Temperature is an indispensable element in the rotomolding process, especially proper temperature control during the heating process is undoubtedly the most important means to improve product quality. Take polyethylene as an example to illustrate this problem. The rotational molding process of polyethylene has a special phenomenon: during the powder melting process, the air trapped between the powder particles forms bubbles, and as the heating process continues, these bubbles disappear again.

       Up. Further studies have shown that the disappearance of these bubbles is not because they move to the free surface of the melt under the action of buoyancy, but because the air in the bubbles gradually merges into the molten plastic melt. Therefore, for polyethylene rotomolding, scientifically controlling the heating process is of great significance to eliminate bubbles in polyethylene products and improve product quality.

       Because the heating time of rotomolding is sometimes longer, especially when the product wall is thick, it may last from half an hour to more than one hour. At this time, it is required to take measures to prevent the thermal oxidation of the material and the degradation of the material performance during the heating process. Usually, antioxidants can be added to the polyethylene plastic to achieve the purpose of prevention.

       However, when the polyethylene material is heated to an excessively high temperature or the heating time is too long, the antioxidant cannot prevent the oxidation of the material. When the thickness of the product needs to be heated for a longer time, the heating temperature must be lowered. If the heating time is shortened by increasing the temperature, the bubbles may remain because the air in the bubbles is too late to disappear.

       When the polyethylene plastic is heated to a molten state, the material will undergo a process of transformation from a crystalline state to a melt, which is exactly what happens when the polyethylene particles begin to melt and become soft. It first appears in a layer of material in contact with the inner wall of the mold to form a uniform layer of molten material. Then, gradually expand to the inner layer, until the full cross-section is completely transformed into a plastic melt. The next step is to continue heating to make the bubbles gradually disappear. The temperature control and time control of this process need to be adjusted.