A twisting operation applied at an intermediate position on a yarn or other similar continuous assembly of fibres, so that no net twist can be inserted, as distinct from twisting at the end of a yarn where real twist is inserted.
Note : Real twisting necessarily involves either rotation of a yam end, as in uptwisting or downtwisting (see ring twisting), or the repeated passage of a thread loop around an end, as two-for-one~twisting. In false-twisting, a yarn normally runs continuously over or through a false-twisting device which may act at either a constant or varying rate. When the twisting rate is constant and equilibrium has been established, the yarn passes through a zone of added twist then, on leaving the twisting device, returns to its original twist level. The added (false) twist level is equal to the ratio of the rotational and axial speeds of the yarn. Equilibrium false-twisting is utilized in one method of yarn texturing where thermal setting is carried out in the zone of temporary twist; it is also used to provide temporary cohesion and thus strength in some staple-fibre processing systems. (See also pin-twisting and friction-twisting.) The self-twist (Repco) process is an example of the use of a varying false-twisting rate. Static elements such yarn guides may, in certain circumstances, generate either equilibrium or varying false-twist in running yarns
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