replacement for conventional

cylinder dryer.

c

3-12

A comparison of operating costs was then made for the three drying methods. Capital equipment

costs were amortized using the straight line method over a 15 year life. The results of this comparison shown in Table 3-7 indicate RF and IR drying of sized warp yarn is 7 to 8 times more expensive

than conventional cylinder drying. To compete with cylinder drying RF and IR drying must provide cost savings in weaving, chemical, or finishing to offset their increased operating costs.

Table 3-7

Operating Cost Comparison

Cost of Energy, $Ab

Amortization 15 year

life, $/lb

Maintenance Parts

$/lb

$Ab Warp

BE lE w .021 .040 .005

.015 .005 .oo 1

m m m

.043 .046 .007

Note:

Based on 3000 actual operating hours per year at 231 1 Ib/hr production.

3-13

Sizing Chemical Cost Reduction

The elimination of wax additives from sizing formulas can possibly allow a 25% reduction in required

sizing chemicals.(l) This could result in a $.036/lb ($.079/kg) savings as shown in Table 3-8.

Table 3-8

Estimate of Potential Size Savings

$1.04/lba x 14% Size Add On x 25% Savings = $.036/lb

aTruckload price (40,500 Ib) of PVA per E. I. DuPont de Nemours & Company, June 29, 1988.

Removal of wax additives also has a potential savings in finishing fabric of approximately $1 13 per

pound ($.250/kg) of warp yarn processed. (See Table 3-9.)

Table 3-9

Estimate of Savings in Finishing Resulting from Removal of Wax

Potential savings in finishing from removal of wax =

$4.30 to $7.00 per 100 Ib fabric.a

Assuming 1 Ib of warp will produce 2 Ib of fabric,

then average savings in finishing will be:

Ave Savings = $1 13Ab warp

aSource: D. L. Nehrenberg, Wax-free Sizing, Textile Short Course Proceedings, Auburn University,

1985, pp. 84-94.

3-1 4

Associated Weaving Costs

An analysis of a study made by the Institute of Textile Technology (ITT) indicates that overdrying of sized warp yarn can cause 1.2 additional warp stops per 100,000 picks woven.@) The reduction in

warp stops due to the elimination of overdrying would result in savings of $240,00O/year for 300 to

350 looms as shown in Table 3-1 0.

Table 3-1 0

Calculation of Possible Savings Through Elimination of Overdrying

Warp a

With overdrying effects ........ 5.2 Stops/CMPXb

With overdrying eliminated

(projected). . ... .... . ... . ... .... . .. .a

Projected Improvement ........ 1.2 Stops/CMPX

Calculation of Savings2

Savings = 1.2 Stops/CMPX x $200,000 = $240,00O/yr

= $240,00O/yr = $.035/lb

231 1 Ib/hr x 3000 hr/yr

Notes:

aBased on report: T. M. Ellis, 3, ITT Biannual Report, October

bStops/CMPX = warp stops per 100,000 picks woven.

CBased on industrial source that indicates improvement of 1 .O $200,000 per year in average weave shed of 300 to 350 looms.

29-30, 1986, pp. 83-89.

Stop/CMPX equals savings of

3-1 5

The 1TT study demonstrates cost increases incurred in sizing by the introduction of RF or IR drying

can possibly be offset by corresponding cost reductions in weaving. It was felt that this important finding needed expansion and verification when applied to the latest ganeration of looms.

In this regard, a program was established with the Russell Corporation located in Alexander City,

Alabama, to study the effects of overdrying on Tsudakoma air jet and Sauer 400 rapier looms.

These types of looms are representative of today’s latest weaving technology.

The Russell study consisted of two parts. During the first part, routinely slashed production loom

beams were monitored for essential characteristics including overdrying. In the second portion of this study, warp yarns were intentionally overdried by running the slasher at creep speed for prede-

termined yardages. The subsequent wsaving performances were examined. Important slashing and

weaving data were collected by continuous computer surveillance. Numerous warp yarn samples

were taken to enable evaluation of yarn properties in normal and overdried conditions.

In the first part of the study, 165,000 yards (150,876 meters) of production slashed warp (see Table

3-1 1) was monitored as it was wound on 30 loom beams. This warp yardage translates into 726

million linear yards (664 million meters) of individual sized yarns.

Table 3-1 1

Investigation on the Effects of Overdrying on Weaving

Part I - Monitoring of Production Sizing and Weaving

Number F,till Yarn Fiber Type Q i l k m l S W m Content Spinning

20 41 90 2411 50P/5CC Ring Spun

6 41 90 2411 50P150C Ring Spun

4 432 1 2211 65P/35C Open End

Fabric Type Construction J oom

64 epi Airjet

x 50 ppi (Tsudakoma)

64 epi Rapier

x 50 ppi (Sauer 400)

60 epi Airjet


Approximate total yardage Part I - 165,000 yds.

3-1 6

h

Table 3-1 1 (Continued)

Part II - Effects of Induced Overdrying on Weaving

Number Mill Yarn Fiber Type Fabric Type

- w size Content Spinning Construction I oom

5 41 90 24/1 50P/50C Ring Spun 64 epi Airjet


Approximate total yardage Part II - 27,500 yds.

In the second part of the study, overdrying was induced in designated areas of five loom beams with

approximately 27,500 yards of warp (121 million linear yds). Other critical parameters such as size

add-on levels, warp stretch levels, and yarn properties were monitored to insure the results were not

distorted by other parameters.

Results of this study indicated:

1. Overdrying cal;sed by running in creep speed caused an increase of .24 warp stops

per 100,000 picks woven.

2. Yarn breaking load, elongation, toughness index, and abrasion resistance were found to be significantly lower at crecp speed than at full speed.

3. The majority of warp stcps in the overdried regions were caused by breaking of adjacent ends,

slubs, and thick places. Most of the warp stops occurred near the loom harnesses.

A survey was then made of prominent textile companies in the southeastern US. to detwnine the

cost of a warp stop during weaving. The average value was found to be $1 .OO per warp stop.

Based on the average worth of a warp stop as $1 .OO per stop, it was estimated that a mill with 325

airjet looms running at 600 picks per minute will have a total weaving cost increase of about

$202,176 annually if 5% of its total yardage were run at creep speed.

The corresponding figure in the case of 325 rapier looms running at 300 picks per minute would be about $191,088. (See Table 3-12.) These numbers confirm and expand ITT’s original findings that

overdrying at creep speed causes additional warp stops.

3-1 7

Table 3-1 2

Calculation of Possible Savings Through Elimination of Overdrying

Warp Stops

Projected improvement .............. .24 Stops/CMPXa

of overall production

Ulculation of Savings

Air Jet Wea vingb

Savings = .24 Stops/CMPX x 2592 CMPX/Loom/Year x 325 looms x $lMlarp stop

= $202,176/year

ier Weavingc

Savings = .24 Stops/CMPX x 1296 CMPX/Loom/Year

x 325 looms x $lMlarp stop

= $1 01,088lyear

Notes:

Source: From study conducted by West Point Foundry and Machine Company, 1989.

aStops/CMPX = Warp stops per 100,000 picks woven.

bAirjet looms weaving 600 picks per minute 300 operating days of three 8 hour shifts (with 5% of the warp overdried).

CRapier looms weaving 300 picks per minute 300 operating days of three 8 hour shifts (with 5% of the warp overdried).

3-1 8

It should be noted that as slashers are run in creep speed, weaving performance will be degraded

with subsequent increased weaving costs.

From the above it follows that cost reductions in weaving can be accomplished by reducing the need

for creep speed operation through improved yarn handling and machine management. However,

some creep speed operation will be needed for certain operating procedures and practices. Thus further benefits may be realized from advanced dryer designs that minimize or eliminate the effect of

creep speed operation on the yarn.

Market Analysis

The findings of the Auburn studies, as enlarged by West Point Foundry and Machine Company to

include potential benefits of RF and IR slasher drying on weaving and finishing costs, were pre-

sented at the conference on Electrotechnology Applications in Fiber, Textile, and Apparel Industries

held at North Carolina State University in April, 1989.

A good response showing general interest was generated from the audience and textile executives. It is clear, however, that additional project development must occur prior to an offering of RF or IR

drying to the textile industry.

Conclusions

Auburn University has not found a significant difference in sized warp yarns dried by RF, IR, or

cylinder drying. Justification for using RF or IR in slashing must therefore be focused on cost com-

parisons including changes in weaving, sizing processing, chemical costs, and finishing costs. Such

a comparison (see Table 3-13) indicates there is a cost advantage in using the unique properties of

RF and IR in drying of sized warp yarns if the downstream savings can be confirmed.

