Quality Control of Knitted Garments

 

 

Quality Control of Knitted Garments :

(1) Fabric Quality

· The word quality in knitted fabric sometimes is used to describe the loop density of particular fabric.
· This dimension, loop density, is the most important one in defining knitted fabric properties, and is directly  related to fabric appearance, weight per unit area, thickness, drape.
· The loop length is the single unit cell formed in knitted fabric and is directly related to loop density
· In general, as the loop size increases, the loop density decrease.

The fabric relationship is

S=K/l2 where S is loop density, l is loop length and K is constant for particular construction.

(2) Course Length

For some structure with complex geometry (like fancy jacquard with different loop length), the average loop length value is largely irrelevant.
The "quality" is expressed indirectly, either as a course length or loop density.

(2.1) Measurement of course length

A course length is determined by unroving yarn from a known number of loops of fabric and measuring its length using a crimp tester (BS 5441:1977).

For circular machine, which is normally composed with different number of feeders, measurement must be done on each individual feeder.

For V-bed machine, care must be taken for the position of -cam system, as the
machine changes the direction on each alternative course.

(3) Weight per unit area and cover factor

The "weight" of a knitted fabric is depended on two factors, namely the loop size and the yarn size.

The effect of loop size is simple to express: if the size of the yarn remains constant, then increase loop size produces a decrease of weight per unit area.

The effect is an inverse ratio.

Example

Using the equation of S=K/Pl2, and let K=20
(a) if l = 0.4cm, then S=20/0.42, S = 125 loops/cm2
Length of yarn in 1 cm2 of fabric = 125 X 0.4 = 50cm
(b) if l = 0.8cm, then S=20/0.82, S=31.25 loops/cm2
Length of yarn in 1 cm2 of fabric = 31.25 X 0.8 = 25 cm

Conclusion : Double the loop size means half the weight per square unit.

Cover Factor

In a knitted fabric, for fabric of similar construction, as the loop length increase, the size of yarn increase.

Cover is a simple ratio of the area of a knitted fabric covered by yarn to the area of covered by the gaps in between loops.
It can be shown that for a given knitted structure, if the cover ratio is maintained through a range of fabrics with different loop lengths, then those fabrics are related in characteristics of tightness/looseness and other physical properties.

The formula of cover factor that take into account of yarn diameter, loop length and loop density is

Cover factor = Ötex/1

Relationship of
(a) yam count against loop length;

(b) weight per square meter against loop length see the diagrams
The graph of the relationship between loop length and weight per square meter
for a given construction while maintaining a cover factor, is a straight line.

i.e double the loop length, double the diameter of the yarn, double the
weight/m2 .