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The reasons of uneven wall thickness of rotomolding products
It is not easy to process the products with abrupt wall thickness in the rotomolding process. The average wall thickness of the products depends on the amount of feeding. Its uniformity is related to the structure of the mold itself and the rolling molding process.
From the perspective of the structure of rotomolding products and molds, generally, the thickness of the corners (convex outside the molds) in the recesses of rotomolding products is smaller, while the thickness of the corners (concave inside the molds) in the convex outside the products is larger. However, if the angle of the convex outside the products is too small, it is easy to cause that the materials can not fill the molds and bring the corresponding holes and other defects. Therefore, the products should not have sharp corners, and usually use large smooth arc transition 。
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The melting and adhesion ability of plastics is mainly related to the mold's temperature. When the mold's temperature is high, the plastic is easy to melt first and coating layer by layer with the rotation of the mold, so the adhesive resin will be more, while the resin adhering to the low temperature part is relatively less, resulting in uneven wall thickness of the products.
The wall thickness of the product is also related to the rotation speed. Uneven rotation speed can easily cause uneven wall thickness and irregularity. Therefore, the motor with constant torque or speed that can be automatically controlled is generally used to ensure the uniform rotation of the main and auxiliary shafts. When there is a big gap between the wall thickness of one part of the product and that of other parts, and the mold cannot be modified, it is necessary to find a solution by supporting the process angle.
1. Fix the rotomolding in a proper position on the mold base, and adjust the balance of the mold base.
2. The rotation speed of the main shaft and the auxiliary shaft shall be kept proportional and uniform.
3. The heating furnace can ensure that the mold is evenly heated in all directions.
4. The heating and cooling process shall be reversed once, and the reversing time shall be rapid, generally the forward and reverse times are the same.
5. In the part where the thickness of the product needs to be increased, the corresponding part of the mold shall be preheated to reduce the influence of heat insulation factors.
6. Add Teflon plate or asbestos pad on the corresponding part of the mold where the thickness of the product needs to be reduced, so that the molten material is not easy to cling to the mold or accumulate continuously, so as to reduce the thickness of this part. This method is also used for lining the thermal insulation layer on the mould, so that the inner surface of the mould can not adhere to the resin to obtain the opening part, but the opening made by this method is generally not regular.