An Experimental Study of Flow and Stress Fields in a Pressurized Mooney Viscometer

The boundary conditions of rubber compounds on solid surfaces during extrusion has long been a subject of question. The concerns of Mooney on this topic date back 60 years. He continued to return to this question throughout his career. In more recent years Vinogradov and his coworkers have called attention to slip phenomena occurring in the extrusion of elastomers through dies. This is associated with fluctuating pressure losses which occur at the onset of extrudate distortion. Such behavior has also been observed with rubber-carbon-black compounds. More recently, Turner and Moore have developed a pressurized rotational rheometer to characterize this type of behavior in rubber compounds. We have recognized the importance of this problem in our own laboratories. Marker experiments have been used in extrusion of rubber compounds to detect slippage. In the present paper, we describe an experimental study of the response of gum elastomers and their carbon black compounds in a pressurized Mooney viscometer of the general design of Turner. We look first specifically at the variations of steady torque (shear stress) with the magnitude of applied pressure. We then look at the characteristics of sheared samples and the responses to pressure transients.