Apron slippage in ring frame : Part I. Establishing the phenomenon and its impact on yarn quality

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 7, March 00, pp. 8 Apron slippage in ring frame : Part I Establishing the phenomenon and its impact on yarn quality A Dasa & P Yadav Northern India Textile Research Association, Sector, Raj Nagar, Ghaziabad 0 00, India and S M Ishtiaque Department of Textile Technology, Indian Institute of Technology, New Delhi 0 0 6, India Received 6 September 000; revised received and accepted February 00] The phenomenon of apron to apron slippage exists in every spindles but with different extent. Due to the absence of positive means of motion transmission from bottom to top apron, the top apron always moves at a slower speed than bottom apron and this speed difference is higher when there is material in between them. This apron to apron slippage causes uncontrolled movement of fibres in the apron zone, resulting in poor yam quality. Keywords: Apron to apron slippage, Bottom apron, Cotton yam, Polyester/viscose yam, Tenacity, Top apron Introduction In double apron drafting arrangements, two sets of aprons (bottom apron and top apron) are used to control the fibre movement in the main drafting zone, i.e. between middle roller and front roller. To guide the fibres, the upper apron must be pressed with controlled force against the lower apron. The bottom apron is driven by the middle bottom roller by frictional contact and guided through bottom apron guide plate as close as possible to the bottom front roller. The top apron is driven by the bottom apron through frictional contact. In the main drafting zone of ring frame, as the number of fibres are relatively small and at the same time the amount of draft is very high, the strict control over the movement of floating fibres is very essential. As there are no positive transmission of motion from bottom apron to top apron, it may be thought that whether the aprons are really controlling the movement of fibres in the main drafting zone. The primary condition of controlling the movement of fibres is that both the aprons should move at the same speed. However, if both the aprons move at the "To whom all the correspondence should be addressed. Phone: 7886; Fax: ; nitra@nde.vsnl.net.in same speed, the fibre strand in between them will also have streamline movement and in that case one can expect a controlled movement of fibres in the main draft zone. But, due to the negative transmission of motion from bottom apron to top apron, there are every possibility of apron to apron slippage, i.e. top apron to move at slower speed than bottom apron which can result uncontrolled movement of fibres in between aprons. This paper deals with the establishing phenomenon of apron slippage and its impact on yarn quality. Materials and Methods. Measurement of Apron to Apron Slippage The amount of apron to apron slippage was observed with and without roving in the drafting zone. To measure the apron slippage, a mark was put on the top and bottom aprons. Another reference mark was put on the frame itself. Time taken to make five revolutions by the top and bottom aprons was measured with the help of stop watch. The process is repeated for five times to get the average time. Then the length of the aprons was measured. With the values of time and length, the surface speed of apron was calculated. Difference of the surface speeds of bottom and top aprons was used to calculate the apron slippage, as per the following relationship:

2 DAS et al. : APRON SLIPPAGE IN RING FRAME : PART I Apron to apron slippage (Sa), %= Bottom apron Top apron surface speed surface speed Bottom apron surface speed.. x l 00 Study on Apron Slippage To establish the phenomenon of apron slippage, a detailed study was carried out in laboratory pilot plant as well as in a most modem 00% EOU. In the pilot plant, the apron slippages were measured in two different ring frames with both short cradle for cotton and long cradle for polyester/viscose (PN). The apron slippages were measured in five different spindles randomly chosen in each case as shown in Table. In the industry also, the Table I Type of material Ne 00% cotton (carded) Ne 00% cotton (carded) Ne polyester/ viscose (6:) Ne polyester/ viscose (6:) Spindle No. 9 apron slippages were observed in three randomly chosen ring frames as shown in Table. The apron slippages were observed for 0 Ne and 0 Ne cotton running with 0.9 and.0 hank rovings respectively and for 0 Ne PN running with 0.9 hank roving. The following drafting details were used in the present study: Drafting details Drafting system Top roller pressure, kg Break draft Tensioning arrangement Front zonelback zone setting, mm 00% Cotton PN Pilot plant Mill SKF. Spring & pulley LR (P ). Spring & pulley /60 69/7 /7 /7 Values of apron slippage in laboratory ring frames Speed of apron without roving, mrnis Apron slippage without Speed of apron with roving mrnls Apron slippage with Bottom apron Top apron roving, % Bottom apron Top apron roving, % I I Table Values of apron slippage in ring frame of a modern 00% EOU Type of material 0 Ne cotton 0 Ne cotton 0 Ne polyester/ viscose (6:) Spindle No. Speed of apron without roving, mrnls Bottom apron Top apron Apron slippage without roving, % Speed of apron with roving, mrnls Apron slippage with roving, % Bottom apron Top apron

