China's FRP industry has developed to this day, and one of the issues that has attracted much attention is how to improve the quality of FRP products: to improve the quality of FRP products, first of all, there must be good molds, and good FRP molds must be able to meet the accuracy of product dimensions; According to product performance, meet their structural mechanics and mechanical properties. In terms of appearance effect, it must have good finish, smoothness and uniform thickness.
In order to meet these requirements, the work involving raw material manufacturers, product structure design technicians, FRP mold making technicians and other parties has the following aspects:
1. The choice of material is very critical
Classified according to the process requirements of the production products, in order to meet the needs of the process, choose the appropriate material to make the mold, such as RTM, acrylic blister, pouring, hand lay-up and other materials have different requirements, especially for a long time without the attention of the upper class. Auxiliary comparisons neglected by the grassroots level play an important role in the quality of FRP molds, product quality and product cost, and the survival of enterprises.
(1) Gel coat layer - pay attention to the heat resistance, gloss and crack resistance of the mold. Vinyl ester resin is the mainstream.
(2) Surface layer - attach importance to heat resistance and crack resistance. The resin uses surface felt as a reinforcing material to reduce the appearance of cloth patterns on the surface of the mold. The resin usually uses vinyl ester resin.
(3) The middle layer - pay attention to strength, pay attention to the mechanical distribution of fibers, and add prestress to the fibers, usually using mold resin or vinyl ester resin or isophthalic acid type resin.
(4) Backing layer - pay attention to strength, water resistance and weather resistance protection.
(5) Reinforcing layer - pay attention to strain and deformation. The water-resistant plywood is pressed and bonded on the back to make it resistant to impact and prevent deformation. However, after a long time of use, the leveling of the mold surface often deteriorates. The reason may be the peeling between the FRP layer and the plywood and the rigid fatigue of the plywood. Therefore, the glass fiber fabric with ternary hollow three-dimensional structure can be used instead of plywood, which solves the original deficiency; in addition, the 3D steel structure grid can also be used as reinforcement, which can greatly improve the efficiency of mold use.
Use new fillers - nano calcium carbonate, fibrous wollastonite powder, etc., especially where it is connected with wood and steel frames, to enhance the overall stability of the mold.
In terms of fiber composition, the mainstream is the combination of glass fiber felt and plain weave. Aramid fiber and carbon fiber are relatively expensive, but because they have very good effects in crack resistance and rigidity improvement, they can also be selected according to the special needs of the mold.
2. Equipment and tools
Everyone thinks that making FRP molds is a simple manual process, and the brush is the main tool for distributing resin. If workers use it properly in operation, the brush will produce less small air bubbles. If it is not used properly, the brush is a tool for making small air bubbles, so choose a good brush before operation (the hair should be neat and the hair root should be straight) .
The roller is the main tool for defoaming. It not only discharges the air bubbles, but also is responsible for compacting the fibers, rolling out the resin that satisfies the fiber penetration, so that the difference between the mold resin and fiber ratio is as small as possible. This is also It is a very important measure to improve the quality of FRP molds and FRP products; on the contrary, the rollers currently available on the market are designed in a horizontal strip shape, which becomes a so-called bubble harvester, which cannot discharge the air bubbles, nor can it Excess resin is rolled out, not to mention reducing the ratio of resin to fiber, so where does the strength of the FRP mold come from? Where does the quality come from?
3. Strict molding process
To make a good FRP mold, to meet the size requirements of the product, to have good flatness, high strength, and good mechanical properties, it must be implemented through a reasonable process and operation process. The main materials of FRP molds are resin, fiber, and auxiliary materials. The relationship is very complicated, and there are many appearance factors in their response, such as temperature, relative humidity, time to complete the operation, etc., so some necessary technological means should be adopted in the operation process.
Take the necessary demoulding treatment on the master mold, calculate the actual area of the gel coat, prepare the auxiliary materials according to the quantity, pay attention to the operation specifications, and stir the gel coat slowly, otherwise there will be many bubbles, which will affect the quality of the gel coat. For spraying and hand-coating, the first layer does not need to be too thick, so that the air bubbles in the gel coat will be easily discharged, but it should be applied evenly, so that when the first layer of gel coat just begins to thicken, The second layer of coating and sweeping can be carried out. At this time, the thickness of the gel coat of the second layer should be about 0.55mm~0.6mm in total. You can also use the gel coat ruler to measure whether the required thickness is reached. When painting the wall, the direction of action is to pull from bottom to top, try not to brush horizontally, so as to reduce a lot of glue flow. After the two layers of gel coat are basically cured, add another layer of gel coat. At this time, the entire gel coat coating is considered complete. Allow it to gel just before laying down the surface and reinforcement layers.
In order to make the quality of the FRP mold achieve the expected best performance effect, some necessary measures are adopted in the layering process to control the deformation and shrinkage of the entire FRP mold to a minimum, and the mechanical properties are in the best state. Relatively speaking, the overall comprehensive cost will be reduced.
