Crimp Percentage of Woven Fabric

Introduction

When warp and weft yarns interlace in fabric, they follow a wavy path. Crimp percentage is the measure of this waviness in yarns. Generally, the waviness is found more in weft yarns because the tension found in weft yarn is less than in warp yarn.

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Objectives

To know about crimp percentage.
To measure the crimp percentage of warp and weft yarn of fabric.

Working Principle

The percentage of crimp is defined as the mean difference between the straightened thread length and the distance between the ends of the thread while in the cloth, expressed as a percentage.

Crimp percentage = (l - p) / p ✕ 100 %

Here, l = without crimp length, p = with crimp length.

Apparatus

Crimp tester
Fabric sample
Scissor
Scale etc.

Machine Description

Wira Crimp Tester

There are two types of grips, one fixed grip attached to one side of the tester and a movable grip attached to another side of the tester. Between the two grips, there is a scale for measuring crimp length. Below the fixed grip, there is a pivoted beam which is placed on the base. A sliding weight is attached to a pivoted beam and there is a hand wheel on one side of the beam.

Yarn Tension for Crimp Tester

Yarn Type	Linear Density	Tension (CN)
Woolen and worsted	15 to 60 Tex	(0.2 ✕ Tex) + 4
	61 to 300 Tex	(0.7 ✕ Tex) + 12
Cotton	7 Tex or finer	(0.75 ✕ Tex)
	Coarser than 7 Tex	(0.2 ✕ Tex) + 4
All man-made filament yarn	All	(0.5 ✕ Tex)

Working Procedure

First, we have to select the warp or weft way of the fabric. Then we should select the test length of the yarn.
According to the test length, we will cut the flap of fabric.
Now a single yarn is (from the top) removed from the flap of the fabric.
One end of the yarn is gripped in the fixed gripper of the m/c and the other end is gripped at the other end (settings for testing length).
Now the tension for the sample is found from its count and set in the machine.
After that, we will apply tension along the yarn length with the hand by taking away the other end of the yarn from the first end.
As soon as the white mark on the tension bar is the same on both sides of the white mark, the length of the yarn after applying tension is taken out from the scale.
Now from this length crimp percentage is calculated from the given formula.
In this way, at least 5 crimps for warp and 5 for weft are taken, and the average crimp is calculated.

Table for Average Crimp Percentage

Sl no	Fabric Type	Straightened Length of Yarn	Crimp % (inch)	Average Straightened Length of Yarn (inch)
1	Warp	102	10	10.48
2		10.5
3		10.3
4		10.6
5		10.8
1	Weft	11.3	10	11.26
2		11.4
3		11.2
4		11.1
5		11.3

Results

Average Warp Crimp % = {(10.48 - 10) / 10} ✕ 100 % = 4.8 %

Average Weft Crimp % = {(11.26 - 10) / 10} ✕ 100 % = 12.6 %

Remarks: We should notice that the variation in crimp can give rise to faults in fabrics, ex: reduction in strength, bright picks, and diamond barring in rayon. We should control it because crimp is related to length; it affects the amount of cloth and the cost of production.

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Ahmedabad