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Comparison of yarn quality, productivity and cost of manufacture of Rotor and Ring spinning

N.Balasubramanian1

Retd. Jt. Director (BTRA) and Consultant

Merits and Limitations of Rotor Spinning in relation to Ring SpinningMerits

1. Elimnation of Roving process. Elimination of one Drawframe passage in coarse counts like 10s and below.

2. Elimination of winding. 3. As a result of shorter processing, space requirement is reduced4. Higher productivity.Table gives a comparison of productivity in ring and

rotor spinning.Table 1 : Comparison of productivity of Ring and Rotor spinning

Ring Rotor Semi automatic Rotor automatic

Count Ne

Spindle Speed rpm

TM Production per spl shift of 8hrs, gm

Rotor SpeedRpm

TM Production per rotor shift of

8hrs, gm

Rotor SpeedRpm

TM

Production per rotor shift of 8 hrs, gm

10s10000 .86 407 70000 5.2 2911 100000 5.2 4247

20s 13500 .88 212 78000 4.9 1223 120000 4.9 1922

30s 15500 .9 139 85000 4.7 760 130000 4.7 1187

40s 18000 .92 109 90000 4.5 537 140000 4.5 872

Productivity increases from 4.9 to 7.1 times in semi automatic rotor machine and by 7.9 to 10.4 times in automatic rotor machines compared to ring frame. This is because of higher rotor speed and efficiency. This is one of the major advantages of rotor spinning

5. Lower power consumption to the extent of 15 – 20 % due to shorter spinning process, lower airconditioning space..

6. Lower labour requirement because of higher productivity, automatic piecing, and package changing.

1 I, Rajeswari, 36, 17th Road, Chembur, Mumbai 400071, 9869716298

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7. Higher level of evenness, lower level of imperfections and faults, lower variability in count and strength, which contribute to better weaving and knitting performance and better fabric appearance. Yarn evenness and imperfections in rotor and ring yarns found in good mills are compared in Table 2 below

Table 2 : Comparison of evenness and imperfections in Ring and Rotor yarns

Rotor Ring

U% Imperfections/km U% Imperfectons/km

Thin(-

50%)

Thick(3)

Neps(3)

Thin(-

50%)

Thick

(3)

Neps(3)

8s – 12s

8.5 5 15 100 11 35 150 200

18s – 22s

9 7 50 150 12 50 200 200

28s – 32s

11.5 10 80 200 14 80 250 250

38s – 42s

13 30 150 250 14.5 100 325 350

Manohar, Rakshit and Balasubramanian1 found that the reductions in evenness and imperfections with rotor yarns are more prominent in waste mixing than normal mixing.

8. Higher elongation at break which assists in weaving.9. Better abrasion resistance. Abrasion resistance of rotor yarn fabrics as

estimated by weight loss, after a preset number of cycles, is lower by 20 to 55% than ring yarn fabrics2.

10.Hairiness is much lower in rotor yarns than ring yarns. Sirang3 et al found that ring yarn has a 20 % higher number of hairs than rotor yarns, and 40 % higher length. But number of hairs of extremely short (< 0.25 mm) and long hairs (> 3mm) of rotor yarns are higher than that of ring yarns. This will be clear from the comparison of frequency distribution of hairs shown in Fig 1

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0 1 2 3 4 5 60

5

10

15

20

25

30

35

40

45

50

Hair Length mm

n/N

%

Rotor

Ring

Fig 1 Frequency distribution of hairs in rotor and ring yarns, n = number of hairs,

N = Total number of hairs, 16s cotton yarn

11.Better cover of fabric because of higher diameter

12 Better dye uptake because of higher specific volume. For the same reason, higher size pick up in sizing.

13.Unique yarn properties that make it ideal for certain materials like denim, jeans and furnishings

14.Low raw material cost because of addition of waste in very coarse countsLimitations

1. Lower yarn strength than ring yarns and the reduction increases with count. Manohar, Rakshit and Balasubramanian1 found 15 – 25 % lower strength with rotor spinning compared to ring spinning with normal mixings. But with waste mixing the strength loss is much lower (about 5 – 14%).Strength loss is partly compensated by lower variability in strength as shown in Fig 2

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Fig 2 : CV of single thread strength of OE rotor and Ring spinning Balasubramanian4 showed that the difference in strength is more in single thread than lea strength because of lower variability of rotor yarn.

