Thermoset

Thermoset injection moulding

Thermoset injection moulding is an automated process transforming granular material into moulded shapes that Merriott Plastics Group has been performing since the company’s inception. It’s typically the most economical way to mould thermoset materials.

Thermosets are materials that cure through a chemical reaction activated by heat and pressure, thus forming a strong molecular bond. This molecular bonding enables thermoset materials to maintain their physical properties at elevated temperatures which is why they are used in applications such as electrical connector housings, automotive ashtrays, and cookware appliance handles and knobs.

The thermoset injection moulding process begins by adding granular or pelletised material to a hopper. The material is gravity fed into a barrel and screw, which heats and moves the material toward the mould. The material is injected into a hot mould which has been clamped shut under enough force to keep the mould together while the material is forced into the cavity under high pressure. The plastic flows through a runner system in the mould to reach all the cavities. When the mould cavities are filled, the parts cure to a solid form. The mould then opens for component removal, and some parts simply drop into a box, while others are removed by hand or automated equipment.

Thermoset versus Thermoplastic Injection Moulding

Unlike thermoplastic injection moulding, cured thermosets cannot be reground and mixed with virgin material for reprocessing. In general, thermoset materials have a low viscosity, so when the material fills the mould cavity under pressure, some of the material will leak between the two halves of the mould, typically at an area of the cavity where vents have been added to allow for gas and air escapement. This is called flash. While this problem can normally be prevented in thermoplastic injection moulding by precise mould construction and processing parameters, flashing cannot be avoided in thermoset injection moulding. Therefore, flash must be removed as a secondary operation. When possible, the parts are de-flashed in an automatic tumbling operation rather than hand de-flashing to reduce costs.

Thermoset Injection Moulding Process at Merriott Plastics Group

Cycle times are longer for thermoset materials than thermoplastic materials due to the chemical reaction and cure that takes place in the mould. Since thermosets are more abrasive than thermoplastics, Merriott Plastics Group’s considerable expertise in mould design (including choice of tool steels, heat treating and plating requirements) as well as mould maintenance, ensures a long productive mould life.

Thermoset injection moulding equipment

Merriott Plastics Group uses the latest processing and ancillary equipment. A current list of this equipment can be found at our facilities list page. We have thermoset injection moulding presses ranging from 25 to 1100 tonnes clamping pressure. Having these types of presses allows us to make different sized parts with the option of making multi-cavity moulds. In addition to the presses, we also use a variety of auxiliary equipment to keep moulding costs down. We often use robots and sprue pickers to remove parts and runners from the mould, and we are able to remove flash from the components by sandblasting or automated feeding and tumbling.

Thermoset materials injection moulded by Merriott Plastics Group include phenolics, DAP, polyesters, melamine and epoxy.

Merriott Plastics Group – your premier injection moulding company in the UK.

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