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The mold for rotational molding products is a single wall closed mold

By admin In Art, News Posted 2023-03-29

There are many factors endangering the quality of rotational molding products, among which the key ones are the shape of the mold, the rotation speed of the mold, the heating temperature and time of the mold, and the physical characteristics of plastic powder.

1. The mold of rotational molding products is a single wall closed mold, which can get the appearance design of the product, but can not accurately get the details of the product interior. General carbon steel plate welding is generally selected as the mold material for rotary molding.

The cost of welding die is relatively low, especially in the application of large rotary molding products. The spinning process has the following basic rules for the mold: the mold is not easy to deform and bend in the process of continuous heating and cooling. The mould should be attached with a clamping structure which is easy to loosen, so that the mould can be closed tightly in the heating and cooling process, and can be opened easily when the product has to be unloaded and discharged. The design and installation of the mould should be conducive to the relative velocity of the cyclone around the surface of the mould, so that the mould can be heated and cooled evenly.

The vertical drainage pipe should be set in the mould to avoid the extrusion of the molten plastic along the closing seam due to the expansion of the gas in the mould during the heating process, and to avoid the deformation of the mould and products caused by the negative pressure in the mould during the cooling process. When designing the structure of the die part, it is necessary to avoid deep cavities and holes, rib plates and solid core protrusions as far as possible, because the powder material is difficult to cover the surface layer of the structure. The sum of mold net weight and material net weight should not exceed the bearing capacity of the spinning machine.

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2. The particle size of polyethylene powder is critical to its melting process. The smaller the particle is, the larger the ratio of area to volume is, and the higher the melting rate is. Generally, the powder particle size of rotary molding should not be less than 30 mesh. However, the size of powder particle is not suitable for being too small. Because the too fine powder is easy to absorb moisture and agglomerate, it is difficult to air dry, so it is difficult to improve the process.

Too fine powder material may agglomerate when rolling in the mold, resulting in uneven powder and heat, resulting in uneven product wall thickness or insufficient melting plastic in the product. The test shows that the particle size of polyethylene powder added in the spinning mold at one time does not have to be uniform or even, and the powder particles with orderly size are in the heating mold, because the melting time of large and small powder has length and speed, so that the molten plastic is slowly deposited and gradually formed.

The fine powder mixed in the coarse particles has the effect of reducing friction on the movement of coarse particles, which is beneficial to the rolling and flow of materials in the mold.

In addition, the existence of fine powder is also conducive to the optimization of the surface layer of the product, reducing the porosity of the cross section of the product, and improving the quality of the product.

3. If the heating time and cooling time are too short, the powder will not be basically melted, and the plastic properties can not meet the appropriate index. If the heating time is too long, the plastic will be oxidized, and then the plastic molecular structure will be destroyed, which is easy to embrittle, and the quality of rotational plastic products will be endangered. However, the cooling time is also very important. If the cooling time is too fast, the products will be easily deformed, and the application and aesthetics of products will be endangered.

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