Rotational molding is a hollow molding method of thermoplastics. There are three types of roll molding, including PE and other dry powder molding, PVC paste resin molding and liquid monomer polymerization molding. The three types of rotational molding have their own characteristics, but the general principle is the same. That is to say, powder or paste or monomer materials are injected into the mold first. By heating the mold and rolling the two axes, the materials are evenly filled with the cavity of the mold by their own gravity and melted. After cooling, they are demoulded to obtain hollow products. Rotational speed is not high, the product almost has no internal stress, and is not easy to deform, sag and other shortcomings. At first, it was mainly used to produce small products such as toys, leather balls, bottles and cans with PVC paste plastic. Recently, it has also been widely used in large products, including polyamide, polyethylene, modified polystyrene polycarbonate, etc.
Rotational molding production design
Production process
Before the rotational molding process, you need to prepare some high-quality molds and place them on the rotary arm of a rotational molding machine, which is generally composed of a heating chamber and a rotary arm, and some are also equipped with cooling devices such as water spray atomization or cooling fans. After placement, first place several molds on the machine. Then, put plastic resin powder into each mold, and then heat it while rotating from both vertical and horizontal angles. The melted resin will glue the hot mold and the outer package together evenly and tightly. After heating for a certain time, it is necessary to stop heating but continue to rotate to the mold exit temperature, so that the mold continues to rotate in it until the thickness of each part is consistent. When the mold temperature is reached, open the mold, take the product out of the mold cavity, and then add new resin to the next rotation. During the whole manufacturing process, the mold rotation speed, heating and cooling time should be strictly and accurately controlled.
The specific steps of rotational molding can be decomposed:
(a) Feeding: loading the weighed plastic into the cavity of the mold in the form of liquid or powder;
(b) Heating: the rotational molding machine rotates with the mold in two directions, and adds the heating furnace to make the mold hot. All plastics adhere to and sinter on the inner surface of the mold cavity;
(c) Cooling: with the continuous rotation of the mold, the mold simultaneously turns out of the heating furnace and enters the cooling chamber, where the rotational plastic is cooled and molded;
(d) Demoulding: the rotational molding machine turns to the opening position, the mold stops rotating, opens the mold, and takes out
Design advantages
Compared with other mold processes, the rotational molding process provides us with more design space. Under the correct design concept, we can combine several parts into a complete mold, which greatly reduces the high assembly cost.
The rotational molding process also includes a series of inherent design thinking modes, such as how to adjust the thickness of the side wall and how to strengthen the external settings. If we need to add some auxiliary designs, we can also add the strengthening rib line to the design.
Rotational molding technology injects endless imagination of designers into the products. Designers can choose the best materials in the production process, including various materials approved by the Food and Drug Administration. The additives added in the production process can effectively resist the invasion of climate, static interference and other external objective factors. In the design process, the insertion port, thread, handle, inverted device and perfect surface design are all the highlights. Designers can also design multi wall molds, which can be hollow or filled with foam.
Cost advantage
When cost becomes one of the factors we consider, the rotational molding process has more market advantages than other types of processes. Compared with blow molding process and injection molding process, rotational molding process can easily produce parts of different sizes within the effective cost range. His mold is relatively cheap, because it does not have some internal cores to complete. And without an internal core, a small change can be made into another model.
As each part in the manufacturing process is finally formed under the high temperature and rotating process, different from those parts formed under heavy pressure, the rotational mold does not need special processing like the injection molding process to withstand the test of heavy pressure.
As for the production cost of conversion products, it has also decreased, because it often requires more raw materials to convert light plastic into heavy plastic. For the rotational molding process, the single master mold that can save the cost will be the development trend of high output in the future.
