Accurate Simulation of the Four Modes of Post-Die Extrudate Shape Distortion

A combined flow, thermal and structural analysis is employed to simulate post-die extrudate distortion in different profile dies. All four factors which can cause extrudate distortion, namely, nonuniform exit velocity distribution, extrudate shrinkage, extrudate draw down, and deformed shape of the calibrator or sizer profile, are simulated. To analyze the effect of exit velocity variation on extrudate distortion, the parameterized geometry of a simple profile die is optimized using an extrusion die optimization software. The simulation results presented for a bi-layer profile die successfully demonstrate how gradually changing profile shape in successive calibrators/sizers can be used to simplify the die design for extrusion of complex profiles. The predicted extrudate shape and layer structure for the bi-layer die are found to accurately match with those in the extruded product.

Utilization of Powdered EPDM Scrap in EPDM Compound

Processability, curing characteristics and vulcanizate properties of EPDM compounds containing ground waste EPDM (W-EPDM) have been studied. Ground waste was prepared from factory scraps, using a mechanical grinder with silicon carbide abrasive wheel rotating at 2950 rpm. The particle size shows a range between 2 and 50 μm, with an average size of 10 μm. Particle surface seems to be rough and convoluted and mild oxidation during the abrasion enhances the aggregation of particles. Mooney scorch time and the maximum rheometric torque of the EPDM compound decrease gradually with increasing W-EPDM content. Migration of curatives between the virgin rubber and waste rubber phases is believed to be the reason for the variation in the curing behavior. The processability of the EPDM compound shows improvement on addition of W-EPDM (that is, both die swell and extrudate distortion are less). The vulcanizate properties of the W-EPDM-filled EPDM compounds reveal the reinforcing nature of the ultrafine W-EPDM particles. Comparison of W-EPDM with an inert filler like precipitated CaCO3 in an EPDM compound reveals the potential of W-EPDM as a cheap filler in EPDM compounds. It is also found that W-EPDM can be incorporated into the window seal compound formulation and the drop in properties even at 100 phr of W-EPDM is within acceptable limit, thus providing a scope for on-site recycling of EPDM.

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.