October 1, 1920.] 



THE INDIA RUBBER WORLD 



11 



at one end and a weight pan is suspended from the other end. 

 A crossbar attached to the scale pan and resting against guides 

 prevents the untwisting of the yarn. The small amount of fric- 

 tion between cross bar and guides may be reduced to a negli- 

 gible quantity by causing the latter to vibrate. 



The insert in Fig. 1 shows the method used for making read- 

 ings. A spring brass clamp carrying an index mark is fastened 

 to the yarn. The movement of the index mark over the scale 

 may be observed directly as the weight on the scale pan is in- 

 creased. The scale is graduated in half-millimeter divisions and 

 readings may be made to quarter-millimeters easily and to 

 smaller sub-divisions with a liltle practice. The weight of the 

 lower clamp, crossarm, weight pan, and yarn below the clamp 

 are included in each statement of the tension applied. 



To make a determination of straight length, the yarn is fast- 

 ened in the upper clamp of the instrument, a load of 2.S grams 

 is applied, and the spring brass clamp is fastened at a point 400 

 milHmcters below the upper clamp. After allowing one-half 



sion at the point (a), it intersects the curve at the point (b), the 

 distance (ab) indicating the load it is necessary to apply to the 

 yarn to obtain this theoretical length directly. It is, however, 

 advisable, in order to expedite the determination, to use a great- 

 er load capable of producing the same length in a shorter time. 

 This load may then be applied to all yarn of the same kind for 

 the proper length of time, and the full straight length determin- 

 ation need be made only when greater precision is required. 



To make crimp determinations the marks are placed on the 

 yarn while in the fabric, the yarn is removed and the straight 

 length determined as above. The total crimp in this case con- 

 sists of the sum of the additional length caused by waviness of 

 the yam in the fabric and that caused by looseness and waviness 

 of fiber and single yarn elements. Fig. 3 shows the results ob- 

 tained from determinations made on warp and filling yams 

 taken from a tire fabric. It is evident that the warp yams con- 

 tain much more crimp than the filling yarns. 



Having determined the straight length (oa), the percentage 



Scale ■■ 



Detail of Reading 

 Device and Clamp 



Elongation of Warp and Filling Yarns 

 taken from JOOmm Length of Fabric B 



Crimp Measuring 

 Apparatus 



400 ^ 500 

 Length -millimeters- 



510 ajjo }40 350 



Length - millimeters 



"560 



I?0 



Fig. 1. Crimp Measur- 

 ing Apparatus. In- 

 sert. Detail of Read- 

 ing Device 



Fig. 2. Elongation of 

 Tire Fabric Yarn Be- 

 fore Weaving 



Fig. 3. Elongation of Tire Fabric W.\rp and Filling Yarns 



hour for the yarn to adjust itself to this condition, the reading 

 is taken opposite the index mark on the scale. Additional loads 

 are then applied up to 340 grams, one-half hour being allowed 

 before each reading. It has been found by experiment that, 

 after this time has elapsed, the unit elongation per unit of time 

 is very small. 



The stress-strain curve obtained from plotting loads and 

 length readings is shown in Fig. 2 for a tj'pical sample of yarn 

 used in making tire fabrics. It may be observed that this curve 

 tends to become a straight line after a load of about 150 grams 

 has been applied. By extending this line to cut the line of zero 

 tension a point (a) is obtained which shows the length that 

 the yarn would have had initially if there had not been present 

 waviness in the fiber and other conditions tending to prevent 

 the constant unit increase in length for unit increase in load. 

 This length may properly be considered as the straight length 

 of the yarn under no tension. 



It is evident that, before weaving, yarns contain crimp as un- 

 derstood in this paper, this crimp consisting of various elements 

 having to do with the nature and interrelation of the fiber and 

 the strands in the yarn. 



If a line (ab) is erected perpendicular to the line of zero ten- 



of crimp is obtained from direct comparison with the length 

 measured in the fabric. If we designate this length as L, the 



formula may be written : 



Crimp = oa — L 

 and 



oa — L 



Percentage crimp =: 



L 



This formula is based on the length in the fabric, which would 

 appear to be the logical basis because the determination used 

 the fabric as a starting point. If, for any reason, it is desired 

 to use the straight length as a basis, the formula : 



oa — L 



Percentage crimp = 



oa 



may be used, provided that it is expressed or understood that 

 the straight length basis is being used. 



All determinations were made upon yarns which had been 

 previously, and during the experiments, exposed to an atmos- 

 phere constantly maintained at approximately 65 per cent rela- 

 tive humidity and 21 degrees C. temperature. 



