In the anti-corrosion construction, hand-fiber reinforced plastics are often encountered. Although there are many types of FRP, the most widely used epoxy fiberglass is still the most widely used construction method. The shrinkage rate of epoxy glass fiber reinforced plastic is the smallest among the three thermosetting resins of phenolic, epoxy and unsaturated polyester, thus ensuring the quality of the hand lay-up method. Epoxy glass fiber reinforced plastic has good resistance to acids, alkalis, solvents and most molds. Especially in alkaline environment, it can highlight excellent corrosion resistance and can resist heat. In order to meet the anti-corrosion requirements under complex conditions, the epoxy resin can be compounded, and other resins can be added to achieve the best condition (such as epoxy novolac, epoxy furan, etc.). Every master who lays hands on FRP knows the three major phases of FRP: resin, fiber, curing agent, and epoxy FRP are no exception. The most common is epoxy resin (E-44, some called 6101), the glass fiber is "three no products", that is, alkali-free, twist-free and wax-free plain weave glass fiber cloth. Of course, it is better to choose medium-alkali fiberglass cloth in acid environment. , Curing agent selection T31. Other additives such as powder, diluent, etc. are described in the following process. A good anti-corrosion project is inseparable from construction and materials, as the saying goes: three-point materials and seven-point construction. Therefore, the focus of hand lay-up epoxy glass fiber reinforced plastics is on hand lay-up construction.
Substrate processing. Most of the hand lay-up FRP is field operations. The common substrates are concrete substrates, carbon steel substrates, and other substrates are generally rare. In order to obtain the ideal adhesion between the base material and the epoxy glass fiber reinforced plastics, the primary treatment is very important. In addition to the cleanliness of the base, a certain roughness is also required. Some people suggested that a simple grinder can be used to grind the base layer. The author believes that the base layer must be treated by sandblasting or shot blasting to ensure the formation of roughness. The essential. The concrete base is shot blasted, and the carbon steel base is sandblasted to achieve a Sa2.5 level or higher and a roughness of about 75 microns. Impurities must be blown clean with dry air at the base layer. Putty repairs are also required for the defective parts of the concrete base (materials are prepared with epoxy bulk and quartz powder).
Epoxy bulk preparation. E-44 epoxy resin semi-solid viscous colloid should be heated and melted, then cooled to about 40 degrees, mixed with diluent and reserved. The heating equipment is resistance wire furnace, induction cooker, etc. The author believes that the induction cooker is safe and convenient, and the temperature can be adjusted. The large iron drum can be used to dispose of the waste diesel drum and cut in half in the middle (note that there is no combustible gas or liquid in the drum when cutting to prevent explosion accidents). The addition of thinner is to reduce the viscosity of the resin compound, to facilitate operation, and to meet the needs of the process. The non-reactive diluent should evaporate and overflow during the curing of the resin compound. This not only consumes materials, but also increases the shrinkage and The porosity of the finished product reduces the impermeability of FRP. Therefore, the use of thinner makes the epoxy resin no longer thickened. After stirring with an explosion-proof mixer, cover it and store it in a cool place. The choice of diluent should be products with good solubility, low volatility, low toxicity and high safety factor or mixed products, such as ethanol plus acetone, xylene, cyclohexanone, etc. During the preparation of the bulk material, the bulk barrel should be kept at a safe distance of more than 15 meters from the heating source to prevent the volatile gas from catching fire.