2. Lower tensile and tear strength of fabricBut reduction in tensile strength at fabric is less than that at yarn because of better fabric assistance

3. Rotor spinning is not very suitable to man made fibres as the reductions in strength are more and improvements in evenness and imperfections are marginal. Moreover polyester fibres with less titatanium diaoxide have to be used to minimise wear and tear of opening roller teeth and rotor.

4. Higher twist level by 0.2 to 0.5 units of TM5. Rough feel. This can be overcome by softener treatment but at the cost of

strength reduction6. Higher stiffness7. Restricted to counts 40s and below.8. Fabric appearance affected by presence of closely wound wrapper fibres

and stripbacks9. Difficulty in dyeing dark shades because of lower density10.Dull appearance11.Higher capital cost of the machine and requirement of air conditioning.12. Spare parts and maintenance costs are also higher in Rotor spinning

As a result of the advantages mentioned earlier, cost of manufacture in rotor spinning is much lower than ring spinning and the difference is more marked in coarser counts. The economics of rotor spinning improves with lower capital cost as interest on loan for capital will reduce. If indigenous manufacturers make automatic 2nd and 3rd generation rotor machines, capital costs will come down and rotor spinning economics will improve and break even point will move

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towards finer count Estimates of cost of manufacture in rotor and ring spinning by Rieter5 are given in Table 3

Table 3Comparison of cost of manufacture in rotor and ring spinning, CHF/Kg, (US. $/Kg)

Type of Spinning High wage country Low wage country

8s 34s 8s 34s

Ring 1.21 (1.31) 2.51 (2.71) 0.65 (0.69) 1.52 (1.64)

Rotor 0.59 (1.64) 1.52 (1.64) 0.39 (0.42) 1.25 (1.34)

RotorRing

×100 48.7 60 60 82

Manufacturing cost benefits from rotor spinning are more in coarse counts like 8s than in 34s and are also of higher order in high wage countries. Weidner Bohnenberger6 gives cost comparison, inclusive of of raw material, in rotor and ring spining for 20 tex (300 Ne) and 30 tex (20s Ne) yarns as given in Table 4.

Table 4Cost of manufacture in rotor and ring spinning (EUR/Kg and US $/Kg in bracket)

Count Rotor Ring

20 tex (30s) 0.68 (0.91) 1.1 (1.47)

30 tex (20s) 0.5 (0.67) 0.85 (1.14)

The costs given in Table 4 are much lower than that given by Rieter. Break even point at which rotor spinning can produce yarn at lower manufacturing cost used to be 24s – 30s earlier in India but has moved up to 40s – 44s in recent times becauses of higher rotor speeds and higher level of automation offered by the 3nd generation machines.Fig 3 below compares the cost of ring spinning over rotor spinning over the years (based on ITMF Report). The extent of reduction in cost of rotor spinning over ring spinning has increased significantly over the years.

