Sintering: a core step
Sintering is a core step in the rotomoulding process. It is the heating of the plastic powder or micropellets in a mould and then rotating it around two perpendicular axes. The plastic material gradually melts and coats the inside of the mould, forming the final shape.
During sintering, the plastic material is heated to a temperature just at its melting point. Now, the plastic particle melts onto the mould surface and sticks to it. Meanwhile, the mould is rotating around two perpendicular axes, ensuring the whole surface inside the mould is repeatedly covered by the plastic powder.
The rotation process continues until all resin powder adheres to the mould and forms the final product. Once all material is molten, the state of the powder has changed from solid into liquid. Densification will now start. The material is molten and has built an even layer across the mould surface. This even layer of molten powder will densify: air that is entrapped between the molten powder particles will diffuse from the plastic when further heated. The airy layer of powder solidifies into a homogenous layer of the plastic resin. The internal surface of the part now is smooth.
Controlling the sintering process
Controlling the sintering process is done by adjusting the temperature and time of the process, as well as the rotation speeds and the ratio of rotation of both axes. Different types of plastic materials will have different sintering temperatures, and the time required for sintering will vary depending on the wall thickness, size and shape of the product.
Overall, the sintering process will define properties of the final rotomoulded product, giving it its durability and resistance to environmental factors, and making it suitable for high-performance applications.