4. Intermittent method
The batch method is to use the time difference to minimize the deformation and shrinkage of the resin. You can make a layer of surface mat or chopped strand mat first, because only one layer of glass fiber is made, and the amount of resin is very small, and the overall shrinkage deformation is very small. , let this layer have enough curing time to set, and then make another layer of fiber. Because the first layer is cured in front, the shape of the latter layer is solidified by the stable shape of the previous layer, so the deformation and shrinkage rate will be much reduced. (Precautions: Be sure to roughen and remove the wax on the surface of FRP after each curing, otherwise there will be delamination between the layers, which will affect its strength and quality.) The amount of intermediate layers can be increased in the future, and 3 to 5 layers can be laid each time , until the FRP mold is laid to the expected strength requirements.
5. RM method
In the process of laying the middle layer, one felt and one cloth, that is, chopped strand mat, is adopted, and the grid cloth is overlapped. Two layers of grid cloth are used for laying, and the shearing force between layers is very poor: only chopped strand mat is used for laying and cutting, Its fiber line is short, its force direction performance is not concentrated, and its rubber content is large. In view of their respective advantages as complements to their respective shortcomings, the RM method is used to promote the penetration between resin fibers and increase the moment between fiber cloth layers, so as to obtain the best effect.
6. Laying method
The bending force, jacking force, and torsion force of glass fiber are very poor, and it has only a strong pulling force. The force direction of the glass fiber cloth is only the warp and weft directions, that is to say, the force direction is only four sides, and after laying at 45°, the four directions are added to obtain eight sides, which is one of them. Second, when the product or mold structure has a right angle, exactly one of the fibers at the right angle is subjected to a 90° bending force and the other is subjected to a torsion force, both of which are in the worst stress state. Therefore, the right angle on the product or mold structure The 45° laying method is adopted in the place, so that the two fibers at the right angle position form 120°. At this time, light prestress is added to the operation process to make the force of the fiber more tight, and the stress on the product structure is obtained. Play better.
Due to the relationship between enterprise benefits, many manufacturers are eager to demould after the mold has been laid for a short curing time, and immediately grind it with water abrasive paper, polish it, and put it into production immediately. At this time, the FRP mold is in a state of incomplete curing, the FRP mold has not yet had the best strength, the resin has not yet fully reacted, and the stress generated by the shrinkage deformation of the FRP mold material has not been released. The impact of the heat on it will gradually reveal the problems of the mold in terms of strength and durability, surface finish, deformation, etc., followed by the appearance of the gel coat, surface texture, and even cracking of the gel coat, whitening of the layup and internal damage, and the overall warping of the mold Therefore, the post-curing treatment of the FRP mold is very important. After a constant temperature of 80°C for 3~4 hours, the stress of the shrinkage and deformation of the FRP mold at different angles in the structural shape can be buffered and released. The complete reaction is obtained at a constant temperature of 80°C, so that it is in the best state before it can be released from the mold.
In addition to being more humane, the grinding and polishing of the mold is the quality of the water sandpaper in the water grinding process. Good water abrasive paper can achieve twice the result with half the effort (the water abrasive paper used now is not only MT, but also Japan, England, Italy, the United States, and the most common one is the Eagle Ball brand sandpaper from South Korea). 600~800# should be used at the beginning of the water milling process. If the mold is too rough, use 400# first. Since you start sanding the paper with water that is too coarse, it has coarse sand marks. The final water scrub takes a lot longer. Every time, the last sand marks should be removed. Until 1500~2000#, no traces of water and sand can be seen at all. This is a very patient and meticulous process. Only after this process can meet the process requirements can it be started. polishing. Use No. 1 polishing water, all coated on the mold to be polished. Polishing with a wool polishing disc, here we must pay attention to the turning of the polishing disc. According to the turning of the polishing disc, the polishing water is brought in to achieve the polishing effect, and the polishing disc cannot be thrown out of the polishing water, so that the polishing will not be achieved. The effect is labor-intensive, time-consuming, and material-intensive. After this process is completed, the mold basically has a bright surface. Then use No. 3 polishing water, also pay attention to the above problems, because No. 3 polishing water itself has a sealing agent, so the following process is much simpler (Note: (1), (3) US Two grades of grinding and polishing water from Meiguiya Company).
Semi-permanent high-efficiency release water PMR, it is a relatively good release agent, but some necessary processes should be taken during use, that is, after the mold is polished, PMR should be applied first, and the coating is thinner, and it will be applied immediately. Brush it clean, and don't let it leave water marks, because it is difficult to clean it after it dries. After one or two times, wait for half an hour and start waxing. According to the waxing process requirements, the new mold To play several times. Brush very clean every time. This is a very important process requirement. On the contrary, it is meaningless to wax first and then apply PMP. Finally, a new high-efficiency mold release water, FREKOTE, has been tested. According to the trial, in addition to good mold release effect, low-molecular substances volatilize less. The advantage of no damage to the gloss of the mold is very obvious, but the mold must be fully cured, high-gloss mirror.
In order to make the FRP mold process better, it is necessary to implement numbering for its FRP mold for tracking management. Only by summing up the gap and making continuous improvements can the quality of FRP molds be guaranteed.