Textile Stenter Frame

Overview

A stenter frame, also called a tenter, is the finishing machine that fixes the final width and stability of woven and knitted fabric. It grips both selvedges in pins or clips carried on two endless chains, pulls the cloth taut to a set width, and runs it through a line of hot-air chambers. The heat does three jobs at once: it dries off the water and finish liquor the cloth carries in from upstream wet processing, it stretches the cloth to the target width while it is soft, and it heat-sets thermoplastic fibres such as polyester and nylon so the fabric holds that width and resists later shrinkage. The cloth that leaves the machine is dry, square, dimensionally stable, and finished to specification.

The machine is built as a straight line. Cloth enters through the In-feed and Padder, is gripped by the Pin and Clip Chain Transport, passes through the Drying Chamber Section heated by the Thermal-oil Heat Source, cools in the Cooling Zone, and leaves through the Exit and Plaiting. The whole line is coordinated by the Control System and held in the insulated Frame, Cabinet and Insulation.

In-feed and chemical application

The entry end prepares the cloth before it reaches the pins. The Entry Frame and Guide centres the open-width cloth, and the Weft Straightener reads the angle of the weft threads with two Weft Scanning Head heads and corrects it. A Bow Roller pulls a bowed pick line straight, and two Skew Roller units shift one selvedge ahead of the other to take out skew, so the finished cloth has square geometry. Most finishing is applied here in the Chemical Padder: the cloth dips through a Liquor Trough of finish liquor and passes a Squeeze Roller nip whose force, set by the Nip Loading Cylinder cylinder, fixes the wet pickup. The Overfeed Rollers rollers then run faster than the chain, banking extra length onto the pins so the cloth can shrink in length during drying without going tight, which controls residual lengthwise shrinkage.

Pin and clip chain transport

Two synchronised chains carry the cloth through the ovens while holding it to width. For most woven goods the selvedge is impaled on a Pin Plate, pressed home by a Pin-in Brush Wheel; for heavier or coated fabric a Edge Clip grips the edge instead so the pins do not tear out. Each Chain Link runs along a Guide Rail, and the rail position is set by the Width Adjustment Screw lead screws. Moving the rails apart over the oven length lets the operator stretch the cloth to width gradually, and moving them together at the exit relaxes it. Because the chains run hot, a Chain Lubrication Unit unit meters high-temperature oil through a Oil Nozzle onto the pins and rail. The Chain Drive pulls both chains in step through a Chain Sprocket at each corner.

Drying chambers and air system

The heart of the machine is the Drying Chamber Section, a row of identical Drying Chamber boxes, usually six to eight, that the cloth threads through. In each chamber a Circulation Fan recirculates air through a Air Heat Exchanger and forces it through a Nozzle Duct that ends in many Slot Nozzle nozzles. The slots blow high-velocity hot air onto both faces of the cloth, which strips off the saturated layer of damp air at the surface and keeps evaporation fast. A Lint Filter catches lint before the air returns to the fan, and an Exhaust Damper bleeds off moist air so the chamber humidity stays at its set point. Each chamber reports its temperature through a Chamber Thermocouple. Spent air from every chamber collects in the Exhaust Stack, and the Exhaust Humidity Control trims total exhaust against measured humidity so heat is not thrown away faster than drying needs.

Heat source, cooling and delivery

Heat usually comes from the Thermal-oil Heat Source, a gas-fired Thermal-oil Heater that brings thermal oil to about 300 C. A Thermal-oil Pump circulates the oil to every chamber exchanger, with a Expansion Tank taking up its volume change and a Gas Burner modulating to hold temperature. Some machines fire gas directly into the chambers instead. After the last hot chamber the cloth enters the Cooling Zone, where it wraps a Cooling Cylinder fed with chilled water and passes a Cooling Fan so the heat-set width locks in cold. At the Exit and Plaiting a Pin-out Guide lifts the selvedge off the pins, a Selvedge Trimmer removes the pin holes, and the cloth is either folded by the Plaiter Folder or wound by the Batch Winder.

Materials and construction

Parts that run hot and carry the cloth are stainless steel: the Liquor Trough, the nozzles, and the fan impellers all sit in steam, lint, and finish chemistry. The chains and pins are hardened alloy steel because they take impact and abrasion at temperature, and the Guide Rail is hardened to resist wear from the running chain. The ovens are clad in Insulated Wall Panel units with a mineral-wool core that keep the outside surface cool and the heat in, and the whole line sits on a Base Track so it can expand lengthwise as it heats without buckling the Structural Frame.

Variants and use

Stenters differ mainly by heat source, transport, and what the finishing line needs. Thermal-oil heating gives even, controllable chamber temperatures and is common on long high-temperature lines; direct gas firing is simpler and cheaper to run where fuel is available. Pin transport suits lightweight wovens and knits, while clip transport handles heavy or coated cloth. Stenters are the standard final step after dyeing and washing in almost every woven and knit finishing plant, and the same machine doubles as a curing oven for resin finishes, coatings, and durable-press treatments by running the cloth dry at the cure temperature held by the Control System.