As shown in the Table, the added cost of the RF or IR equipment is almost offset by the improve-

ment in weaving efficiency obtained by eliminating creep speed operation. Reductions in chemicals

and finishing costs provide the major contribution to the savings.

If the above projected savings are obtainable, the payback period for RF and IR dryer installations

could be as short as 1/2 to 11/~ years as seen in Table 3-1 4.

3-1 9

c

Table 3-13

Overall Cost of RF and IR Drying Compared to Cylinder Drying

Weaving Efficiency

Run Savings

Creep Savings

Processing Costs Sizing

Operating

Less cy1

operating cost

Operating Cost Additions

Chemical Savings

Finishing Savings

Total Savings, $Ab Warp

BE

0 - $.035

+ $.043

- $.007

+ $.036

- $.036

- $.148

0 - $.035

+ $.046

- $.007 + $.039

- $.036

-$.113

- $.145

COMMENTS Yarn properties

do not change

Table 3-1 0

Table 3-7

Table 3-7

Table 3-8

Table 3-9

Notes:

Savings equals - Additional cost equals +

Table 3-1 4

Potential Annual Savings of RF and IR to Cylinder Drying

Total Savingsa $l,026,084Iyr $l,005,2851yr

Required Capital Investment $1,564,000 $ 467,652

Payback Period 1-112 yr 1/2 yr

aBased on warp production of 231 1 Ib/hr and 3000 hrlyr slasher operation

3-20

Section 4

RECOMMENDATIONS FOR FURTHER STUDY

The research work documented in this report shows that IR and RF drying can be used successfully

in the sizing of warp yarn. The economic benefits of these alternative methods of drying are theoreti- czlly significant. However, confirmation of these benefits will require additional work.

The maior contributors to projected cost savings were found to be related to the removal of wax

additives f: om size formulas. Such a removal would possibly reduce size material requirements and

the cost of finishing woven fabrics. Further investigation is required to confirm that these major

contributors to savings are, in fact, obtainable.

The dryer configurations employed in developing economic comparisons between IR, RF, and

cylinder drying were designs using only one type of drying. Hybrid designs employing two or more

types of drying may offer certain advai.:ages and should be explored. The considerations must

address typical operating variables of running speed, creep speed, and stops, as well as operator

access require men ts.

The deleterious effect of creep speed overdrying has been confirmed in this study. Management

attention to procedures in slashing operations as well as improvements in the quality of the previous

processes of yarn manufacturing and warping will be beneficial in reducing the amount of yarn sized

in cl'eep speed. However, design of a drying system to eliminate the overdrying at any speed is

needed.

It is recognized that only with a full scale mill application can the downstream savings be fully con-

firmed and the new technology evaluated. When additional laboratory confirmation of the major

contributors to savings is obtained, this step can be considered.

4-1

h

Section 5

REFERENCES

1.

2.

3.

4.

5.

Personal communication with Prof. Warren S. Perkins, Department of Textile Engineering,

Auburn University, Auburn, Alabama.

Nehrenberg, D. C. Wax-Free Si7ina Textile Short Course Proceedings, Auburn University, 1985,

pp. 84-94.

W. S. Perkins and M. W. Reed. W i o Freauencv Dry ina of Textile Yarns in SiAng, Auburn

. University, November, 1987, pp. 1-30.

M. W. Reed and R. H. Broughton, Jr. m e d O m of Text ile Yarn , Auburn University, Janu-

ary, 1989, pp. 3-15.

T. M. Ellis. Fvaluation of New S lashina Technoloay . ITT Biannual Report, October 29-30,

1986, pp. 83-89.

5-1

L

Appendix A

RADIO FREQUENCY DRYING OF TEXTILE YARNS IN SIZING

ACKNOWLEDGMENTS

Significant technical support and cost sharing was provided by PSC, Inc. and West Point Foundry

and Machine Company. This assistance is gratefully acknowledged. Appreciation is also expressed

to Ida E. Reed who performed or supervised many of the experiments which yielded the data re-

ported herein.

A-iii

CONTENTS

Section

Introduction

Background

Methods of Procedure


Conclusions

References

Paae

a1-1

A2-1

A3-1

A4-1

A5-1

A6-1

A-V

ILLUSTRATIONS

Fiaure

3-1 Callaway Laboratory Slasher Equipped for Radio Frequency Drying

Power Consumption vs Slasher Speed

Effect of Air Gap on Energy Coupling

Dryer Effectiveness, 1 vs 2 Pass, 1 CM

4-1

4-2

4-3

Paae

A3-1

A4-5

A4-6

A4-6

A-vii

TABLES

Table Paae

4- 1

4-2

4-3

4-4

4-5

4-6

4-7

Physical Properties of 65/35 Polyester/Cotton Yarns Dried Using Radio

Frequency or Conventional Cylinder Methods

Physical Properties of Yarns Dried Using Normal Drying Conditions and

Prolonged Drying Conditions

Comparison of Drying Rates of Cylinder and Radio Frequency Dryers

Illustration of Self-limiting Characteristic of Radio Frequency Drying

Effectiveness ot RF Dryer as a Function of Yarn Distance from the

Electrodes and Sksher Speed (water evaporation requirement = 63%)

Effectiveness of RF Dryer Threaded with Single Yarn Sheet and Split Yarn Sheet at Air Gap of ‘i .O cm Between Yarn Sheet and Electrodes (water ev-

aporation requirement = 63%)

Estimate of Annual Savings Potential of RF Dryer Retrofitted to

Existing Slasher

A4-2

A4-2

A4-3

A4-7

A4-7

A4-a

A4-10

A-ix

The objective of the research was to evaluate the technical and economic feasibility of the use of

radio frequency (RF) energy for drying of yarns in sizing. The work had two distinct aspects. First, the quality of yarn produced by RF drying as compared to conventional cylinder drying was deter-

mined. The second aspect involved measurement of drying rates and dryer efficiencies at various

slasher speeds, RF applicator air gap, and other conditions.

A i -2

INTRODUCTION

Textile manufacturing plants which produce woven fabrics must size the warp yarn before the fabric

can be woven. The process, called slashing, consists of applying a coating of a water soluble or

water dispersible polymer to the surface of the yarns for the purpose of making the yarn perform better in weaving. The process is critical to textile manufacturing because the efficiency of the

weaving process has a major effect on the profitability of the weaving plant. The size is applied by

passing the yarn through an aqueous solution of the size material, squeezing the yarn between

rubber-covered rolls to remove the excess size solution, and then drying the yarn by conduction

heating on steam heated cylinders. In some slashers, hot air or infrared dryers are used to predry

the yarn before cylinder drying.

Control of moisture content of yarns exiting the slasher is considered to be critical to successful

sizing. The thermal inertia of drying cylinders is too great for adjustment of cylinder temperatures to

be used for control of moisture content so speed of the slasher is normally adjusted as required to keep the moisture within the required tolerances. This method normally works well when the slasher

is running at normal production speeds. However, during the frequent periods when the slasher

must be slowed down or stopped for repairs of yarn breaks or other reasons, control of the degree of dryness of the yarn is lost.

Size materials are tacky by nature until part of the moisture is removed and the material begins to

solidify. This tackiness causes two problems in the slashing process. First, the tacky size material tends to stick to drying cylinders causing fibers which would be cemented to the yarn surface to be

pulled up making the yarn "hairy" (fuzzy). Modern high-speed looms require sized yarns having a

very low degree of hairiness for high weaving efficiency and fabric quality. Several techniques are

used to minimize sticking of tacky size material to the drying cylinders. One of these is the addition

of waxy release agents to the size formulation. These release agents have been shown to adversely

affect properties of the size material. The net effect is that more size must be added to the yarn to provide the level of yarn properties required for weaving. The second problem caused by tackiness

in the wet size is binding together of adjacent yarns as the yarn sheet is passed over the drying

cylinders. Hairiness is generated and the coating of size is partially destroyed when the stuck yarns

are separated from each other prior to take up on the beam which supplies the yarn to the loom. Partially or completely drying the yarn as separate strands provides less hairy, more uniformly coated

yarns.

A1 -1

draw-warping/sizing polyester filament yarns has been developed (1 3). The paper industry in Eu-

rope is reportedly using RF energy for drying during the manufacturing process (14).

Both microwave and radio frequency energy have been applied in dyeing processes. Several ar-

ticles have described the use of microwaves and radio frequency waves to assist in fixation of acid or

reactive dyes on cotton, wool, or nylon (1 5-20).

A2-2

BACKGROUND

Textile materials are wetted and dried several times in the course of fabric manufacturing processes.

