Damage to Viscose Staple Fibers in Cotton Spinning Process

Transcription

1 7 Damage to Viscose Staple Fibers in Cotton Spinning Process By Kouji Yamaga, Member, TMSJ Faculty of Engineering, Gumma University Abstract During the processing of viscose staple fibers by cotton spinning machines, the breaking strength, breaking elongation, crimps and length of fibers are more or less affected by the action of each machine. We have tried to find the relation between (1) the cut length and denier of the fiber and (2) the degree of damage. We have found that: (1) The degree of breaking strength is negligible. (2) material Yarn shows a 4 does. 5% smaller breaking elongation than the raw (3) The bulk of crimps are lost in the machine prior to the carding process. However, Only 15 to 20%, of them are retained in the final product. the amount of the retained crimps is influenced by the pressure of draft rollers and by the amount of draft. (4) The amount of broken fibers in the final process is an average of 13% for 11/8-inch staple and 15% for 11/4-inch staple. The finer denier fibers should normally be subject t o more damage, but no remarkable difference is found between 1 denier and 3 denier staples of the lengths mentioned. Introduction Table 1 Mixing and Beating Machine The nature of spun yarn is much influenced by the property of the constituent single staple fibers. The strength and evenness of yarn are much influenced by the amount of broken fibers contained in the yarn. The raw material for staple fiber, unlike cotton, does not contain broken fibers. Broken fibers in rayon spun yarn result from the action of each machine. Hence stroger and better yarn can be produced by locating the source of broken fibers and lessening them. Crimps of single fibers give a soft and voluminous hand to the fabric and increase the spin-property. We have tried to find out how much the crimps decrease in the process and how much they remain in the final product. 1. Method of Experiment We made 30's spun yarn from the follow ing fibers by cotton spinning machines. Staple fibers : Viscose, dull, crimped. Cut lengths: 11/8-in. and 11/4-in. Deniers: 1.5, 2 and 3. Fig. 1 Flat card Table 2 Flat Card (Unit: 1/1,000 in.) \ Spinning process : Raw meterial \HBB \H0 \C0 \HF \LF EO \SS \FC \DF \SFF \SF \Setting. Humidity : 65 }5%. Temperature : 20 }3ßC. Gauge setting of machines used: For mixing and beating process, see Table 1. For flat card, see Table 2 and Figure 1. For drawing and simplex frame, see Table 3 and Figure 2. For spinning frame, see Table 4 and Figure 3. Twisting setting : 30 min. at steam 100 Ž.

2 8 Fig. 2 Drawing frame and simplex fly frame Table 3 Drawing and Simplex Frames (Unit: in. ature and humidity 20 }1 Ž, 60 }2% (R.H.) The breaking strength of fibers of every denier increases before the carding process and decreases between the drawing frame and the spinning frame but again increases somewhat in the setting process. But breaking strength in the final process is almost the same as that of raw materials. It is thought that weak fibers are cut by the action of the beater and short fibers removed by carding action, and that, therefore, breaking strength increases in the carding process. The main action of drawing, roving, and spinning frames is draft by roller. Fibers are pressed and drafted between rollers, but fibers cut and removed are so few that breaking strength decreases. Twist: 1.3/in. for 11/s-in. staple, 1.0/in. for 11/4-in. staple Fig. 4 Breaking strength Fig. 3 Spinning frame Table 4 Spinning Frame (Unit: mm) Twist: 22/in. for 11/s-in. staple, 21/in. for 11/4-in. staple 2. Breaking Strength and Elongation They are shown in Figure 4 and Table 5, Figure 5 and Table 6. Number of specimens : 50. Apparatus used: K.S. senimeter. Temper The finer fibers are in denier, the larger numb the er of fibers subject to breakage. Breakages mostly occur before the carding process, after which they increase slightly. However, we see no remarkable difference in breaking strength between the raw materials and the final products. The standard deviation of breaking strength is improved because weak fibers are cut, strong fibers remain and break ing strength becomes uniform. Breaking elon gation decreases with each process and recovers somewhat in the setting process. The breaki ng elongation in this experiment showed a fairly larger value than the inherent breaking elongation induced by crimps(1). The breaking elongation of the final products is 4 `5% smaller than the raw materials.

3 9 Fig. 5 Breaking elongation Fig. 6 Curve of strength and elongation are extended to the axis direction by the action of various machines. Table 7 is a comparison of these results and the results obtained by Tsujimoto and Motoji. According to their data, breaking elongation increases with each process. Tsuji moto and Motoji[2] say fibers are fatigued by the repeated actions of each process, which narrow down the arrangement of micell of fibers and increase the moisture content and breaking elongation. The present author's data show that the absolute value is larger than is given by Tsuji moto and Motoji and decreases with each pro cess. The explanation is that, as shown in Figure 6, parts of the crimps are extended and their value adds itself to the inherent breaking elongation. However, according to the author's data, breaking elongation decreases with the loss of crimps. Therefore, Tsujimoto and Motoji's data and the present author's are nearly equal after the spinning process. Another reason for the decreases of breaking elongation is that the plastic parts of fibers 3. Crimps The experiment under review was made by the Japanese Industrial Standards method. Single fibers were placed across a hole, 20mm long and 7mm wide, drilled in a piece of heavy black paper. The upper part of the fiber was gripped by the arm of a torsion balance, the lower part was attached to the grip of a seni meter, and the left and right edges of the paper were cut off. The length of the fiber was a when the needle of the torsion balance was raised to indicate, on the scale, a weight equalling the weight of the upper part of the paper plus 5 mg-and when the grip of the senimeter was pulled down until the pointing needle of the torsion balance stopped on the zero line. When another 50 mg/den. was added, the length was b. The average of crimps =[ (b-a) /a] ~100 (%). The results are shown in Figure 7. Number of specimens is 50. Temperature and humidity were 20 } 1 Ž and 60 } 2% (R.H.), respectively.

