1 00:00:00,010 --> 00:00:05,139 >> Skewness, or torque, is the annoying characteristic of some fabrics and 2 00:00:05,149 --> 00:00:10,990 garments to twist after laundering. As a result of skewing, side seams, sleeves, 3 00:00:11,009 --> 00:00:14,849 legs, and other parts of a garment will become displaced, leading to an 4 00:00:14,869 --> 00:00:22,169 unsatisfactory appearance. "AATCC Test Method 179: -- Skewness Change in Fabric 5 00:00:22,189 --> 00:00:27,119 and Garment Twist Resulting from Automatic Home Laundering." This test method 6 00:00:27,139 --> 00:00:31,640 determines change in skewness in woven and knitted fabrics, or twist in 7 00:00:31,660 --> 00:00:36,019 garments, when subjected to repeated automatic laundering procedures commonly 8 00:00:36,039 --> 00:00:40,919 used in the home. Washing and drying procedures used for shrinkage tests, and 9 00:00:40,939 --> 00:00:45,859 other home laundering tests, are specified for this method. For some fabrics, 10 00:00:45,879 --> 00:00:50,039 the degree of twist in the garments is not solely depended on its behavior in 11 00:00:50,059 --> 00:00:55,179 the unsewn state. It also may be dependent on the manner of garment assembly. 12 00:00:55,199 --> 00:00:59,879 Notice that one pant leg on this garment has skew and the other does not. 13 00:00:59,899 --> 00:01:04,500 Garment twist is defined as a rotation, usually lateral, between different 14 00:01:04,519 --> 00:01:08,739 panels of a garment, resulting from the release of latent stresses of the woven 15 00:01:08,759 --> 00:01:13,019 or knitted fabric forming the garment, that build up in manufacturing during 16 00:01:13,039 --> 00:01:19,320 laundering. Twist may also be referred to as torque or spirality. Skewness is 17 00:01:19,340 --> 00:01:23,680 defined as a fabric condition resulting when filling yarns or knitted courses 18 00:01:23,700 --> 00:01:28,219 are angularly displaced from a line perpendicular to the edge or side of the 19 00:01:28,239 --> 00:01:38,849 fabric. Change in skewness in fabric, or twist in garment, is measured using 20 00:01:38,869 --> 00:01:43,670 benchmarks applied to the specimens before laundering. The displacement measured 21 00:01:43,689 --> 00:02:13,689 from the original marks is the basis for determining skewness. Two test methods 22 00:02:14,989 --> 00:02:19,609 are used for determining skewness. The first method makes use of a square that 23 00:02:19,629 --> 00:02:23,909 is drawn on the fabric or garment prior to laundering. After laundering the 24 00:02:23,930 --> 00:02:32,839 distortion of the square is measured. The other method makes use of lines that 25 00:02:32,859 --> 00:02:36,839 intersect at a right angle. After laundering, the displacement of the 26 00:02:36,859 --> 00:02:42,539 intersecting lines is expressed in percentage skew. Three specimens are tested 27 00:02:42,560 --> 00:02:47,489 for each sample, to increase the precision of the average. When testing fabrics, 28 00:02:47,509 --> 00:02:52,089 where possible, cut specimens from different areas of the fabric so that each 29 00:02:52,109 --> 00:02:56,759 specimen will contain different groups of lengthwise and widthwise yarns. 30 00:02:56,780 --> 00:03:02,679 Identify the fabric face. Mark the lengthwise direction on each specimen. 31 00:03:02,699 --> 00:03:07,599 Whenever dimensional change, appearance, and skewness measurements are required 32 00:03:07,620 --> 00:03:13,239 for fabrics, the specimen dimensions can be the same for that used in "AATCC 33 00:03:13,259 --> 00:03:18,869 Method 124: Smoothness Appearance of Fabrics After Repeated Home Laundering," or 34 00:03:18,889 --> 00:03:24,869 in "AATCC Method 135: Dimensional Changes of Fabrics After Home Laundering." In 35 00:03:24,889 --> 00:03:30,529 these cases, marking by skewness method one is used. Method one makes use of 36 00:03:30,549 --> 00:03:36,209 benchmarks placed on fabric swatches, or on large panels of a garment. Here, a 37 00:03:36,229 --> 00:03:41,549 knit fabric has a 15 by 15 inch square template placed with the vertical edges 38 00:03:41,569 --> 00:03:45,969 parallel