Reaction injection moulding

What is S-RIM (Structural Reaction Injection Moulding)

Simply it is a moulding method to produce structural rigid polyurethane foam.

The cross linking “reaction” happens, when the liquid pre polymer, polymer and catalyst are mixed together. In this case, by a high pressure stream into a mixing chamber and cast into an open mould, controlled by a robotic arm. The foaming agent is water vapour, and the reaction time is approximately 30 seconds, with a cure time of 10 minutes. The moulded density is typically 0.25 specific gravity, (i.e. fours times lighter than water).

The polyurethane also acts as a cement and will bond to a huge variety of coverings, like veneers and fabrics, placed in mould before casting. The moulding can also be painted, post moulding or in moulding.

Our machine is unique, in that it can also introduce a variable length and quantity of fibres, into the mixing chamber, to be cast with the reacting polyurethane i.e. glass fibres. This allows for an extremely strong, rigid structure which traditionally could only be achieved by placing fibre matts into the mould first, this being inherently problematic.

The casting stream is continuous, so the size of the moulded part, is only restricted by the reach of the robotic arm and the size of the mould, in our case in an arc of two metres.

The on board computer controls how much is cast, and alters the variable density, as required. The software package includes a comprehensive SPC program for data collection on each and every moulding. The new generation robot is self learning, so variable pour patterns are easy to set up.

The casting and foaming process is low pressure, so tooling is comparatively lower cost and typically aluminium.