Removal of the water is usually by a combination of mechanical and thermal means (1). Mechanical

dewatering with squeeze rolls, centrifuges, or suction slots is inexpensive, but much of the moisture

in wet textile materials cannot be removed by these mechanical means. Thermal dryers for textile materials normally utilize indirect heat wherein the heat is generated external to the material and

transferred t3 the material by conduction, convection, or radiation. In each of these cases the heat is transferred primarily from the surface gradually to the center of the material.

Radio frequency waves and microwaves generate heat directly within the material to be dried. This

direct heating makes RF heating potentially advantageous for heating and drying of materials in

many textile processes. Therefore, there has been some interest for many years in the heating and drying of textile materials using radio frequency energy. Possible benefits of RF heating and drying

and some successful applications are discussed in recent literature (2-8). Some specific potential

benefits of RF drying in yarn sizing are as follows:

Absence of thermal lag and thermal inertia associated with other drying methods.

Nonpolar fibers such as polyester do not heat in RF fields.

Rapid drying rates which may allow smaller dryinq sections on sizing machines.

Little or no radiation of heat to the room.

Self-limiting characteristics may allow simpls process control systems.

RF drying is a noncontact method which eliminates sticking of size material to drying cylinders.

Therefore, release agents such as sizing wax which adversely affect size material performance

are not needed.

Use of RF energy for heating and drying of bulky materials such as yarn packages, hanks, loose

stock, and bales has become widespread in Europe (9), and there are a number of installations in

U.S. textile plants (4). Heating and drying of thin textile substrates such as warps and fabrics are not

yet widely practiced although some development work has been done (10-1 2), and a process for

A2- 1

The radio frequency generator was a Thermal1 Model 67, 12.5 kW unit. Power was taken from the

generator to the strayfield (fringefield) electrode assembly constructed specifically for Auburn's

Callaway Slasher. The RF generator operated on 240 volts service through a 3-wire delta connec- tion. Both the dryer cavity and the RF generator were interlocked to eliminate shock hazards to

operators using the dryer.

Yarn and Size Materials

The yarn was a 50/50 polyester/cotton blend having the properties given in Table 4-1. The type of

starch used throughout the project was an acid modified cornstarch having a fluidity value of 19.

Two polyvinyl alcohol types were used in the project. One was a medium molecular weight, partially

hydrolyzed product commonly used for warp sizing. The other was an experimental polyvinyl alcohol

have a relatively low molecular weight. This product was also a partially hydrolyzed type and was

used because of its applicability by the foam sizing technique utilized in some of the experiments.

The wax used in some of the experiments was a solid sizing wax having a melting point of 140°F

(60°C).

Tensile Properties

All tests of physical properties of the yarns were performed according to ASTM standards when an

appropriate standard method exists. In cases where a published standard test method does not

exist, the tests were done according to methods and specifications most often used by researchers in the yarn sizing field. Strength and elongation at the break were measured on an lnstron Tester. A

test consisted of the average strength or elongation of 25 specimens randomly chosen from across

the yarn sheet.

Abrasion Resistance

The K. Zweigle yarn abrasion tester was used to measure abrasion resistance of the yarn. The

tester rubbed the yarn under a predetermined tension level against a standard abrasive paper. The

number of abrasive cycles required to cause the yarn to break was determined. The abrasive paper

used was type P800, and the tension level was 30 grams per yarn. Values reported are the average

cycles to break for 40 specimens.

Yarn Hairiness

A Shirley Hairiness Meter was used. The meter measures the number of protruding fibers per meter

which are greater than a predetermined length. A hair length of 3 millimeters was used in this work

because most published data on yarn hairiness is reported for this particular hair length.

A3-2

METHODS OF PROCEDURE

Slasher

The slasher used in the work was a Callaway Model 50 laboratory slasher. Yarn was supplied to the slasher from a cone creel having a capacity of 150 yarn packages. Figure 3-1 is a schematic dia-

gram of the machine which includes the modifications that were made to equip it for radio frequency

drying. The slasher has two radiant drying cavities which were not used in this work and four electri-

cally heated drying cylinders which were used in this work for comparison to drying in the RF dryer.

Tension on the yarn sheet was controlled at both the takeup beam and in the zone between the

squeeze rolls and drying cylinders. The RF dryer was designed for a vertical yarn path so that

sagging of yarn into the electrodes would not be a problem. The RF dryer was also designed so that

the direction of the yarn sheet could be reversed at the top of the dryer for an additional pass down

the back side of the electrode assembly. Speed of the slasher was variable from 0 to 42 yards per minute (38.4 m/min).

I TAKE UP

3

0

RADIANT H A T sEcnoN

a ( W T K ) N c>o FAN

L

0 0 0 0

0 0 0 0

C0NDUCTK)N HARK; 0" W T H A T sECTKN(

Figure 3-1 Callaway Laboratory Slasher Equipped for Radio Frequency Drying

A3-1

Power Requirements

Power requirements for the RF dryer were measured using a Dranetz Power Demand Meter.

Wet Pickup, Formulation Solids, Size Addon, Moisture Regain

The solids content of the formulations was measured by evaporating known weights of the formula-

tion to dryness. Size add-on was measured by extracting the size from yarn samples by the gener-

ally accepted method (21). Wet pickup was then calculated using the following relationship:

Wet pickup = size add-on/solids content of formulation.

Moisture regain was determined by measuring weight loss of yarn samples in a convection oven.

A3-3

Table 4-1

Physical Properties of 65/35 Polyester/Cotton Yarns Dried Using Radio Frequency or Conventional Cylinder Methods

~~ ~ ~

Property

Strength Elongation Abrasion Hairiness

(pounds) (“w Size Material

Resistance (#/meter)

(cycles)

Conv. RF Conv. RF Conv. RF Conv. RF

PVAhax 1.11 1.09 7.6 8.9 363 349 9.4 10.0

starch/ PVNwax 1.05 1.09 8.6 9.4 202 192 12.0 13.7

experimental PVA 0.91 1.08 7.3 8.1 381 38 1 2.4 5.2

Table 4-2

Physical Properties of Yarns Dried Using Normal Drying Conditions and Prolonged Drying Conditions

Property Drying Condition

Strength Elongation Abrasion Resistance

(pounds) (”/) (cycles)

Normal Speed, RF 1.1

Prolonged drying, RF 1.2

Normal drying, conventional 1.1

Prolonged drying, conventional 1.1

8.9

5.9

7.6

6.4

349

363

363

350

A4-2

RESULTS AND DISCUSSION

Yarn Properties

Table 4-1 shows results of measurements of physical properties of yarns dried using conventional

cylinder drying or radio frequency drying. The first two formulations in the table were applied using

conventional immersion techniques for application of the size while the third formulation described as

experimental polyvinyl alcohol was applied by a metered foam technique. Differences in strength,

abrasion resistance and hairiness of the yarns dried by the two techniques were not significantly

different. However, each of the three formulations produced yarns with higher residual elongation

when the yarn was dried by the RF technique than when drying was done on cylinders. This obser-

vation regarding yarn elongation is intriguing since higher residual elongation is believed to have a

large beneficial effect on weaveability of sized yarns (22). Ordinarily, residual elongation in sized yarns depends mainly on how much the yarn is stretched as it is processed through the slasher. In

order to process yarn through the RF dryer, modifications were made in the Callaway Slasher.

Whether the difference in residual elongation resulted from this difference in threading of the slasher

or whether the difference was caused by some fundamental difference in RF and cylinder drying is unknown at this time.

Yarns sized by the metered foam technique had generally better resistance to abrasion and lower

yarn hairiness than did the yarns sized by the conventional immersion technique. The reduced

hairiness of the foam-sized yarn resulted mainly from the wiping action of the grooved roll which

served as the metering device to apply the foamed size. This technique produced yarns with some-

what lower residual elongation presumably as a result of the tension created by friction of the yarn on

the grooved applicator roll. The high level of abrasion resistance of the yarn sized by the foam

technique was achieved even though the experimental polyvinyl alcohol used was a low viscosity

type and had considerably lower inherent strength than the types used commercially for warp sizing.

This experimental PVA produced yarns with good resistance to abrasion mainly because the tradi-

tional lubricants were omitted from the size formulation. These lubricants act as release agents which

discourage sticking of size to the hot drying cylinders and make splitting of yarn at the lease rods

occur more easily. However, these lubricants also detract from the ability of the size to adhere to the

yarn. The net result is that more size must be used to achieve the same level of abrasion when the

lubricant is used than when the lubricant is omitted. Size application by low wet pickup techniques or

the use of noncontact drying methods such as radio frequency can eliminate the requirement to use

wax in the size formulation possibly leading to very large savings in size material requirements.

