Experimental and Theoretical Study of the Flow Characteristics of Rubber Compounds in an Extruder Screw

Abstract We describe an experimental and theoretical study of the mechanisms of flow of rubber compounds in a screw extruder. Two compounds, a typical synthetic rubber (butadiene-styrene copolymer-cis-1, 4 polybutadiene) based passenger tire tread (PTT) and a natural rubber based truck tire tread (TTT), were investigated in a 1½ inch NRM cold feed screw extruder using a screw with a constant channel depth and constant channel pitch along the whole screw length. The rubber was cured in place and the screw removed. The screw exhibited starvation behavior except near the die. The length of the rubber strip in the screw is proportional to the pressure developed at the die. Marker studies showed transverse circulating flows beginning in the region immediately downstream from the hopper. These observations indicate that cold feed extruders exhibit a metering region flow, albeit sometimes starved, from entry port to die. Under these conditions the extruder is independent of the pressure developed in the screw ch...