Rubber injection moulds are equipped with insulation plates between the mould heating plate and the mould clamping plate, in addition to the external tooling insulation. These insulation plates have to withstand high pressures ranging from 100 to 200 bar and temperatures from 100 to over 300 degrees Celsius. These loads occur in cycles. Consequently, the requirement for such plates are excellent thermal insulation, and high cyclical resistance to moulding pressures, temperatures and release agents over a long period of time.
Thermal insulation plates
Once the appropriate thermal insulation plate has been selected, the plate’s qualitative condition and proper handling are decisive factors in subsequent production. The plate has an enormous impact on product quality, the amount of work needed for deflashing, and wear on tool edges. This is often overlooked.
Excessive use of the insulation plate, improper operation of the machine, or the use of a plate with an unsuitable polymer compound (matrix) that does not meet requirements can cause surface burns on the insulation plate due to the high heating plate temperature and can thereby result in an undersized plate-centre.
The reduced thickness in the centre is usually a result of improper tooling set-up. Deformation typically occurs when tools of different dimensions are installed in succession and the moulding pressure is not matched to the size of the tool. This can be prevented to a large extent by reducing the moulding pressure in proportion to the mould surface.
Polyester resin systems should not be used above an operating temperature of approximately 150 °C. In high-temperature applications, temperature differences ranging from 100 °C to 300 °C between the upper plate (hot plate) and the lower plate (mould plate temperature up to 60 °C) are common. In such applications, high-grade, temperature-resistant polymers with an extremely dense network, combined with high-strength reinforcing materials that have low thermal conductivity, and specialised manufacturing processes are crucial. The plates can then withstand these extreme thermal stresses (shear stresses) without damage over a long period of time, even under cyclical loads.
Would you also like to increase service life? Experience has shown that it is best to select a plate with a higher temperature resistance.
At the time of installation, ensure that the plates are subjected to minimal pressure perpendicular to the plate surface. Slippage can cause high stress peaks and should be prevented. Elongation of the insulation plates always corresponds to the respective metal plate on the upper or lower side.