In my last blog ‘5 Reasons Why CPL/Bit Wash Is Robbing You Blind’, we saw how a widely practiced solution like CPL/Bit wash, to counter high shrinkages in knit fabric, is snatching millions of dollars in profit margins away from garment manufacturers.
Now let’s figure out the other sensible options we have at our disposal to ensure that the shrinkages remain within the acceptable range.
A word of caution: Although I will try to keep the explanations as little complicated and jargon free as possible, this might get a bit technical in a few places. Bear with me, and I am sure you will find a lot that you can take away from this article.
So, let’s first try and understand exactly how knitted cotton fabric end up with so much inherent shrinkage in the first place.
Shrinkage is, for most garment manufacturers, the unfavorable change in fabric dimension after washing or dry relaxing.
Majority of shrinkage is added on the knitted fabric in two distinct stages:
1. During the constant pulling and tugging of yarn and knitted loops during the construction of fabric and
2. The incredible length-wise mechanical stress, the fabric is subjected while undergoing wet processing (Scouring, Bleaching, Dyeing, Extraction etc.)
The physics behind shrinkage is the tendency of the knitted loop to acquire the configuration of lowest energy state, which is a more rounded configuration from the usual elongated structure it has been forced to acquire after the mechanical stresses applied during the above stages.
Please see the image below.
The significant amount of this relaxation occurs when the tensions working on the fabric is lifted: for example, when the fabric rolls are unwound, relaxed and dipped in water. The fabric swells upon absorbing water and the yarn crimp increases. It helps the loops to acquire a more rounded, well packed configuration which leads to shortening of the loops and hence shrinkage occurs.
Another round of intense shrinkage can be induced by providing uniform mechanical agitation while the fabric is undergoing de-swelling or drying. At a critical moisture content of around 15-20% during the drying cycle, the mechanical agitation coupled with lubrication from water and added softeners helps the loops to snuggle into an even more relaxed rounded configuration causing further shrinkage.
6 Steps for complete Shrinkage Control
Now, when we have peeked into the causation and mechanism of shrinkage in a knit fabric, let’s try to assess solutions to circumvent the same.
1. Knitting Parameters: To take care of the shrinkage added during the fabric construction stage, it is imperative to have a detail oriented, focused approach towards finding the right set of knitting parameters like: Machine cut (Gauge) and Course length or Stitch length (Course length/No. of needles) for every yarn count and knit type. It is a well-established fact that fabric with shorter stitch length (leading to tightly knitted fabric) is far less likely to shrink uncontrollably when compared with a lightly knitted fabric with a longer stitch length.
2. Low Tension Wet-Processing Equipment: The most damaging of all shrinkages is added during the wet processing of fabric. The conventional high tension equipment for Jet Dyeing, Scouring and Bleaching coupled with stressful extraction, leads to heavily elongated fabric which is highly susceptible to shrinkage. There has to be a conscious collaborative effort in the fabric mills and garment manufacturers to move towards the modern low tension ‘soft-flow’ or ‘over-flow’ Jet dyeing machines. This can be coupled with over-feed, low tension extraction machinery. This in itself will reduce the inherent fabric shrinkage substantially and prepare the fabric for a better shrinkage control through the next stages.
3. Continuous Tumbler or Open Width Relaxation Drying: This stage mimics the Tumble dry mechanism used in CPL, but in an efficient open width form. It involves following steps:
Click here to know about some ‘Relaxation Drying Machines’. The proper introduction of these equipment can take care of most shrinkage which is added on the fabric during the wet processing.
4. Compacting/ Sanforizing/ Zero-Zero Finishing: This widely used process can be highly effective in ensuring that shrinkages are within the controllable range, provided that it is employed after relaxed drying. This is achieved by mechanically compressing the fabric between rubber sheets and heated rollers to overpower the inter-yarn static friction This also allows the yarns to settle up to each other, as tightly as possible, in well-rounded configurations.
5. Low Tension Roll Packaging: At this last stage, the mill must ensure that the fabric is wound up with as low tension possible for any unwanted lengthwise stressors and elongation. This can also be countered at the manufacturer facility by un-wounding the rolls and letting them relax for 1-2 hours before proceeding for cutting.
Click here to know about the right ways to handle the fabric and how they can be implemented in order to avoid any adverse effect on the fabric tension.
These processes need to be implemented at the textile mill stage for shrinkage control. Garment manufacturers should ask their fabric supplier to install modern machineries at different stages mentioned above, to counter the problem at fabric construction stage itself.
At the factory level, manufacturers can refine their processes by performing 100% inspection for shrinkage:
6. 100% Shrinkage Inspection: Factories can start 100% shrinkage inspection for ensuring that they have a complete information of individual fabric rolls. Most denim/washed bottom-wear factories are already following this protocol to ensure proper batching of fabric before cutting. It ensures that level of measurement disturbances caused by uneven shrinkages in rolls can be checked with proper measures in marker making.
These set of processes when practiced carefully and sequentially can eliminate the mayhem of unpredictable shrinkages in knit fabrics. The cost apparel manufacturers are losing each day using CPL, can be completely avoided by partnering and working with the fabric mills to get the fabric right the first time.
“A guide to improved shrinkage performance of cotton fabrics” Cotton Incorporated, 2004″
About the author:
Saurav Ujjain is Principal Consultant at ThreadSol Softwares and an established industry expert with over 8 years experience in the garment industry in the areas of production, merchandising and retail. He holds a degree in Fashion Technology from NIFT, Delhi.