Pultrusion FRP molding process was studied as early as 1948. In 1951, it was first registered in the United States and obtained a patent. It developed slowly in the 1960s, and entered a stage of rapid development in the 1970s-1980s.
The research of pultrusion FRP forming process in China is not too late. In 1968, Beijing 251 factory produced FRP by pultrusion, in 1974, the trough shaped FRP profiles were produced, and in 1982, the horizontal bars of parallel bars and uneven bars were produced; The slot wedge based on phenolic resin was successfully manufactured. In 1970s, Wuhan University of technology produced small diameter circular cross-section rod and antenna by pultrusion method. The above products are all pultrusion technology developed by using domestic resin and glass fiber raw materials, self explored technology and equipment.
Since 1985, more than 30 pultrusion FRP production lines have been imported from abroad, and 70 production lines have been designed and processed by relevant units in combination with production practice and foreign technology. The total production capacity of pultrusion FRP in China is nearly 30000 tons. In the early 1990s, Hubei Shashi steel pipe plant and Qinhuangdao Yaohua Glass fiber reinforced plastic plant of China National Petroleum Corporation developed and produced oil extraction sucker rod by combining imported technology with self-developed technology, which was recognized by the petroleum department and has been used in actual production. In the 1990s, China's pultrusion FRP industry ushered in the first spring. Large and small pultrusion plants were established one after another, and began to develop the pultrusion method to produce FRP door and window profiles. After nearly ten years of hard research, China's FRP doors and windows technology has entered a mature stage. Through the national construction engineering quality supervision and inspection center and the national construction engineering quality supervision and inspection center, the test results of FRP profiles and windows meet the national standards of doors and windows.
2.1 raw materials
Pultrusion is a process of producing FRP linear profiles. Its raw materials are unsaturated polyester resin, continuous glass fiber roving and felt. Its high-performance composite materials are suitable for various industries.
In addition, there are epoxy resin, vinyl resin, thermosetting methyl propionic acid resin, modified phenolic resin, flame retardant resin, etc.
With the in-depth study on the pultrusion molding process of unsaturated polyester resin in China, people put forward higher and higher requirements for the curing system of unsaturated polyester resin pultrusion molding, such as increasing the speed of pultrusion molding to improve the production efficiency, improving the curing degree of resin system to improve the strength of products, Therefore, the domestic major resin enterprises develop suitable pultrusion resin and curing system to meet the domestic market demand. In recent years, because of the advantages of phenolic resin such as fire resistance, phenolic resin suitable for pultrusion FRP has been developed abroad, which is called the second generation phenolic resin and has been widely used. In addition to thermosetting resins, thermoplastic resins are also used as required.
2.1.2 reinforcing materials
The reinforced materials used in pultrusion process are mainly glass fiber and its products, such as roving, continuous fiber felt, etc. In order to meet the special performance requirements of products, aramid fiber, carbon fiber and metal fiber can be selected. No matter what kind of fiber is used in pultrusion process, its surface must be treated to make it adhere well to the resin matrix.
2.1.3 auxiliary materials
The auxiliary materials of pultrusion FRP mainly include internal release agent and powder filler.
2.2 importance of pultrusion FRP process mold design
In the pultrusion process of FRP profiles, the die is the intersection of various process parameters, and is one of the core of pultrusion process. Compared with the already mature plastic extrusion forming, the pultrusion forming has some similarities with it, but the plastic extrusion forming is only? Pultrusion is accompanied by dynamic chemical reaction. The working condition of the die is much more complex than that of the plastic extrusion, so the design and manufacture of the pultrusion die is of great significance. It not only affects the success or failure of the pultrusion process, determines the quality of the pultrusion products, but also affects the service life of the pultrusion die. Pultrusion process of FRP is generally composed of two parts: preform die and forming die（ 1) In the pultrusion process of preform die, after the reinforcement material is impregnated with resin (or is impregnated at the same time), it must pass through the preform die composed of a group of yarn guide elements before entering the forming die. The function of the preform die is to gradually form a preform with approximate shape and size of the forming die control according to the configuration form of profile section after the reinforcement material is impregnated, And then enter the molding, so that the yarn content of the cross section of the product can be uniform（ 2) Generally, the ratio of the cross-sectional area of the forming die to the cross-sectional area of the product should be greater than or equal to 10, so as to ensure that the die has enough strength and stiffness, and the heat distribution is uniform and stable after heating. The length of pultrusion die is determined according to the traction speed and resin solidification speed in the forming process, so as to ensure the degree of demoulding and curing when the product is pulled out. Generally, chrome plated steel is used, and the surface of die cavity is required to be smooth and wear-resistant, so as to reduce the friction resistance of pultrusion forming and improve the service life of die.
