Purpose of Finding Twist Number in Yarn Twist is the number of turns or helix per unit length. Twisting enables the fibers to rub together to form the yarn structure in continuous and discontinuous yarns. In continuous (filament) yarns, although a very loose structure can be obtained without twisting, the use of the filaments will be very limited. Since the tenacity of an untwisted yarn will be low, the tenacity of the textile product will also be low and adversely affect the properties of the textile product.
>>> Twisting is essential for the formation of yarn in staple fibers.
>>> The amount of twist to be given to the yarn in yarn formation depends on the fineness of the fiber, its length, the yarn number and the place where it will be used. As the amount of twist increases, the strength of the yarn also increases. However, starting from a certain point (critical point) of the twist increase, the strength starts to decrease.
>>> It is very important to know the number of twists in the yarns. Because as the number of twists increases, the diameter of the yarn will expand, which will cause the yarn number to change. Twist also affects the yarn's ability to take up dye. Low-twist yarns absorb more dye, while high-twist yarns absorb less dye.
For these reasons, yarn twist must be controlled very carefully.
Twist Measuring Device While the test samples are being taken, the area to be measured should not be touched by hand in order not to change the yarn twist. For sample selection, 5 bobbins or cops are taken. The first 25 meters of yarns in each bobbin or cop are not used as samples and discarded as there will be differences in the number of twists. Test samples are taken at random intervals greater than one meter across the yarn. 5 or fewer measurements should be made from each bobbin or cop. If a sample is taken from the lot, an equal number of measurements should be made for each bobbin or cop taken.
Determination of the twisting direction of the yarn
The twisting direction depends on the direction of rotation of the spindles on the spinning machine. If the spindles rotate clockwise, right twist (Z), if they rotate counterclockwise, left twist (S) is given to the yarns.
The twist direction of a twisted yarn is found as
The thread is held with the fingertips and suspended. If the twist traces (helices) on the yarn are oriented in the right direction, the yarn twist direction is right-handed. If the helices on the yarn are parallel to the middle line of the letter Z, the twist direction is the right direction. If the twist helices on the yarn are oriented to the left, the yarn is left-twisted. The direction of the helices on the yarn is in the middle of the letter S. If it is parallel to the line, the yarn twist direction is to the left.
Measuring the twist
Twisting of single and double ply yarns is done with a twist measuring device. First of all, the number and twist direction of the yarn sample to be measured are determined. There are tension weights according to the yarn number.
Performing the twist test
>>> The thread end is first attached to the thread jaw at the counter.
>>> The other end is attached to the second jaw together with the tension weight, and it is started to be turned in the opposite direction of the twist on the yarn.
>>> In this method, the test length is 250 mm for single ply yarns. When the pointer showing the elongation is in the zero position, the bending begins.
>>> As the yarn stretches as the twist unfolds, the needle moves to the left and is stopped after a while with the help of a brake. However, the twist continues to unfold, and after it is fully unfolded, the twist is given again without stopping the rotational movement. This process is continued until the pointer reaches the zero point again.
>>> When the pointer reaches zero, the value on the counter is read. The value read is divided by two to find the bend value at that test length.