A Detailed Report About Yarn Twist (Part Two)

Yarn Twist Report

We discussed some aspects about yarn twist in the previous report part one. Let’s finish the balance part about yarn twist s and z today.

Yarn Twist Shrinkage and The Calculation

The yarn length will become short after the yarn twist process. So we call it twist shrinkage.

We use μ instead of the difference between the yarn length before and after twist. L0 stands for the yarn length before twist. L1 refers to the yarn length after twist process. And here comes the formula.

twist shrinkage calculation

Twist shrinkage directly influences the yarn density, denier and yarn twist. During the yarn weaving and twist process, the more tension yarn gets, the smaller twist shrinkage it has. Besides, the twist shrinkage will become smaller if the temperature of production area is higher. For the same thickness yarn, the more twist it has the more twist shrinkage it shows. if the yarns are in different thickness, they will not have the same twist shrinkage even they have the same twist. The twist shrinkage of small yarn count yarn is higher than big yarn count yarn. Besides, different fiber related to different twist shrinkage. For example, the twist shrinkage for cotton fiber is normally 2%-3%.

How Does Twist Affect Yarn?

In a certain range, the yarn strength grows with the twist increasing. But when the twist achieves a certain number, the yarn strength reduces with the twist increasing. We have a technical name for it. The critical twist. The twist coefficient at the critical twist called critical twist coefficient which is αk. The real twist coefficient is smaller than the critical one.

Different yarn made from different fiber will have different critical twist coefficient.

The blend composition influences the critical twist coefficient of polyester blend yarn. We take polyester cotton blend yarn as an example. The critical twist coefficient of full cotton yarn is the biggest. And the critical twist coefficient reduces with the polyester composition increasing.

Polyester filament without twist has some strength. The twist process let each single fiber in the filament hug more tight. It can increase the unity of the filament. So here we get the conclusion that the strength of filament enforced with the twist coefficient increasing. But the critical twist coefficient of filament is small. So the space to enforce the strength by increasing the twist coefficient is limited.

Twist Coefficient Calculation

After reading these cold words, let me introduce you the formula to calculate the critical twist coefficient (αk). I think it will help you to digest these words easily.

critical twist coefficient calculation

F refers to the break strength of cotton fiber, mM.

l refers to length of cotton fiber, mm.

Nm refers to cotton fiber yarn count

C refers to a constant (when the break strength of single fiber is lower than 58.8mN, the constant is 800. But it will be 720 when the break strength is above 58.8mN.

Relationship Between Twist Coefficient, Yarn Volume, Weight and Diameter

Twist can increase the yarn density. In a certain range, yarn volume will increase according to the increase of twist coefficient. And the yarn diameter will reduce based on the increasing of twist coefficient.

The yarn twist will influence the fabric thickness, strength and abrasion resistance. It also affects the fabric hand feel and style. Especially for wool fabric.

Twist Coefficient Between Plied Yarn and Single Yarn

What is plied yarn? The plied yarn twists by 2 or more than 2 single yarns. If we twist 5 or less than 5 single yarns, each single yarn takes the same pressure during the twist process. The plied yarn is stable with high strength because the inner side is empty. When there’re more than 6 single yarns during the twist procedure, there will have 1 or 2 single yarn in the central part of the diameter. The plied yarn is not so stable because the pressure on each single yarn is not the same. In mass production, we will strictly control the single yarn do not more than 5.

Twist direction is another important issue in fabric construction. The plied yarn is soft, shiny and stable when the twist direction of single yarn and plied yarn is different. If the direction is the same, the plied yarn will show the properties like tough, less shiny. We can see the single yarn twist effect easily. Most important, the plied yarn is not so stable. It’s easy to twist the yarn into a small ball.

You may have a brief idea about yarn twist through these 2 posts. Textile industry is like a library. It has many deep knowledge for us to find out. I will share more textile ideas in the future posts. So please stay tuned for that. 

Have a great day!

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