Rubber Extrusion Line

Overview

A rubber extrusion line turns a mixed rubber compound into a continuous profile of constant cross-section: door and window seals, automotive weatherstrip, sponge and dense profiles, garden and industrial hose, and cord. Unlike injection or compression molding, which make discrete parts, extrusion runs without stopping, so the economics favor long lengths of the same section. The Cold-Feed Extruder shapes the compound and pushes it through a Die Head, then a sequence of downstream machines cures the soft profile, cools it, pulls it through at a set speed and cuts or coils it.

Rubber extrusion differs from plastic extrusion in one decisive way: the compound must not vulcanize inside the barrel. The screw and barrel run warm enough to make the rubber flow but cool enough to keep it un-cured, and cross-linking only happens later in the curing oven. That single constraint shapes the whole line.

The extruder

Modern lines use a cold-feed Cold-Feed Extruder: pre-warmed rubber strip from a mill enters the Feed Throat, where a driven Feed Roller forces it onto the screw. The Single Screw has deep feed flights and a shallower metering section, so it conveys, works and pressurizes the compound as it turns. A Screw Tip sets the gap to the breaker plate.

Temperature control is split along the Barrel into zones. Each Barrel Temperature Zone carries band or cartridge Heating Element units and an RTD, and each is paired with a Cooling Water Jacket carrying water. The dual heat-and-cool arrangement matters because the screw itself generates shear heat. Without active cooling the compound would climb past its scorch temperature and begin to cure in the barrel, which would scrap the run and clog the head. A Screw Thrust Bearing takes the large axial load the screw develops against the die back-pressure.

Drive

The screw turns slowly with very high torque, so the Main Drive uses a Main Motor feeding a multi-stage Reduction Gearbox of helical Helical Gear Pair stages in a Gearbox Housing. A Drive Coupling links the gearbox to the screw. Screw speed sets output, and on a synchronized line the control trims it against haul-off speed to hold the profile dimensions steady.

Die head and tooling

The Die Head is where the section is formed. A Breaker Plate straightens the rotating flow and supports a Screen Pack that filters contaminants and raises back-pressure for better mixing. The Extrusion Die is the shaped orifice, and for tube and hose a Die Insert with a mandrel pin sets the bore. Rubber swells and relaxes after the die, so the die opening is not the same shape as the finished profile; die design compensates for that die swell and for draw-down in the haul-off. A Head Melt-Pressure Sensor watches head pressure to flag a blinded screen.

Curing and cooling

The profile leaves the die soft and un-cured. The UHF / Hot-Air Curing Oven is a vulcanization tunnel that cross-links the rubber on the move. UHF lines use a UHF Generator with a Magnetron feeding a UHF Applicator; microwaves heat the rubber volumetrically from the inside, which is far faster and more even than surface heating, then Hot-Air Zone sections hold the cure temperature to finish vulcanization. A PTFE-coated Tunnel Conveyor carries the soft profile without marking it. Salt-bath and pure hot-air tunnels are the older alternatives. After cure the Cooling Trough runs the profile through water to set its dimensions, followed by an Air Wipe.

Downstream line

A twin-belt Haul-Off Caterpillar draws the profile through the whole line at a controlled speed; the ratio of haul-off speed to extruder output sets the draw-down and thus the final size. A Cut-Off Station station cuts strip and gasket lengths with a Guillotine triggered by a Length Counter, while hose and cord run to a Take-Up / Coiler coiler with a Traverse Guide for even winding. Because freshly cured rubber is tacky, a Talc Dusting Station station coats it with talc so it does not stick to itself in the coil.

Control, use and maintenance

The Control Cabinet cabinet holds the PLC, a HMI Panel, VFD Drive drives and a Zone Temperature Controller per zone, coordinating screw speed, temperatures, line speed and cut length so the line runs as one process. Common problems are scorch from lost barrel cooling, surface porosity from poor degassing in the Vacuum Feed Hopper, and dimensional drift when haul-off and extruder fall out of sync. Maintenance focuses on screw and barrel wear from filled compounds, die cleaning and polishing, screen-pack changes, and keeping the cooling water and vacuum systems working.