Development and Application of Pultruding FRP Technology
1. Overview
The pultrusion FRP forming process was studied as early as 1948, and it was first registered in the United States in 1951 and obtained a patent. It developed slowly in the 1960s, and entered a stage of rapid development in the 1970s and 1980s.
It is not too late to start research on pultrusion FRP forming technology in my country. In 1968, Beijing No. 251 Factory produced glass steel pipes by pultrusion. In 1974, it produced trough-shaped glass fiber reinforced plastic profiles. In 1982, it produced gymnastic equipment parallel bars and horizontal bars for uneven bars; Motor slot wedge. In the 1970s, Wuhan University of Technology produced small-diameter garden cross-section tie rods and antennas by pultrusion. The above products are all made of domestic resin and glass fiber raw materials, and the pultrusion technology developed by self-explored technology and equipment research and development.
Since 1985, more than 30 pultruded FRP production lines have been imported from abroad. The relevant units have also combined with actual production conditions to design and process 70 production lines based on foreign technology. The total production capacity of pultruded FRP is nearly 30,000 tons nationwide. In the early 1990s, Hubei Shashi Steel Pipe Factory and Qinhuangdao Yaohua FRP Factory of Petroleum and Natural Gas Corporation combined imported technology and self-developed respectively to develop and produce oil extraction sucker rods, which were recognized by the petroleum department and have been used in actual production. In the 1990s, my country's pultrusion FRP industry ushered in the first spring, large and small pultrusion factories were established one after another, and began to develop the production of FRP door and window profiles by pultrusion. After nearly ten years of assiduous research, my country's FRP door and window technology has entered a mature stage. The inspection results of FRP profiles and windows by "National Construction Engineering Quality Supervision and Inspection Center" and "National Construction Engineering Quality Supervision and Inspection Center" have reached the national door and window standards.
2. Pultrusion FRP Forming Process
2.1 Raw materials
Pultrusion is a process for producing FRP linear profiles. The raw materials used are unsaturated polyester resin and continuous glass fiber roving and mat. The high-performance composite materials it produces are suitable for use in various industries.
2.1.1 Resin
The pultruded FRP mainly uses unsaturated polyester resin, which accounts for more than 90% of the resin used in the pultrusion process. In addition, there are epoxy resin, vinyl resin, thermosetting methylpropionic acid resin, modified phenolic resin, flame retardant Sexual resin, etc.
With the in-depth research on the pultrusion molding process of unsaturated polyester resin in my country, people have put forward higher and higher requirements for the pultrusion molding curing system of unsaturated polyester resin, such as: increasing the speed of pultrusion molding to improve production efficiency , to increase the curing degree of the resin system to increase the strength of the product, so major domestic resin companies have developed special resins and curing systems suitable for pultrusion to meet the needs of the domestic market. In recent years, due to the advantages of phenolic resins such as fire resistance, foreign countries have developed phenolic resins suitable for pultrusion FRP, called second-generation phenolic resins, which have been widely used. In addition to thermosetting resins, thermoplastic resins are also used as needed.
2.1.2 Reinforcement materials
The reinforcing materials used in the pultrusion process are mainly glass fiber and its products, such as roving, continuous fiber mat, etc. In order to meet the special performance requirements of the product, aramid fiber, carbon fiber and metal fiber can be selected. No matter what kind of fiber is used in the pultrusion process, its surface must be treated so that it can be well bonded to the resin matrix.
2.1.3 Auxiliary materials
The auxiliary materials of pultruded FRP mainly include internal release agent and powder filler.
2.2 The importance of mold design for pultrusion FRP process
In the pultrusion process of FRP profiles, the mold is the intersection of various process parameters and one of the cores of the pultrusion process. Compared with the well-established plastic extrusion molding, pultrusion molding has similarities with it, but plastic extrusion molding is only a physical change process, while pultrusion molding is also accompanied by dynamic chemical reactions. The working condition of the mold is much more complicated than that of plastic extrusion and pultrusion, so the design and manufacture of the pultrusion mold is of great significance. Extrusion die life. The pultrusion FRP process generally consists of two parts: a preforming die and a forming die.