to the edge of the fabric. The parameter of the template is marked to 39 00:03:45,989 --> 00:03:51,019 define the size of the specimen. Then the specimen is marked with 10 inch pairs 40 00:03:51,039 --> 00:03:55,779 of benchmarks parallel to the length of the specimen and two 10 inch pairs of 41 00:03:55,799 --> 00:04:00,699 benchmarks are marked perpendicular to the length of the specimen. Next, the 42 00:04:00,719 --> 00:04:05,959 benchmarks are labeled as A, B, C, and D in clockwise direction, starting with 43 00:04:05,979 --> 00:04:10,219 the lower left corner. A line is then drawn through each of the four sets of 44 00:04:10,239 --> 00:04:40,240 adjacent benchmarks so that a square is formed. Finally, the specimen is cut 45 00:05:23,529 --> 00:05:29,360 down to the 15 by 15 inch marks for laundering. When testing fabrics, test three 46 00:05:29,379 --> 00:05:34,910 specimens whenever possible. When testing garments using this method, test three 47 00:05:34,930 --> 00:05:39,509 garment specimens, or a total of three areas of two garments, to increase 48 00:05:39,529 --> 00:05:58,089 precision of the average. Use the largest panels in the garments. After 49 00:05:58,109 --> 00:06:06,230 laundering, follow the procedures found in AATCC Test Methods 124, 135, 143, and 50 00:06:06,250 --> 00:06:12,589 179 for preparation and condition prior to testing. After conditioning, lay each 51 00:06:12,609 --> 00:06:17,129 test specimen -- without tension -- on a flat, smooth, horizontal surface for a 52 00:06:17,149 --> 00:06:22,509 measurement. Method one, which uses a square with the corners marked A, B, C, 53 00:06:22,529 --> 00:06:27,810 and D, measures the sheer distortion of the square by analyzing the diagonals of 54 00:06:27,829 --> 00:06:33,120 the square. The analysis of the skewness square requires the measurements of the 55 00:06:33,139 --> 00:06:38,100 diagonal lines and a percent skewness calculation is made from those diagonal 56 00:06:38,120 --> 00:06:44,019 lengths. Diagonal line AC is measured in inches and recorded to the nearest one 57 00:06:44,039 --> 00:07:12,620 hundredth of an inch. The diagonal length for BD is also measured and recorded. 58 00:07:12,639 --> 00:07:17,199 As stated, method one calculates the percentage change in skewness of the 59 00:07:17,219 --> 00:07:22,759 displaced square. The lengths of the diagonal lines AC and BD are measured to 60 00:07:22,779 --> 00:07:28,480 the nearest tenth of an inch. In this option, the diagonals AC and BD are used 61 00:07:28,500 --> 00:07:34,050 in a formula that expresses sheer distortion of a plain. The value is expressed 62 00:07:34,069 --> 00:07:40,230 to the nearest 0.1 percent, as follows. The difference between the diagonals is 63 00:07:40,250 --> 00:07:45,870 multiplied by a factor of two and then divided by the sum of the diagonals. This 64 00:07:45,889 --> 00:07:51,230 number is multiplied by 100 to give the percentage of skewness. For example, if 65 00:07:51,250 --> 00:08:00,050 diagonal AC is 13.70 inches and BD is 13.65 inches, then the percent skewness 66 00:08:00,069 --> 00:08:09,589 would be 13.70 minus 13.65 times 2. And this product, divided by 13.70 plus 67 00:08:09,609 --> 00:08:16,319 13.65, and this value multiplied by 100, will give 3.7 percent skewness. A 68 00:08:16,339 --> 00:08:20,319 positive percent change indicates product skewness to the left, which is 69 00:08:20,339 --> 00:08:25,100 referred to as left-hand skew. A negative percent change indicates product 70 00:08:25,120 --> 00:08:29,909 skewness to the right, which is referred to as right hand skew. Marking method 71 00:08:29,929 --> 00:08:34,789 two uses different benchmarks as compared to method one for fabric specimens and 72 00:08:34,808 --> 00:08:39,950 garments. Using a suitable marking device, a horizontal reference line is drawn 73 00:08:39,970 --> 00:08:45,539 across the width of the specimen and is labeled YZ. Line YZ should be 74 00:08:45,559 --> 00:08:49,500 approximately three inches above the bottom edge of the fabric specimen, or the 75 00:08:49,519 --> 00:08:54,409 hem of the garment. If the bottom edge, or hem, is not straight, draw the 76 00:08:54,429 --> 00:09:00,169 reference line perpendicular to the vertical axis of symmetry of the specimen. 