The STARFISH Approach to Shrinkage Fabric Engineering Shrinkage

The STARFISH Approach to Shrinkage & Fabric Engineering

Shrinkage - Definition Shrinkage is the change in dimensions caused by a relaxation process (e. g. laundering) LS Lo Lr Original Dimensions Lo, Xo Relaxed Dimensions Lr, Xr WS Xr Xo LS% = 100. ( Lo - Lr ) / Lo WS% = 100. ( Xo - Xr ) / Xo

Fully Relaxed Dimensions After several cycles of laundering the Relaxed Dimensions will become stable Start Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5

Fully Relaxed Dimensions After several cycles of laundering the Relaxed Dimensions will become stable These are the Fully Relaxed Dimensions Practically speaking, no further shrinkage is possible Some fabrics may require ten or more cycles to relax fully, though most of the shrinkage occurs in the first five cycles.

Reference Dimensions It is very convenient to know what are the fully relaxed dimensions of each of our fabric qualities. But, in the real world, nobody has time to discover them Reference State Dimensions STARFISH standardises on a five-cycle Reference Relaxation Procedure. After this procedure, a fabric is said to be in its Reference State.

Shrinkage - Variation If I took the original piece of fabric and stretched it in length and width. . . it would shrink more because the Original Dimensions are greater. But the Reference Dimensions would still be the same (within practical limits). LS Reference State Dimensions do not change WS Because (practically) no further shrinkage is possible at this stage.

In General Fabric Dimensions, as delivered at the end of the finishing line, can vary over quite a wide range. . . depending on the skill of the finisher and the targets he is trying to hit. But, for a given basic fabric quality and wet processing treatment. . . the Reference Dimensions will always be the same.

Now Consider This Fabric dimensions are a reflection of stitch density. . . ¯ Length is inversely proportional to the density of Courses ( CPI, C/cm ) ¯ Width is inversely proportional to the density of Wales ( WPI, W/cm )

It Follows That Fabric Width, Weight, and Shrinkage Can be calculated from Course and Wale Densities For example. . .

Shrinkage can be calculated from changes in the densities of courses and wales Original Course & Wale Densities Co, Wo LS Reference State Densities Cr, Wr LS = 100. ( Cr - Co ) / Cr WS WS = 100. ( Wr - Wo ) / Wr

Fabric Width There is a fixed number of total wales, depending on the knitting machine that was used to make the fabric. Therefore, the width is determined by the wale density. . . Width (cm) = Needles / Wales per cm

Therefore If I know what is the wale density in the Reference State fabric. . . … I can easily calculate what must be the wale density in the As-delivered fabric for any given shrinkage value. For example. . . … if the width shrinkage has to be 5%, then Wales/cm (del. ) = 0. 95 * Wales/cm (ref. )

Fabric Area Weight Can also be calculated from Courses and Wales. . . Area weight is the number of loops per unit area multiplied by the weight of each loop Wt = C * W * tex * loop length number of loops tex is yarn weight per unit length weight per loop

By the way. . . For a fixed area weight (e. g. customer specification) and a given basic fabric quality. . . ¯ If the fabric width is fixed (as it usually is) then the fabric length must also be fixed. ¯ Therefore the number of Courses per cm (and hence the length shrinkage) is also fixed. In other words, there is a particular value for the course density that goes together with certain values of weight, width and shrinkage.

So, It Comes Down To This If I know what are the course and wale densities in the Reference State for a particular fabric quality (after dyeing and finishing) then. . . … I can easily calculate the course and wale densities that must be in the As-delivered fabric in order to guarantee a certain level of shrinkage. . . … and I can calculate the corresponding width and area weight of the delivered fabric.

Engineering of Fabrics In order to be able to guarantee specific values of weight, width and shrinkage in the fabrics that I deliver to my customers. . . … I need to be in possession of a detailed knowledge of the course and wale densities in the Reference State of any fabric that I am likely to be asked to supply. This knowledge is built into the STARFISH software

STARFISH Version 6. 5 The faster, cheaper, more reliable way of doing product development.