Base material. After the concrete or carbon steel substrate is processed, the primer must be brushed and closed within 4 hours. Long time will cause secondary rust or the accumulation of new pollutants and water vapor in the air, which is not conducive to the perfect combination of resin and substrate , It is easy to make the epoxy glass fiber reinforced plastic peel off from the interface of the substrate. Epoxy primer can be diluted with epoxy bulk material, and the concentration should be low to facilitate the penetration of the primer and enhance the bonding force between the substrate and glass fiber reinforced resin. The curing agent uses T31 or a new type of cashew nut shell curing agent. Toxic, it is rarely used now. The curing agent and the primer should be mixed evenly. Use an electric mixer to mechanically stir. The author believes that manual stirring is incomplete and affects the sufficiency of curing. The amount of T31 added is between 15% and 25% according to the ambient temperature. . The primer is applied by roller or brush. Before operation, remove the roller fluff, apply evenly, cross, do not pile up or sag. For the uneven base, use primer and quartz powder to mix and make a ring Oxygen putty is embedded and leveled. It is best to use barium sulfate powder or other acid-resistant powder in acid environment. Natural drying and curing for 12 hours to enter the next procedure.
Hand paste. There are 1m, 0.5m and 0.3m non-alkali, non-twisting and non-wax glass fiber cloths, which can be selected according to the construction equipment or current situation. However, in my long-term construction experience, 0.3m is the most convenient. In the acidic environment, use medium-alkali glass fiber cloth with a thickness of 02 to 04. The latitude and longitude can be 10*10 or 12*12. The plain weave does not twist, and the edge of the glass fiber cloth will cause stress for the hand lay-up method. Twisted is not easy to penetrate the epoxy resin material, and is not easy to bend, so the hand-lay method generally uses non-twisted cloth. It is best to use Shanghai Zhang Xiaoquan Tailor Scissors for cutting glass cloth. The cutting is fast and the cloth is sharp without folding. The epoxy resin bulk material is thicker than the base material, adjusted appropriately with a thinner, the viscosity should be suitable for soaking the cloth eye, the powder is added with 200 to 300 mesh quartz powder, and the acidic environment is used with barium sulfate powder, and the addition amount should not exceed 40 %, T31 curing agent is still between 15%-25% according to the ambient temperature. The authors experience that T31 is 20% at 25 degrees normal temperature. The curing agent and resin should be fully stirred evenly. It is recommended to use an electric mixer to stir mechanically for 10 minutes. Is appropriate. Use a brushing tool such as a roller brush, in the order of rubber material-spreading-smoothing the cloth-recoating the rubber material, the lap seam width is not less than 10CM. If two consecutive layers are constructed together, the method of tiling can be adopted, and the subsequent covering will cover half of the front road cloth. The key rubber material in this process should be saturated with cloth eyes and not piled up or sag. Before secondary lamination between each layer of cloth, be sure to clean and repair the upper layer of cloth, preferably polished. In order to reduce the shrinkage of epoxy glass fiber reinforced plastics, you can consider the first hand lay-up chopped strand mat at the base layer, and then lay the glass fiber cloth. The method of hand lay-up epoxy glass chopped strand mat is the same as that of glass fiber cloth. If you want to modify the epoxy resin, such as epoxy-phenolic, epoxy-furan, epoxy-polyester, etc. can be selected according to their own characteristics, but the amount of secondary resin added should not exceed 30%.
Fabric painting. Hand-laminated FRP fabric is directly against the corrosion layer, so the resin content is high and no powder is required, and the thinner should be added in an appropriate amount. The author believes that it is not difficult to apply the fabric if it is possible. The thinner can be added without high solid content. It is an important indicator of corrosion resistance. The fabric is painted at least 2 or more. The amount of T31 and the precautions are the same as above. The brushing should be cross-crossed, even and leak-free, without sagging or accumulation, without pinholes, without bubbles, and the curing time should be at least 24 hours, and the finished product can be used after 10 days, because the resin curing and crosslinking is not yet complete, so the time The longer it is, the more complete the curing, and the conditions allow heating and curing, so that the product can achieve the best quality effect.
In short, hand lay-up epoxy glass fiber reinforced plastic is a mature anti-corrosion construction process, but it is difficult to be skilled in this process, and quality accidents often occur. Therefore, we glass fiber reinforced plastics are old revolutions who encounter new problems, so the author takes this The old craftsmanship came out to discuss with you, and it will be more handy in the future construction of hand-paste epoxy glass fiber reinforced plastics, making this traditional anti-corrosion process play a greater role.