3 0 INDIAN J. FIBRE TEXT. RES., MARCH 00. Study on Effect of Apron Slippage To study the effect of apron slippage on yarn quality only two spindles one with short cradle for cotton and another with long cradle for PN were selected. The spindles were so selected that normal apron slippages with material were on the higher side, i.e..% for cotton and.7% for PN to represent slippage level (Table ). The apron slippages were then increased to level, keeping all the other parameters constant, by making the top apron tight by wrapping cellotape very uniformly on the cradle roller. As the top apron becomes tight, the frictional resistance between the inner surface of top apron and top apron cradle increases, which, in turn, resists the motion of the top apron, resulting in higher apron to apron slippage. It is well known that the increase in tension of top apron to a very higher level leads to intermittent movement of apron. Sufficient care has been taken so that the tension of the aprons does not increase to a very higher level to have the uniform movement of the aprons. Only idea was to increase the apron to apron slippage to level (Table ) with uniform movement of top apron. On the other hand, the apron to apron slippage was reduced to levell by rubbing mm of both the edges of bottom and top aprons with the help of emery paper to have better frictional contact between aprons (Table ). Ten roving bobbins of the hank. were prepared each from 00% cotton and 6: polyester/viscose of mm staple length. From each roving bobbin, Ne yarns were prepared with three different levels of slippages. Therefore, at each slippage level ten ring bobbins were prepared in the same spindle from ten different roving bobbins. The cotton yarns were spun with.0 TM and PN yarns with. TM and the spindle speed was kept at 0,00 rpm both for cotton and PN yarns. All the yarns were tested for evenness and imperfections in UT at a speed of 00 mlmin. Tensile properties were measured on SDL universal tensile tester using 0 cm test length and 0 cmlmin extension rate. The mean values of tenacity and elongation were averaged from 00 observations for each sample, i.e. 0 readings from each bobbins. Hairiness index and diameter U% were measured in Keisokki hairiness tester LASERSPOT Model LST at a speed of mlmin for min. The details of the test results for both cotton and PN yarns at different level of slippages are given in Table.. Fibre Movement in the Apron Zone The fibre strand in the main drafting field consists of only a few required fibres. There is hardly any friction field, and the fibre guidance provided by rollers alone is inadequate. Therefore, in the main drafting zone double aprons are provided to reduce the uncontrolled movement of floating fibre l Thus, the aprons really have the most important task on the spinning machines; a controlled increase in the fibre speed in the main draft up to the full speed on the delivery roller, at the same time reducing the fibre mass to the prescribed values. To perform the above functions properly, the most important condition is that both the aprons should move at the same speed. As the fibre strand is transported by the frictional contact of both the bottom and top aprons, any variation in speed between the aprons results in turbulent movement of fibres. Figs. and show the streamline and turbulent movement of fibres in the apron zone respectively. Ideally, both the aprons should move at the same speed (Fig. ) which will result in straightening of the fibres in the drafting zone by removal of hooks during drafting. But in actual practice, as the top apron moves at a slower speed than the bottom apron (Tables and ) there is turbulent movement of fibres due to the rubbing action generated by the relative movement of aprons, and friction between aprons and fibres, and between the fibres themselves. The backward drag force on the top layer of the fibre band Type of yarn Level of slippage Ne cotton Level l Level Level Ne polyester/ Level I viscose (6 :) Level Level Table Effect of apron to apron slippage on yarn quality Apron slippage % U% Imperfections/km Thin Thick Neps +00% 0% +0% Tensile properties Hairiness Diameter Tenacity Elong index (HI) U%. cn/tex ation %

4 DAS el at. : APRON SLIPPAGE IN RING FRAME : PART I in the apron zone by the top apron results i n retardation of the fibres i n that zone while, o n the other hand, the fibres in contact with bottom apron move relatively at a faster speed and this results in nonstreamline movement of fibres in the apron zone (Fig.). This apron to apron slippage results in rolling or rubbing of fibres in the drafting zone, thereby showing entanglement of the fibre instead of straightening in the idealised condition. Figs. and show the photographs of the drafted rovings collected from the front roller nip of the same ring frame spindle, drafted from the same PN roving with two different levels of apron slippage. Figs. and show that as the apron slippage increases the fibre entanglement also increases due to the reason as discussed earlier. between top and bottom apron, frictional resistance of inner surface of top apron and apron cradle, condition of apron, contact pressure, surface speed of bottom apron, pressure distribution between aprons, etc. The above factors cannot be identical for all the spindles and, therefore, a wide variation in apron to apron slippage in different spindles is expected as is evident from Tables and. When fibre strands are there in between aprons, the slippage values are always higher than that in the absence of material in between aprons. This is due to the fact that when fibre strand is present in between the aprons, it hinders the flow of motion further. Apron to apron slippage in a particular ring frame also varies widely from spindle to spindle when. there is fibre strand in between. Apron to apron slippage with and without material, in general. is found to be higher in the industry than Results and Discussion. Extent of Apron to Apron Slippage The apron to apron slippage data in laboratory ring frames and that in ring frames of an industry are given in Tables and respectively. It is observed that always there is apron to apron slippage, i.e. top apron always moves at a slower speed than bottom apron even when there is no material in between them. This is due to the fact that the top apron is getting its motion from bottom apron only by frictional contact. There is no positive means of motion transmission. The slippage between aprons, when there is no material between them, depends on many factors, e.g. friction _ VI vam mmvozzililov7m Tap Apua ::...::: + DirocIioa of lilnllow :...jll " 'j.. :. Fig. Photograph of fibre strand coming out from the front roller nip at negligible apron to apron slip (0.%) == Apua..f'%\\\S BoIIaaa _ Vb Fig. l Idealised streamline flow of fibres in the apron zone (Vb VI, where Vb is surface speed of bottom apron and VI, the surface speed of top apron) = _ Vt Vb Fig. Turbulant flow of fibres in the apron zone (Vb > VI, where Vb is surface speed of bottom apron and VI the surface sd of top apron) Fig. Photograph of fibre strand coming out from the front roller nip at very high level of apron to apron slippage ( 0.6%)