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2002 2003 2004 2005 2006 2007 2008 2009 2010 20110

0.5

1

1.5

2

2.5

3

3.5

Year

Cost/Kg $

Ring

Ro-tor

Fig 3 : Comparison of cost of rotor spinning aginst ring spinning over the years (ITMF Report)

The various elements contributing to cost of manufacture in rotor spinning in different countries is given in table 5 based on a survey by ITMF7

Table 5 Break up of Cost in US $/kg of yarn in rotor spinning in different countries, 20s Cd (2006)

Item of cost India China Turkey USA

Waste 0.07 0.12 o.09 0.08

Labour 0.01 0.01 0.05 0.11

Energy 0.16 0.13 0.14 0.08

Auxiliary Material

0.08 0.08 0.08 0.08

Capital 0.18 0.18 0.17 0.27

Production cost excluding raw material

0.50 0.52 0.53 0.62

Raw Material 1.02 1.76 1.36 1.13

Total cost 1.52 2.28 1.89 1.75

Power is the major production cost in rotor spinning next only to capital cost in all the countries as seen from Table 5. Labour forms a very low part in production costs particularly in automatic machines. Labour cost is further reduced in latest

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machines by increasing the number of rotors per machine up to 540 and number of piecing carriages up to 4. Automatic transportation of drawing cans to rotor machines and rotor packages to package room found in modern set ups will further reduce labour costs.

Power consumption

ITMF survey also gives power consumption in rotor spinning in various countries, which is given in Table 6

Table 6. Comparison of power consumption per kg in rotor and ring spinning, 20s

Ne

Country Power cost $/KWh

Ring yarn 20s cbd Rotor Yarn 20s Cd

Pwer consumption

KWh/kg

Pwer cost/k

g

Pwer consumption

KWh/kg

Pwer cost/kg

India 0.095 3.368 0.32 1.684 0.16

China 0.080 3.375 0.27 1.625 0.13

Turkey 0.140 2.000 0.28 1.667 0.14

USA 0.045 3.334 0.15 1.778 0.08

Power consumption is nearly double in 20s combed ring yarn compared to 20s carded rotor yarn in India, China and USA. Only in Turkey the difference in power consumption is lower. Rieter8 reports power consumption of 0.18 CHF/Kg in rotor spinning, 0.25 CHF/Kg in ring spinning and 0.20 in Air jet spinning in 30s. Krause and Soliman9 have reported that in counts corser than 60 tex (10s) rotor spinning consumes less power than ring spinning. But in counts finer than 30 tex (20s), rotor spinning consumes more power. Kaplan and Koc10 suggest a method for estimating power consumption in different sections of rotor spinning by estimating the time for which the machine runs to make a known quantity of yarn. From this basis they determined the share of pwer consumption in different departments in 20s carded rotor yarn, which is given in Fig 4

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Fig 4 : Share of power consumption in different departments in Rotor spinning, 20s Cd

75 % pwer is consumed in rotor spinning, 16 % in carding in 20s as per Kaplan and Koc. Rieter8 has given share of power consumtion in different departments in Indian mill for 30s viscose knitting yarn which is given in Fig 5 .

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Blowroom3%

Carding7%

Drawing5%

Rotor85%

Fig 5 : Share of power consumption in different departments, 30s Viscose (Rieter) Share of Rotor is much higher at 85 % while that of carding is much lower at 7 % compared to Kaplan and Koc. Power consumption in rotor spinning inclusive of air conditioning works out as 2.95 KWh/Kg in 20s as per Kaplan and Koc. Further while machines share of power is 73.4 %, the share of compressors is 3.5 %, Lighting 3.6 % and air conditioning is 19.7 %.

Measures to reduce power consumptionIn rotor spinning, power is consumed mostly by opening action by opening roller, rotor and winding.

Rotor Speed and Diameter

10

30000 40000 50000 60000 70000 80000 90000 100000 110000 120000 13000075

80

85

90

95

100

105

110

115

120

Rotor Speed, rpm

Power Cosumtion%

56 mm 40

mm30 mm

Fig 6 : Effect of rotor speed on Power consumption with different rotor diameters

