What are the main plastic forming processes?
5. low pressure molding. A touch or laminating method using a molding pressure equal to or less than 1.4 mpa.Low pressure molding is used to make reinforced plastic products. Reinforced materials such as glass fiber, textiles, asbestos, paper, carbon fibers, etc.. Most resins used are thermosetting, such as phenolic, epoxy, amino, unsaturated polyester, silicone and other resins.Low pressure molding includes bag pressing and spraying.(1) bag pressing forming. A method of forming a workpiece by applying fluid pressure to an elastomeric plastic between a rigid mold and an elastic bag by means of an elastic bag (or other flexible diaphragms). According to the different methods caused by fluid pressure, can generally be divided into pressure bag molding, vacuum bag molding and autoclave molding etc..(2) spray forming. When molding reinforced plastic products, a method of spraying a short cut of fibers and resins simultaneously onto a mold and solidifying them into an article by means of an airbrush is described.
3. cold pressing molding. Cold pressing molding is also called cold pressing sintering molding. The difference between the cold press molding and the ordinary compression molding is that the material is pressurized and molded at room temperature. The mold after release can be heated or cured by chemical action. This method is used in the forming of polytetrafluoroethylene and some high temperature resistant plastics (such as polyimide, etc.). The general process is three steps of billet sintering cooling.4. transfer molding. Transfer molding is a molding process for thermosetting plastics. When molding, the mold is heated and softened in the heating chamber and then pressed into the mold cavity where it has been heated. According to the different types of transfer molding equipment form: trap type; the tank; the piston.The requirement of plastic molding for transfer molding is that the plastic should have a greater fluidity before reaching the curing temperature, and the curing rate must be faster at the curing temperature. Phenol, melamine, formaldehyde and epoxy resins can meet this requirement.Transfer molding has the following advantages: less waste edge products, can reduce the processing quantity; second molding with fine or brittle insert and perforation of the products, and can keep the insert and the hole position is correct; the product performance is uniform, accurate size, high quality; the mould wear small. The disadvantage is that the manufacturing cost is high compression mold die; the plastic loss; the fiber reinforced plastics for fiber orientation and anisotropy; and around the insert around the plastic, sometimes due to melting is not strong and make the products according to the strength reduction.
The main equipment used for molding compression is to press and mold. The most used hydraulic press is self support hydraulic press. The tonnage varies from tens to hundreds of tons. There is a lower press and an upper press. The die used for compression molding is called pressing die. It is divided into three kinds: overflow mould, half overflow mould, no overflow mold.The main advantage of compression molding is that it can be molded into larger flat products and can be produced in large quantities. Its disadvantage is long production cycle and low efficiency.2. lamination forming. A method of combining two or more layers of material of the same or different material by heating and pressurizing with or without a binder.A layer of floating hot pressing plate is arranged between the movable plate and the fixed plate of the press.The reinforcing materials used in laminated forming are cotton cloth, glass cloth, paper and asbestos cloth. The resins are phenolic, epoxy, unsaturated polyester, and some thermoplastic resins.
Plastic processing is a complex process, generally divided into the following processing methods:In order to improve the quality of the product and improve the molding efficiency, the pre pressing is used to press the powder or fibrous molding material into a certain shape in advance.Preheating, in order to improve the processing performance and shorten the molding cycle of molding plastics, the molding plastics are heated prior to molding.Molding in the mold to add the required amount of plastic, closed mold and exhaust, at the mold temperature and pressure to maintain a period of time, and then release mold cleaning operations
