The Roving Frame

by: Beyene Dumecha

Wolkite university

Ethiopia

Introduction

The roving frame is the machine that comes after the draw

frame in short-staple spinning system.

The input is the finisher draw frame sliver in sliver cans and

the output of the roving frame is called roving.

The roving frame is called by various names in the industry

and in the literature.

The machine is called a fly frame or a flyer frame - as it

employs a flyer.

The draw frame produces a sliver that already

exhibits all the characteristics required for the

creation of yarn, namely an ordered, clean strand of

fibers lying parallel to one another.

In fact, the roving machine is :

Complicated,

Liable to faults,

Causes defects,

Adds to production costs and delivers a product

that is sensitive both in winding and unwinding.

Two principal reasons for the use of roving

frame are:

1) The required high draft in the ring frame (DT = 300 –

500), and

2) Draw frame cans are not convenient for transport and

presentation of feed material to the ring frame.

Objectives of draw frame

To draft the sliver to a thin strand,

To impart to the drafted strand a protective twist and

To wind the drafted and twisted roving material onto

a suitable package for further use.

Roving frame is a comparatively a slow and complicated

machine.

Not much improvement has been possible in terms of

speeds in comparison with say, a card or a draw frame.

Efforts to eliminate this process have not met with

success so far, at least in the case of ring spinning system.

It is hoped that this machine may become redundant in

the future.

Advantages of roving frame

1) The amount of material content in the roving package for its

size is quite substantial; sliver cans cannot hold this amount

of material within the same volume.

2) The handling of roving bobbins and creeling them in the ring

frame are standardised and occupy less space in the ring

frame creel.

The draw frame sliver cannot hope to match the roving

bobbin in this regard.

1) The small amount of twist given to the roving appears to be

more advantageous for good drafting.

Operating Sequence

The draw frame sliver cans are arranged in 4 or 6 rows in the

creel zone and the sliver from each can is fed to the drafting

system.

The drafting system drafts the sliver to a fine strand of material

ready for twisting.

The draft usually employed in fly frames ranges from 5 to 20.

Coarser rovings need less and finer rovings need higher drafts.

The delivered roving has a hank (or, count) in the range of about

1s to 3s Ne.

The material delivered from the drafting system is led

to the top of the flyer.

From the front roller nip to the flyer top, the material

remains unsupported.

From the top of the flyer, the material is guided

through one of the legs of the flyer; at the bottom of

the leg of the flyer, the material is wound on the

presser (usually two or three turns around the presser

arm).

The material is then passed through the eye of the

presser from which point, it can be wound onto the

package.

The strand delivered by the drafting system is thin

and weak.

Therefore, a protective twist - of the order of about 1

to 3 turns per inch is given to the strand before

winding it onto a wooden or plastic package.

The flyer imparts twist to the delivered material by

its rotations.

One rotation of flyer imparts one turn of twist to the

delivered material.

The flyer is mounted on the top of a spindle.

The spindle and flyer rotate together.

• The flyer rotates at a constant speed.

• The most common speeds employed range from

about 1000 to 1500 revolutions per minute.

• The twisted roving is wound onto the surface of

the bobbin in the form of closely spaced helical

coils.

• Each of the spiral coils is spaced close to each

other i.e. the coils touch each other.

To effect winding in this manner, the roving bobbin

is moved up and down.

Once a layer of roving has been wound, the direction

of movement of the bobbin is reversed and a fresh

layer is wound over the previous layer.

The process continues till the bobbin is full.

• The bobbins and the associated driving gears are

placed in a bobbin rail; the spindle and the associated

driving gears are housed in the spindle rail.

• The spindle rail is stationary.

• The bobbin rail along with the bobbins moves

vertically up and down during the running of the

machine to enable winding of the material in

traverses.

To effect winding of material onto the bobbin, the bobbin

has a rotational speed which is equal to flyer speed plus the

additional rotations for winding.