(1) During the pultrusion molding process of the preforming mold, after the reinforcing material is impregnated with resin (or while being impregnated), it must pass through a preforming mold composed of a group of yarn guide elements before entering the forming mold. The role of the preforming mold The reinforced material after dipping is gradually formed into a preform with a shape and size similar to that controlled by the molding mold according to the configuration of the section of the profile, and then enters the mold, so that the yarn content in the section of the product can be guaranteed to be uniform.
(2) Forming mold The ratio of the cross-sectional area of the forming mold to the cross-sectional area of the product should generally be greater than or equal to 10 to ensure that the mold has sufficient strength and rigidity, and the heat distribution is uniform and stable after heating. The length of the pultrusion die is determined according to the traction speed and the solidification speed of the resin during the molding process, so as to ensure that the product reaches the degree of demoulding and solidification when it is pulled out. Generally, steel is chrome-plated, and the surface of the mold cavity is required to be smooth and wear-resistant, so as to reduce the friction resistance of pultrusion and improve the service life of the mold.
2.2.1 Selection of mold
For pultrusion dies, the choice of die materials directly affects the performance of the dies, especially for pultruded window frame profiles. Due to the broad market prospects and large demand for window frame profiles, this requires the mold itself to have a particularly long service life. The selection of mold materials 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 description of the pultrusion FRP process
The untwisted roving yarn cluster is loaded on the creel, and the uncoiled yarn bundle passes through a series of guide rollers, gathering grids and yarn gathering rollers, and then enters the resin impregnation tank to soak the resin. The yarn bundle then passes through a preforming die, which is a guide configured according to the desired cross-sectional shape of the product. After expelling excess resin and air bubbles in this mold, it enters the cold mold. The cold mold is cooled with cooling water to increase the viscosity of the resin and reduce the loss. Finally, it enters the forming mold, so that the fiber reinforced material and resin are formed and solidified in the mold, and then pulled out by the traction device, and cut into the required length by the cutting device. products.
2.4. Features of pultrusion FRP products
(1) High strength The tensile strength of the pultruded profile is 150-300MPa, the bending strength is 200-300MPa, and the bending strength retention rate after 1000h artificial accelerated aging can reach 78%.
(2) Low deformation rate After 1000h artificial accelerated aging of FRP pultruded profiles, the length change is +0.03%, and the width change rate is -0.07%. Therefore, the geometric shape and size of the products made of the pultrusion profile can be kept stable for a long time.
(3) High thermal deformation temperature The thermal deformation temperature of the pultrusion profile is 186°C, it will not soften at high temperature, and will not be brittle at -60°C, which ensures normal use under various ambient temperatures.
(4) Low water absorption The water absorption of ordinary FRP products is less than 0.5%, while the water absorption of pultruded profiles is only 0.257%, which is suitable for use in humid environments.
(5) Low thermal insulation coefficient The heat transfer coefficient of the pultruded profile is close to that of rigid PVC, and the thermal insulation coefficient of the single-frame double-glass thermal insulation window made of it is only 2.69W/(m2? The thermal insulation coefficient of the same-type windows made of steel and aluminum is as high as 4.0W/(m2?K), which shows that the energy-saving performance of FRP doors and windows is very obvious.
(6) Strong corrosion resistance After immersion in 3% HCI aqueous solution for 24 hours, the hardness retention rate of pultruded profiles is 95%; after immersion in 3% NaCl aqueous solution for 24 hours, the hardness retention rate is 89%. Therefore, the doors and windows made of FRP pultruded profiles are not only suitable for ordinary houses, hotels, restaurants, but also for industrial plants in coastal areas and corrosive operating environments.
(7) Adapt to environmental requirements The production process adopted for processing pultrusion profiles has the characteristics of low noise, high efficiency, low power consumption, and low pollution, and meets the relevant national environmental requirements.