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What should be paid attention to when designing the distance between walls of rotational molding products

2020-09-15 15:19:01

Rotational plastic products belong to hollow plastic products, so double wall hollow products become a common form. For example, the rotational plastic insulation box is a typical double wall hollow products, usually the insulation box will be filled with foam between the double walls to play the role of heat preservation and reinforcement. So, in the design of rotational molding products, how much distance should be left between the two walls, especially between the parallel walls? This involves the problem of rotational molding process and raw materials.

Most of the rotational molding materials are in the shape of powder, but the apparent density of the powder is relatively low, and its volume is about three times larger than that after crystallization. Therefore, in order to make the raw powder fully reach each embedded surface in the rotational molding process, it is necessary to leave enough space between the walls of the rotational molded products at least three times the wall thickness. That is to say, even if the distance between the walls of the rotational molding products is three times of the average wall thickness, the powder filled in between will just become two walls after melting. The gap between the powder filling space can easily lead to the powder bridging during the rotational molding, thus preventing the powder from flowing freely to other parts of the mold cavity. In this way, the wall thickness of some parts of the product will be uneven, and the bridge area will also cause local thickening. The thickened area will cause internal pores and external shrinkage marks. These thickening parts are heated for a long time and shrink more than the surrounding thin-walled parts, which will lead to the increase of internal stress and deformation. Therefore, in order to avoid the occurrence of these undesirable conditions, the larger the design of the distance between the two walls of the rotational plastic products is more conducive to the flow of raw materials, generally at least four to five times the average wall thickness.

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