Increase of power consumtion with increase of rotor speed with different rotor diameters is shown in Fig 6. Power consumtion increases more rapidly with rotor speed at 56 mm diam than at 30 mm diameter. As a result, power consumtion at 130000 rotor speed with 30 mm rotor diameter is nearly same as that at 62000 rotor speed with 56 mm rotor diameter. So rotor diameter has to be reduced with increase in rotor speed to keep down power consumtion. Rotor shape and weight have been made by computer aided design to reduce air friction in corobox SE 12 by Schlafhorst. This brings significant reduction in power. Opening RollerApart from rotor speed opening roller speed also affects power consumption with higher speed leading to more power11. Suction systemSuction system for producing vacuum also consumes significant power. Vacuum level decreases with machine running time and so higher rating motor is used. But Autocoro 312 offers an electronically controlled vacuum system with the help of a frequency invertor drive to suction fan to maintain constant suction throughout spinning. In Reiter R 40 model, vacuum level in rotor is kept constant by autmotic actuaation of filter cleaning in the event of drop in suction to reduce power consumption. Further a bigger volume main fan is fitted to improve its efficiency.Drive to rotorDiameter of twin discs driving rotor has been increased to 78mm and width of tangential belt reduced to 20mm by Suessen in their new spinbox to reduce power consumption. Pressure on tangential belt is reduced in R 40 model to reduce power consumption. This is facilitated by the ability of robot to increase pressure for increasing the speeding up of rotor after piecing. An economic cooling sytem to inverter and improved bearing technology in the spin box and drive in Rieter R60 help to reduce power. Oerlikon Schlafhorst claim reduction in

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manufacturing costs by use of plastic bushings. Schlafhorst has developed magnetic rotor positioning system in place of steel balls to reduce power.Piecing by RobotCoromat by Schlafhorst employs a shutter that allows suction air only at the time when it is needed like yarn search, suction for yarn piecing and doffing of package.Air conditioningInstead of air conditioning the entire spinning room, Schlafhorst has developed a system of providing direct air conditioning to the required areas like sliver feed to spin box. This helps to reduce air conditioning costs substantially. Online quality monitoringSchlafhorst uses energy saving LEDs and optimised electrically controlled sensors to reduce power in yarn quality monitoring system.

References

1. .J.S.Manohar, A.K.Rakshit and N.Balasubramanian, Influence of rotor speed, rotor diameter and carding conditions on yarn quality in open-end yarns, Textile Research J, 1983, 53, p 497

2. K.N.Seshan,P.Chellamani, K.P.R.Pillay, S.K.Khurana, R.M.Mittal, M.C.Sood, N.Balasubramanian and A.N.Desai, Rotor spinning comparisons –Spinning, Weaving, Processing and Overview, A joint project paper presented at 26th Joint Technological Conference, 1985, RP 1

3. N.Balasubramanian,Merits of Lea CSP and Lea Ratio, J. Textile Association, 2005 April, p94

4. Y.Sirang, G.Dinfon and H.M.Behery, A study of yarn hairiness and diameter of open-end yarns processed through single and double cylinder carding machine and its comparison with ring yarns, Textile Research J, 1982,52, p274

5. http://www.rieter.com/en/rikipedia/articles/rotor-spinning/economics-of-rotor-spinning/cost-structures-of-comparable-rotor-spun-andring-spun-yarns/print/

6. Weidner – Bohnenberger S. „Rotor spinning – a process with a future“ Melliand International Vol. 7, December 2001.7. ITMF International manufacturing costs Spinning/Weaving/Knitting, Sweden, International Textile Manufacturers Association, 20068. Rieter, Maximum energy efficiency in Yarn production, Spinning Textiles, 2013, 7, 1, p 8.

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9. H.W. Krausa and H.A. Soliman, Energy consumption of rotor type open end spinning machines as compared to ring spinning frame, International Textile Bulletin, 1982, 3rd quarter, p 285.

10. E. Kaplan and E.Koc, Investigation of energy consumptionin yarn production with special reference to open end rotor spinning, Fibres and Textiles in Eastern Europe, 2010, 18, 2, p 7

11.S.Syen, The optimisation of open end spinning with respect to energy consumption, M.Sc. Thesis, Georgia Institute of Technology, Georgia, 1976