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).
http://www.garmentsmerchandiser.info/shrinkage-and-twisting/