DETERMINATION OF YARN TWIST (According to ISO standard)

DETERMINATION OF YARN TWIST (According to ISO standard)

Yarn twist is very important for knitting. And it cause spirality of garments. So its very important to test yarn twist before knitting. H... 5:17 AM

Yarn twist is very important for knitting. And it cause spirality of garments. So its very important to test yarn twist before knitting. Here how to test yarn twist -

One of the effects of putting into a strand of fibre or filament is to cause the strand to contract in length.Suppose a yarn is twisted Z way and has a length, h.Let the twist be completely removed to produce an untwisted strand of length h+c, c being the contraction due to twist.

If the strand is now twisted S way with a number due to turns equal to those removed,we would expect that the strand will again contract to the original length, h .Several twist testers are based upon this concept.The yarn is first gripped in the left hand clamp which is mounted on pivot and carries a pointer.After led through the rotating jaw,The yarn is pulled through until the pointer lies opposite a zero line on a small quadarnt scale; the jaw is then closed.

At this stage the specific is under a small tension and has a nominal length of 10 in.As the twist is remove,the yarn extends and the pointer assumes a vertical position,so removing the tension.Eventually all the twist is taken out but the jaw is kept rotating in the same direction until sufficient twist has been inserted to bring the pointer back to the zero mark again.

The total number of turns registered on the revelation counter is divided by 20, that is twice the number of inch in the test length.The result of this division is the turns per inch in the specimen.A moments reflection will show that twice the number of inch is used as a divisor since only half the revolution of the jaw actually remove the twist.

• PURPOSE AND SCOPE:
• Following the test method is to used to determine twist in all single spun yarn and 100% cotton open end yarns. For all open-end spun that are not 100% cotton, this test method has not been found to be satisfactory for determine twist but may be used to measure deviation from an average value.
• Yarn has “S” twist if, when the yarn is held in vertical position, the visible spirals or helices around its central axis confirm in direction of slope to the central portion of the letter “S” and the yarn has “Z” twist if the visible spirals or helices more yarns, either single or piled are twisted together, the letter “S” and “z” are used in a similar manner to indicate the last twist inserted.

• APPARATUS AND MATERIALS REQUIRED:
• Twist tester with all accessories.
• Yarn for testing.
• Calculator for calculation.

• PROCEDURE:
• Take four yarn cones from a single dispatch and condition them.
• Clip the yarn from a conditioned cone to the twist tester.
• Attach the weight (an accessory of twist tester) to the yarn at ten-inch distance from the point of clipping. Remember not cut the yarn from the cone/package side.
• Check the counter meter of twist tester. Meter should be at zero.
• Pull the needle lever to let the needle on the twist tester more freely.
• Push the speed lever on the twist Tester to start the test. At this point the needle starts to move in left direction.
• When the needle return at the starting point. Stop the speed lever and note the counter meter reading.
• Calculate the yarn twist according following formula:
• Twist per inch (TPI) equals counter meter reading divided by 10.
• Twist Multiplier factor (TMF) equals TPI divided by yarn count.