Optimization of Ring Frame Process

Introduction:   
Although the new spinning technologies have solved the problem of production and automation to a greater extent, the ring spinning still dominates over others and is likely to continue as a most widely used form of spinning, because it exhibits significant advantages in terms of yarn strength and flexibility in comparison with the new spinning processes. Increasing ring spindle speed with the existing machines in consideration of yarn quality and running performance is the cherished goal consistently sought by every spinner for minimizing the cost of yarn. As ring frame cost constitutes a major portion of total cost, the productivity at ring frame has assumed considerable importance and every effort to maximize production at this stage is worth exploring1. In the present work, an attempt has been made to optimize ring frame process parameters, viz. spindle speed, top roller pressure and traveller mass, to achieve better yarn quality and production. 

Ring Frame

Materials and Methods:Preparation of Samples:
Using the optimized speed frame parameters2, the roving was prepared and used for optimization of ring frame process parameters. The yarn samples of 30s Ne with 3.79 twist multiplier were prepared on Lakshmi LG/5 ring frame for all the combinations by using three-variable factorial design proposed by Box and Bhenken3 (Table 1). The actual levels of variables were taken within the range of industrially acceptable limits (Table 2).

Testing of Samples:
Starting from the initial doff to full doff, the total breakage was observed for each run of the samples in ring frame. The breakage rate was calculated as the number of end breaks / 100 spindle / h. The other parts of yarn testing are similar as discussed earlier2.

Results and Discussion:
Experimental results for various responses of different yarn characteristics are given in Table 3. The response surface equations for various spinning performances are given in Table 4 along with the square of correlation coefficients.

End Breakage Rate:
The contour diagrams show the influence of spindle speed, top roller pressure and traveller mass on end breakage rate. It is found that the end breakage rate decreases with the decrease in spindle speed. Further, when both traveller mass and spindle speed increase the end breakage rate also increases. This can be explained due to the fact that the increase in spindle speed and traveller mass increases the spinning tension, which may often exceed the safe spinning tension limit, resulting in more number of end breakage. The top roller pressure has similar influence on the end breakage rate as shown in case of speed frame2.

Table 1: Box and Behnken design for three variables
Experiment No.	Levels of variables
	x1	x2			x3
1	-1	-1			0
2	-1	1			0
3	1	-1			0
4	1	1			0
5	-1	0			-1
6	-1	0			1
7	1	0			-1
8	1	0			1
9	0	-1			-1
10	0	-1			1
11	0	1			-1
12	0	1			1
13	0	0			0
14	0	0			0
15	0	0			0
Table 2: Actual levels corresponding to coded levels
Variable			Coded level
			-1	0		+1
Spindle speed (x1), rpm			13000	15000		17000
Top roller pressure (x2), kg / cm2			2.0	2.25		2.5
Traveller mass (x3), ISO No.			40	45		50
ISO No. = Mass of a traveller in mg.

Yarn Irregularity:
 Fig. 2 shows the influence of traveller mass and top roller pressure on yarn U%. From the contour plots, it is clear that yarn U% decreases with the increase in top roller pressure and traveller mass and according to the experimental result the influence of spindle speed on yarn U% is not appreciable. The above findings can be explained on the basis of the fact that the increase in top roller pressure consolidates fibres strand in the drafting zone and fibres move in a more controlled manner so that the erratic movement of floating fibres is restricted. This reduces the yarn U%. Furthermore, with the increase in traveller mass, the twist flow increases in the spinning zone that may lead to better binding of edge fibres in the yarn body and they do not eject out from the spinning triangle, resulting in better yarn evenness.

