Sanforizing Machine and Process

Sanforizing process moves the yarns closer together and the fabric becomes thicker and heavier. As a result of this, the net yardage yield is reduced. Sanforized is now used for a fabric which has low residual shrinkage and sanforization is a process for shrink-proofing fabrics.

Figure 1: Sanforization Machine

The machine used for the sanforizing process is called "Sanforizing Machine". Sanforizing Machine means a machine consisting of a large steam-heated cylinder, an endless, thick, woolen felt blanket which is in close contact with the cylinder for most of its perimeter, and an electrically heated shoe which presses the cloth against the blanket while the latter is in a stretched condition as it curves around feed-in roll.

Sanforizing Process

Sanforizing is a mechanical finishing process of treating textile fabrics to prevent the normal dimensional alternation of warp and weft. It is also called anti-shrinkage finishing process. It is a process of treatment used for cotton fabrics mainly and also for some other textiles made from natural and synthetic fibers. It is a method of stretching, shrinking and fixing the woven cloth in both length and width, before cutting and producing to reduce the shrinkage which would otherwise occur after wash.

Principle

Figure 2: Sanforizer Head

• Sanforizing process is based on the principle that when an elastic felt blanket is passed around a metal roller in contact with it, its outer surface is process extended and the inner surface contracted. So the process is called controlled compressive shrinkage process.
• The process of sanforizing includes the stretching and manipulation of the fabric before it is washed.
• During the sanforization process, the fabric is fed into a sanforizing machine where it is treated with water or steam to promote shrinkage, then pressed against a heated rubber band to relax and re-contract the fibers.

• 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 width wise shrinkage has been determined, the compressive shrinkage machine can be adjusted accordingly.
• The cloth is continually fed into the sanforizing machine and therein moistened with either water or steam. A rotating cylinder presses a rubber sleeve against another, heated, rotating cylinder. Thereby the sleeve briefly gets compressed and laterally expanded, afterwards relaxing to its normal thickness. The cloth to be treated is transported between rubber sleeve and heated cylinder and is forced to follow this brief compression and lateral expansion, and relaxation. It thus gets shrunk.
• The greater the pressure applied to the rubber sleeve, the bigger the shrinking afterwards. The process may be repeated.

Schematic Process

The process of Sanforizing can be described by the following schematic below:

Figure 3: Movement of fabric through different parts of sanforizing machine during sanforization process.

• Fabric (F) passes through the skyer (S) or other moistening device and is moistened by water and/or steam. This will lubricate the fibers and promote shrink ability within the fabric.
• Fabric is moistened in such a way that every single thread achieves a moisture content of approximately 15%.
• Above step 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 transports 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 above figure, we see the endless rubber belt (R). By squeezing rubber belt (R) between pressure roll (P) and rubber belt cylinder (RB), we obtain an elastically 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.