A4- 1

Performance of RF Dryer

Several tests were performed to gain insight into the performance of the RF dryer. The drying rate

and efficiency of the RF dryer were measured under various conditions. The effect of each of the

following variables was measured:

slasher speed, which determines the moisture load in the dryer

size of air gap between the dryer electrodes and the yarn sheet

one pass versus two passes of yarn through the dryer

split sheet with one-half of yarns on each side of electrodes

electrolyte addition to the size formulation

prolonged exposure of yarn to the RF energy

Following are the “idling” power requirements of the radio frequency generator:

Cooling fan only (no RF power)-0.9 kW

Cooling fan and filament-1.9 kW

RF power on with no load-5.3 kW (dry yarn in dryer; slasher stopped)

Figure 4-1 shows the steady state power pull as a function of material throughput rate (upper curve)

and energy consumption in kWh per pound of water removed (lower curve). The steady-state power

. pull is directly proportional to the amount of water being vaporized and therefore to yarn throughput if

the yarn is dried well. The efficiency of the dryer improves as the slasher speed increases since the

baseline power consumption is distributed over more material as the throughput increases.

Radio frequency drying has self-limiting characteristics. Table 4-4 shows that the moisture regain of

yarn dried using RF energy Qaried little over a wide speed range. Furthermore, yarn left in the RF

dryer operating at full power for a period of 5 minutes still contained about 2% moisture. RF energy

apparently removes physically entrapped moisture very effectively but does not easily remove chemi-

cally bound moisture from the cotton/polyester blend yarn.

Figure 4-2 shows the effect of air gap between dryer electrodes and the yarn sheet on steady-state

power pull of the RF generator. The relationship between yarn throughput and steady-state power

A4-4

Effect of Prolonged RF Drying on Yarn Physical Properties

Typical dwell time in the RF dryer of 2 to 8 seconds resulted in removal of all of the water added

during size application. An experiment was performed wherein the slasher was stopped for 5 min-

utes with yarn in the dryer with the RF power remaining on. Physical properties of these yarns are

compared to properties of yarns dried at normal operating speeds in Table 4-2. Prolonged exposure to either RF energy conventional drying cylinders had little or no measurable effect on strength or

abrasion resistance of the yarn. Prolonged drying by either the RF or cylinder method caused lower

residual elongation in the yarn. The practical implication of this is that overdrying of some sections of the warp is inevitable in a conventional cylinder dryer because of the thermal inertia of the cylinders.

On the other hand, the RF energy can be turned on and off almost instantaneously during machine

stops so that overdrying can be prevented.

Drying Studies

Drying Rates

Drying rate data for the radio frequency dryer are compared to conventional cylinder drying in Table

4-3. The drying rate is affected by the degree of dryness achieved. If the dryer is operated so that

the yarn is dried below the required moisture regain, the drying rate is lower than would be the case

when the normal amount of moisture is left in the material. The numbers in the table represent the

condition where the dryer is operating at steady state conditions with the yarn at approximately 4%

moisture regain at takeup. The drying rate was faster by a fact or of approximately 4 with the RF

dryer as compared to the cylinder dryer.

Table 4-3

Comparison of Drying Rates of Cylinder and Radio Frequency Dryers

Drying Rate

(Ib. water evaporated per minute

per foot of dwell in dryer)

for yarn sized using

Drying Method PVNStarch PVA

Cylinder 0.56 0.56

Radio Frequency 2.23 2.27

A4-3

S T E A D Y

S T A T E

P 0 w E R

P U L L

S T E A D Y

S T A T E

P 0 w E R

P U L L

12

10

8

6

4

2

0 0 10 20 30 40

SLASHER SPEED, YPM 50

0.2 CM 1.0 CM -++ 2.0 CM -

Figure 4-2 Effect of Air Gap on Energy Coupling

10 [

2 t 1

0 I I I I

0 10 20 30 40 50 SLASHER SPEED, YPM

2PASS - 1 PASS _c

Figure 4-3 Dryer Effectiveness, 1 VS 2 Pass, 1 CM

A4-6

pull becomes more nearly linear as the distance between the electrodes and the yarn is decreased.

This indicates that the ability of the RF energy to couple with the moisture in the yarn decreases as

the air gap becomes greater. Therefore, less drying occurs with the larger air gaps and drying is incomplete at the higher slasher speeds. Table 4-5 shows that the RF dryer effectively dried the

yarn at speeds only up to about 10 yards per minute (9.1 m/min) at 2 cm air gap and 30 yards per

minute (27.4 m/min) at 1 cm air gap. However, the yarn was dried well at top slasher speed of 40

yards per minute (36.6 m/min) using an air gap of 0.2 cm (.078 in).

The RF dryer on the Callaway Slasher was designed to allow for two passes of the yarn sheet through the dryer cavity as shown in Figure 3-1. However, most of the moisture in the yarn is removed during the first pass through the dryer. Figure 4-3 shows that at slow slasher speeds the RF energy actually coupled better with the moisture using a single pass than when the two-pass

threadup was used. This behavior resulted because the moisture still in the yarn during the second pass pulled some of the electrical field away from the front of the electrodes. As the slasher speed

became greater, the single pass threadup did not completely dry the yarn so less power was pulled by the dryer.

Since one pass of yarn through the dryer removes most of the moisture, it should be possible to split

the warp into two sheets and pass half of the yarn up each side of the dryer electrodes. Table 4-6

shows that this arrangement worked, but drying was not as effective as was the case when all of the

yarns were on one side of the electrodes. Apparently, balancing the moisture load on both sides of

the electrodes caused the electrical field to be held closer to the electrodes so that the RF energy did

not couple as well to the moisture in the yarn. The benefits of split sheet drying may be obtainable

with RF drying, but a smaller air gap between the yarn and the electrode system will probably be

required when a balanced load is used on both sides of the electrodes.

1 2 ; K

0 101

a -

,’ --- ,

-;-

o---- --- - -~

0 5 10 15 20 25 30 35

SLASHER SPEED, YPM

- KW (STEADY STATE) - KWH/LB. WATER

Figure 4-1 Power Consumption VS Slasher Speed

A4-5

Table 4-6

Effectiveness of RF Dryer Threaded with Single Yarn Sheet and Split Yarn Sheet at Air Gap of 1 .O cm Between Yarn Sheet and Electrodes (water evaporation requirement = 63%j

Moisture Regain of Yarn Dried using

Slasher Speed Single yarn sheet Split yarn sheet

10 15

20 25

30

40

4.1

4.1

4.1

4.1

4.1

4.1

5.4

5.7

6.8

10.5

14.3

22.5

The electrical conductivity of the solution in the yarn dramatically enhances coupling of the RF

energy with the moisture. However, amounts of sodium chloride greater than about 2% on weight of

the size solution caused localized overheating and breakage of yarns. The effect of small amounts of electrolytes in the formulation on physical properties of the yarn was not determined.

Economics of RF Drying

The economics of drying using radio frequency energy will depend on many factors. Following is an analvsis of drying energy costs and discussion of other considerations affecting economics of RF

drying.

Energy for Drying

Nehrenberg reported (23) that slasher using cylinder drying has energetic efficiency of about 75%.

This figure is corroborated by Viallier (24) and by West Point Foundry and Machine Company,

lnc.(25) A recent Canadian study of seven different systems for drying of textile materials reports the

overall energetic efficiency of conventional drying on the slasher as 55%. (26) Therefore, energy

consumption for drying yarn on a conventional slasher is estimated to be

(1 Ib steam)/.75 to .55 efficiency =

1.33 to 1.82 Ib steam/lb water evaporated

A4-8

Table 4-4

Illustration of Self-limiting Characteristic of Radio Frequency Drying

Machine SDeed Moisture Water EvaDoration Power

(YPm) Regain Requirement Requirement

(“/4 (% of dry fabric wt) (KW)

15

20

25

30 35

40

4.1 63

4.1 63

4.2 63

4.2 63

4.1 63

4.3 63

6.8 7.3

7.8

8.1

8.5

9.0

Table 4-5

Effectiveness of RF Dryer as a Function of Yarn Distance from the Electrodes and Slasher Speed (water evaporation requirement = 63%)

