What is Twist Per Inch or TPI or Turns Per Inch?

Twists per inch are the number of times the strand has been twisted in a one inch length. This is the method of designating twist in a roving.

Twists per inch are often called “turns per inch”. It is difficult to measure twist per inch in a roving, because it is generally quite low and the untwisted strand is weak.

The amount of twist to use varies with the staple of the cotton and the size of the roving into which it is being made.

Longer cotton requires less twist because individual fibres extend further in the strand and so help to bind themselves together more securely than do short fibres.

Finer roving needs more twist than coarse roving. As the strand becomes finer, the strength due to bulk alone decreases.

Also, as the fibres are drawn to be more nearly straight and parallel, there is less strength due to entangling with one another.  

Read the full article

How is the twist inserted in the roving?

Twisting is accomplished by the ‘flyer’ which is carried on the spindle. As the strand is delivered at the front rolls, it is led downward and forward to the top of the flyer, through the flier and on to the bobbin.

The flyer revolves rapidly and carries the roving around with it. The result is that the front roll is delivering a narrow ribbon of fibres in a fixed plane; the flyer, holding the other end of the exposed strand, turns rapidly and twists it.

The twist runs quickly up to the front roll as there is nothing to prevent. As rapidly as the front roll delivers a new length of ribbon, the flyer makes additional turns and they run back to the front roll.

For any given condition, the flyer speed and the front roll speed are fixed, which gives a constant ratio between the turns of twist and the inches delivered at the front roll. This is the “twist per inch”.

Read the full article

Purpose of using twist in roving

As a Textile student/teacher and learner you must know what the roving is? Now I will try to mention the Purpose of using twist in roving or why twist is required in roving?

I will answer this topic very simply mentioning the basics in this one. See below

The purpose of using twist in roving is

- to give the strand sufficient strength to withstand the strain of turning the bobbin on which it is wound, in the creel of the next operation.

Hope, you got the answer in one sentence and this is helpful.

Read the full article