2.2.1 selection of mould
For pultrusion die, the selection of die material directly affects the performance of the die, especially the pultrusion window frame profile. Due to the broad market prospect and large demand of window frame profile, the service life of the die itself is required to be particularly long. Therefore, the selection of die material requires the following properties: (1) high strength, fatigue resistance and wear resistance（ 2) High heat resistance and small thermal deformation（ 3) Good corrosion resistance（ 4) Good machinability and surface polishing performance（ 5) Small thermal deformation and good dimensional stability.
2.3. Brief introduction of pultrusion FRP process
The untwisted roving mass is installed on the frame, and the uncoiled yarn passes through a series of guide rollers, bundle grid plate and yarn collecting roller, and then enters the resin impregnating groove to soak the resin. The yarn then passes through the preform die, which is a guide device configured according to the required cross-section shape of the product. After the excess resin and air bubbles are discharged from the mold, it enters the cold mold. In the cold mold, cooling water is used to increase the viscosity of the resin and reduce the loss. Finally, it enters the molding mold to solidify the fiber-reinforced material and resin in the mold, and then it is pulled out by the traction device and cut into products of the required length through the cutting device.
2.4. Characteristics of pultruded FRP products
(1) The tensile strength and bending strength of high strength pultruded profiles are 150-300mpa and 200-300mpa respectively. The retention rate of bending strength can reach 78% after 1000h artificial accelerated aging.
(2) After 1000h artificial accelerated aging, the length change rate is + 0.03%, and the width change rate is - 0.07%. Therefore, the geometric shape and size of the products made of the pultruded profile can be kept stable for a long time.
(3) The hot deformation temperature of pultruded profiles is 186 ℃, which does not soften at high temperature and remains brittle at - 60 ℃, ensuring normal use at various ambient temperatures.
(4) The water absorption of common FRP products is less than 0.5%, while that of pultruded profiles is only 0.257%, which is suitable for use in humid environment.
(5) The heat transfer coefficient of pultruded profiles is close to that of rigid PVC. The heat transfer coefficient of single frame double glass thermal insulation window made of pultruded profiles is only 2.69w / (M2? M)? K) The thermal insulation coefficient of the same type window made of steel and aluminum is as high as 4.0w / (M2? K) It shows that the energy saving of FRP doors and windows is obvious.
(6) After immersion in 3% HCI aqueous solution for 24 hours, the hardness retention rate of the corrosion resistant pultrusion profile is 95%; After soaking in 3% NaCl solution for 24 hours, the hardness retention rate is 89%. Therefore, the doors and windows made of FRP pultrusion profiles are not only suitable for ordinary houses, hotels and restaurants, but also for industrial plants in coastal areas and corrosive working environment.
(7) To meet the environmental requirements, the production process of pultrusion profiles has the characteristics of low noise, high efficiency, low power consumption and low pollution, which meets the relevant national environmental requirements.
In addition to the corrosion resistance, aging resistance and insulation of traditional FRP materials, pultrusion FRP products also have the characteristics of stable size, good appearance quality and high production efficiency. Because of its excellent performance and characteristics, it has been applied in more and more fields and has a very broad market at home and abroad.
The application examples of pultrusion FRP are as follows:
Electrical: cable bracket, ladder, bracket, insulation ladder, insulation rod for transformer, etc., motor slot wedge, accessories for lighting, street lamp post, antenna pole, suspender for live maintenance overhead line, power supply pole, etc? Radio tower, optical fiber cable core material, etc
Civil building materials: shed, fence, window frame, greenhouse frame, roof decoration materials, bridge components, gas station sunshade and rainproof ceiling, stair handrail, tunnel ventilation window, house compartment wallboard, sidewalk bridge, concrete formwork, scaffold, sound barrier, snow avalanche prevention shed, etc
Land transportation vehicles: refrigerator car components, truck structural components, bus side wall panels, trailer floor, bus exhaust pipe, luggage rack, direction sign, seat, etc
Corrosion resistant equipment: chemical equipment, water treatment equipment, brewing equipment, cover plate of sewage treatment plant, corrosion-resistant storage tank protection frame, scrubber assembly components, aquarium inspection corridor, cooling tower support, sucker rod, offshore oil production equipment, etc
Sports and entertainment: bow and arrow, fishing pole, tent pole, operating pole for sailboat, surfboard component, sailboat tension component, snowboard, side panel of combined swimming pool, snowboat, balance bar, golf club, etc
Marine related products: marine tank, pipe (including Minesweeper tank, coastal road lamp post, marine keel, marine railings, handrails, stairs), Floating Wharf, marine grille, etc
Aircraft interior decoration materials: structural materials, shelves, etc
Agricultural supplies: Livestock pen, enclosure fence for poultry house, greenhouse frame for planting, supporting components, frost proof net pillar, rattan fence, irrigation water tank, etc
Others: flagpole, bed component, tool handle, etc
It can be seen from the above that pultrusion FRP products are widely used in the fields of electrical, land transportation, corrosion resistance, building materials and so on. The following is a further elaboration of the relevant parts.
