FRP is a kind of high-strength engineering plastic. Its full name is a glass fiber reinforced plastic. Because it has much higher strength than ordinary plastics, after molding and curing, it has higher specific strength (i.e. the ratio of strength to density) and can be comparable to steel, so people give it the nickname of glass steel. Its appearance can be traced back to 1940. China began the research and application of FRP in 1958. In the early 1960s, after the advent of sheet molding compound (SMC), steel for automobile manufacturing replaced many metal automobile parts, and its maintenance is simple, beautiful appearance, sound insulation, heat insulation and shockproof performance are better than metal, simple process, lightweight and durable, and the price is also relatively cheap.
Raw materials and chemical basis of FRP
The main raw materials of FRP are resin Reinforcing materials and other auxiliary materials. Resins include unsaturated polyesters, epoxy resins, phenolic resins, etc Reinforcement materials include glass fiber, carbon fiber, boron fiber, graphite fiber, ceramic fiber, metal fiber, organic fiber, whisker, etc; Auxiliary materials include curing agent, accelerator, diluent, flame retardant, UV absorber, filler, pigment, release agent, etc.
FRP is a plastic based composite material, which is composed of synthetic resin, glass fiber and its products. Synthetic resin is an organic compound, and glass fiber is an inorganic compound. Glass fiber reinforced plastics are made of synthetic resin with some additives. Synthetic resin is usually divided into thermoplastic and thermosetting. a. Thermoplastic resin is usually a solid in the shape of powder, particle, plate or block. When heated, it will soften or melt, flow and deform. If it is cooled again, it can return to solid. As long as it is not decomposed by excessive heating, the properties before and after heating are unchanged. Typical thermoplastic resins include polyethylene, polyvinyl chloride, polyvinyl alcohol, polyamide (nylon 66), etc. Extrusion and injection are generally used in thermoplastic resin molding
Injection, blow molding, die casting and other methods.
b. Thermosetting resin thermosetting resin is generally a very viscous fluid or powder, massive solid, and its properties before hardening are similar to those of thermoplastic resin However, it will deform, flow and solidify at a certain temperature. After forming, it can no longer return to its original properties, and its structure has also changed. Typical thermosetting resins include phenolic resin (bakelite), unsaturated polyester resin, epoxy resin, furan resin, polyurethane, silicone resin, etc. the molding method of thermosetting resin generally adopts wedge pressing. This kind of resin has plasticity before curing. It flows into the mold frame under normal temperature or heating. It will be cured and formed at a certain temperature. After demoulding, it is the finished product. Some thermosetting resins, such as unsaturated polyester resin, epoxy resin and polyurethane, can also be cured at room temperature
Because some curing agents and accelerators are added to the resin, the reaction between the curing agent and the resin will release heat and keep opening the temperature to accelerate the reaction. Even if the curing agent is not easy to participate in the reaction at low temperature, the low-temperature accelerator will activate and decompose it and promote the curing reaction.
3 forming mechanism of FRP
3.1 general
The composite of synthetic resin and glass fiber mainly relies on synthetic resin to bond the loose glass fiber together to form composite materials with excellent performance. Although the fiber is soft and the resin matrix is flowing before compounding, they can be compounded into high-strength FRP after curing.
3.2 composite molding
When synthetic resin is compounded with glass fiber, resin is used as binder. Under the action of solid crosslinking agent, the network has better strength. It consolidates loose and soft glass fibers in the middle, Glass fiber becomes the "skeleton" of FRP, which plays a reinforcing role. Composite molding mainly depends on the choice of resin and glass fiber, and different raw materials will have different composite effects. FRP molding is also directly related to curing temperature, pressure and time. The curing temperature is generally divided into normal temperature curing (15 ~ 25C), medium temperature curing (60 ~ 90C) and high temperature curing (90 ~ 170C) Three, hand paste molding usually adopts normal temperature curing, winding molding adopts medium temperature curing, and only molding sheet molding compound (SMC) and bulk molding compound (BMC) adopt high temperature curing. Hand paste molding is generally atmospheric molding, and molding is pressure molding.