Kinetics and Mixing in the Phenolics Reaction Injection Moulding Process
September 15th, 1991
Paper to the Polymer Processing Society European Regional Meeting, Palermo, Sicily, 15th-18th September 1991.
S F Bush with C A Benson
Introduction
The design of reaction injection moulding processes requires knowledge of the system chemistry, an evaluation of the possible mixing processes which can be used, and characterisation of the subsequent in-mould behaviour of the reacting mixture. Mixing times are required to be a few milliseconds, moulding filling times typically a few seconds, and cycle times from one to three minutes.
The major problems in handling the phenolics chemistry for process design are how to characterise the variety of resins used and how to reduce the complexity of the chemical mechanisms to manageable proportions.
Phenolic reinforced reaction injection depends on rapid mixing of two or more unequal reactant streams with flow rate ratios typically somewhere in the range from 1 to 20 to 1 to 3. The major stream may contain reinforcing fibres of lengths up to 1.5 mm. The work reported here has concentrated on phenolic foams of densities up to about 500 kgm-3. Fibre reinforcement at about 5% of final part weight can increase strength and modulus by about 50% for foams in the range 300 to 400 kgm-3. On the basis of the chemical and mixing models an RRIM machine and mixhead have been designed and built for maximum shot volumes of 3 litres and an injection rate of 1 litre s-1. This gives for instance a 1 m x 0.5 m x 19 mm foam moulding of 400 kgm-3 density.
See also the section on Development of New Products and Processes.