4 10 An average of 60% of the crimps was lost before the carding process; 15-20% remained through a 3-time drawing process ; a slight decrease was noted in the roving and spinning processes; and some recovery was made in the setting process. The main reason for the decrease in crimps is that fibers were given shocks by the beater and pressed in a stretched condition by rollers after the draw ing process. Crimps were easily lost to some extent, but the remaining crimps, amounting to 15-20%, were strong and able to stand heavy pressure. It is said[3]lthat lost crimps are recovered to a large extent in the setting pro cess, but in the experiment under review, only 3% was recovered, in a stretched condition, in yarn. 4. Rate of Broken Fibers and Length of Fibers these three points in the author Œs experiment. The sample was collected by Hirako's method and the diagram was made by a person with three years Œ experience. See Figure 8, con sider the upper curve of staple diagram AB as X, and draw a line along the level parts of X. Consider the point at which this line separates from X as S Œ, SS Œ as perpendicular to OB. Then, the rate of broken fibers= [( çsbx dx)/ ( çobx dx) )X 100 (%). To calculate the area Œ of 0 the diagram, cover the diagram with section paper and count the number of those squares of the area of the diagram which are visible through the section paper. However, as is shown by the photograph, AS is not a curve but almost a straight line and S ŒB, too, is a straight line. Therefore, by thinking of AOSS Œ as a trapezoid and SS ŒB as a triangle, we may use the simple triangle method as follows : The average of broken fibers was examined by the staple diagram method. This method is influenced considerably by (1) the quality of that part of sliver which is collected for use as a sample, (2) the method of collecting, and th(3) e degree of skill of the person making the diagram. Special attention was paid to Table 8 Average of Broken Fiber Let us compare this result with the section paper method. When the S ŒB curve is convex, the value obtained by the section paper method is smaller than the value obtained by the simple triangle method. When the S ŒB curve is concave, the value obtained by the section paper method is larger. In both cases, the difference is only an average of %. This simple tri angle method was used in the author's experi ment. Table 9 Length of Fiber (Unit: mm) Fig. 8 Sample of staple diagram

5 11 The length of fibers increases with each process, because crimps are extended with each process. Since coarse fibers have stronger crimps, 3,2 and 1.5 deniers make an ascending scale in the rate of increase in fiber length. The rate of broken fibers also increases in order of 3,2 and 1.5 deniers. The results for the broken fibers agrees with the results for the breaking strength and impact strength of single fibers. Most broken fibers develop before the carding process, after which they increase slightly with each process, the total being 2-3%. The amount of broken fibers of card sliver in the experiment under review was an average of 10-13%, but actually the amount is larger because flat cards operate to remove short fibers. The rate of broken fibers for 11/4-inch staple is larger than for 11/8-inch for every denier. Fine fibers are subject to a higher rate of breakage than coarse fibers. Fiber breakage, then, is a matter of fiber strength. Table 10 The Result of Impact Test Conclusions The decrease in the breaking strength of single fibers is so slight that we can calculate the strength of spun yarn on the basis of the strength of the raw meterial. The breaking elongation of fibers is smaller in the final pro duct than in the raw materials. The main reason is that crimps of fibers are lost. Most crimps are lost through the whole spinning process. The cotton spinning process is not suitable for spun yarn, which has crimps as one of its characteristics. The fibers in the final product are longer in length than the raw meterial. The gauge setting of every machine must be fitted to this extended length. Special attention must be paid to the combina tion of the mixing and the beating machines, the gauge-setting and the revolutions of every part of those machines. The amount of broken fibers in the final product in the experiment under review is 13 14, for 11/8-inch staple, and 14 `16% for 11/4-inch. These results are not excellent, but it will be possible to do better by changing the conbination of the mixing and the beating machines. Literature cited Sample of specimens: 50, Apparatus used: Matsui's Impact Tester Temperature and humidity: 20 } 1 Ž, 60% (R.H.) [1] A. Brown; Text. Res. J., Vol. 25, p (1955) [2] I. Tsujimoto, N. Motoji; J. Text. Mach. Soc., Jap anese edition, Vol. 6, No. 7 (1953) [3] I. J Okamoto, E. Fujimoto; J. Text. Mach. Soc., apanese edition, Vol. 9, No. 9 (1956) [4] R. Hirako; J. Text. Mach. Soc., Japanese edition, Vol. 7, No. 11 (1954)