77 00:09:00,189 --> 00:09:05,769 Place a bench mark -- A -- perpendicular to, and midway, on line YZ. Place one 78 00:09:05,789 --> 00:09:10,850 leg of a right angle marking device along YZ so that the second leg is on a 79 00:09:10,870 --> 00:09:16,509 perpendicular upward from point A. At a distance of 20 inches up the right angle 80 00:09:16,529 --> 00:09:22,439 marking device, directly above point A, draw a benchmark parallel to line YZ. 81 00:09:22,459 --> 00:09:27,659 Draw a vertical benchmark starting at 19 inches from point A perpendicular to 82 00:09:27,679 --> 00:09:33,480 line YZ to intersect the previous benchmark. Label the intersection of the 83 00:09:33,500 --> 00:09:42,460 benchmarks S.B. If the specimen size is insufficient to mark a 500 millimeter -- 84 00:09:42,480 --> 00:09:47,580 20 inch -- length, mark the longest available length, which is at least 75 85 00:09:47,600 --> 00:09:53,659 millimeters -- three inches -- below the upper edge of the test specimen. As 86 00:09:53,679 --> 00:09:58,519 described earlier, the second method uses intersecting perpendicular lines that 87 00:09:58,539 --> 00:10:03,259 can be expressed as an inverted T marking on garment panels and some fabric 88 00:10:03,279 --> 00:10:08,289 specimens. The percentage skewness is obtained by how much the inverted T has 89 00:10:08,309 --> 00:10:13,509 distorted. After laundering, a right angle marking ruler is placed with one leg 90 00:10:13,529 --> 00:10:18,490 of the ruler placed along the line YZ, so that the vertical second leg passes up 91 00:10:18,509 --> 00:10:24,210 through point B. A new benchmark is drawn along the perpendicular on line YZ. 92 00:10:24,230 --> 00:10:30,529 The intersection of the new benchmark and the line YZ identifies point A prime. 93 00:10:30,549 --> 00:10:35,149 The length of the line AA prime is measured and recorded to the nearest tenth of 94 00:10:35,169 --> 00:10:39,970 an inch or smaller increment. This distance is the displacement of the right 95 00:10:39,990 --> 00:10:53,009 angle. The length of line AB is also measured and recorded. Finally, the 96 00:10:53,029 --> 00:11:02,899 skewness to the left or right is indicated. The percent skewness in this method 97 00:11:02,919 --> 00:11:07,279 is a simple proportion of the amount of the displaced distance of point A as 98 00:11:07,299 --> 00:11:13,159 defined by AA prime to the length of the vertical line segment AB. Skewness is 99 00:11:13,179 --> 00:11:20,129 reported to the nearest 0.1 percent. The equation used is as follows: AA prime 100 00:11:20,149 --> 00:11:26,269 is divided by AB and multiplied by 100 to give the percent change in skewness. 101 00:11:26,289 --> 00:11:33,389 In this example, line AA prime was 0.425 inches in length and line AB was found 102 00:11:33,409 --> 00:11:41,350 to be 18.85 inches. Therefore, the percent skewness is 0.425 divided by 18.85, 103 00:11:41,370 --> 00:11:47,230 multiplied by 100, and equals 2.3 percent skewness. An important factor in 104 00:11:47,250 --> 00:11:52,189 skewness is that the longer the garment, the more obvious the skewness. This 105 00:11:52,209 --> 00:11:56,490 illustration shows a couple of pairs of knit pants made from the same fabric and 106 00:11:56,509 --> 00:12:01,480 having the three percent skewness for both pairs. Normally this level of 107 00:12:01,500 --> 00:12:06,590 skewness is considered acceptable. Pair A has an inseam of 10 inches, while pair 108 00:12:06,610 --> 00:12:13,090 B has an inseam of 30 inches. Therefore, the side seam shown for A is displaced 109 00:12:13,110 --> 00:12:20,159 0.3 inches. The side seam for B is displaced 0.9 inches. Pair B appears to have 110 00:12:20,179 --> 00:12:25,840 much more skewness. However, the percentage change is the same. This example 111 00:12:25,860 --> 00:12:30,043 shows that panel lengths in garments may appear to be worse than the actual 112 00:12:30,063 --> 00:12:31,749 skewness measured.