Textile Finishing

Finishing is the final series of operations that produces finished textile fabric from greige goods. Finishing operations are predominantly wet operations requiring large amounts of thermal energy for water heating and drying. Woven greige goods require some additional steps prior to dyeing, as compared to knit goods. As the first step in finishing woven goods, singeing burns protruding fibers by passing the fabric over an open flame or heated plates to produce a cleaner fabric and enhance future operations. Hot exhaust air is produced.

Sizes and other ingredients added during slashing in the weaving mill are removed in the desizing operation by washing them in a detergent solution at temperatures up to 200°F and then rinsing them with fresh water. The process produces a wastewater stream of 100 to 120°F. Scouring is another washing process using steam and detergents to remove oils and mineral material. The scouring can be done by batch in pressurized vessels known as kiers or on a continuous basis. In either case, high temperatures, to 250°F, and long retention times, up to 12 hours, are used to ensure thorough saturation and cleaning. Finally, the fabric is rinsed. A waste stream of warm, contaminated water is produced.

Next, the fabric is bleached, washed, and rinsed several times to achieve uniformity and improve its ability to absorb dyestuffs later in the finishing operation. Contaminated, warm wastewater is produced. Mercerizing is an optional step and consists of a caustic spray, tensioning, water rinse, water wash, acid dip, and final water wash, and produces a warm wastewater stream. For the drying step, conventional steam-heated drying cans arranged in sequence are most usually used. Finishing is the final wet process wherein size and/or other ingredients are applied to the fabric to provide particular characteristics, such as stiffness, water proofing, etc.

The fabric is dried and finally heat cured with a direct flame on a tender frame to bring it to its final dimensions. Large quantities of hot exhaust gas in the 200°F range are produced. The woven fabric is now ready for dyeing. Knit goods do not require desiring and bleaching. The finishing process requires only scouring to thoroughly clean

the goods prior to dyeing. As with woven fabric, the step involves hot water washes and rinsing, and produces warm, contaminated waste water.

Dyeing Process

The dyeing process varies considerably, depending on the type of dyestuff, type of fabric, and desired final characteristics (for example, solid color or prints.) Dyeing is a wet process and may be done in batches or continuously. Dye vats are known as dye becks and may be atmospheric dye becks (open) or pressure dye becks.

Frequently, a time-temperature ramp is employed. The dye beck may start at 120°F and may be slowly raised in temperature to 160°F or higher through steam-heated heat exchangers. After the dye is set by aging or heating, the fabric may be washed again and dried and/or heat cured. Large quantities of warm, contaminated wastewater are produced.

Finishing Wet Process

Finishing plants are thermal energy-intensive, requiring large quantities of hot water from 120 to 200°F for desiring, scouring, bleaching, mercerizing, dyeing, washing, and rinsing. The hot water is almost universally heated with steam using steam-to-water heat exchangers, direct sparing, or storage tank heating. Many plants recover heat from waste streams with heat exchangers to preheat the process water. Large quantities of steam are also used for heating drying cans and, to a lesser degree, for humidifying space conditioning air.