Advantages of the rotational molding process:
1. Suitable for molding large and extra large parts
Most plastic molding processes, such as injection molding, compression molding, extrusion, blow molding, etc., are widely used. During the molding process, plastics and molds are under relatively high pressure (pressure), so these moldings are applied. When manufacturing large-scale plastic parts, it is necessary not only to use molds that can withstand a lot of pressure, but also to make the molds cumbersome and complicated, and the plastic molding equipment must also be designed and manufactured very firmly, and the difficulty in processing and manufacturing the molds is correspondingly increased. Increased costs.
In contrast, since the rotational molding process only requires the strength of the frame to support the weight of the material, the mold and the frame itself, and the mold closing force to prevent material leakage, it is not necessary to rotate large and extra large plastic parts. Using very cumbersome equipment and molds, the mold is easy to manufacture and manufacture, with short manufacturing cycle and low cost.
In theory, there is almost no upper limit in the size of the parts formed by the rotational molding process. We have used a rotational molding process to prepare a polyethylene cylindrical rotomolded container with a diameter of 1.2 m and a height of 1.2 m. The mold is only cold-welded with a 3 mm thick steel plate, and the rotomolding frame uses a No. 8 groove. Steel is welded to produce such a large plastic container. If blow molding is used, it is impossible to use a very expensive and bulky blow molding device.
2. Suitable for the production of multi-variety and small batch plastic products
Since the mold for rotational molding is not affected by external force, the mold is simple, the price is low, and the manufacturing is convenient, so that the exchange product is very convenient; in addition, the rotomolding equipment also has greater maneuverability, and one rotomolding machine can be installed. Only large molds can be arranged with a small number of small molds; it can not only mold different sizes of parts at the same time, but also can form products with different sizes and shapes at the same time, as long as the raw materials used in the rotational molding products are the same, the thickness of the products Quite, both can be rotationally molded, so the rotational molding process is more maneuverable than other molding methods.
3, Rotational molding is very easy to change the color of the product
Rotational molding directly adds the material to the mold each time, which causes all the materials to enter the product. After the product is taken out of the mold, the material needed for the next molding is added, so when we need to change the color of the product, it is neither It wastes a little bit of raw material and does not require time to clean the machine and mold. When we use more than one mold to shape the same plastic product, we can also add different colors of materials to different molds, and simultaneously rotate plastic products of different colors.
4, suitable for molding hollow parts of various complex shapes
During the rotomolding process, the material is gradually coated and deposited on the inner surface of the mold, and the product has a strong ability to reproduce the fine structure such as the pattern on the mold cavity; and at the same time, the mold is not subject to the outside during the molding process. Pressure, you can directly use precision casting methods to obtain molds with complex structures and complex shapes, such as toys and animal molds.
5, saving raw materials
The wall thickness of the rotomolded product is relatively uniform and the chamfer is slightly thicker, so that the material efficiency can be fully utilized, which is conducive to saving raw materials; in addition, in the rotomolding molding process, there are no waste pipes, gates and the like, once the debugging is completed, There is almost no charge back in the production process, so the process has a very high utilization rate of materials.
6. It is convenient to produce multi-layer plastic products by using the rotational molding process. It is only necessary to put the materials with reasonable matching and different melting temperatures into the mold for rotomoulding. The plastics with lower melting temperature are first melted by heat and adhered to the mold. Upper, the outer layer of the article is formed, and then the material having a higher melting temperature is melted thereon to form an inner layer of the article.
Alternatively, the outer layer of plastic is first loaded into a mold, and after the outer layer is rotationally molded, the inner layer material is added, and then a plurality of layers of the rotomoulded article are produced by rotational molding. Either way, no complicated equipment is required. If a multi-layer plastic product is produced by blow molding or injection molding, a special multi-layer molding machine and a complicated mold are required.
Disadvantages of the rotational molding process:
1, the energy consumption is larger
Each rotomolding cycle, the mold and the formwork are repeatedly subjected to alternating high and low temperatures, so the rotational molding process is generally more energy intensive than other plastic molding processes. In order to reduce the energy loss of repeated heating and cooling of the mold, a jacketed rotomolding machine was developed, which pumped the cold and hot medium into the jacket of the rotomolding mold through a special circulation system to directly heat and cool the mold. The equipment has obvious effects on reducing the energy consumption of the mold base, but the condition that the mold is repeatedly subjected to cold and hot conditions still exists, so the energy loss is still large.
2, longer molding cycle
In the rotational molding process, the material does not undergo the strong action of the external force, and the material does not have the motion of the turbulent state, and it is gradually heated and melted to adhere to the surface of the cavity during the contact with the surface of the mold cavity, in the cavity. After the surface is coated with molten plastic, the heat required to heat and melt the inner surface of the plastic needs to be transferred through the heat transfer of the molten plastic layer. The thermal conductivity of the plastic is generally poor, so the heating time of the rotational molding is quite long, usually 10 minutes. The above, sometimes even twenty minutes, so the entire rotational molding cycle is also relatively long.
3, the labor intensity is greater
In the rotomolding molding process, the processes of charging and demoulding are not easy to mechanize and automate, and usually manual operation is used, so the labor intensity is larger than that of blow molding, injection molding and the like.
4, the product size accuracy is poor
The size of the rotomolded product is not only affected by the variety of plastics, but also by various factors such as the cooling rate, the type and amount of the release agent (total effect of demolding), etc., so the dimensional accuracy of the rotomolded product is difficult. Control, so rotomolding is only suitable for plastic products that have no special requirements on dimensional accuracy, such as containers, toys and other parts.
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