Table 3—Experimental results
Experiment No.	Breakage rate breaks/100spindle/h	U %	Hairiness index	Yarn imperfections/ km	Tenacity g/tex	Elongation- at-break, %
1	6.0	9.28	6.03	128	15.17	4.30
2	4.7	8.62	6.14	85	16.21	4.21
3	14.6	9.41	5.88	137	16.15	3.49
4	13.4	8.73	5.94	98	16.32	3.41
5	5.8	9.34	6.32	133	15.40	4.49
6	4.3	8.72	5.79	121	16.08	4.20
7	13.8	9.44	6.28	138	15.09	3.58
8	16.3	8.87	5.71	113	16.71	3.38
9	7.1	9.14	5.93	105	16.17	3.57
10	6.5	9.05	5.60	97	16.52	3.38
11	6.2	8.78	5.67	90	16.63	3.41
12	5.2	8.59	5.51	89	16.80	3.39
13	6.9	9.19	5.79	111	16.31	3.35
14	7.3	9.23	5.58	115	16.08	3.40
15	8.1	9.09	5.71	114	16.37	3.42

 

Yarn Imperfections:
It can be observed from Fig. 3 that the yarn imperfection level reduces with the increase in traveller mass. However, the imperfections first increase and then decrease with the increase in top roller pressure. The yarn imperfections initially decrease and then increase with the increase in spindle speed. As the spindle speed increases the drafting speed also increases. Therefore, the ratio of dynamic to static frictional force of the drafted ribbon increases. As a consequence, the floating fibres would like to take the intermediate speed and ensure shuffling of the fibres in the drafting zone4. These factors may be responsible for the decrease in imperfections. But, at higher spindle speed, there will be more rubbing action between yarn surface and thread guide, balloon control ring and traveller. As a result, long hair may get rolled up and cause neps. This leads to more imperfections at higher spindle speed.

Table 4—Response surface equations for various parameters:
Parameter	Response surface equation	Coefficient of determination (R2)
End breakage rate	7.185 + 4.663x1 – 0.588x2 + x1x3+ 3.052 x12 – 0.748 x22	0.916
U%	9.126 – 0.27x2  - 0.184x3 - 0.176x22	0.813
Imperfections	112.154 – 13.125x2 – 5.75x3 + 14.981x12  – 16.019x22	0.829
Hairiness index	5.684 – 0.059x1 – 0.199x3 + 0.327x12	0.857
Tenacity	16.411 + 0.244x2 + 0.353x3 – 0.052x12	0.703
Elongation-at-break	3.386 – 0.418x1 – 0.04x2 – 0.088x3 + 0.043x2x3	0.992

Yarn Hairiness Index:  
The effect of spindle speed, top roller pressure and traveller mass on yarn hairiness. It is very clear that hairiness index reduces with the increase in traveller mass. This can be ascribed to the fact that with heavier traveller the resistance to twist flow past the traveller (i.e. at winding zone) increases and thus the excessive twist flows back to the spinning zone. This reduces the length of spinning triangle and hence the number of free ends at the edge of the spinning triangle decreases. Again, due to the higher twist density at the spinning zone the peripheral fibres get twisted into the yarn body. The above phenomena are the cause of reduction in yarn hairiness while using heavier traveller5. However, as the spindle speed increases the yarn hairiness index first reduces up to 15180 rpm and then increases with the further increase in spindle speed. This is explained on the basis of the fact that with the increase in spindle speed the spinning tension increases and this facilitates better twist flow right up to the front roller nip, resulting in shorter spinning triangle. This causes better binding of edge fibres, which consequently reduces the yarn hairiness. But at the higher level of spindle speed, the size of the balloon also increases, which increases the frictional contact at balloon control ring and traveller. This may result in more rubbing action of yarn surface, thereby leading to higher yarn hairiness6. The top roller pressure has no significant influence on yarn hairiness.

Table 5—Response surface equations for various parameters
Parameter	Response surface equation	Coefficient of determination (R2)
End breakage rate	7.185 + 4.663x1 – 0.588x2 + x1x3+ 3.052 x12 – 0.748 x22	0.916
U%	9.126 – 0.27x2  - 0.184x3 - 0.176x22	0.813
Imperfections	112.154 – 13.125x2 – 5.75x3 + 14.981x12  – 16.019x22	0.829
Hairiness index	5.684 – 0.059x1 – 0.199x3 + 0.327x12	0.857
Tenacity	16.411 + 0.244x2 + 0.353x3 – 0.052x12	0.703
Elongation-at-break	3.386 – 0.418x1 – 0.04x2 – 0.088x3 + 0.043x2x3	0.992

