The Sizing process, also referred to as slashing, is one of the most sophisticated processes in textile manufacturing. Although the sizing process is a key to successful weaving, it is considered to be a non-value added process in woven manufacturing because the size is applied before weaving and then removed during the finishing process. This means that any reduction in waste in this process, whether it is raw material, time, or labor waste will directly affect bottom line profits.
The prime function of the slashing process is to produce weavability in the warp. This is accomplished by selecting sizing materials which are the most suitable for the yarn or filament being slashed and by applying the size properly to the warp
It is important for the size to strengthen the yarn, reduce the yarn hairiness,increase the abrasion resistance of yarns against one another and against loom parts, and reduce the fly in the weaving process. the ultimate goal of sizing is to reduce or eliminate warp related stops in the weaving process. These stops or breaks can be attributed mostly to defects and to excessive tension or lack of strength in the yarn.
Selecting the correct sizing material depends upon the fiber type, the type of sizing equipment, and the end use of the yarn. It is important that all size materials adhere to the yarn and produce a protective covering or film which encapsulates the yarn and gives it added strength, but also allows for flexibility and extensibility. It must give lubricity to the yarn and also must be desized, or removed, easily. Ease of handling, slasher runability, and weavibility are also key factors in choosing a size material.
Filament yarns are sized differently than spun yarns for several reasons.Filament yarns are stronger than spun yarn as a bundle. However, individual filaments are more susceptible to breaking if they are separated from the bundle. Filament yarn packages should be handled more carefully to avoid filament breakage. The sizing process provides bundle integrity to keep the filaments held tightly together. Unlike spun yarns, filament yarns do not have protruding fibers, also called hairs; therefore surface coating to reduce hairiness is not necessary. Size must penetrate the filament bundle and act as a welding agent to keep the filaments from separating. The spun yarns, conversely,need to be fully encapsulated with size to lay down these hairs.
The sizing machine influences the amount of size pick up in several ways. The amount of size pick up, or take up, is affected by the amount of tension applied to the yarn and the length of time the yarn is exposed to the size bath. Exposure time is influenced by the length that the warp sheet is dipped into the size bath, as well as the processing speed. The squeeze roll pressure, temperature of the size bath, and the size concentration all directly affect the amount of size applied to yarns. The configuration of the drying section and its temperature impact the yarn’s size encapsulation and penetration.