Analysis and Solution of Uneven Wall Thickness in Rotational Plastic Processing
In the process of rotational molding, it is actually not easy to produce plastic products with sudden changes in wall thickness. The average wall thickness of the product mainly depends on the amount of feeding, and its uniformity is greatly related to the structure of the mold itself and the rotational molding process. If uneven wall thickness occurs during the rolling process, it is highly likely that there is an issue with the structure, temperature, and speed.
Rotational molding product processing
(1) From the perspective of rotational molding products and the structure of rotational molding molds, the thickness of the concave corner (mold outer convex) of the rotational molding product is generally smaller, while the thickness of the convex corner (mold inner concave) of the product is larger. However, if the angle of the convex part of the product is too small, it is easy to cause the material to not fill the mold and bring corresponding defects such as holes. Therefore, products should not have sharp corners, and large smooth arc transitions are usually used.
(2) The melting and adhesion ability of plastics is mainly related to the mold temperature. In areas with high mold temperatures, plastic is more likely to melt first and coat layer by layer as the mold rotates, resulting in more adhesive resin. In areas with low temperatures, there is relatively less adhesive resin, resulting in uneven wall thickness of the product.
(3) The wall thickness of the product is also related to the rotational speed. Uneven rotation speed can easily cause uneven wall thickness and irregularity, so motors with automatic control of constant torque or constant speed are generally used to ensure uniform rotation of the main and auxiliary shafts. When there is a significant wall thickness difference between a certain part of the product and other parts, and the mold cannot be modified, a solution needs to be sought from a process perspective.
(1) Fix the rotational molding mold in the appropriate position on the mold base and adjust the balance of the mold base.
(2) The rotation speed of the main and secondary axes remains proportional and uniform.
(3) The heating furnace can ensure uniform heating of the mold in all directions.
(4) During the heating and cooling processes, the direction should be reversed once, and it should be done quickly. Generally, the forward and reverse rotation times are the same.
(5) In areas where the thickness of the product needs to be increased, the corresponding parts of the mold should be preheated or the influence of insulation factors should be reduced.
(6) In areas where product thickness needs to be reduced, polytetrafluoroethylene sheets or asbestos pads are added to the corresponding parts of the mold for insulation, making it difficult for molten materials to adhere to the mold or continue to accumulate, in order to reduce the thickness of this area. This method is also used to lining the insulation layer on the mold, making it impossible for resin to adhere to the inner surface of the mold, and obtaining the opening area. However, the openings made by this method are generally not regular.