Twist And Twist Measurement

In its wider connotation,the word "spinning" embraces all the various processes which are necessary to transform fibrous raw materials into yarns.Even in the man-made continuous filament plant where extrusion processes produces the yarn,one stile talks of spinning   .A more particular meaning is given to the word when we consider the process in which a strand of fiber in a more or less parallel order is spun or twisted on its exist to from a yarn.The necessity for twist in yarn construction is reflected in most but not all definition of term "Twist".

Twist is the measurement of the spiral turns given to a yarn in order to hold the constituent fibers or threads together.
When a strand is twisted the component fibers tends to take on a spiral formation ,the geometric perfection of which depended on their original formation.
Twist may be defines as the rotation about the yarn axis of any line drawn on the yarn which was originally that is before twisting parallel to the yarn axis

Accepting the fact that twist is necessary to give a yarn coherence and strength,many question now arise,amongst them the two important ones of " How much twist be inserted into a yarn" and " what effect have varying amounts of twist on the yarn properties? Before dealing with such question the methods of describing twist and expressing the amount of twist be considered.

Twist Direction: The directions of twist at each stage of manufacturer is indicated by the use of the letters S or Z in accordance with the following Convention.

A single yarn has S twist if, when it is held in the vertical position ,the fibers inclined to the yarn conform in direction of slope to the central portion of the letter S . Similarly, the yarn has  Z  twist if the fibers inclined to the axis of the yarn conform in direction of slope to the central portion of the letter Z .This figure illustrate these definition .Other methods of describing the twist direction will be found in order text box on spinning , but since they lead to confusion it id considered wise to omit them here.From the spinning point of view ,it normally matters little which way the twist goes.However, when single yarns are plied or combined in the form of fabric,the direction of twist become important because it influence the character and the appearance of the finished article.

Amount Of Twist-For many practical purpose this method of expressing the amount of twist serves quite well,but the expression contains no reference to the count of the yarn.A coarse yarn with 20 T.P.I has vastly different twist characteristics to a fine yarn with 20 T.P.I .By using an expression known as the "twist factor" or "Twist Multiplier"  it is possible to appreciate the twist character of yarn even without knowledge of the yarn count.

This figure represents an idealized element  of yarn ,showing one fiber on the yarn surface following a helical path and making one turn round the yarn axis.The twist angle is the between a tangent to the helis formed by the fiber and the yarn axis.By unrolling the surface layer we see that the fiber become the hypotenuse of a right angled triangle.

We noted earlier when the count system is an indirect system,the yarn diameter is proportional to the reciprocal of the square root of the count.

 This is more conveniently expressed in the following form

                                                     Turns per inch = K root count
The constant K is termed  the twist factor or twist multiplier and is directly proportional to the tangent of the twist angle.A range of say cotton yarns spun to different  count ,but with the same, twist factor throughout,will possess the same degree of hardness and twist character.The spinning frame over looker can readily calculate the T>P>I required to spin a give count with a specified twist factor and calculate the twist wheel required from the twist constant of the frame.