~ ~~

Slasher Speed

~~~ ~~~~ ~ ~~

Moisture Regain of Yarn Dried using Air Gap of

1 .O cm 2.0 cm 0.2 cm

10

15

. 20

25

30

35 40

4.1

4.1

4.1

4.1

4.1

4.1 4.1

4.8 5.0

4.4 6.2 4.4 10.4

4.5 16.8

5.0 23.3

5.9 31.2 6.8 42.8

A4-7

Cost (installed) for RF drying is $3,00O/kW.

Improvement in weaving efficiency is valued at $3,00OAoom/yr/l O h improvement.

If drying is solely by RF, approximately 500 kW is required. If RF is used in combination with conventional the RF requirement is proportionally lower.

Labor and other operating costs not changed by RF drying.

The estimates in Table 4-7 make it obvious that weaving efficiency is the most critical factor in deter- mining the economic impact of changes in the slashing process. The estimates also point out that

there is great economic potential for improvements in the slashing process which improve efficiency of weaving.

Table 4-7

Estimate of Annual Savings Potential of RF Dryer Retrofitted to Existing Slasher

ITEM Situation 1 Situation 2

Capital Investment cost

SAVING

Energy

Weaving efficiency

Chemicals

Finishing

NET SAVINGS

Approximate simple payback period (yr)

(60,000)

900,000c

0

0

$840,000

2.75

(30,000)

1,800,000d

200,000e

600,000f

$2,570,000

0.45

aRF as sole drying mode

bCombined RF and Conventional 1/2 by each mode.

CAssuming 1 % absolute improvement in weaving efficiency.

dAssuming 2% absolute improvement in weaving efficiency.

eAssuming 20% savings as a result of elimination of wax from the size

formulation.

fBased on published data on effect of elimination of wax from the size

formulation (27).

A4-10

Steam cost is presently about $3.50/1000 Ib to $5.00/1000 Ib, respectively, from gas and oil fired

boilers. Therefore, the cost of energy for drying yarn on conventional cylinder dryers is in the range

$0.005 to $0.009/lb of water evaporated.

The energetic efficiency of the RF dryer used is this study was about 40% in many of the experi-

ments performed. However, the RF generator was overpowered for the amount of drying needed in

the laboratory slasher. Furthermore, most of the hot air from the cooling fans on the RF generator

was lost to the surroundings. Radio frequency dryers available today generally operate at about 60%

energetic efficiency. Therefore, the cost of energy for drying using a radio frequency dryer is

(970) (1/3415 Btu’s)/.G eff ($.04/kWh)

= $0.01 9/lb water evaporated

Since it appears that use of radio frequency energy to dry yarn in slashing will increase the cost of drying energy for the process, use of RF energy will only be economical used for partial drying in

combination with other drying techniques or if there are benefits which offset the additional energy

costs.

Economics of RF Drying in Hypothetical Mill

In order to put the possible benefits of RF drying in the proper perspective, an analysis of some of

the cost considerations was made. The following assumptions were made:

A mill running 7200 hours per year uses 300 looms to produce 20 million pounds (9.1 million

kg) of fabric.

The fabric contains 10 million pounds (4.53 million kilograms) each of warp and filling yarn.

The warp yarn is sized on one slasher at wet pickup of 130%.

Size add-on is 13% of a size costing $0.75 per pound (dry basis).

Drying energy cost by conventional cylinders is $0.0082 per pound of yarn ($0.007/lb water x

1.3 Ib formulation/lb yarn x 0.9 Ib water/lb formulation).

Energy cost for RF drying is $0.0222 per pound of yarn ($0.001 9 x 1.3 x .9).

A4-9

Possible Benefits of RF Drying

Possible benefits of noncontact drying using radio frequency energy and the economic value of some of these benefits are as follows:

Weaving efficiency could be improved. Improvement in weaving efficiency is estimated to be

worth $500 to $5000 per loom per year per 1% improvement in efficiency.

Size material consumption may be decreased. Noncontact drying allows wax to be eliminated

from the size formulation dramatically reducing size requirements and need for high temperature washwater in the finishing plant.

Horsepower requirements to drive noncontact dryer should be lower than for cylinder dryer

saving about $1 000 per year.

Less floor space will be required for the slasher.

Yarn does not heat much during slasher stops. This may prevent dye defects and other types

of yarn damage.

Yarns are apparently not damaged by extended time of exposure to RF energy during machine

stops.

RF energy can be turned off almost instantaneously and recover full power in about 1 second

under automatic control. Therefore, in addition to being self-limiting, use of RF heating is particu-

larly suitable for automatic process control.

The fringefield electrode design provides capability for drying of yarn in split sheets which

should produce smoother yarn with a more uniform coating of size material.

Rapid drying rate provides flexibility in sizing machinery design.

RF drying should produce less off quality sized yarn resulting from sizing machine stops be-

cause of the absence of the thermal lag that is present with indirect heating methods.

Low radiant heat losses to the surroundings that are experienced with RF heating should pro-

vide improved working conditions in the slasher room.

Industrial experience with RF drying is needed in order to determine if the process control and other

apparent advantages of RF drying will actually result in improved weaving efficiency of warp yarns.

A4-11

CONCLUSIONS

1. Radio frequency (RF) energy can be used to dry sized yarns.

2. Drying rates are much faster with RF energy than with conventional cylinder drying.

3. RF drying of polyesterkotton yarns is somewhat self- limiting.

4. Efficiency and effectiveness of the RF applicator are determined by processing conditions such

as distance of yarn from the applicator electrodes, speed of the slasher, path of yarn through the RF applicator, nature of the size formulation, and other factors.

5. Energy cost of RF drying is presently higher than for conventional cylinder drying.

6. There are potential benefits of RF drying of sized yarns which may offset the higher energy cost

and high capital investment cost for RF drying.

15. Burkinshaw, S. M. and W. J. Marshall, Journal of the Societv of Dvers a nd Colorists 103,

November 1986,336-341.

16. Burkinshaw, S., S. Leicester and W.J. Marshall, Jextile Month , May 1985, 17, 19,21,33.

17. Catlow, N. and R. M. Perkin, JSDC, Volume 100, September 1984, 274-280.

18. Delaney, M.J. and I. Seltzer, U n a 1 of the Societv of Dvers and Co lorists 88 , February 1972,

55-59.

19. Metaxas, A. C., N. Catlow, and D. G. Evans, Journal of M icrowa ve Power, 1978,341 -350.

20. Evans, D. G. and J. K. Skelly, Journal of the Societv of Dve rs and Co lourists, December 1972,

429-433.

21. Perkins, W. S., “Testing of Sized Yarns,” in Theory and Practice of Textile Slashing, J. C. Farrow,

David M. Hall and Warren S. Perkins, editors, Alabama Textile Operating Executives and Auburn University Department of Textile Engineering, Auburn, AL, 1972.

22. Andrews, Gerald B., 191 m i n a Short Course Lecture Notes , Alabama Textile Operating

Executives and Auburn University Department of Textile Engineering, Auburn, Alabama, 19? ,.

23. Nehrenberg, D. L., 1976 Tex-hina S~-IQI? Course I ectu re N o w , Alabama Textile Operat-

ing Executives and Auburn University Department of Textile Engineering, Auburn, Alabama,

1976, 93-104.

24. Viallier, P., Jnternat ional Text ile Bulletin: Wea vina - Editiw, April 1981,286,291,292,297,298.

25. private communication with Mr. Howard Ruddick, West Point Foundry and Machine

Company, Inc.

26. Langlois, C. and R. Maissonneuve, Book of P w , 1986 International Conference and

Exhibition, AATCC, Research Triangle Park, N.C., 1986,8594.

27. Nehrenberg, D. L., -one to Qualltv Fabr &, AATCC, Research Triangle Park, N.C.

1987,32-35.

A6-2

Appendix B

INFRARED DRYING OF TEXTILE YARN IN SIZING

ACKNOWLEDGMENTS

Appreciation is expressed to Rajiv Rajadhyaksha, Candidate for Master of Textile Science, Auburn

University, for his help in this project.

B-iii

CONTENTS

Section

Summary

introduction

Experimental Procedures


Recommendations for Further Work

References

Paae

B1-1

82-1

B3-1

84-1

85-1

B6-1

B -V

ILLUSTRATIONS

Fiaure

3-1

3-2

3-3

3 -4

4-1

4-2

4-3

4-4

4-5

4-6

4-7

4-8

4-9

Callaway Pilot Slasher Schematic

Schematic Cross Section of IR Heater

IR Dryer for Textile Warp

Warp Yarn Path thru IR Dryer

Abrasion Resistance for Different Drying Methods

Yarn Hairiness for Different Drying Methods

Yarn Tensile Strengths for Different Drying Methods

Yarn Elongation at Break for Different Drying Methods

Efficiency vs Drying Rate - Corrected for Width

Efficiency vs Regain - Corrected for Width

