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FRP Bonding Process

Jun 11, 2020

1. Production of FRP parts

FRP is abbreviated as "FRP" or "GRP". It is a kind of glass fiber reinforced plastic. It is a non-metallic material composed of glass fiber felt, glass fiber and synthetic resin (such as polyester resin and epoxy resin). The most widely used is FRP containing polyester resin. The production process of glass fiber reinforced plastic parts is as follows: brush the mold release agent on the mold → lay a resin layer (0.5-1.0mm thick gel coat) on the mold → after the gel coat layer becomes hard, lay the first layer of glass cloth on the mold →Coated with resin and glass cloth→Resin begins to solidify when FRP is molded→Remove FRP parts.

Second, the bonding process of glass fiber reinforced plastic parts

Because of the diversity of polyester resins and manufacturing processes, there must be a wider range of processes when bonding and sealing them. The most commonly used adhesives for bonding glass fiber reinforced plastic parts are generally polyurethane glue and silica gel. These adhesives form an elastic body after bonding glass fiber reinforced plastic parts, and are firmly bonded to the glass fiber reinforced plastic parts, safe and reliable.

(1), aging treatment. The glass fiber reinforced plastic parts just taken out of the mold cannot be used for bonding and sealing immediately, and must undergo aging treatment in order to remove some substances that have not been completely reacted when making the glass fiber reinforced plastic parts, such as monomeric styrene and other volatile substances. In addition, the aging treatment also helps to release and eliminate the internal stress of the FRP parts. The aging treatment mentioned here refers to the FRP parts placed at 23 degrees Celsius and 50% relative humidity for at least two weeks. Before the aging treatment, the FRP parts should also be heated at 60-80 degrees Celsius for 4-6 hours.

(2) Polishing. The glass fiber reinforced plastic parts after aging treatment must be polished on the surface with coarse sand cloth generally 80#-120# to remove some chemical substances precipitated during the aging treatment.

(3), clean. Cleaners and adhesives should be used together. The cleaning agent used generally has two purposes: ① cleaning. Hold the bottle mouth with industrial wipes and shake gently to ensure that only a small amount of cleaning agent gets on the paper towel. When wiping, you can only wipe in one direction, not back and forth. Immediately after wiping, wipe the cleaner with a dry paper towel (the paper towel should be free of any stains). After cleaning, leave to dry for a period of time according to temperature conditions to ensure that the detergent is completely dry. ② Activation. The cleaning agent matched with the adhesive generally has the function of activating the substrate, so that the adhesive and the substrate have better adhesion.

(4). Primer. The fiberglass parts used in passenger cars are generally translucent, and some are even transparent. This allows ultraviolet rays to pass directly through the glass fiber reinforced plastic parts and act on the adhesive, thereby accelerating the aging of the adhesive, reducing the adhesive strength of the adhesive, and even causing bonding failure. Therefore, before bonding, a layer of primer should be painted on the glass fiber reinforced plastic parts to block the ultraviolet radiation. If the penetration rate of ultraviolet rays to the FRP parts is less than 0.5%, or the penetration rate of the visible light does not exceed 20%, brushing the primer at the bonding part of the FRP parts can effectively prevent the ultraviolet rays from damaging the adhesive. If the penetration rate of ultraviolet or visible light exceeds the above limits, in addition to the method of primer coating, you must also use masking tape or opaque materials to cover the adhesive layer, otherwise it will not completely prevent ultraviolet light from the adhesive Of destruction. The body frame as the bonding surface should be designed and arranged according to the characteristics of the bonding process to make it advantageous for bonding. Before the FRP bonding, the treatment of the frame to be bonded (usually carbon steel or galvanized profile or aluminum profile) is the same as that of FRP parts, that is, grinding, cleaning, and primer coating.

(5). Glue. Apply polyurethane glue or silicone on the body frame, and the shape of the glue should be triangular. The size of the triangle depends on the thickness and width of the required adhesive layer. When the glass fiber reinforced plastic parts are bonded to the skeleton, the triangular glue shape also helps to completely expel the air from the adhesive, avoiding air from remaining in the adhesive to form bonding defects.

(6) Precautions during the bonding process.

① The surface drying of the glue before bonding will obviously weaken the adhesive strength of the glue. Therefore, during the bonding process, the time for glue application must be controlled to be less than half of the surface drying time of the adhesive.

② Elastic bonding has certain bonding thickness requirements. In order to obtain the ideal thickness, rubber or plastic pads with Shore A hardness equal to or close to the hardness of the adhesive layer can be used to ensure. This is very important for bonding.

3. Conclusion

In short, the bonding of glass fiber reinforced plastics eliminates the stress concentration caused by riveting and the cracking of glass fiber reinforced plastics, and the bonding of glass steel will greatly improve the surface flatness of the car body and the torsional strength of the car body. Access technology is being recognized and applied by more and more bus manufacturers.