Prepreg refers to the combination of resin and fiber before it is cured, and maintains a certain storage period. During the storage period, it can be designed and formed at any time. It is an intermediate material for making composite materials. Carbon fiber prepreg is made by spreading carbon fiber tows (or carbon fiber woven cloth), under the action of pressure and temperature, and pre-coated on the release paper resin, combined, and then cooling, coating, winding, etc. The intermediate product composite material processed by the process is also called carbon fiber prepreg.
The common components of prepreg are: the bottom is a layer of release paper (white), the middle is the finished prepreg (black), and the surface is covered with a layer of polyethylene film (blue), the middle of which is the finished prepreg It is composed of resin and fiber.
Prepreg means to infiltrate the fiber with resin in advance, lay up, shape, and heat to cure in the subsequent process. Therefore, the resin of the prepreg is an uncured resin, mostly thermosetting resin. There are many kinds of thermosetting resins, the commonly used ones are phenolic resin, epoxy resin, dima resin, vinyl resin, cyanate resin and so on. Among carbon fiber prepregs, epoxy resin is the most widely used, and bimarine and cyanic acid resin are used in some high temperature resistant occasions.
There are many applicable processes for prepregs, mainly autoclave process, but also non-autoclave process.
Autoclave process
The autoclave process is one of the most common forming methods for fiber composite materials, especially in the field of aerospace, which is as high as 80%. The formed components are mostly used in primary and secondary bearing structures such as the aerospace field, as well as many fields such as national defense, rail transit, electronic communications, automobile manufacturing, and sports equipment.
Lay the carbon fiber prepreg on the mold according to the layering requirements, seal the blank in a vacuum bag and place it in a carbon fiber autoclave. In the vacuum state, through the process of heating, pressurizing, heat preservation, temperature reduction and pressure relief of the autoclave equipment, the uniform temperature and uniform pressure provided in the autoclave are used to achieve solidification, so as to form a high surface and internal quality, Carbon fiber composite parts with complex shapes. An important reason for using autoclaves is to provide sufficient pressure to the prepreg to inhibit the generation of pores, so the finished product has good performance and can be used as a structural part. Therefore, the autoclave process is widely used in aerospace, but the autoclave process also has the disadvantages of high cost and low efficiency.
Vacuum bag pressing process
Aiming at the high cost of autoclave, the vacuum bag pressing process was developed. The pre-process of vacuum bag pressing is similar to autoclave. The latter curing does not use autoclave, but uses curing furnace.
The curing oven is cheap, but there is no pressure. In the case of vacuuming, the pressure difference is only one atmosphere. Therefore, to obtain similar porosity, higher requirements are placed on resin and prepreg. Studies have shown that semi-impregnated prepregs can effectively improve gas permeability. OoA prepregs are semi-impregnated with resin, and dry fibers are used as a channel for exhaust gas. When the parts are solidified, the gas and volatile components can pass through. Channel discharge.
Prepreg molding process
A method of adding a certain amount of prepreg into a metal pair mold and curing it by heating and pressing.
The relative production efficiency of prepreg molding is relatively high, which is convenient for professional and automated production. Especially when fast curing prepreg is used, the time can be shortened to less than 10 minutes for one mold; the product has high dimensional accuracy and good repeatability; the surface is smooth and can be used once Forming products with complex structures; suitable for mass production. The disadvantage is that the mold manufacturing is complicated, the investment is large, and the press is limited, it is most suitable for mass production of small and medium composite products, and it is not easy to produce large-size products. Moreover, the prepreg itself has a certain processing cost.
There are many applications of prepreg molding, such as aerospace, automotive, electronics, medical equipment, sports equipment, etc.
Prepreg blow molding
This process is developed on the basis of prepreg molding and is mainly used to produce hollow carbon fiber products. The craft was developed from Taiwan, China. Initially, the racket is filled with a foaming agent, placed in a mold, pressurized, and foamed after heating, and a certain pressure is generated to expand the prepreg and shape it. However, the racket will squeak and the weight cannot be controlled properly. Later they creatively developed the "blowing molding" method. It is said that the first blow-molded air bag that was blown inside was developed by people from a food company who used hot dog casings as the blowing tube. (So innovation is not always so lofty, but practical. The Chinese have a lot of native methods in this area. It would be nice if they can improve better.) It is said that this kind of material has been used for many years. Later The nylon airbag was invented.
This process is currently the mainstream technology for sporting goods, including carbon fiber badminton rackets, golf clubs, baseball rackets, bicycles and other products, all produced by this process.
Coiling process
The carbon fiber coiled tube forming process is a composite material product molding method that uses carbon fiber prepreg to be hot-rolled on a tube coiling machine. This process is currently the most important production process for carbon fiber fishing rods. The tube rolling process is also known as the tube rubbing process. I have really seen the most earthy carbon fiber fishing rod factory, and it is really made by the old lady using prepreg to rub the tube.
The tube winding process, specifically, uses the hot roller on the tube winding machine to soften the prepreg and melt the resin adhesive on the prepreg. Under a certain tension, during the rotating operation of the roller, the friction between the roller and the mandrel is used to continuously roll the prepreg onto the tube core to the required thickness, and then cool and set the shape by the cold roller. The machine is taken out, then wrapped with heat shrinkable film, and cured in the oven. After the pipe is cured, the heat shrinkable film and the inner core mold are removed to obtain the composite coiled pipe.
In addition to the production of round tubes like fishing rods, this process can also produce square tubes, triangles and other special-shaped tubes for use in different fields.
Winding process
Broadly speaking, the previous pipe rolling process can also be said to be a winding process, but this process does not use continuous prepreg, but has a certain laminated design. In our daily winding process, continuous prepreg can be used to produce pipes, gas cylinders, etc. through a certain angle design. Therefore, the prepreg here is different from the traditional prepreg, and narrow prepreg tapes are mostly used.
Carbon fiber prepreg has obvious advantages and is widely used in fishing tackle, sports equipment, sporting goods, aerospace and other fields, and is used in the military to manufacture rockets, missiles, satellites, radars, bulletproof vehicles, body armor and other important military products.