Hair severity: A new yarn hairiness parameter - Part II

Introduction

Hairinessis a key parameter that affects the yarn performance in the subsequentprocesses and degrades fabric appearance. This necessitates a precise yarnhairiness measurement and control. Yarn hairiness measurement has beendiscussed for several years, but it still remains a complex subject, whichrequires further in-depth understanding. The distribution of hair length is oneof the most important characteristics of the yarn. To an extent, hairiness isrequired for further processing and to give a soft feel to the fabric. At thesame time more number of long hairs on the yarn surface leads to pilling andfuzzy fabric appearance.

HairSeverity (HS) represents the severity of the long length hairs, which ismeasured by Premier iQ QualiCenter.

Hair Severity shows a goodcorrelation with key raw material characteristics

• What are the cotton parameters to be considered?
• What is the relationship between Raw material properties and Hair Severity?
• What are the statistical levels achieved by mills?

To address all the above questions and to gain a betterunderstanding of the effect of Raw material characteristics on Hair Severity,quantitative studies have been conducted for different count and material. Thefollowing are the critical raw material quality parameters which have beenconsidered:

• Uniformity Index(UI)
• Micronaire (Mic)
• Short Fibre Index(SFI)

Hair Severity (HS) Vs Uniformity Index (UI)

Cotton fibre is a highly variable material whose intrinsic quality cannot be changed after harvesting. The variability in fibre length plays a crucial role in the process performance, as reflected in UI. The Uniformity Index contributes significantly towards Hair Severity (as observed in various count and material).

In all the graphs illustrated in this article, the following format is used:

• X1 represents the statistical level achieved by mills who have participated in the study
• X2 represents the count and material
• Y1 represents the raw material property/process parameter ( e.g. Uniformity Index in the above graph)
• Y2 represents the Hair Severity

It is clear from the above graph that, lower the uniformity Index, higher will be the Hair Severity. For a detailed understanding, please refer to the Table 1.

TABLE - 1

Hair Severity (HS) Vs Micronaire (Mic)

Fibre fineness is considered as the most important parameter impacting the yarn quality. The number of fibres in the cross section determines the yarn irregularity. For a given yarn count, yarn irregularity comes down when there is an increase in no. of fibres. Similarly finer micronaire also result in increased level of yarn neps which leads to dyeability issues. Studies carried out in various count and material reveals that the Micronaire has a high influence on Hair Severity.

Coarser Micornaire leads to higher Hair Severity. However, the reverse trend observed in 60s CW is due to the imported cotton used by mills.

Hair Severity (HS) Vs Short Fibre Index (SFI)

Traditionally, Short Fibre Content (SFC) is an indication of cotton quality: defined as a percentage of fibres less than 12.7mm. Raw material with higher SFC is inferior as it leads to high waste % in the process and yarn produced from this cotton will have low strength, more unevenness and high hairiness. Studies conducted for various count and material shows that SFI has a good correlation with Hair Severity.

However Premier recommends using only True Short Fibre - TSF, instead of SFI and SFC (n) because two different raw materials will have similar SFI/SFC (n), but the TSF is more representative of the short fibre as illustrated in Table 2.

TABLE 2

TABLE 3

Hair Severity is a significant indicator of critical process parameters

In general, the preparatory machines do not contribute towards hairiness except in a few cases where fibre rupture takes place, thereby increasing the short fibres. Other process parameters such as Draw Frame settings and passages, Hank selection in Roving Frame, Spacer size in Ring Frame, TM applied in Ring frame, Spindle speeds, combination of Rings and Ring travellers affects yarn Hairiness. Among all the above, following are the critical process parameters which shows a significant impact on Hair Severity.

• TSF at Draw Frame stage
• Spacer size in Ring frame
• Ring Frame Spindle speed

Hair Severity (HS) Vs TSF at Draw Frame stage

TSF is a new parameter which represents the most appropriate short

fibre against the fixed length of 12.7 mm. TSF is a relative measure of short fibre length based on the Fibre length distribution. This provides a true representation of the Short Fibre as compared to the existing absolute measurement, as shown in Table 2. TSF has a bearing on yarn strength, evenness and Hairiness. TSF influences Hair Severity as substantiated by studies conducted for various count and material.

Hair Severity (HS) Vs Spacer size in Ring Frame

Spacer size plays a significant role in the reduction of Hair Severity. In general, there is a tendency to use thin spacers in order to reduce Imperfections and Unevenness. An optimum spacer delivers the yarn with a least Hair Severity. Any smaller spacer used beyond a limit increases the Hair Severity due to the excessive force applied on the fibre fleece.

Table 4 provides the statistical levels for Hair Severity for various spacer sizes.

Hair Severity (HS) Vs Spindle speed at Ring Frame

Yarn hairiness is greatly influenced by the increased tension created by the balloon. Higher spindle speed exerts higher load on the yarn, which increases hair severity. The trend between Ring Frame spindle speed and Hair Severity is well brought out by the studies done for various count and material.

Table 4 provides the statistical levels for Hair Severity for different spindle speed.

TABLE - 4

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