What factors will have a major impact on the quality of spin-molded products
There are many factors affecting the quality of spin-molded products. Among them, the shape of the mold, the rotational speed of the mold, the heating temperature of the mold, the heating time, the physical characteristics of the plastic powder, and the like.
1. Mould for spinning products
The mold for spin molding is a single-wall closed mold which gives the outline of the product and the inner contour of the product cannot be precisely detailed. The molding material of the mold for spinning is generally selected from ordinary carbon steel sheets for welding. The cost of the welding die is relatively low, especially for large rotary molded products.
The spin-molding process has the following basic requirements for its mold:
The mold is less prone to deformation and deflection during repeated heating and cooling.
The mold should be provided with a clamping mechanism that facilitates loosening so that the mold can be tightly closed during the heating and cooling process, and can be easily opened when the product and the material need to be removed.
The design and installation of the mold should facilitate relative movement of the gas flow around the surface of the mold to provide uniform heating and cooling of the mold.
The mold shall be provided with a venting duct to prevent the gas from being thermally expanded in the mold during the heating process to extrude the molten plastic along the die slit, and to prevent a negative pressure in the mold during the cooling process from causing deformation of the mold and the article.
The local structure of the mold should be designed to avoid deep cavities and holes, as well as structures such as ribs and solid bulges, because powdery materials are difficult to cover the surface of the above structure.
The sum of the die weight and the material weight cannot exceed the maximum capacity of the spin molding machine.
2, the rotational speed of the rotary mold
Usually, the rotary molding machine uses two adjustable speed motors to provide power for the rotation and rocking motion of the mold around the main shaft and the secondary shaft, so that the rotation speed of the mold around the main shaft and the swing around the secondary shaft can be adjusted. By adjusting the speed of the two speed control motors, the operator can obtain a relatively uniform product wall thickness in any product shape. The basic function of the mold rotation and rocking is to evenly mix the powder material and spread over the surface of the mold.
3, the particle size of polyethylene powder
The size of the polyethylene powder particles has an important influence on the melting process. The smaller the particle, the greater the ratio of surface area to volume and the higher the rate of melting. Usually, the spin-on powder particles should be no less than 30 mesh, but the powder particle size should not be too small, because the too fine powder is very easy to absorb moisture, agglomerate, difficult to dry, and increase the technical difficulty. Too fine powdery material will agglomerate when tumbling in the mold, resulting in uneven heating of the powder, eventually resulting in uneven wall thickness of the product or formation of insufficiently molten plastic in the article.
Experiments show that the particle size of the polyethylene powder added to the spin-molded mold at one time is not uniform or uniform, and the powder particles of orderly size are heated in the mold. Due to the length and speed of the heat-absorbing melting of the coarse and fine powder, the molten plastic gradually accumulates. , gradually formed. The fine powder mixed in the coarse particles has a friction reducing effect on the movement of the coarse particles, which is favorable for the tumbling and flowing of the material in the mold. At the same time, the presence of fine powder is also beneficial to the refinement of the surface of the product and reduce the porosity of the cross section of the product, thereby improving the quality of the product.
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