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The basic processing steps of rotational molding
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The basic processing procedure of rotational molding is quite simple: powdered or liquid polymer is placed into a mold, which is then heated and rotated simultaneously around two perpendicular axes—both spinning on its own axis and orbiting around the other axis.
1. Applying a release agent: Applying a release agent to the mold facilitates the removal of the molded part from the mold and effectively prevents damage to the part during demolding caused by strong adhesion between the part and the mold.
2. Install the inserts and related molding accessories: The inserts primarily serve to locally reinforce the molded part, while the molding accessories mainly refer to modules used for forming threads or special features. All of these components must be securely installed in their newly designated positions before the material is introduced into the mold.
3. Loading: Before adding the materials, strict measurement must be carried out. When additives need to be incorporated, the relevant components should also be pre-mixed beforehand. Accurately weigh the required amount of powdered resin for the final part, add it to the bottom of the split-type mold, then securely fasten the two mold halves together and mount them onto the support shaft.
4. Closing the mold: Before closing the mold, be sure to remove any residual material remaining at the parting line. Ensure that the two parting surfaces are tightly and properly aligned to prevent leakage of material during machining.
5. Heating: Place the mold, which has been loaded with the material, into a heating furnace (or heat it using other sources such as a gas flame). Set the furnace temperature above the resin’s melting point. Simultaneously, as the mold rotates around two mutually perpendicular main and auxiliary axes—both in a co-rotational and self-rotational manner—along with the supporting frame. During rotation, the mold is heated to the specified temperature and then held at that temperature for a period of time. Under the combined effects of rotation and heating, the material gradually melts, evenly coating the entire inner surface of the mold cavity and progressively expelling any gases entrapped within the material, until a fully formed part is obtained.
6. Cooling and Shaping: Once the resin has fully melted, transfer the mold to the cooling chamber for cooling. While continuing to rotate the mold, cool it down using forced ventilation or water spray.
7. Demolding and mold cleaning: The former aims to prevent damage to the molded product during demolding, while the latter involves thoroughly removing any residual material and debris from the mold to ensure it is clean and ready for loading in the next molding cycle.
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