What is Sanforizing Finishing in Textile?
Sanforizing is a mechanical finishing process for woven fabrics, particularly cotton, in which the fabric is stretched, fixed, and stabilized so that it does not shrink significantly after washing. It is also called anti-shrinkage finishing process. The process involves treating the fabric with steam and heat to shrink and stabilize the fibers. The fabric is then wound onto a roller and passed through a series of heated rolls, where the pressure and temperature are carefully controlled to create a tight, uniform fabric.
Sanforizing 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 washing.
Sanforizing is a controlled compressive shrinkage process, which is applied on woven fabric to achieve shrinkage before making the garments. After sanforizing the residual shrinkage of woven fabric may be zero. In sanforizing process shrinkage is achieve by passing the cotton fabric onto a movable elastic felt blanket is released it assumes a shortened conditional. Thus the cotton fabric is forced to confirm this compression.
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.
Residual Shrinkage:
Residual Shrinkage is the latent shrinkage of a fiber, filament, yarn or fabric.
The shrinkage amount of fabric is dependent on:
The nature of fibers
The character of threads
The way of interlacing of thread in the fabric.
Crimp in yarn.
Cycle of washing no. of washing.
Purposes of Sanforizing Finishing: The purpose of sanforizing or zero–zero finishing is to give shrink-proof finish to cotton fabrics. Sanforized fabrics should not shrink more than 1%. There are a number of mechanical finishing treatments to make fabrics shrink-proof.
The purposes of sanforizing finishing is to:
Prevent shrinkage: The primary purpose of sanforizing is to prevent shrinkage in the finished fabric. This is achieved by stretching and stabilizing the fibers so that they do not shrink significantly after washing.
Improve appearance: Sanforizing can also improve the appearance of the fabric, making it smoother and softer. The process helps to reduce pilling, which is the formation of small balls of fiber on the surface of the fabric.
Enhance durability: Sanforizing makes the fabric more durable by stabilizing the fibers and reducing the likelihood of shrinkage, which can cause the fabric to become misshapen and wear more quickly.
Ease of care: Sanforized fabrics are easier to care for because they are less likely to shrink and lose their shape after washing. This makes them a popular choice for clothing and home furnishings.
Consistency: Sanforizing provides a high degree of consistency in the finished product, as the process is carefully controlled to produce a uniform fabric with a consistent size and shape.
Mechanism of Sanforizing Finishing: Sanforizing is a process in which fabric is stuffed together along its length (warp-way) on a machine resembling a felt calender and setting it in this state, so that when it is subsequently washed, no further shrinkage will occur (Figure 1).
Figure 1: Sanforizing head
The goods are extended to full width on a short frame at a higher speed before reaching the shrinking device. The shrinkage takes place immediately after passing the hot shoe at a temperature of approximately 180°C. The flexural strength of the fiber is decreased, the physical cross-linking is broken, and the textile material is more easily compressed. Drying takes place immediately after the subsequent felt calender. The shrinking capacity of this machine is maximum 10%. The degree of shrinkage is determined by the thickness of the felt. The thicker the felt, the higher the shrinkage capacity. The degree of shrinkage is regulated by altering the shrinking shoe.
Working Principle of Sanforizing Machine: The cloth is continually fed into the sanforizing machine (Figure 2). It is moistened with either water or steam. A rotating cylinder presses a rubber band against another heated rotating cylinder. The rubber band briefly gets compressed and afterwards shrinks to its final size. The cloth to be treated is transported between rubber band and heated cylinder and is forced to follow this brief expansion and recontraction and thus gets shrunk. The bigger the pressure applied to the rubber band, the bigger the shrinking afterwards.
Figure 2: Sanforizing machine
The process can be described by the following schematic diagram (Figure 3).
Figure 3: Schematic representation of sanforizing machine
Fabric (F) passes through the skyer (S) or another moistening device and is moistened with water and/or steam. This will lubricate the fibres 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), fabric gets the required width. The clip expander also transports the fabric to the most important part of the machine, the rubber belt unit (indicated by curved arrow in above figure). In the close-up of figure, the endless rubber belt (R) can be seen. By squeezing rubber belt (R) between pressure roll (P) and rubber belt cylinder (RB), an elastically stretching of the rubber belt surface is obtained. The more the rubber belt is squeezed, the more the surface is stretched. This point of squeezing is known as the pressure zone or the nip point.
Fabric (F) is next 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 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.
References:
Handbook of Value Addition Processes for Fabrics By B. Purushothama
Principles of Textile Finishing By Asim Kumar Roy Choudhury
Textiles for Industrial Applications by R. Senthil Kumar
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
