What are the difficulties of rotational molding technology?

What are the difficulties of rotational molding technology?

There are some difficulties in rotational molding technology:

Long molding cycle: During the rotational molding process, the material is not subjected to strong external forces, and there is no intense turbulent state-like movement. It only relies on it to gradually melt and adhere to the surface of the mold cavity during the contact process with the mold cavity surface. After the mold cavity surface is fully coated with molten plastic, the heat required for the plastic inside to heat up and melt needs to be conducted through the heat conduction of the molten plastic layer, and the thermal conductivity of plastic is generally poor. Therefore, the heating time for rotational molding is quite long, usually more than 10 minutes, and sometimes even more than 20 minutes, resulting in a relatively long entire rotational molding cycle.
High energy consumption: In each rotational molding cycle, the mold and mold frame must repeatedly undergo alternating high and low temperatures, so the rotational molding process usually consumes more energy than other plastic molding processes. Although the jacketed rotational molding machine has a significant effect on reducing the energy consumption of the mold frame, the situation where the mold is repeatedly subjected to cold and hot conditions still exists, and the energy loss is still very large.
High labor intensity: During the rotomolding process, loading, demolding and other processes are not easy to be mechanized and automated, and are usually operated manually. Therefore, the labor intensity is greater than that of blow molding, injection molding and other molding processes.
Poor product size accuracy: The size of rotomolded products is not only affected by the type of plastic, but also by many factors such as cooling speed, type and amount of release agent. Therefore, the size accuracy of rotomolded products is difficult to control. Therefore, rotomolding is only suitable for plastic products that have no special requirements for size accuracy, such as containers, toys and other parts.
Limited material selection: Rotomolding has special requirements for materials. Usually, 30-40 mesh granular raw materials are used, and the raw materials are required to have good fluidity and thermal stability. At present, in the domestic rotomolding product market, more than 99% of the rotomolding products are made of polyethylene (PE), and 95% of them are rotomolding-grade linear low-density polyethylene (LLDPE). Although nylon, polycarbonate, ABS and other plastics are also rotomolded by rotomolding, the application range is very narrow.
Product quality control is difficult: bubbles are easily generated inside the rotational molded products, and voids are easily formed on the surface. The products are also prone to bending, shrinking, and discoloration. These not only affect the appearance of the products, but more importantly, seriously damage the mechanical properties of the products.