How To Control Shrinkage And Twisting In Fabric

What Causes Shrinkage and Twisting?

During spinning, weaving, bleaching, dyeing and the various finishing processes, yarns and cloth are under a continuous tension that causes Shrinkage And Twisting in the fabric. Yarns and/or fabrics are not fixed materials. They consist of separate, stretchable fibers which submit to the tension. In other words, fabrics do stretch in length and width. The tension within the yarns, which is caused by
This stretching, can be eliminated when the friction within the fabric is reduced. This reduction in friction occurs during laundering where both water and soap act as a lubricant. The lubricant, along with the mechanical action of the washer, helps the fibers relax and contract to their original length before the elongation takes place. This means that the fabric shrinks and recaptures its original equilibrium.

Controlled Comprehensive Shrinkage and Twisting Process:

The internationally well-known and most important shrinking process today dates back more than 70 years. Though the correct expression for this process is Con-trolled Compressive Shrinkage, the average person knows it as SANFORIZED. The process is a purely mechanical treatment without any addition of chemicals. The word SANFORIZED is derived from the first name of the inventor of the compressive shrinkage process, Mr. Sanford L. Cluett. The Sanforized Company, a division of Cluett Peabody & Co., Inc., New York, USA, is sole owner of the registered trademarks Sanforized, Sanfor and Sanforizado. The Sanforized label means dimensional stability for
garments made up of Sanforized labeled fabrics. The purpose of the process is to shrink fabrics in such a way that textiles made up of these fabrics do not shrink during washing.
The amount of potential wash shrinkage must be determined prior to shrinking. A full width sample is wash-tested according to the test method. After the lengthwise and widthwise shrinkage has been deter-mined, the compressive shrinkage machine can be adjusted accordingly.

The shrinkage and Twisting Control Process Can be Described by the Schematic Below:

Fabric (F) passes through the skyer (S) or other moisten-ing device and is moistened by water and/or steam. This will lubricate the fibers and promote shrinkability within the fabric. Normally, a fabric must be moistened in such a way that every single thread achieves a moisture content of approximately 15%. This allows compression of the fabric with very little resistance. When the fabric passes through the clip expander (C), we obtain the required width. The clip expander also trans-ports the fabric to the most important part of the machine: the rubber belt unit (indicated by arrows in above figure). In the close-up of fig. 1, we see the endless rubber belt (R). By squeezing rubber belt (R)
between pressure roll (P) and rubber belt cylinder (RB), we obtain an elastical stretching of the rubber belt surface. The more we squeeze the rubber belt, the more the surface is stretched. This point of squeezing is known as the pressure zone, or the nip point. Fabric (F) is now fed into the pressure zone. When leaving the pressure zone, the rubber belt recovers itself and the surface returns to its original length carrying the fabric with it. The effect of this action is a shorting of the warp yarn which packs the filling yarns closer together. At this actual moment, shrinkage occurs. After compaction within the rubber belt unit, the fabric enters the dryer (D). Here the fibers are locked in their shrunken state by removing the moisture from the fabric. After the compressive shrinkage process is completed, another sample of the fabric is taken. This sample is also wash-tested. The final result of this test must meet the Sanforized Standard in length and width before it may carry the Sanforized label. All Sanforized Licensees are contractually obligated to follow the required test method and meet the standards set forth by The Sanforized Company.

Shrinkage and Twisting Standards for Woven and Knit Fabrics

Standards for Shrinkage of Sanforized Labeled Woven Fabrics: Woven fabrics shall not either shrink or gain in excess of 1% in either the warpwise or the weftwise direction when subjected to the wash-test method of the United States Federal specification number CCC-T-191A or ISO 675.
Standards for Shrinkage of Sanfor-Knit: Labeled Knit Fabrics Knit fabrics shall not either shrink or gain in excess of 5% in either the longitudinal or the cross direction when subjected to the wash-test AATCC 135-1987 or ISO 6330 (60 degree, tumble dry).

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