Rubber extrusions are similar to molded rubber products, in that both are created by forcing heated rubber in a near-liquid state into a specially made mold or die under pressure. The extrusion process begins with an unvulcanized rubber compound being fed into an extruder. Revolving screws within the extruder carry the rubber toward the die; temperature and pressure increase as the material is forced through the opening. As it passes through the opening, the material generally swells to a certain extent, based on its chemical makeup and hardness. Plus/minus tolerances in the design of the extruded part’s cross section are often required to account for this swelling.
Extruded products are often left unvulcanized prior to extrusion, which leaves the rubber in a softer, more pliable state post-extrusion. If this is the case, rubber extruded products generally need to be vulcanized before they can be used. Depending on the type of rubber being extruded, the vulcanization process will cause the material to either swell or shrink, both in its cross section and its length. In most cases, a length of rubber extrusion will experience greater dimensional reduction or expansion across the center than at its ends.
A primary benefit of extrusion is the ability to create custom rubber shapes with tight tolerances. In addition to standard tube, rectangular and square extrusions, this process cane be used to create custom rubber seals including “P” shapes, “J” seals, “T” shapes, and oddly-shaped extruded rubber products.
