Each step of a manufacturing process such as twisting, spinning, etc. causes tension in yarn, filament, yarn, and thread. Yarns tend to snarl/kink up to relax and rid themselves of tension.
Thermally conditioned or Heat-set stressed fibers and/or filaments by imparting dimensional stability through their exposure to a wet or dry heat source.
Heat setting process of yarns
Heat setting is a textile industry process for removing spinning- and cabling-induced torque and imparting dimensional stability in fibers and yarns. The process may also cause synthetic fibers to gain bulk or volume and is also used to stabilize fibers after processes such as freezing. Heat setting is a thermal process that utilizes either steam or a dry convection heat source to set the fabric or yarn. This process is typically carried out in an enclosed pressure chamber or autoclave or on open conveyors exposed to steam sprays. The steam setting is a standard post-production process for a wide selection of natural and synthetic fibers intended for the garment and carpet industries.
When fibers are spun, tufted, or woven into workable yarns, the process induces a torque reaction which can cause kinking or twisting of the finished product. To neutralize these torque effects, manufacturers expose the yarn to a process known as heat setting or thermal fixing. During this process, the fibers are exposed to a wet or dry heat source which reduces the induced torque by a combination of thermal expansion and chemical or molecular reactions to the heat and moisture. The process can also cause synthetic fibers to gain volume in a reaction known as bulk development. Heat setting is also extensively used to stabilize carpet fibers after they have been subjected to frieze processing.
Heat setting process
Conditioned heat setting is a process used to stabilize and set the twist of twisted yarns. The process involves passing the yarn through a series of heated rollers or plates that apply pressure and heat to the yarn, allowing the fibers to set in place.
The process of heat setting involves exposing yarns and fabrics to wet or dry heat in the form of superheated steam sprays or hot air convection. One of the older methods of heat-setting fabrics is the autoclave which, although still in use, is being replaced by more efficient methods with higher turnover rates. An autoclave is an enclosed vessel that heats its contents under high pressure or deep vacuuming. The fabrics or yarn are loaded into the autoclave in skeins, on bobbins, or in a separate container and heated to stabilize the fibers. Although effective, the autoclave method is slow, labor intensive, and does not lend itself to integration into a seamless production process.
The conditioned heat setting process typically involves the following steps:
- Preconditioning: The yarn is first conditioned to a specific moisture content, which helps to ensure consistent results during the heat setting process.
- Heat setting: The conditioned yarn is then passed through a series of heated rollers or plates, which apply pressure and heat to the yarn. This process allows the fibers to set in place and stabilize the twist.
- Cooling: After heat setting, the yarn is cooled to room temperature, which helps to maintain the stabilized twist.
The conditioned heat setting process is commonly used for synthetic and blended yarns, which tend to have a higher tendency to untwist and lose their shape. The process helps to ensure that the yarn maintains its twist and shape, even during washing and wearing.
A device that is commonly used for stabilizing and even curing materials is an autoclave. The autoclave allows for the treatment with steam under vacuum, subjecting materials to high-pressure saturated steam and thus, in some cases working temperatures as high as 140°C. (At atmospheric pressure water will boil at 100°C, but when the pressure is 15 psi (1 atmosphere) above standard pressure (760 mm Hg), water boils at 121°C. Increasing the pressure increases the temperature). Autoclaving will generally impart a permanent memory into yarn and will change many of its physical characteristics e.g. denier, elongation at break, and shrinkage.
Works Cited: What is Heat Setting?