3.1 electrical related fields
No matter now or in the past, electrical related products have always been one of the important application fields of pultruded FRP. A few years ago, the market development of pultruded FRP in Europe made remarkable achievements, and various cross-section structural shapes of profiles were developed, which were used as materials for cable support of Haixia tunnel between Britain and France, Aluminum hydroxide filler was used to modify acrylic resin to achieve high flame retardancy and low smoke. The mobile phone line bracket made of pultrusion material is 80% lighter than the steel bracket, and it can be installed on the top of the building and tower without special reinforcement.
3.2 construction, civil engineering and building materials
Due to the further improvement of mechanical properties, durability and combined connection technology of pultruded FRP, its credibility has been enhanced. Now it has entered the structural materials from the internal and external decoration materials and civil materials used in the past. For example, large-scale pultruded I-shaped FRP products are used as beams to build a 19 m high stair tower, which can withstand strong wind and is designed according to the wind load above 650kg / cm2. The trial use of pultruded FRP as bridge structural material is expanding, and the sidewalk bridge has become practical. There are also examples of building highway bridges. For example, the bridge span is 6 m, the bridge width is 3 m, and 11 ton trucks can pass. In Japan, pultrusion FRP is used to make concrete formwork instead of plywood to save natural wood. This kind of FRP formwork is 1 / 3 lighter than steel formwork, which is easy to handle, install and decompose; It has good peeling property with concrete, beautiful processing surface, no rust and corrosion resistance. It is suitable for coastal construction and can be inlaid with other materials. The sound insulation panel for expressway is a new field of pultrusion FRP products. Because this kind of sound insulation board has good strength, weather resistance and radio wave transmission, it can compete with PVC sound insulation board. Japan has developed the anti avalanche grid plate to replace the previous steel plate, which can solve the problems of easy rusting, difficult moving, difficult construction, high maintenance cost, and the weight can be reduced by 1 / 2.
The reason why pultruded FRP products can be used in the construction industry is that this material itself has good comprehensive properties such as high strength, light weight, corrosion resistance, low water absorption, flame retardant, thermal insulation, sound insulation, long-term light and no deformation, which is superior to wood, steel, plastic, aluminum alloy and other materials. Therefore, FRP doors and windows will become the ideal new building doors and windows in China, The market potential at home and abroad is huge.
3.3 corrosion resistance
Corrosion resistance has always been an important application field of FRP profiles. Pultrusion FRP can be used as structural material because of its own characteristics. For example, it can be used as the center beam and chassis of cooling tower, with cross section of 120 × 25cm large hollow pultrusion FRP profile has a bright future. In addition, pultruded FRP can be used to make the cover plate of sewage treatment plant, which is more suitable than hand laid FRP and RTM FRP. Pultrusion FRP profiles can be used as the tire of offshore oil production equipment, instead of steel, to achieve the characteristics of light weight, corrosion resistance, no need to weld, reduce maintenance costs and so on.
3.4 other areas
Pultruded glass fiber reinforced plastic (FRP) pillars, stalks, rods and other materials for agriculture and fishery have a bright future. In Japan, pultruded FRP sluice doors reinforced with glass fiber and carbon fiber are used to replace steel sluice doors. The weight is reduced from 300kg to 70kg, which is easy to open and does not rust. Japan has also developed pultruded FRP irrigation water tank with glass fiber and carbon fiber as reinforcement materials to replace reinforced concrete or steel water tank. The width of water tank is 1.7m, the depth of water tank is 800mm, and each section is 12m long. It is made of 60mm square profile. It is not only resistant to acid soil corrosion, but also can reduce project cost, killing two birds with one stone.
It has become a consensus that pultruded FRP has high production efficiency, excellent performance and stable quality. As long as there is a breakthrough in pultrusion technology to produce high-quality FRP pultrusion products, the market can quickly accept.
The development of domestic FRP raw material industry has created a good material foundation for FRP pultrusion technology and market development. At present, except for a few reinforcing materials, the main raw materials for pultrusion production can be provided in China. More than 150 pultrusion production lines in China have laid a solid hardware foundation for the development of pultrusion technology and market, with a production capacity of more than 30000 tons.
At present, China's large-scale pultrusion enterprises learn from the successful experience of foreign countries, after in-depth study of pultrusion forming process, developed their own characteristics of stable performance of hydraulic and tape type pultrusion production line, and basically realized the localization of pultrusion process raw materials, developed grille, guardrail, trench cover, electrical ladder, sucker rod, doors and windows and other general products; At the same time, we have developed a series of high-tech and difficult pultruded FRP profiles, such as mobile communication base station radome, automobile air-conditioning wind deflector, by using our own technical advantages, and become the supplier of international well-known enterprises. They have grown into a high-tech enterprise specializing in the research and development of FRP pultrusion technology, as well as the design, manufacture and sales of FRP pultrusion equipment and molds. Technological innovation and product renewal bring vitality to enterprises and constantly form new sources of profits, which is the mainstream of FRP pultrusion technology and market development in China.
In short, China's FRP