The rotational molding process is a high-temperature, low-pressure plastic-forming process that uses heat and bi-axial rotation to produce hollow, one-piece parts.
The process consists of four distinct phases:
- Loading a measured quantity of polymer (usually in powder form) into the mould.
- Heating the mould in an oven while it rotates, until all the polymer has melted and adhered to the mould wall. The hollow part should be rotated through two or more axes, rotating at different speeds, in order to avoid the accumulation of polymer powder.
- Air cooling the mould. The polymer must be cooled so that it solidifies and can be handled safely by the operator. The part will shrink on cooling, coming away from the mould, and facilitating easy removal of the part.
- Removal of the part.
The machine is an independent model. The independent machines are available with up to three arms that can move separately from the others. This allows for different size moulds, with different heating and thickness needs.
It consists of an oven, a cooling chamber, and mould spindles. The spindles are mounted on a rotating axis, which provides a uniform coating of the plastic inside each mould.
The rotational molding process offers several advantages. Manufacturing large, hollow parts such as our poly snouts is more easily done by rotational molding than any other method. Rotational moulds are considerably less expensive than other types of moulds. The products can be custom-designed to meet precise market requirements more economically than by conventional injection or blow molding.
Very little material is wasted using this process, and excess material can often be re-used, making it a very economically and environmentally viable manufacturing process. What material is wasted, through scrap or failed part testing, can be recycled.
The process also has fundamental design strengths, such as consistent wall thickness and strong outside corners that are essentially stress free.
More than 80% of all the material used is from the polyethylene family:
- Linear low-density polyethylene (LLDPE)-Stocked
- Cross-linked polyethylene (PEX)
- Low-density polyethylene (LDPE)
- High-density polyethylene (HDPE)
Other compounds are PVC plastisols, nylons and polypropylene
The order of materials most commonly used by industry is:
- Polyvinyl chloride