Determinants Of The Shape Of Rotomolded Products
The rotomolding container is determined by the shape of the rotomolded product, but it is generally a shell structure. In order to facilitate demolding, a split mold is generally used.
1. It should be as thin as possible (can save energy) and has a direct impact on the wall thickness and performance of the product (too thick can easily lead to different material temperatures in the mold cavity). It is also related to the rotomolding method and heating system, such as: the hot liquid conduction heating mold δ should be thickened = 12-15mm to ensure that the liquid quickly heats the tear mold and the temperature is uniform. For molds used for hot air circulation heating, δ is thinner (5-7mm).
2. The rotomolding container should have an exhaust port to discharge the low molecular weight compounds that are decomposed due to the increase in pressure in the mold. The exhaust port is a thin-walled metal plastic tube that extends to the center of the mold cavity. To prevent the powdered resin from overflowing from the exhaust port during rotation, the hole is filled with materials such as glass wool and graphite powder.
3. The material requirements are not high. Good thermal conductivity, elongation, weldability, and heat resistance are sufficient. Steel and aluminum are common. The time required for heating the roto-molded container is the primary part of the heating cycle, so the mold material has a great influence on the heating cycle. For example, when a nickel mold with a temperature of 205°C and a thickness of δ=3.2m is heated equally with a lead mold with a thickness of 614mm, the time h1 is smaller than h2. Roto-molding container mold: mold rotation and revolution speed, etc. To obtain products with uniform wall thickness, the mold rotation and revolution speed and speed ratio are very important factors.
The rotation speed of the roto-molded container cannot be too fast, as the centrifugal force will cause the material to fly out of the mold cavity. The appropriate speed should ensure that a layer of material sticks to the mold wall every time the mold rotates. It mainly depends on the viscosity of the resin. The viscosity is high and the mold cavity can be evenly covered at a slow speed. The revolution speed is less than the rotation speed, generally 1:4, sometimes 1:1 or 1:8. The speed ratio depends on the product shape and the mold hanging method.