What are the production stages using rotomolding moulds?

About 80% of plastic products in daily life are injection molded. Injection molding is the use of injection molding machine, with the use of aluminum molds or steel molds for production, rotomolding mould is composed of core and cavity. The injection molding machine heats the resin material until it melts, and uses pressure to inject the molten plastic material into the cavity of the rotomolding mould. After cooling, the core and the cavity are separated, and the product is ejected from the mold.

• What are the production stages using rotomolding moulds?

• What is the follow-up work of using rotomolding mould production?

• What release agents are used in combination with rotomolding mould?

What are the production stages using rotomolding moulds?

1. Load a quantity of polymer (usually in powder form) into the rotomolding mould.

2. Heat the mould in the oven while the rotomolding mould is spinning until all the polymer melts and adheres to the mould walls. The hollow part should be rotated by two or more axes at different speeds to avoid accumulation of polymer powder. How long the mold stays in the oven is critical: too long and the polymer degrades, reducing impact strength. If the time the mold is in the oven is too short, the polymer melt may not be complete. The polymer particles did not have time to completely melt and coalesce on the mold walls, resulting in large bubbles in the polymer. This can impair the mechanical properties of the finished product.

What is the follow-up work of using rotomolding mould production?

Cool the rotomolding mould, usually by means of a fan. This phase of the cycle can be quite long. The polymer must be cooled so that it solidifies and can be safely handled by the operator. This usually takes tens of minutes. The part shrinks as it cools and is released from the mold for easy part removal. The cooling rate must be kept within a certain range. Very rapid cooling (eg, water spray) can cause cooling and shrinking at an uncontrolled rate, resulting in warped parts.

Remove the parts and save the rotomolding mould.

What release agents are used in combination with rotomolding mould?

A good mold release agent (MRA) will allow the material to be removed quickly and efficiently. Release agents can reduce cycle time, defects and browning of finished products. There are several types of release agents available; they can be classified as follows:

Sacrificial coating: MRA coating must be applied every time, as most MRA will come off the moulding when it is demolded from the rotomolding mould. Silicones are typical MRA compounds in this class.

Semi-permanent paint: When applied correctly, the paint will last for multiple releases before needing to be repainted or retouched. This type of coating is most prevalent in the rotational molding industry today. The reactive chemicals involved in these coatings are usually polysiloxanes.

Permanent Coating: Usually some form of polytetrafluoroethylene (PTFE) coating applied to the mold. Permanent coatings do not require operator application but can be damaged by misuse.

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