This paper reviews recent development in the design of extruders used in the rubber industry. The most significant development has been the widespread adoption of the cold feed extruder. Unlike the warm feed machine which ruled undisputed for so long, the cold feed machine combines the functions of mixing the compound, warming it to a plastic state and forming it. In the cold feed machine the screw must perform a variety of functions, not only transporting the rubber, but also subjecting it to a high shear to mix it and heat it and, finally, homogenizing it into a homogeneous mass before it passes through the die. A further development of the cold feed machine which is coming into increasing use is the vented barrel extruder, which allows the removal of volatiles from the compound and thus prevents porosity when the extrudate is subjected to a continuous curing system at ambient pressure. Other developments reported are concerned with temperature control and with the inlet end of the machine enabling powdered rubber processing.
