Thermosetting
The heat setting is a finishing process for yarns , fibers and yarns , and for materials and fabrics of man-made fibers . The goods are subjected to heat treatment and shrink . This state is fixed and consequently a subsequent entry of the finished products and thus a later, undesired, dimensional change is prevented.
The material
Heat setting can only be carried out on products made from synthetic fibers that have a partially crystalline, supermolecular structure. For example, these would be polyester , polyamide or elastane . The treatment takes place, depending on the material, with hot water, steam or dry heat and eliminates internal stresses that have arisen from previous manufacturing and / or finishing processes. The dimensional stability, creasing and pilling and the tendency to curl are also improved. Most important, however, is the dimensional stabilization of the goods, which prevents later, undesired shrinkage, e.g. B. when washing clothes or technical textiles when used at high temperatures is prevented.
Procedure
The heat setting of a textile fabric (fabric / knitted fabric) is usually done in a tenter machine . First the edges of the cloth are pinched or needled on both sides and held in place while the machine is running. This sets the required shrinkage or tension in width. The cloth is continuously fed into the machine by means of a conveyor device, where it is subjected to a predefined longitudinal tension between the rollers . The cloth, now held on all sides, is transported through several heat or moisture departments. When exposed to hot water, steam or dry heat, the fibers relax and the cloth shrinks. The achieved state is then fixed in a cooling compartment. Since the cloth is clamped like in a frame, the shrinkage only happens up to a preset limit and is fixed in this state. This controlled shrinkage is necessary because the fibers could otherwise lose desired material properties, such as elasticity or density . With different voltage, temperature and throughput speed, the process can be adapted to different materials and individual product features can be increased or reduced.
environment
Due to the high temperatures (over 200 ° C) required in some cases, heat setting is an energy-intensive process. In wet treatment, wastewater pollution from chemicals washed out from previous finishing steps is problematic. The dry treatment leads to toxic exhaust gases , which are only partially reduced by filter systems. In addition, chemicals (e.g. anti-yellowing agents) are often used, which further worsens the environmental balance.