Fabric Coating Machine

Overview

A fabric coating machine takes a roll of base fabric and turns it into a technical textile by laying a measured film of liquid or paste coating onto one face, then drying and curing that film into a continuous layer bonded to the cloth. The base can be woven polyester, nylon, cotton or glass, and the coating can be PVC plastisol, polyurethane, acrylic, rubber latex or silicone. The finished product is sold by the roll for tarpaulins, truck curtains, awnings, tents, inflatables, conveyor belting, airbags, blackout blinds and waterproof membranes.

The line runs as one continuous web. Fabric pays off at the entry, passes through the coating head where the film is applied, travels through a long hot-air oven, cools on chilled drums and rewinds into a finished roll at the exit. Every section is driven so that web tension and line speed stay matched from end to end. A typical line handles a web 1.6 to 3.2 metres wide at 5 to 60 metres a minute, the speed set by how fast the oven can dry the chosen add-on weight.

How it works

The raw roll sits on the Fabric Unwind & Let-Off stand. A Magnetic-Particle Brake holds back tension as the web pays off, and a Dancer Tension Roller senses tension swings and trims the brake so the web enters flat. From there the web passes into the Accumulator & Tension Control, a festoon that stores several metres of web. When a roll runs out, the unwind stops and the splice is made on the Splice Table while the stored length keeps the coating head fed, so the line never stops at a roll change.

The web then reaches the Coating Head, where the film is applied. In knife-over-roll mode a ground Coating Knife Blade sits at a fine gap above the rubber Rubber Backing Roll, and as the web passes under the blade it scrapes the coating down to the wanted wet thickness. The Knife Holder & Gap Adjuster carries micrometer screws across the width so the operator can set the gap to a few microns at each point and keep the film even edge to edge. For thin uniform films the head changes to a Slot-Die Applicator that pumps an exact volume onto the moving web, giving a coat weight that does not vary with line speed. Reverse-roll mode uses the Applicator Roll and a Doctor Blade to meter heavier paste films.

Coating supply

The coating is mixed and held in the Coating Mix Supply. A jacketed Jacketed Mix Tank keeps the batch at temperature, a Stirrer & Motor holds fillers in suspension, and a Metering Feed Pump meters a steady volume to the head. An Inline Viscometer reads viscosity in the supply loop so solvent or thinner can be trimmed to hold the film weight as the batch ages. A Coating Filter strains out lumps and gel before the coating reaches the die, since a single particle leaves a streak the full length of the roll.

Drying and curing

The wet web enters the Drying & Curing Oven, a hot-air tunnel split into four to eight zones. Each Oven Zone has its own Air Circulation Fan, heater bank and Slot Air Nozzle boxes that blow a sheet of conditioned air at the web from above and below. The zones are set to a rising then falling profile so solvent or water comes off the film gradually without skinning over and trapping bubbles, then the coating gels or cures at the hottest zone. A Zone Thermocouple reports each zone temperature to the controller. Because the air carries solvent vapour, a Solvent Exhaust Fan bleeds it off at a controlled rate to keep the concentration well below the lower explosive limit, and the bled air goes to an abatement stack.

Cooling and rewind

The cured web is still hot, so it wraps the chilled drums of the Cooling Section section, where heat passes from the coating into water circulated by a Water Chiller Unit through a Rotary Water Union at each drum end. Cooling sets the coating firm so it does not block when wound. The finished web then reaches the Fabric Rewind & Wind-Up, where a Surface Contact Roller presses the building roll to squeeze out trapped air and wind it firm. Throughout the line a Web Guiding & Edge Control watches the edge with an Edge Position Sensor and steers the web so the coating lands square and the roll winds straight.

Materials and control

The backing roll carries a hard nitrile rubber cover, the knife is hardened tool steel, and the trough and nozzles are stainless because many coatings are abrasive or corrosive. The frame is welded structural steel so rollers stay parallel over the length of the line. The Control Cabinet cabinet holds the recipe: line speed, coating gap, pump rate, zone temperatures and rewind tension. Its Drive Controller closes the tension loop from the load cells and dancer so the web is never stretched or slack as it moves between stations.

Variants and use

Lines are built around the coating chemistry. PVC plastisol lines run hotter to gel and fuse the film and often coat both faces in two passes. Polyurethane and silicone lines add a curing tower after the oven for slower cure chemistries. Direct coating lays the film straight onto the fabric, while transfer coating casts the film onto release paper first and laminates it to the cloth for a softer hand. A single line can usually switch methods by changing the head element, so one machine covers tarpaulin, awning and membrane work from the same frame.