Doubling || Yarn Properties || Parameters

Types of Doubling Twists / Twist direction:
  • Majority of the ring frame yarns are ‘Z’ twisted and the reason for using Z-twist in both warp and weft is more of a practical nature. This is because; the direction of rotation of ringframe spindle in this case is more favorable for the ringframe tenter to stop if by left hand while mending a break.
  • When a doubled yarn is made by using ‘Z’ twist in singles and ‘S’ in doubling it is termed as S/Z doubled yarn. Like wise, when a doubled yarn is made by using Z twist in both singles and doubling it is called as Z/Z yarn.
  • S/Z yarns are fuller, softer and has better luster. This is because the torque produced due to Z twisted singles is balanced by that produced by S twisted doubled yarn. Thus, they are less lively and more stable.
  • Z/Z yarns are harder, more wiry and harsh in feel and less lustrous because the torque produced due to twist in both singles as well as doubling is unidirectional and hence these types of yarns are lively and unstable.
  • Application: For shirting and suiting purpose mainly S/Z yarns are used and for viols and crepes Z/Z yarns are used.
  • The latter type of yarn produced are more lively thus they are steamed and conditioned or else it becomes difficult to process these yarns in weaving and weaving preparatory.
  • The doubled yarns may be further doubled again to produce yet another category of yarns called ‘Cabled Yarns’. The counts, in this case of yarn become very coarse.

Effects of Doubled yarn parameters on Doubled yarn properties:
There are various doubling parameters like doubling twist, doubling tension which is due to spindle speed, traveler weight and ring diameter; can be varied to influence the physical properties of doubled yarn like extension, strength, snarling tendency, doubling twist , take up, luster and yarn irregularity. Let us understand each parameter:

The effect of doubling twist follows the same pattern as single yarn strength. The strength increases with twist to the maximum and then it falls-off. To examine this in detail let us consider following cases:

When the single yarn is soft twisted and the doubling twist is high, a strongest yarn is produced. The following figure shows the effect of doubling ratio on strength of yarn.

When the single yarn is hard twisted and doubling twist is low, a strong yarn is obtained. When doubling tension is increased by providing high spindle speed, heavier traveler or larger ring diameter, all these produce a stronger doubled yarn but it is less extensible.

2-Snarling Tendency:The snarling tendency is inversely proportional to the doubling tension that is, the snarling tendency of the yarn decreases if the doubling tension increases and vice versa.Steamed or conditioned or simple wetting of yarn reduces snarling tendency.
3-Extension:The effect of a single yarn twist on the extension of doubled yarn is small. It has the inverse relation, doubling tension effects the extension value of doubled yarn lower the tension higher the value of extension in doubled yarn.
4-Luster of doubled yarn:
  • With S/Z doubled yarns, the most lustrous two fold yarn is produced around the doubling ratio 0.6 but the strength and luster is incompatible. This means that a doubling ratio of 0.6 the luster is maximum but the yarn strength is not good.
  • By choosing a medium twisted yarn say with doubling ratio 0.7, it is possible to get a stronger yarn without affecting the luster much.

5-Doubling twist and Take –up:
Whenever the yarn is twisted it contracts in the length and this contraction makes the yarn coarser. Considering, a doubled yarn (S/Z twisted yarns). Following cases are considered:
CASE 1: If the doubling twist is low.
The twist in the yarn is partly removed. This results in the extensions of single yarn. Therefore, the yarn delivered by delivery rollers of doubling frame is more than expected. This gives lower T.P.I thus, for low doubling twist the actual TPI is always less than set on the machine. 

CASE 2: If the doubling twist is high.

The extension in single yarn is over compensated by the contraction of doubled yarn. Therefore, when doubling twist is high there is net contraction of doubled yarn. Contraction due to doubling twist is greater extension of singles.
6-Irregularity:The irregularity of folded yarn is independent of the doubling twist, but it varies inversely with the square root of number of component threads in doubled yarn. The tension during doubling affects practically all the physical properties.
  • Higher the doubling tension leads to higher yarn strength
  • Higher tension improves luster
  • Higher tension reduces snarling tendency
  • Higher tension leads to lower yarn extension 

Post a Comment