01 people's technical quality is very important
Hand lay FRP products belong to an "emotional product". The same materials and the same environment, due to different human qualities, the products produced are different. Therefore, in the process of making FRP molds, we must be very concentrated in our thoughts and take them very seriously. Each operation process includes a comprehensive understanding of the characteristics of materials, the role and data between materials (resin reaction theory, classification of fibers, product structure mechanics).
02 The choice of materials is the key
According to the process requirements of the production products, it is classified to meet the needs of the process. Select the appropriate materials to make the mold, such as RTM, acrylic blister, casting, hand lay-up, and other materials have different requirements, especially for a long time without the attention of the upper layer, The auxiliary level ignored at the grassroots level plays an important role in the quality of the FRP mold, product quality and product cost, and the survival of the enterprise.
(1) Gel coat layer-attach importance to the heat resistance, gloss and crack resistance of the mold. Mainstream is vinyl ester resin.
(2) Surface layer—emphasis on heat resistance and crack resistance. The resin uses surface felt as a reinforcement material to reduce the appearance of cloth on the mold surface. The resin usually uses vinyl ester resin.
(3) Intermediate layer-Attach importance to the strength and the mechanical distribution of the fiber. The implementation of prestressing the fiber usually uses mold resin, vinyl ester resin or isophthalic resin.
(4) Backing layer-pay attention to the protection of strength, water resistance and weather resistance.
(5) Reinforcement layer-attach importance to strain and deformation. The back side is pressure-bonded with water-resistant plywood 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 three-dimensional hollow three-dimensional glass fiber fabric can be used instead of plywood. This measure solves the original deficiency. In addition, the 3D steel structure grid can also be used as a reinforcement, which can greatly improve the efficiency of mold use.
Using 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 fiberglass mat and plain weave. The price of aramid and carbon fiber is relatively high, but because of the very good effect in terms of crack resistance and stiffness improvement, it can also be appropriately selected due to the special needs of the mold.
03 Equipment and Tools
Everyone thinks that making glass fiber reinforced plastic molds is a simple process of manual operation, and the brush is the main tool for distributing resin. Workers use it properly in the operation, the small bubbles generated by the hair brush are less, it is not used well, the hair brush is a tool for making small bubbles, so we choose the hair brush before the operation (the hair should be uniform, the hair root should be straight ).
The roller is the main tool for evacuating bubbles. Not only is it necessary to expel the air bubbles, but it is also responsible for pressing the fibers tightly, rolling out the resin that meets the fiber penetration, and making the mold resin to fiber ratio as small as possible, which is also It is a very important measure to improve the quality of FRP molds and FRP products; on the contrary, the shape design of the rollers currently available on the market is a horizontal strip, which becomes a so-called bubble harvester. The excess resin is rolled out, let alone reducing the resin to fiber ratio, so where does the strength of the FRP mold come from? Where does quality come from?
04 Implementation process of strict molding process
We need to make good FRP molds, to meet the size requirements of the products, good straightness, high strength, good mechanical properties, all through the implementation of reasonable technological processes and operating processes, 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 reaction, such as temperature, relative humidity, time to complete the operation, etc., so we have to take some necessary technological measures in the operation process.
Take the necessary demoulding treatment on the master mold, calculate the actual area of the gel coat, equip the auxiliary materials according to the amount, pay attention to the operation specifications, stir the gel coat slowly, otherwise there will be more bubbles, which will affect the quality effect of the gel coat. For spraying and hand-coating the gel coat, the first layer does not need to be applied too thick, so that the bubbles in the gel coat will be easily drained away, but should be applied evenly, so that when the first layer of gel coat begins to thicken, The second layer can be coated and scanned. At this time, the thickness of the gel coat of the second layer should be about 0.55mm~0.6mm. We can also use the gel coat ruler to measure whether it reaches the required thickness. The action direction when painting the wall surface 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 coating of the entire gel coat is considered complete. Allow it to lay the surface layer and the reinforcement layer just after the gel.
In order to make the quality of the glass fiber reinforced plastic mold reach the expected best performance effect, we adopt some necessary methods in the layering process to control the entire glass fiber reinforced plastic mold to minimize the deformation and shrinkage problems, and the mechanical properties are in the best state Relatively speaking, the overall comprehensive cost will be reduced.
4.1 Intermittent method
The intermittent method uses the time difference to minimize the deformation and shrinkage of the resin. You can first make a layer of surface felt or chopped felt. Because only one layer of glass fiber is used, the amount of resin is also small, and the overall shrinkage deformation is very small. After this layer has enough curing time to set, make another layer of fiber. Because the first layer is cured in the front, the setting of the latter layer is cured by the stable shape of the previous layer, so such deformation and shrinkage will be reduced a lot. (Precautions: Be sure to roughen and dewax the surface of the glass fiber reinforced plastic after each curing, otherwise it will cause delamination between the layers, affecting its strength and quality.) The amount of intermediate layers will be increased in the future, with 3 to 5 layers laid each time Until the glass fiber reinforced plastic mold is laid to the required strength requirements.