As each layer is completed, the diameter of the bobbin

increases.

This would mean that the additional rotations required for

winding have to be reduced after the completion of each

layer.

Note that the delivery rate from the drafting system remains

constant.

Effect Of Arrangement Of Bobbins In

Two Rows

• In fly frames, the spindles are arranged in two rows (in

a zigzag manner).

• This arrangement is made in order to economise on the

space requirements.

• Though there is a large economy in space, the

arrangement has some technological disadvantages.

The free unsupported lengths (L1 & L2) are different for

the two rows of bobbins. (Fig. F 6.3 (a)).

The rolling angles (β) are different (Fig. F 6.3 (b)).

The spinning triangle sizes are different for the two

rows(Fig. F 6.3 (c)).

These differences result in:

more complicated design

Operation of the machine is made less convenient

Automation is hindered

uneven twisting

uneven binding of fibres and

ultimately count variation between front and back

rows.

Operating regions of the roving

frame

The creel

• Above the cans there are several rows of driven

rollers to help the slivers on their way to the drafting

arrangement.

• Guide rollers should run smoothly to avoid false

drafts.

• A perfect drive to the rollers is effected by chains or

shafts.

The Drafting Arrangement

A. 3-over-4 drafting arrangement: used relatively rarely since it

gives less drafts.

B. Double apron drafting system with 3/3 or 4/4 (for high drafts)

roller arrangements:

is used in the roving frame since it enables drafts of

20 while holding the fibers more or less under control

during their movements.

• Lower rollers are usually fluted.

• Top rollers are rubber coated pressure rollers.

Top roller weighting can be carried out by:

– Spring (all manufacturers)

– Pneumatic pressure (Rieter)

– Spring + magnet

Maximum Total Draft = 20

Minimum Total Draft for cotton = 5 and

for synthetic fibers = 6.

Break drafts for cotton = 1.05 – 1.15 (usually 1.1), and for

synthetics and strongly compressed cotton sliver delivered

from high performance draw frames = 1.3.

Break draft affects roving evenness.

Aprons are used to guide and transport fibers during

drafting.

• They are made of leather or synthetic rubber.

• They are usually about 1mm thick.

• They should extend as closely as possible to the nip

line of the front rollers.

• The guiding length, referred to as the cradle length,

must be adapted to the staple length.

• Material Cradle Length (in mm)

Cotton up to 11/8”; 40mm synthetic fibers -----------------36

Cotton greater than 11/8”; 50mm synthetic fibers ---------43

60mm synthetic fibers ---- ----------------50

Spindle and Flyer

The spindle is simply a support and drive element for

the flyer.

The spindle tip is conical and is provided with a slot.

When the flyer is set on the spindle cone, a pin on the

flyer projects into the slot so that the flyer and spindle

are converted into a unit for drive purposes.

Functions of the flyer:

1) Inserting twist

Each flyer rotation creates one turn in the roving.

Since the flyer rotation rate is held constant, twist per unit

length of roving depends upon the delivery rate because twist is

given by:

Twist = Flyer rotation rate

Delivery speed

High levels of roving twist always represent production loses and possibly

draft problems in the ring frame.

Low twist levels can cause false drafts or even roving breaks during

bobbin winding.

2). Leading the very sensitive strand from the flyer

top to the package without introducing false

drafts.

This is very difficult task because:

I. The strand has only protective twist and is very

liable to break; and

II. The flyer, along with the roving, is rotating at a high

rate (up to 1500rpm).

Cont..

The fiber strand must, therefore, be protected against

strong air currents.

For this purpose, in most roving frames to date, one of

the two flyer legs has been grooved, i.e., open in a

direction opposite to the direction of rotation.

The second full flyer leg serves to balance the

grooved leg.

• New designs are no longer provided with this easily accessible,

“service-friendly” groove.

• Instead, they have a very smooth guide tube set into one flyer leg.

