Last updated: September 2026
Rubber manufacturing runs on release surfaces. Uncured rubber is deliberately tacky, and it has no structural integrity until it is vulcanised, so from the moment a profile leaves the extruder die until it comes out of cure it has to be carried, supported and pressed against something it will not stick to. PTFE coated glass fabric does that job across the whole line: as the belt through microwave and hot-air curing, as release sheet on moulding and splice presses, and as film on calender rolls and green stock benches.
GORTEF supplies coated fabric to rubber and polymer manufacturers across Australia and New Zealand, cut and made to the line rather than to a catalogue size.
Tell us the process stage and the dimensions and we will quote the right fabric.
Where Does PTFE Fit in a Rubber Line?
A continuous profile line runs cold-feed extruder, shock or preheat, UHF microwave, hot-air vulcanising tunnel, cooling bath, haul-off, then cutting and coiling. Batch moulding and calendering lines share the same release problem at different stations. The table below maps the stage to the part.
| Stage | Part | Why this one |
|---|---|---|
| Extruder take-off and cooling table | Coated fabric belt or sheet | A hot, sagging extrudate needs flat continuous support and a release surface |
| UHF microwave curing | Open mesh PTFE coated glass | Must pass 2,450 MHz energy through to the rubber instead of absorbing it |
| Hot-air vulcanising tunnel | Open mesh, or solid belt | 150 to 300°C, and an open weave lets hot air reach the underside of the profile |
| Salt bath and LCM lines | Coated glass in entry and rinse zones | Nitrate and nitrite eutectic salts demand chemical inertness |
| Cooling, accumulator, festoon | Belt or sheet | The profile stays tacky until it is fully cooled |
| Moulding and vulcanising presses | Self-adhesive or non-adhesive sheet, film tape | Platen and caul sheet release with no liquid agent to contaminate the part |
| Splice and corner moulding stations | Sheet, adhesive or plain | Corners are moulded onto extruded lengths, which is a small press job |
| Calender rolls, take-off and guides | Film tape | Thin, conformable release on rolls and guide surfaces |
| Green stock storage, trays, benches | Non-adhesive sheet | Uncured slabs bond to each other and to the bench in stacks |
Why Does Uncured Rubber Need a Release Surface?
Building tack is designed into the compound, because it is what lets components bond to each other before cure. Extrusion makes it worse: shear heating in the barrel pushes the profile out at roughly 80 to 120°C, and tack climbs with temperature. The profile will also deform under its own weight until it is cured, so it cannot be carried on rollers or allowed to stretch. It needs a flat, continuous, non-stick surface for the entire run from die to the end of vulcanisation, which on an automotive weatherstrip line can be most of 70 metres.
The traditional alternative is to dust the profile with zinc or calcium stearate or talc, or to dip it in soap solution. That works, but it puts a contaminant on the surface immediately before flocking, adhesive and paint operations, and it creates a housekeeping problem around the line. A release belt removes the reason to do it at all.
Why Do Microwave Curing Lines Need PTFE Specifically?
This is the one stage where PTFE is not really substitutable. Modern profile lines cure with a UHF microwave stage at 2,450 MHz ahead of the hot-air tunnel, and the belt sits directly in the field. If the belt absorbs that energy it heats, wastes power and burns out, and the rubber gets less of the energy it was supposed to receive.
PTFE has a dielectric constant of roughly 2.0 to 2.1 and a loss tangent near 0.0003, and both stay flat from 100 MHz well into the gigahertz range. That is about as close to microwave-invisible as a solid material gets. The rubber compound, meanwhile, is carbon-black loaded precisely so that it will absorb the field. The belt has to behave as the opposite of the product it is carrying, which is why open mesh PTFE coated glass is the standard specification here. The same reasoning applies to infrared and UV conveyorised curing.
Should You Use PTFE or Silicone on the Oven Belt?
Worth saying plainly, because it is checkable: silicone coated belts are more common than PTFE on the main vulcanising oven belt. PTFE’s surface can be too slick, and a profile will creep on it. Silicone grips enough to hold the profile in place, and is sometimes chosen deliberately to impart a texture on the hot extrusion before it cools.
