Processing

Cold Press Moulding / Warm Press Moulding

In these so-called “wet press processes” the reinforcing materials – glass mats, cut to shape, woven glass or pre-shaped glass mats, (also called preforms) – are placed dry in the mould. The mould is always a double mould, made of UP- or epoxy resin or of metal, fixed in a hydraulic press.

On top of the reinforcement, a carefully metered quantity of resin, containing all necessary fillers, pigments and curing agents, is poured and the mould is closed. The speed of closing the mould is slowed down in the last stage of closing. This results in a better impregnation of the reinforcement. It also prevents any movement of the reinforcement due to a high resin flow and gives some time for air to escape from the glass reinforcement.

In general high reactive resins are used in this process. As a result of the polymerisation heat the mould is heated to a temperature of 40 – 70°C. This will accelerate the curing process even more. When the process is running well, equilibrium is formed between the heat generated by the polymerisation and the heat dissipated to the surroundings.

Arriving at that situation, four to eight products can be produced per hour.

When heated steel moulds are used, the cycle time can be further reduced. The process is then called warm pressing. Heating of the moulds can be done with steam, heating oil or electricity. A temperature of 80 – 140°C is reached.

Depending on the resin type, wall thickness and temperature a cycle time of 3-5 minutes can be reached.

Warm pressing is a very economic process, suitable for the production of larger series in a good quality, free of porosity.