• The advantages are:

the strand is completely protected against the air flows and

frictional resistance is significantly reduced so that the strand

can be pulled through with much less force.

These reduce false drafts and strand breaks while allowing high

production speeds.

The disadvantage is that piecing of strand break is difficult.

Various designs of the flyer

• The limit on performance of the roving frame is determined by

both the delivery speed and the rotation rate of the flyer.

• Depending upon its form and drive, there are three flyer types:

1. Spindle mounted flyers: Simple as far as design and drive are

concerned. Piecing is easier. However, automation is difficult.

2. Top-mounted (suspended) flyers: Facilitates automation of the

doffing operation, but piecing is difficult.

3. Closed flyers: Reduced spreading of the legs at high operating

speeds.

Types of Flyers (a) Spindle mounted (b) Top mounted; (c) closed

flyer

The flyer inserts false twist which results in:

Strongly twist roving in the unsupported length

between the drafting arrangement and the flyer.

• Roving breaking rate in the spinning triangle is thus

reduced and fly and lap formation are decreased

A more compact roving which increases the capacity of

the bobbin and enables higher flyer speeds.

• The compactness of the roving also enables winding

with higher tension, and

A significant reduction of the difference in roving

fineness between the front and back rows of bobbins.

Build up of the bobbin

A roving bobbin is a cylindrical body with tapered ends.

The angle of taper of the ends normally lies between 80o

and 95o (maximum 100o), and depends upon the adherence

of material.

The angle is made as large as possible to wound more

roving onto the package.

However, the angle must be small enough to ensure that the

layers do not slide apart.

Dimensions of Roving Package

• Laying down of roving in the package is effected in parallel

layers, i.e., each wrap is laid on wooden or plastics tubes

closely adjacent to the neighboring wrap.

• To wind over the whole length of the tube, the winding

point must be continually shifted.

• This is achieved by:

1) Raising and lowering the flyer or

2) Up and down movement of the tube together

with the bobbin rail (by means of racks or lever).

• Variation in bobbin speed originates from the cone

drums.

• When the builder motion shifts the cone belt, the

rotation rate of the lower cone is changed.

• This continuously reducing rotation rate is

transmitted via gearing to the differential and is there

superimposed on the constant speed of the main shaft.

• Further gearing then transmits the resultant movement

arising in the differential to the bobbin drive.

• Furthermore, in order to prevent falling away of

individual layers, the bobbin ends are made conical and

consequently the lift of the bobbin rail has to be

reduced after each stroke (layer).

For winding and controlled twisting of the roving to a

selected degree, the flyer and the bobbin must have

the same sense of rotation.

However, the bobbin must rotate faster than the flyer

(leading bobbin) or the flyer faster than the bobbin

(leading spindle).

Advantage of leading spindle: With a preset fixed

spindle speed, the operation can be run with lower

bobbin speeds – lower than the spindle speed.

Advantages of leading bobbin are:

1. Fewer roving breaks or faultily drafted places at the winding

point because the drive transmission path from the motor to the

spindle is short, whereas that of the bobbin is long

2. No unwinding of the layers during roving breakage and

3. Speed reduction with increasing package diameter.

However, with a leading spindle, the bobbin speed must be

gradually increased with increasing package diameter which

demands more power.

Let VB = nB DB

Vs = ns Ds

Then,

Delivery length, L = VB – Vs

= nB DB - ns Ds

But, DB = Ds at the winding point.

Therefore, L = nB D - ns D = (nB - ns) D

Hence, the bobbin speed at any given bobbin

diameter is:

nB = L + ns

D

The builder motion

It performs three important tasks during a winding

operation:

1. Shifts the cone belt corresponding to an increase in the

bobbin diameter

2. Reverses the direction of movement of the bobbin rail at

the upper and lower ends of the lift stroke, and

3. Shortens the lift after each layer to form tapered ends on

the bobbins.

Thank you!