Differences Between Molded and Extruded Silicone and Rubber
First, the rubber profiles are extruded from the die and are then cured in a line of microwave units to maintain the finished form. For extruded rubber products, they are forced through the dye of the cross section under pressure of an extruder. It is common for extruded products to be unvulcanized before being extruded. This leaves the rubber in a soft and malleable state post-extrusion. When this is the case, the product will need to be vulcanized before it can be used. Extrusion processes begin with a unvulcanized rubber compound that is fed into the extruder.
Next, the flutes of the revolving screw carry rubber into in the dye while increasing pressure and temperature as the material gets closer to the die. When the material reaches the die, the pressure forces the material through the openings. Here, it will swell in multiple degrees depending on the material compound and hardness. Due to a tendency of swelling, extruded parts require plus or minus tolerances on their cross sections. In the vulcanization process, extruded rubber will swell or shrink in both the cross section and length depending on the type of compound employed.
Once vulcanization is complete, a length of rubber extrusion will be reduced more in the center of the length than in the ends.