Wuhan Handern Rotary Forming Process Control
DATE：2020/9/30 8:50:33 / READ： / SOURCE：This station
Wuhan Handern Rotary Forming Process Control
1. Resin conditions for rotational molding
The grease used for rotary molding is mainly PE, modified PS, PA, PC, ABS, etc.
In rotational molding, changes in resin melt index and density have a greater impact on the molding cycle than injection molding and blow molding, while the increase in product wall thickness has a much smaller impact on the molding cycle than injection molding and blow molding. Plastic molding. The particle size and shape of the resin also have a great influence on the rotational molding process. In the process of rotary molding, the heat required for molten resin is obtained from the mold wall through heat conduction. To achieve good heat transfer, the contact area between the raw material particles must be as large as possible. For a sheet of thickness z, the ratio of surface area to volume 1/Z. For a cube with side length Z, the ratio is 6/Z; and for a sphere with a radius of Z, it is 3/Z. If the particle has only one surface in contact with the mold surface or the surface of other particles, the ratio of the heat transfer area to the particle volume is 1/2Z for flakes, 1/Z for cubes, and spheroids are close to zero. Therefore, the more spherical particles in the resin raw material, although the fluidity is improved, the thermal conductivity is worse. The finer the particles, the greater the ratio of surface area to volume, and the better the heat conduction effect. Therefore, the raw material for rotary molding is preferably a cubic powdered resin. www.handern.com Wuhan Handern Hollow Board Machinery
It is found through experiments that the powder with a fineness of 80 mesh is as easy to shape as that of 35 mesh, and the mechanical strength of the product is also very close. Therefore, from the perspective of heat transfer and flow requirements, the ideal particle size is 35-37 mesh.
2. Heating cycle and influencing factors
Rotary molding heating cycle includes four parts of time ①The time required to heat the mold: ②The time required to heat all powdered materials to the melting temperature, ③The time needed to fuse the material into a three-dimensional network structure ④Remove bubbles and pores, The time required for the product to become a dense homogeneous structure.
(1) The influence of heating temperature The heating temperature has a great influence on the heating cycle. The higher the heating temperature, the shorter the heating cycle. Generally, the temperature range of the heating chamber of the circulating hot air heating device is 285～345℃; the temperature of the hot oil jacket heating device is 190～230℃. When the temperature of the heating chamber increases from 205°C to 315°C, the heating cycle of high-density polyethylene products changes as shown in Figure 11-3.www.handern.com Wuhan Handern Hollow Board Machinery
(2) The influence of heating medium speed The heating medium flow speed is different, and the time required to heat the mold can differ by 3 times.
(3) The influence of the ratio of mold surface area to volume. Under general conditions, the increase of this ratio can shorten the heating of the mold. As the temperature increases, the influence of this ratio decreases.
(4) The influence of product wall thickness The fusion time of resin is mainly controlled by the product wall thickness. Taking polyethylene as an example, if the thickness of the product is increased by 50%, the fusion time will increase by about 25%, but when the thickness of the product exceeds 10mm, the fusion time will be doubled.www.handern.com Wuhan Handern Hollow Board Machinery
(5) The influence of mold heat capacity and mold material Since the time required to heat the mold is the main part of the heating cycle, the heat capacity of the mold and the mold material have a great influence on the heating cycle. Experiments have shown that, at 205°C, the heating time of a 3.2mm thick nickel mold is 250% longer than that of a 614mm thick lead mold.
The heat capacity of the mold has little effect on the material sintering time, because once the resin temperature reaches the melting point, the mold temperature does not need to rise.www.handern.com Wuhan Handern Hollow Board Machinery
(6) The influence of resin melt viscosity: The resin with low melt viscosity is easier to cover the inner wall of the mold to be sintered, and the best sintering state can be reached in a shorter heating period. The heating cycle required for the resin with high melt viscosity to achieve the best sintering is very close to the heating cycle of excessive sintering, so it is difficult to make the best sintered products, especially thin-walled products. In this case, it is often only required to achieve a slight insufficient sintering, or close to 90% of the optimal degree, so as to avoid the ills of excessive sintering.www.handern.com Wuhan Handern Hollow Board Machinery
Author：admin