Moisture Regain vs Residence Time for Third Drying Trial

Drying Rate vs Residence Time for Third Drying Trial

Efficiency vs Regain for Third Drying Trial

Paae

B3-1

B3-2

B3-2

83-3

84-7

B4-7

84-8

84-8

84-9

B4-9

B4-11

84-1 1

84-1 2

B-vii

TABLES

Table

3-1 Size Formulation

3-2 Testing Procedures

4-1 Process Measurements with Three Heater Modules

4-2 Yarn Property Comparison - Various Drying Techniques

Process Measurements - Single Infra-Red Heater Bank

Third Set of IR Drying Data

Impact Systems Primary Emitter Data

4-3

4-4

4-5

4-6 Drying Rate Comparison

!w!z

83-4

B3-5

84-2

84-4

84-6

B4-10

B4-14

B4-14

B-ix

SUMMARY

A “high temperature” electric infrared dryer was installed on a laboratory scale slashing machine and

the effectiveness and efficiency of infrared drying in the slashing process was evaluated. In particu

l a , the performance of the infrared dryer was compared to that of both radio frequency (RF), and

conventional heated cylinder drying techniques.

The infrared dryer (Impact Systems Model 4083, 18 inch Test Profiler with Reflector, Model 4082)

was installed and operated successfully to dry sized yarn. Engineering assistance during iostallation

was provided by West Point Foundry and Machine Co. The quality of the yarn (insofar as it can be

determined by laboratory techniques) does not appear to be significantly different from that of RF

dried yarn or of conventionally dried yarn. Certainly there is no inherent deterioration of yarn proper-

ties with the infrared drying system.

The maximum obtainable energy efficiency of the infrared drying process was 30% in our laboratory

apparatus if the yarn was dried to < 10% moisture regain. The estimated maximum efficiency

reaches 50 to 60% if significantly more residual moisture can be left in the yarn. The geometry of a

yarn sheet (with spaces between yarns) allows infrared energy to pass through and, to a large

extent, be wasted in heating the reflector and surrounding air. There is some indication o! 2. slightly

better energy efficiency at lower emitter temperature.

The drying unit is significantly overdesigned (60 kW maximum power) for the drying load which can

be presented by the laboratory slasher. The length of the drying zone was reduced from 18 inches

(45.7 cm) tc only 6 inches (15.2 cm). This reduced the maximum power to 20 kW which was still

sufficient for drying the yarn. Since production units operate at 2 to 4 times the speed of the labora-

tory slasher, the dryer may be appropriately sized for production use.

The infrared dryer could be started concurrently with the start of slashing (no warm up required);

however, a few seconds cool down time is required before stopping the yarn in the infrared heating

zone. Both start up and stopping of the slasher involve the risk of overheating or even burning the

yarn in two. The slasher will require some simultaneous or feed forward control, coupling machine

speed to heater power in order to minimize this risk.

B1-1

Additional testing to optimize the design of the IR applicator is recommended. Testing should be accomplished at longer wavelengths closer to the absorption wavelength of water. Also, other

arrangements for reducing energy losses should be evaluated. All of this work should be directed at

increasing the efficiency of IR applicators.

B1-2

INTRODUCTION

Each warp yarn which breaks during weaving causes the loom to stop and requires the attention of weaving personnel to repair the break and restart production. In addition to the personnel time and

the lost production, yarn breakage during weaving may produce a noticeable defect in the fabric. A

major cause of yarn breakage is the abrasion resulting from friction between yarns and between

individual yarns and the shedding components of looms. Textile yarn (particularly warp yarn) for

weaving is, therefore, often coated with a polymeric film (size) to provide abrasion resistance suffi-

cient to allow processing with a minimal amount of yarn breakage. The size film is usually applied to

the yarn from solution (in water), with the water being evaporated to precipitate and harden the film. The coating process (called slashing or sizing) is very energy intensive (expensive) and has the potential for creating yarn defects and its own set of weaving problems. The purpose of the work

reported herein was to examine the energy efficiency of recent infrared drying technology and to

evaluate the resultant yarn to determine if the new drying process produces yarn equivalent in quality

to that of a conventional slashing process.

82-1

EXPERIMENTAL PROCEDURES

A 50/50 polyesterkotton yarn of 25’s cotton count (25x840 yd/lb) was evaluated on a pilot scale

Callaway slasher. The slasher was modified by installation of a laboratory scale Impact Systems

(Model 4083) infrared dryer directly after the squeeze rolls (Figure 3-1 ). Engineering assistance was

provided by West Point Foundry and Machine Company. The dryer is constructed with three 6 inch

(1 5.2 cm) wide banks of 12 inch (30.4 cm) quartz infrared heating tubes. Figure 3-2 illustrates the

design. Figures 3-3 and 3-4 are photographs of the actual system and its components.

TAKE UP I

Figure 3-1 Callaway Pilot Slasher Schematic

B3-1

I. R. EMITTER ASSEMBLY

YAW PATH

TMGSTEN EMTTER

QUARTZ W L D

REFLECTOR ASSEMBLY

Figure 3-2 Schematic Cross Section of IR Heater

*4\, Fan Motor

/Fan Plenum

Air Duct

Path for

\

Yat

IF? Heater

Reflector

Figure 3-3 IR Dryer for Textile Warp

83-2

Figure 3-4 Warp Yarn Path Through IR Dryer

The heating tube banks were mounted perpendicular to the travel of the yarn sheet to distribute the

plenum air more evenly over the yarn sheet. This provided 18 inches (45.7 cm) of dryer in the

machine direction and a capability to dry a 12 inch (30.4 cm) wide yarn sheet.

The heating tubes are designed for a maximum filament temperature of about 2200°C. The tubes are housed in a metal box with ceramic reflectors and protected on the heating side by transparent

quartz plates. The system requires air circulation through the box to prevent overheating of the tubes. Another ceramic reflector (Impact Systems Reflector, Model 4082) is located about 1 to 2

inches (2.5 to 5.1 cm) in front of the heater to intercept and reflect heat passing through the yarn. A 6 inch (1 5.2 cm) wide sheet of 150 yarns was dipped into a size bath with a formulation as given in

Table 3-1. The bath temperature was controlled at 180°F. The yarn sheet was passed through a nip

between a stainless steel and a hard rubber roll (durometer hardness of 55 Shore A). The rolls are 6

inches (1 5.2 cm) in diameter and are squeezed with air cylinders to a pressure of about 45 Ib/lineal

inch.(78.8 Newtons/lineal cm). The yarn sheet passed immediately beneath the infrared dryer,

between the dryer and reflector. The yarn sheet progressed to the end of the slasher, through a

Strandberg Moisture Monitor and onto a flanged metal spool (beam). The Strandberg Moisture

Monitor was used to ensure that the moisture content of the sized yarn stayed within acceptable

limits. Yarns were wound onto the beam with plastic film to separate different experimental condi-

tions and subsequently unwound for testing.

83-3

Table 3-1

Size Formulation

CornDonen t Parts bv weiaht

PVA, WS-42 Poly Vinyl

Alcohol, nonfoaming

from Air Products

100

Wax (Griffwax 91 -D) 5

Water (4 dilutions) 800- 1300

To select a reasonable set of size application operating conditions for drying rate and efficiency

studies, yarn was first run with the application of water only. Subsequently, a sizing trial was run.

The difficulty of obtaining exactly the desired coating level (add-on) dictates that sizing trials be run

over a range of coating levels, and that the yarn properties for a particular add-on are read from a graph of yarn property versus add-on. The results of the first trials indicated an overcapacity of the drying system and the desirability of running only one of the three banks of heaters, so a second set

of trials was run with two banks of heaters disconnected.

Moisture contents (and wet pick up values) were determined by measuring weights of yarn samples

before and after oven drying. Size add-on was determined by measuring the oven dry weight of a

sample before and after desizing. Yarn was evaluated by measurements of tensile strength, breaking . elongation, abrasion resistance, and hairiness (procedures listed in Table 3-2).

83-4

Table 3-2

Testing Procedures

1.

2.

3.

4.

5.

6.

7.

8.

Wet pick up (wate r onlv) - Cut and weigh sample immediately after squeezing and after oven

drying. Wet pick up is expressed as a per-cent based on oven-dry yarn weight.

