INJECTION-MOLDING OF RUBBER COMPOUNDS - EXPERIMENTAL AND THEORETICAL-STUDY

The aim of this study is to show the relevant physical parameters rela ted to rubber injection moulding, and especially compressibility, vulc anisation and wall slippage. Three materials ave studied. an SBR compo und, without and with a lubricant, and an EPDM compound. The viscosity is deter mined by capillary rheometry. The modified SBR exhibits wall slippage. Rheological vulcanisation kinetics are determined with a Mo ving Die Rheometer. Precise moulding experiments are carried out with an injection moulding machine and a mould equipped with pressure and t emperature transducers. Ar low flow rate, the influence oft he curing reaction on the pressure appears clearly especially for the fast curin g EPDM. The conditions in which surface scorch defects appear are dete rmined. The SBR with lubricant needs a lower pressure to fill the cavi ty than without lubircant. A model of moulding filling is developed. T he material is purely viscous, with a state of cure dependence of the viscosity. A Norton friction law is introduced to rake into account a possible slippage at the cavity walls. A compressible calculation in t he injection chamber allows a realistic evaluation of the flow rare at the entry of the cavity. The comparison with the experimental data co nfirms the importance of the compressibility and the influence of the vulcanisation on the viscosity at low flow rate. In moulding condition s for which vulcanisation is not activated during the filling stage, d espite uncertainties on the friction law parameters appropriate to the cavity wall roughness, the agreement with experiments is better when wall slippage is taken into account.