5 INDIAN J. FIBRE TEXT. RES., MARCH 00 that in the laboratory (Tables and ). This is due to the higher surface speed of bottom apron in the industry than that in laboratory ring frame. Table shows that the slippage is higher in case of 0 Ne PN than that in case of 0 Ne cotton, probably due to the higher bottom apron speed and different fibre properties. Level Level Level From the Tables and, it is also clear that the speed of bottom apron is always lower when the rovings are drafted than that observed without materials, which is due to the drafting force of the break draft zone that acts opposite to the bottom aprons direction of motion and restricts its movement6. Mass Irregularity Table and Fig. show that the apron slippage has a significant influence on yarn unevenness both for cotton and PN yarns. The higher the apron to apron slippage, the higher is the yarn unevenness. The same trend is observed both for cotton and PN yarns. As the apron slippage increases, keeping all other parameters same, the movement of fibres gets disturbed as discussed earlier. Due to the uncontrolled movement of fibres in the main drafting zone, the distribution of the number of fibres in the cross section gets disturbed and this results in the increase in unevenness. The diameter U% also follows the similar trend as shown in Table.. Imperfections Figs. 6 and 7 show the effect of apron slippage on thick, thin and neps of both cotton and PN yarns respectively. A drastic increase in the imperfections is clearly evident when the slippage increases. As already been discussed, when the apron to apron slippage increases there is a turbulent movement of fibre strand in drafting zone, causing rolling of fibres which results in generation of neps and thick. As the thick or neps are generated due to the fibre rolling, this also leads to the formation of thin.. Tensile Property The tenacity of both the cotton and PN yarns deteriorates when apron to apron slippage becomes higher (Table and Fig.8). With higher slippage, the movement of fibres gets disturbed and the fibres become entangled, causing improper migration in the yam structure. Also, due to the nonstraightness of fibres the ratio of mean fibre extent to original fibre length7.9, which is defined as spinningincoefficient Cotton Fig. Effect of apron to apron slippage on yam irregularity (U%) 800 r, eveI Level. Level o T h in Th ick pla ce s Fig.6 Effect o f apron t o apron slippage o n cotton yam imperfections

6 DAS et al. : APRON SLIPPAGE IN RING FRAME : PART I 600 E 00 level S level f,. level c c:: e 0 'is 00 &. E Ill_I.' leyei.l_s 00 PoiyHtwM6cose Fig. 8 Effect of apron to apron slippage on yam tenacity Thin Fig.7 Effect of apron to imperfections ((,,), Thick apron. As the apron to apron slippage increases the yam quality Neps deteriorates in terms of evenness, imperfections and tenacity. But, no clear trends have slippage on PN yam been observed in breaking elongation and hairiness. From the present study, it is clearly evident that apron to apron slippage is existing in all the spindles reduces and this results in reduction in tenacity. to varying extent which is detrimental for yam No clear trend has been observed in case of breaking quality. Efforts can be made to either reduce the elongation. slippage to a negligible level or eliminate it by positive drive of top apron. The factors responsible. Hairiness No clear trend has been observed for hairiness in both the yams when apron slippage increases (Table ). Rererences Conclusions. The phenomenon of apron to apron slippage exists in all the spindles, but the extent of slippage varies widely from spindle to spindle and this may be responsible for spindle to spindle variation in yam quality.. The amount of slippage is always higher when there are fibre strands in between bottom and top aprons than that observed without fibre strands.. The extent of slippage found to for apron slippage will be higher at higher speed of bottom apron, i.e. at higher spinning speed. be studied in details in PartII of this series. I Balasubramanian N, Text Res J, 9 ( 969). Klein W, Short Staple Spinning Series, Vol. (The Textile Institute, UK), 987. Bay E & Baier F, Melliand lnt, () ( 998) 6. Karuer H & Bomhauser P, Int Text Bull, () ( 998) 8. Lord P R & Grover G, Text Prog, () ( 99) 9. 6 Singh A K, Effect of speedframe apron slippage on yam quality, M.Tech. thesis, Indian Institute of Technology, Delhi, Ishtiaque S M & Saxena A K, Indian J Fibre Text Res, ( 998). 8 Kasparek J, Text Month, 8 ( 97). 9 Ishtiaque S M, Indian J Text Res, ( 986) 08.