Size solids conte n t - Weigh size solution before and after oven drying. Size expressed as a per-

cent based on the weight of solution.

add-on - Weigh an oven dry sample of a sized yarn before and after 3 washes of 10 minutes each with hot water (180-F). Size add-on expressed as a per-cent of oven dry yarn weight.

Wet pick up (s ize solutiou - Calculate from items 1,2,and 3 above. WPU = item 3/item 2 for PVA trials.

Abrasion res istanm - Zwigle abrasion tester. 3 sets of 20 yarns under 30 g tension each, with

800 grit sandpaper.

Hairiness - Shirley Hairiness Meter set to detect 3 mm hairs. Five samples of 10 meters each were run.

Tensile strenath - An lnstron tester was used with 10 inches (25.4 cm) gage length, strain rate of

120 per-cenVminute. Results are an average of 25 yarns, measured in pounds force.

Flonaation at W - Determined on an lnstron tester from the data used in test 7 and normalized with the sample length.

83-5

I

RESULTS AND DISCUSSION

With water in the size box, startup was not difficult. The slasher was started at the desired speed and

after it was running the dryer was turned on. This resulted in a small quantity of wet yarn being

wound onto the beam (an acceptable condition for water, but not for sized yarn). The dryer was

tested under a variety of intensity and speed conditions (results in Table 4-1). It will be noted that

several combinations of high intensity with low speed provided more heat than the yarn could with-

stand. Even at the highest speed, the yarn was scorched by the heater at maximum intensity. The

heater, as installed, has excess power and would allow much faster speeds than the capability of our

pilot slasher.

The results (Table 4-1) were used to determine initial conditions for the sizing trial. Conditions se-

lected were 260 volts and 25 yd/min (22.9 m/min).

B4- 1

Table 4-1

Process Measurements with Three Heater Modules

Speed Power Moisture Drying YPm v A kW Regain Rate

per-cent Ib/hr

En erg ya Efficiency corrected

WATER ONLY

5 0 0 0 80.6 15 0 0 0 71.3

25 0 0 0 78.6

35 0 0 0 58.5

5 220 15 220

25 220

15 330

25 330

35 330

35 440

scorched and burned out 2.25 4.43

3.04 8.10

scorched and burned out

12.8 7.05

5.06 8.07

4.46 8.10

SIZING TRIAL

25 260 37 16.7 2.44

25 2GO 37 16.7 2.16

25 260 37 16.7 2.24

25 260 37 16.7 1.98

9.87 35.1

9.89 35.16 9.36 33.0

9.39 33.4

Corrected to a yarn sheet occupying the full width of heater

84-2

The water in the size box was replaced by size solution. Initial startup with size solution was difficult

because of the danger of burning the dry yarn when the heater was turned to a high level (sufficient for drying) while the yarn was stationary or moving slowly. One must thus anticipate the arrival of the

wet sized yarn front into the drying zone and quickly adjust the dryer intensity to a level which will just dry the yarn. An alternate procedure of starting the slasher with water and switching to size solution

“on the fly” was also successful but results in an initial layer of wet yarn on the beam. Once the

slasher is running, a feed-back moisture sensing control near the dryer exit would likely be able to

adjust the heater intensity and maintain the proper dryness. Both start up and slow down conditions,

however, appear to require some anticipation by a control system to avoid underdrying or overheat-

ing the yarn.

Results of yarn testing appear in Table 4-2 along with a comparison of results with previous results (1) from conventional and RF drying trials. The comparisons are shown graphically in Figures 4-1

thru 4-4. We see neither a marked improvement nor a marked degradation of yarn properties be-

tween the infrared drying process and the previous drying methods.

B4-3

Table 4-2

Yarn Property Comparison - Various Drying Techniques

Conventional Drying (heated cylinder)

Test Number 1 2 3 4 5 6

Size add-on (Yo) Oa 8.1 9.8 11.7 12.6 16.2

Zwigle abrasion (cycles) 120b 200 292 363 383 48 1

Elongation at break (Yo) 7.4 6.9

Hairiness (no./M) 30b 10.7 11.4 7 .O 8.2 9.5

Tensile strength (Ib) 1.12 1.11

RF Drying

Test Number 7 8 9 10

Size add-on (Yo) Hairiness (no./M) Zwigle abrasion (cycles) Tensile strength (Ib) Elongation at break (Yo)

7.44 10.1 13.1 16.7 9.98 9.16 9.64 11.2 220 291 406 523 1.06 1.08 1.09 1.18 9.07 9.00 8.08 9.04

Infra-Red Drying (all heaters - low emitter temperature)



9.06 11.2 14.1 17.6 11.6 11.7 10.1 8.04 354 383 505 556 1.11 1.06 1.1 1 1.11 7.73 5.64 6.60 7.49

Infra-Red Drying (one heater bank - high emitter temperature)



8.92 12.2 15.8 20.4 8.40 6.52 5.62 3.74 253 378 52 1 685 1.09 1.08 0.97 1.07 8.39 8.26 6.87 8.21

aControl - no drying, no size on yarn bApproximately

84-4

Preliminary energy efficiency calculations were made on the basis of the sizing trial and appear in

Table 4-1. These calculations are corrected for the fact that our yarn sheet is only 6 inches (1 5.2 cm) wide, while the heated area is 12 inches (30.5 cm) wide. Such a correction is justified since we

could easily heat a 12 inch (30.5 cm) wide yarn sheet in our heater, which would evaporate more

water but not change the energy used by the heater. The calculations are not corrected for the

spaces between yarns (where the radiation passes unhindered) because the yarn sheet on a slasher

has such spaces by design, and we have not been able to devise a way of using this escaped en-

ergy. The escape of energy is reduced by the reflector below the yarn sheet which absorbs energy and acts as a secondary emitter. No optimization of reflector design or operation was attempted.

Since infrared energy transfer between two objects depends on the difference between !he fourth

powers their temperatures, and since efficiency of energy conversion to radiation also increases with

emitter temperature, it was considered desirable to evaluate the heater at a filament temperature

close to the upper design limit. As indicated previously, operation of the dryer at high intensity was

not possible, because the yarn burned through. With two of the banks of heaters disabled, however,

it was possible to obtain high intensity operation without damage to the yarn. As before, an experi-

ment with water only was run over a range of slasher speeds and dryer intensities to select appropriate conditions for sizing trials with a single bank of heaters. The results of this preliminary experi-

ment appear in Table 4-3 along with the energy efficiencies calculated for each experimental condition. The data (corrected for width) are presented graphically in Figures 4-5 and 4-6. The results

show when power level increases with other factors constant, efficiency decreases. This occurs

presumably because as drying progresses, the remaining water becomes more difficult to remove.

This is consistent with the observation that calculated efficiency generally increases with an increase

in moisture regain in the yarn as it exits the dryer. The limited range of data and the scatter prevent

a definitive answer to the question of selecting an optimum wavelength for maximum absorption of the energy. The results of the subsequent slashing trial at the selected conditions appear in Table 4-

3 and Figures 4-5 and 4-6. Yarn properties are not markedly different from the previous infrared

results, or from the results of other drying processes.

B4-5

Table 4-3

Process Measurements - Single Infra-Red Heater Bank

ID Speed Power Moist. Drying Eff iciencya Regain Rate Calculated

(I b/h r) Corrected no. (YPm) (VI (A) (kW)

(Yo)

1

2

3

4

5

6

7

8

9

1

2

3

4

5

10

10

10

20

20

20

30

30

30

200

300

400

200

300

400

200

300

440-

32

40

47

32

40

47

32

40

50

WATER ONLY

6.4 32.4

12.0 6.1 0

18.8 1.62

6.4 21.6

12.0 17.9

18.8 6.81

6.4 40.5

12.0 31.9

22.0 12.0

Sized According to Table 4. for IR Single Bank

17.67 400 47 18.8 3.94 9.39

17.67 400 47 18.8 3.43 8.46

19.67 400 47 18.8 3.80 8.80

19.67 400 47 18.8 3.12 8.03

19.67 400 47 18.8 2.53 7.89

3.26

4.39

4.58

6.22

6.53

7.48

5.60

6.71

9.27

14.9

13.4

14.0

12.77

12.55

15.2

10.9

7.28

29.0

16.3

11.9

26.5

13.4

12.6

29.8

26.8

28.0

25.54

50.20b

30.4

21.9

14.6

58.0

32.5

27.8

50.3

26.7

25.2

aEfficiency corrected for the fact that the heater is 12 inches (30.5 cm) wide but the yarn sheet is only

6 inches (1 5.2 cm) wide.

bEffect of using a 3 inch (7.6 cm) wide web instead of 6 inch (15.2 cm). This higher efficiency may

be due to a much closer yarn spacing. - Included in the figures with the 400-Volt water data only.

B4-6

Abrasion Cycles 800

700

600

500

400

300

200

100

0 0 5 10 15 20 .25

Percent Size Add On

_c Conventional 4- RF -+- IR 3 Banks IR One Bank

Figure 4-1 Abrasion Resistance for Different Drying Methods

Hairiness (no./M) 35

30

25

20

1 5

10

r L

0 0