4.2 RM method
In the process of laying the middle layer, we adopt the process of one felt and one cloth that is short-cut felt, and the checkered fabric overlaps. Two layers of checkered fabric are laid, and the shear force between the layers is very poor: only use short-cut felt to cut The fiber line is short, the performance of the force is not concentrated, and the content of the glue is large. In view of their respective advantages as complementary to their respective shortcomings, the RM method is used to promote the penetration between resin fibers and increase the moment between the fiber cloth layers, thereby obtaining the best results.
4.3 45° laying method
The bending force, top force and torsion force of glass fiber are very poor, it has only a strong tensile force. The force direction of the glass fiber cloth is only warp and weft, that is to say, the force direction has only four sides, and after laying at 45°, the eight directions are added in four directions, which is one of them. Second, when the product or mold structure has a right angle, the fiber at the right angle is exactly 90° bending force and one is torsion, which are in the worst stress condition. Therefore, the right angle on the product or mold structure The 45° laying method is used to form two fibers at a right angle to form 120°. At this time, we add light prestress to the operation process to make the fiber force tighter and stress the product structure. Get better play.
Due to the benefit of the enterprise, many manufacturers rushed to release the mold after the mold was laid in a short curing time, and immediately ground with water abrasive paper. After polishing, it was immediately put into production. At this time, the glass fiber reinforced plastic mold is in a state of incomplete curing, the glass fiber reinforced plastic mold has not yet had the best strength, the resin has not yet fully reacted, and the stress caused by the shrinkage deformation of the material of the glass fiber reinforced plastic mold has not been released, plus the production of the product The effect of the heat on the mold will gradually reveal the problems of the mold in terms of strength and durability, surface finish, deformation and other aspects. With the appearance of the gel coat, the surface texture and even the gel coat cracks, the whitening of the layer is damaged, and the mold is warped. It can't be used due to bending deformation. Therefore, the post-curing treatment of the FRP mold is very important. After a constant temperature of 3 to 4 hours at 80°C, the stress of the FRP mold contracting and deforming at different angles in the structural modeling can be buffered and released. A complete reaction is obtained at a constant temperature of 80°C, and it can be demolded only when it is in the best state.
In addition to being more user-friendly, the grinding and polishing of the mold is a key factor is the quality of the water sandpaper in the water grinding process. Good water-grinding sandpaper can achieve double the result with half the effort. Water-grinding process should start with 600~800#. If the mold is too rough, use 400# first. Because I started to use too coarse abrasive sandpaper, its sand marks are very rough. The final water scrub time will be much longer. Every time you have to remove the last sand mark, until 1500~2000#, you can't see any traces of water and sand at all. This is a very meticulous and meticulous process. Only after this process can meet the process requirements, it will start. polishing. Use No. 1 polishing water, which is applied to the mold to be polished. Polishing with wool polishing discs, we should pay attention to the turning problem of a polishing disc. According to the turning of the polishing disc, bring the polishing water into it to achieve the polishing effect. The polishing disc can not be thrown out of the polishing water, so that it will not be polished. The effect is labor-intensive, time-consuming and material-intensive. After this process is completed, the mold basically has a shiny surface. We use No. 3 polishing water again, and we should pay attention to the above problems. Because No. 3 polishing water itself already has a sealing agent, the following procedure is much simpler.
Semi-permanent high-efficiency mold release water, it is a relatively good mold release agent, but in the process of use, it is necessary to take some necessary processes, that is, after the mold is polished, the PMR must be applied first, the coating is thin, and brushed immediately It should be clean, and it should not be left with water marks, because it is difficult to clean it after it is dried. After one or two times, it will be waxed after half an hour. According to the waxing process requirements, the new mold should be Play a few more times. Brush it very clean every time. This is a very important technological requirement. On the contrary, it is meaningless to apply wax first and then apply PMR. Finally, we have started to try a new high-efficiency mold release water FREKOTE. From the trial point of view, in addition to having a good mold release effect, low molecular substances have less volatilization. The advantage of no damage to the mold gloss is very obvious, but the mold must be fully cured, high gloss mirror.
In order to make our glass fiber reinforced plastic mold process better, it is necessary to track and manage the glass fiber reinforced plastic mold number. Summing up the gaps and constantly improving them, the quality of the FRP mold can be guaranteed.