From the point of view of the heating mode of the rotational molding machine, there are only two types most commonly used at present, direct fire and hot box heating.
The production of large products is often heated by direct fire, that is, the direct fire heating swing roll molding machine; The production of small and medium-sized products is mostly heated by hot box, and the most common models are hot box heating swing type plastic roller, hot box heating 2-arm shuttle type plastic roller, 3-4 arm tower type plastic roller. The hot box heating 'clam' type plastic roller has developed rapidly in recent years.
Rotational molding is also called rotary molding and rotary casting molding. The invention relates to a hollow molding method of thermoplastic. That is to say, powder or paste materials are injected into the mold first. By heating the mold and rolling vertically and horizontally, the materials can be evenly filled into the cavity of the mold and melted under their own gravity and centrifugal force, and then demoulded after cooling to obtain hollow products. During the whole forming process of rotational molding products, the pressure in the mold is atmospheric pressure. Allow air to enter and exit the mold to achieve pressure balance. Avoid internal materials leaving the mold. Avoid water entering from the outside of the mold. Maintaining the same pressure inside and outside the mold helps to avoid blowing holes in the clamping line. Eliminate flash caused by pressure on the clamping line. During the cooling phase, the possibility of warping due to pressure reduction is reduced. Avoid mold damage. Organic silicone oil or silicone resin with excellent heat resistance is usually used for polyethylene rotational molding. The organic silicon internal release agent is used and uniformly coated on the entire surface of the cavity; If silicone resin release agent is used, the temperature shall be raised slowly after evenly coating the release agent, so that the solvent will dissipate and form a thin layer of resin. Then, the release layer with a certain strength can be obtained by heating and curing at 250~280 ℃ for 1~2h. After that, materials can be added and rotational molding can be carried out. The silicone oil release agent can only be used once after being coated on the mold cavity, and must be coated once for each molding. The silicone resin release agent has a prominent advantage, that is, the coated release layer is "semi permanent" and can be used repeatedly. Because the mould for rotational molding is not affected by external forces, the mould is simple, cheap and convenient to manufacture.
In addition, the rotational molding equipment also has greater mobility. A rotational molding machine can not only install a large mold, but also arrange several small chess pieces; It can not only mold parts with different sizes, but also simultaneously mold products with very different sizes and shapes. As long as the materials used for rotational molding products are the same and the thickness of products is the same, they can be simultaneously rotational molded. Therefore, the rotational molding process has greater flexibility than other molding methods.