___i__

5 10 15 Percent Size Add On

20 25

Conventional --c RF -%+ IR 3 Banks -G- IR One Bank -

Figure 4-2 Yarn Hariness for Different Drying Methods

64-7

Tensile Strength (Ib.)

f 1.2

1.15

1.1

1.05

1

0.95

10

9

8

7

6

5

i’ /

u/

I

\ \

\

\ b

L

\ \

0 5 10 15 20 25

Percent Size Add On

Conventional + RF IR 3 Banks -S- IR One Bank _c

Figure 4-3 Yarn Tensile Strengths for Different Drying Methods

Percent Elongation

0 5 10 15 20 25

Percent Size Add On

Conventional -+- RF +K- IR 3 Banks - IR One Bank _c

Figure 4-4 Yarn Elongation at Break for Different Drying Methods

84-8

Efficiency 60

50

40

30

20

10

0 0 2 4 6 8

Drying Rate (Ib/hr) 10

Water Only

200 Volts +- 300 Volts +++ 400 Volts -

Figure 4-5 Efficiency VS Drying Rate - Corrected for Width

Efficiency 60

50

40

30

26

10

0 0

12

\ P

/

10 20 30 40 Percent Moisture Regain

Water Only

200 Volts -+ 300 Volts ++ 400 Volts -

Figure 4-6 Efficiency VS Regain - Corrected for Width

B4-9

50

Because of the scatter in efficiency results, previousiy noted, a third drying trial was run with water in

the size box using a single heater. Precautions were taken to assure that temperature conditions in the heating zone had stabilized before beginning the measurements. Results appear in Table 4-4 and Figures 4-7 thru 4-9.

Table 4-4

Third Set of IR Drying Data

WPU MR RES. TIME DRYING RATE EFFICIENCY (Actual)

72.8 60.8 0.2857 1.8022 75.7 57.7 0.4000 1.9334 78.7 45.7 0.6667 2.1 198 81.6 9.7 2.0000 1.5408

- - - m a e = 200. AmDs - 31.5. kW 6.9

72.8 50.6 0.2857 3.3322 75.7 42.4 0.4000 3.5726 78.7 22.8 0.6667 3.591 9 81.6 3.7 2.0000 1.6694

- - Amps - - 37.5. kW - - 10.31 75

72.8 29.6 0.2857 6.4822 74.3 26.2 0.3333 6.1817 75.7 20.8 0.4000 5.8869 77.2 14.0 0.5000 5.41 80 78.7 10.4 0.6667 4.3891 80.1 8.0 1 .oooo 3.091 7 81.6 1.9 2.0000 1.7080

, 72.8 13.7 0.2857 8.8672 75.7 6.8 0.4000 y 7.3869 78.7 4.8 0.6667 4.7491

72.8 6.0 0.2857 10.0222 75.7 4.3 0.4000 7.6548 78.7 2.3 0.6667 4.9098

45.5 48.8 53.5 38.9

40.1 42.9 43.2 20.1

47.2 45.4 43.2 40.0 36.2 22.7 12.5

43.6 36.4 23.4

37.2 28.4 18.2

WPU: Wet Pick Up MR : Percent Moisture Regain = (Wet WtlDry Wt - I)*lOO RES TIME: 10Narn Speed in yards per min, sec DRYING RATE: Lbs Yarn per hr-(WPU-MR)/lOO, Ib waterhr EFFICIENCY: 2-0.3788-drying rate/kW power. Corrected for the width of the yarn sheet. Correction factor = 2.

B4-10

Percent Moisture Regain 70

20

10

0 0.5 1 1.5 2 2.5 Residence Time, sec

Third Drying Trial

125 Volts -4- 2 0 0 Volts - 350 Volts - 4 2 5 Volts

- ++-- 2 7 5 Volts

Figure 4-7 Moisture Regain VS Residence Time for Third Drying Trial

Percent Moisture Regain 25

10

5

0 ' 1 I I I

0 0.5 1 1.5 2 2.5

Residence Time, sec

Third Drying Trial

125 Volts - 200 Volts --lc 2 7 5 Volts - - 350 Volts - 425 Volts

Figure 4-8 Drying Rate VS Residence Time for Third Drying Trial

84-1 1

Efficiency 60 j

50

40

30

20

0 ' I I I I 1 I

10 20 30 40 50 60 Percent Moisture Regain

Third Drying Trial

125 Volts 200 Volts -I+- 275 Volts

350 Volts ++- 425 Volts

Figure 4-9 Efficiency VS Regain for Third Drying Trial

70

B4-12

Figure 4-9 shows energy efficiency as a function of exit moisture in the yarn. The results are similar

to those obtained previously in this study (Figure 4-6). The efficiency values are (and should be

expected to be) somewhat lower than reported for infrared drying of fabric (2). As the moisture

content of the yarn decreases the efficiency approaches zero. What is different from the previous

results and may be surprising (without some thought) is that the efficiency seems to be decreasing at

high moisture content. This can be explained by the fact that these points represent the time just as

drying begins, and includes the heat-up of the yarn and water which requires energy but does produce rapid evaporation. There is a slight indication of improved efficiency at the lower emitter tem-

peratures since the curve for 125 volts shows slightly higher efficiency than the other voltages for all the exit fiber moisture levels.

Table 4-5 is data from Impact Systems which allows the voltage data to be converted into emitter

temperature. The emitter temperature at 125 volts is about 1250°C which corresponds to a black

body wavelength maximum of 1.9 microns. The efficiency difference resulting from changes in

emitter temperature appears to be small (less than 3%) and should be confirmed in other tests since

the limited speed of our machine prevents the collection of complete data at the higher residual

moisture contents. The air blower which supplied cooling air to the lamps could have been a factor

in the rate of removal of moisture from the yarn sheet. Drying requires both heat and mass transfer.

Mass transfer could have been a limiting factor instead of lamp temperature.

B4-13

Table 4-5

Impact Systems Primary Emitter Data

Voltage Filament Temp. Wavelength

Degrees K microns

125 1525 1.89

200 1759 1.65 275 1950 1.48

325 2130 1.35 400 2240 1.29

Other types of pilot dryers are compared to IR in Table 4-6. In making heater comparisons, it is

desirable to determine the dynamics of each drying method. In conventional slashers with steam

heated cylinders, the zone steam pressures are kept at a constant set point. Exit moisture content is

read and fed back to a speed control system which changes the overall slasher speed to maintain a

constant exit moisture content. When a problem occurs, the slasher is slowed to creep speed, or

stopped in order to fix the problem.

The dynamics of drying of a conventional pilot slasher were studied previously (3). The thermal

inertia is significant and requires substantial warm-up and cool-down time. The warm-up time wastes

energy and time but does not significantly affect the quality of the yarn. When a problem occurs,

which requires slowing of the slasher, cool-down occurs much slower than the speed change. In

conventional drying, the quality of the yarn may be damaged by overdrying when the slasher is

slowed or stopped. The heat intensity is usually low enough to prevent the yarn from being de-

stroyed in the dryer during these periods.

Table 4-6

Drying Rate Comparison

Drying Method Drying Rate Source Ib water/ft hr

cylinder 0.56 RF 2.27

Inf rareda 2-20

published data (1)

published data (1) this study

aDepending on the power delivered to the dryer emitter temperature

B4-14

RECOMMENDATIONS FOR FURTHER WORK

1.

2.

3.

4.

Further investigations on the mechanisms of infrared drying in slashing are recommended.

Frequently, commercial drying installations employ more than one type of dryer. This report has not investigated the use of combinations of drying technologies. In this regard, a combination of IR and conventional heated cylinder drying has been suggested. One advantage of non-contact

drying of sized yarn is the elimination of wax from the size formulation. Wax is included to pre-

vent yarn sticking on the heated cylinder. We recommend making additional trials of a combina-

tion process using an infrared pre-dryer to provide "instant" startup and rapid heat dissipation

when slowing the slasher, and using less expensive conventional heating to provide much of the

drying capacity during normal running. This combination will be much more attractive if the

infrared predrying allows the elimination of wax from the formulation.

Design of a control system which will respond to step changes in speed when they are made

rather than through feed back control based on moisture content will be necessary if infrared

dryers are to be used successfully in slashing. Simulation and control system design work are

recommended.

There has been no attempt to optimize the reflector design or operating conditions for yarns. It is

reasoned that typical reflector material (gold or other smooth metallic surface) would produce specular reflection (rather than absorption and reemission at lower energy) which could produce

some increase in efficiency. This should be investigated if use of the process hinges on a modest

change in energy efficiency. More data on the fundamental absorption spectra of sizes should be

collected and compared to the wavelengths obtained by IR heaters.

B5- 1

REFERENCES

1. M. W. Reed and W. S. Perkins. “Radio Frequency Drying of Textile Yarn in Sizing”, Final report to TVA on Project TVA 68097, Tennessee Valley Authority, Chattanooga, TN, 1988.

2. C. Langlois and R. Maisonneuve. “Electric Infrared Technology in Textile Drying Processes”,

Book of Paoers, 1986 International Conference and Exhibition, AATCC, Research Triangle Park,

NC, 1986.

3. A. M. Haas, M.W. Reed, and D. C. Williams. “Pilot Slasher Drying Model Identification”, Textile

Research Journal 58;(1), 1988.

B6-1

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