PTFE is the better answer on the microwave stage, in salt bath and solvent contact, where an open mesh has to pass hot air, where a smooth finish is required, and for every release sheet around the line. Temperature is not the tie-breaker people expect: both coatings run to the same 260°C continuous on a glass substrate, so neither is the answer above it. High-temperature silicone vulcanising tunnels do run past that, and if yours does, say so when you enquire.
We coat fabric both ways, so there is nothing to defend here. PTFE vs silicone coated belts compared works through it stage by stage, and the heavy-duty coated belting page covers the fabric specifications.
What About Moulding, Calendering and Splicing?
Not every rubber plant runs a continuous profile line, and the release problem does not go away on a press. Compression and transfer moulding needs platen and caul sheet release without a liquid agent that will interfere with bonding or finishing later. Calendering needs thin conformable release on rolls, take-off and guide surfaces. Splice and corner moulding stations, where corners are moulded onto cut extruded lengths, are small press jobs with the same requirement.
For these, PTFE film tape for mould release suits rolls and detailed tooling, while a non-adhesive Teflon sheet is more economical for a whole platen, bench or green stock table. Where the sheet needs to stay put on a platen, the self-adhesive version saves taping it down.
How Is a Curing Oven Belt Specified?
Oven belts on profile lines are narrower than people expect, commonly 100 to 300 mm wide running over a 7 to 20 metre oven. That suits coated fabric well, because the belt is slit to width from wide stock rather than built to a standard size. To quote one we need the width, the developed length, the mesh or solid construction, the join, and whether the belt carries guide strips.
Two specification points are worth getting right, because they are what actually fails. The dominant failure mode on oven belts is joint delamination from sustained heat rather than surface wear, so the join type matters more than it does on a cold conveyor. The second is edge reinforcement and tracking, which is what keeps a narrow belt running straight over a long oven. If you would rather configure it yourself, the custom belt builder covers material, thickness, join and tracking options.
GORTEF Products for Rubber Manufacturing
Frequently Asked Questions
A coated fabric belt carries the profile from the extruder take-off through curing, in open mesh where a hot-air tunnel or a microwave stage needs air and energy to pass through, or solid where the profile needs full flat support. Around the line, non-adhesive sheet covers green stock benches and trays, self-adhesive sheet covers press platens at splice and corner moulding stations, and film tape handles calender rolls and detailed tooling.
Yes, in the entry and rinse zones. Liquid curing medium lines use a nitrate and nitrite eutectic salt running anywhere from 150 to 400 degrees Celsius, and PTFE is chemically inert against it. The limit is temperature rather than chemistry: PTFE coated glass is rated to 260 degrees Celsius continuous, so tell us the actual zone temperature when you enquire.
Silicone is more common on the main oven belt, because PTFE can be too slick and the profile creeps on it. Silicone grips enough to hold the profile, and is sometimes chosen to impart surface texture before the extrusion cools. PTFE is the better choice on UHF microwave stages, in salt bath and chemically aggressive zones, where an open mesh has to pass hot air, and for release sheets. GORTEF coats fabric both ways.
We need the belt width, the developed length, whether you want open mesh or solid, the join type, and whether the belt runs guide strips. Oven belts on profile lines are usually 100 to 300 mm wide over a 7 to 20 metre oven, and are slit to width from wide stock rather than supplied in standard sizes. Measuring the belt coming off the machine is more reliable than working from the line drawing.
The dominant failure mode is joint delamination from sustained oven heat rather than wear on the belt surface, so the join specification matters more than it does on a cold conveyor. Edge reinforcement to carry guide strips is the other specification point, because a narrow belt tracking off over a long oven will damage its own edges. Running the belt within its temperature rating is the third.
Sources
- US Patent 4,198,554, microwave vulcanisation of extruded rubber profiles (UHF stage and belt transparency).
- US Patent 4,402,760, salt recovery in liquid curing medium lines (salt bath composition and temperature range).
- Published dielectric data for PTFE, dielectric constant 2.0 to 2.1 and dissipation factor near 0.0003 across the UHF and microwave bands.
