The purpose of the experiment is to determine the twist amount of sized yarns. Twist; It is applied to give the fibers a permanent appearance, to increase the contact surface with each other, and to keep the fibers together. The fibers in parallel with the twist add strength to the yarn. A twist is given to the yarn in each turn of the twisting element.
Twist is expressed by the number of turns per unit length (such as laps/m, laps/inch, laps/cm). The amount of twist to be given to the yarn varies depending on the type of yarn (cotton, polyester, viscose, etc.), the place where it will be used (weaving, knitting, etc.) and the spinning machine used (ring, rotor, air-jet, friction, etc.). Twisting is given in the S (left) or Z (right) direction.( TS 247 EN ISO 2061 )
Sample preparation
While the test samples are being taken, the area to be measured should not be touched in order to prevent the yarn twist from changing. When sampling from batch production, 5 bobbins or cops are selected as samples. The first 5 meters of the yarns in each bobbin or cop are not used as samples and are discarded because of the possibility that the twist may have changed due to the looseness of the yarn. Test samples are taken at random intervals greater than one meter across the yarn. Usually 10 test samples and 50 cm test length are sufficient for each yarn taken from the bobbin or bobbin. In addition, yarn samples should be conditioned for 24 hours under standard atmospheric conditions.
The amount of tension obtained by attaching a weight (tex/2 grams) equal to half the yarn number in Tex is used as a standard.
Experimental Procedure
The twist direction of the yarn is determined. A yarn sample of at least 10 cm in length is held in a vertical position between the thumb and forefinger of both hands. Bend to the right with the right hand. If the yarn twist opens and the yarn loses its strength or the fiber becomes parallel at the ends, it is a “Z” twist. If there is an increase in the twist of the yarn, it is “S” twist. The measuring range in the bending measuring device is adjusted according to the distance specified in the standard between the movable jaw and the rotating jaw.
The test piece is held by taking care not to deform the twisting, and it is pulled through the guides to reach the rotating jaw and the test piece is placed in the gripping jaws with a pre-stress equal to (0,5 ± 0,1) CN/tex. Then half of the yarn count (in tex) is attached to the yarn end. The movable jaw is brought to the "0" position. Excess thread is cut off and discarded. Yarn properties are entered into the twist measuring device. (yarn number, twist direction, blend number) Twist measuring device is operated.
The twist measuring device continues to twist the yarn in the twist direction. Twist value at the time of yarn breakage due to excessive twist is read from the counter of the device and recorded. (t1) The pulled thread is removed between the jaws of the device. Another sample of the same yarn is placed between the jaws. The counter is reset. The yarn is twisted until it breaks in the opening direction of the twist. The twist value at the moment of breaking the yarn is read from the device's screen and recorded. (t2) As a result of the measurements, yarn twist values are calculated with the following formula.
T = t2 - t1/ 2
T : amount of twist
t1: first measured value
t2: second measurement value
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