Yarn Tenacity:  
The influence of spindle speed, top roller pressure and traveller mass on yarn tenacity. From the contour diagrams, it can be concluded that yarn tenacity increases with the increase in top roller pressure and traveller mass. This can be explained on the basis of the fact that the higher top roller pressure increases the normal force over the fibres and this may reduce the fibre slippage and cause some fibre straightening. Also, with the increase in top roller pressure there will be better control over the movement of fibres during their sliding. These factors are responsible for greater yarn strength. With the increase in spindle speed the yarn strength first increases approximately up to 15350 rpm and then starts decreasing. This can be attributed to the fact that as the spindle speed and traveller mass increase the spinning tension increases. Therefore, the fibres get straightened out as they emerge out from the front roller nip. This increases the spinning-in-coefficient. Again due to the higher twist density in spinning zone at higher spindle speed, the edge fibres get twisted into the yarn body. These factors result in higher yarn tenacity. But at higher spindle speed, the rubbing force between the yarn surface and the different machine parts on which it passes through increases6 and hence the surface fibres are more abraded and protrude from the yarn surface. Thus, while tensile testing of yarn the protruding fibres do not bear the load properly. These factors are responsible for lower strength of yarn as the spindle speed is increased beyond a certain level.

Yarn Elongation-at-break:  
The contour diagrams for breaking elongation at three different levels of spindle speed, top roller pressure and traveller mass. It can be observed that with the increase in spindle speed, top roller pressure and traveller mass the breaking elongation decreases. This can be ascribed to the fact that with the increase in spindle speed and traveller mass, the spinning tension increases which causes straightening of fibres as they emerge from the front roller nip, thereby reducing elongation. Again, as the top roller pressure increases, the fibre tension in the drafting zone increases to some extent, which may lead to straightening out of fibres and hence reduce the yarn breaking elongation.

On the basis of above findings, the optimum values of ring frame parameters are: spindle speed, 15000 rpm (0 level); top roller pressure, 2.5kg/cm2 (+1 level); and traveller mass, 50 ISO No (+1 level).

Table 6—Yarn characteristics at different levels of traveller mass [Spindle speed, 17000 rpm; and Top roller pressure, 2.5 kg/cm2]
Parameter	Traveller mass (ISO No.)
	40	45	50
End breakage rate breaks/100 spindle/h	8.79	13.4	16.9
U %	9.03	8.81	9.29
Hairiness index	6.27	5.94	5.95
Imperfections/km	115	102	126
Tenacity, g/tex	15.59	16.2	16.52
Elongation-at-break, %	3.78	3.52	3.3

With the optimum values of top roller pressure and traveller mass, a trial was conducted on the machine at high spindle speed (17000 rpm). But, it was observed that the end breakage rate increased significantly at higher traveller mass. The lighter traveller mass reduces the end breakage rate at this speed and also produces yarn with acceptable quality limit. The data as given in Table 5 for yarn properties and end breakage rate were obtained on the ring frame by using three combinations of traveller mass, while the spindle speed and top roller pressure were kept at maximum level (the roving was prepared with optimized parameters of speed frame). From the above data, it can be concluded that to maintain the spindle speed of 17000 rpm the lower traveller mass and higher top roller pressure are required.

Conclusions:

1. The optimum values of different parameters of ring frame are: spindle speed, 15000 rpm; top roller pressure, 2.5 kg/cm2; and traveller mass, 50 ISO No.
2. With the increase in spindle speed, the end breakage rate increases and yarn elongation-at-break decreases. However, the yarn imperfections, hairiness index and strength initially improve and then deteriorate at higher speed.
3. Most of the yarn properties are optimized at higher level of top roller pressure.
4. Yarn U%, imperfections, hairiness index and tenacity improve with the increase in traveller mass but breaking elongation reduces significantly. Furthermore, the high traveller mass at higher spindle speed increases the end breakage rate marginally. The lighter traveller at higher speed reduces the end breakage rate and also produces yarn with acceptable quality limit.
5. Higher values of square of correlation coefficients between the experimental values and the calculated values were obtained from the response surface equations and it is found that the response function agrees fairly well with the experimental data. Thus, ring frame process variables influence significantly the various yarn characteristics

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