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How To Improve The Quality Of Hand Lay-up FRP Products

Nov 05, 2020

To improve the quality of FRP products, we must first have a good mold, a good FRP mold must be able to meet the accuracy of the product size; also according to the product performance, to 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, raw material manufacturers, product structure design technicians, glass fiber reinforced plastic mold production technicians and other aspects are integrated, and work together to do the following aspects.

1. The technical quality of people is very important

    Hand lay-up FRP products and FRP Liushaming are a kind of "emotional products." The same material, the same environment, and because of the different qualities of people, the products produced are different. Therefore, in the process of making FRP molds, we must be very concentrated and take it very seriously at all times. Each operation process includes a comprehensive understanding of the characteristics of the material, the interaction between the material and the data (resin reaction principle, fiber classification, and product structure mechanics).

2. The choice of material is the key

    According to the process requirements of the products to be produced, to meet the required process, select the appropriate material to make the mold, such as RTM, acrylic blister, pouring, hand lay-up and other materials have different requirements, especially for the long-term lack of attention from the upper level. The secondary level ignored by the grassroots plays an important role in the quality of FRP molds, product quality and product cost, and the survival of the enterprise.

    (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-pay attention to heat resistance and crack resistance. The resin uses surface felt as a reinforcing material to reduce the appearance of cloth patterns on the mold surface. Vinyl ester resin is usually used for the resin of the willow and dark flower.

    (3) Intermediate layer-pay attention to the strength, the mechanical distribution of the fiber, and the implementation of prestressing the fiber, 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) Reinforcement layer-pay attention to strain and deformation. Pressure-bonded water-resistant plywood on the back to make it resistant to impact and deformation, but 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, glass fiber fabric with ternary hollow three-dimensional structure can be used instead of plywood, which solves the original shortcomings; 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 to 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 mat and plain cloth. Aramid and carbon fiber are relatively expensive, but because they have a very good effect on crack resistance and improved stiffness, they can also be selected appropriately for the special needs of the mold.

3. Equipment and tools

    Everyone thinks that making FRP molds is a simple manual process, and the brush is the main tool for resin distribution. Workers use it properly in the operation, and the small bubbles generated by the hair brush will be less. If used badly, the hair brush is a tool for making small bubbles, so we choose the hair brush before operation (the hair should be straight and the root should be straight. ).

    The roller is the main tool for defoaming. It not only discharges the bubbles, but is also responsible for compacting the fibers, and rolling out the resin that satisfies the fiber penetration, so that the difference between the mold resin and the fiber ratio is as small as possible. It is a very important measure to improve the quality of FRP molds and FRP products; on the contrary, the roller shape design on the market now has a horizontal strip shape, which becomes a so-called bubble harvester, which cannot discharge bubbles or remove 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 is the quality guaranteed?

Implementation process of molding process

    We must make good FRP molds to meet the size requirements of the product, with good flatness, high strength, and good mechanical properties. They must pass the implementation of reasonable process and operation techniques. The main materials of FRP molds are resin, fiber, and auxiliary materials. The relationship is very complicated. There are many appearance factors in their reactions, such as temperature, relative humidity, time to complete the operation, etc., so we must adopt some necessary technological means 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 operating specifications, stir the gel coat slowly, otherwise there will be more bubbles, which will affect the quality of the gel coat. For spraying and hand-painting the gel coat, the first layer does not need to be applied too thickly, so that the bubbles in the gel coat will be easily drained, but it must be applied evenly so that when the first layer of gel coat just begins to thicken, The second layer can be applied and scanned. At this time, the thickness of the second layer of gel coat should be about 0.55mm~0.6mm in total. We can also use a 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, which can 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. Let the surface layer and reinforcement layer be laid just after the gel.

    In order to make the quality of the FRP mold to achieve the expected best performance effect, we adopt some necessary methods in the layup process to control the deformation and shrinkage of the entire FRP mold to the minimum, and the mechanical properties are in the best state , Relatively speaking, the overall overall cost will be reduced.

4. The implementation process of strict molding process

    We must make good FRP molds to meet the size requirements of the product, with good flatness, high strength, and good mechanical properties. They must pass the implementation of reasonable process and operation techniques. 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 reactions, such as temperature, relative humidity, time to complete the operation, etc., so we must adopt some necessary technological means 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 operating specifications, stir the gel coat slowly, otherwise there will be more bubbles, which will affect the quality of the gel coat. For spraying and hand-painting the gel coat, the first layer does not need to be applied too thickly, so that the bubbles in the gel coat will be easily drained, but it must be applied evenly so that when the first layer of gel coat just begins to thicken, The second layer can be applied and scanned. At this time, the thickness of the second layer of gel coat should be about 0.55mm~0.6mm in total. We can also use a 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, which can 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. Let the surface layer and reinforcement layer be laid just after the gel.

    In order to make the quality of the FRP mold to achieve the expected best performance effect, we adopt some necessary methods in the laying process to control the deformation and shrinkage of the entire FRP mold to the minimum, and the mechanical properties are in the best state , Relatively speaking, the overall overall cost will be reduced.

    4.1 Batch 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 mat first, because only one layer of glass fiber is used, and the amount of resin is very small, and the overall shrinkage is very small. , Make this layer have enough curing time to shape, then make a layer of fiber. Because the first layer is cured before, and the shape of the next layer is cured by the stable shape of the previous layer, the deformation and shrinkage rate will be much reduced. (Note: After each curing, the surface of the glass fiber reinforced plastic must be roughed and waxed, otherwise it will cause delamination between the layers, which will affect its strength and quality.) The amount of intermediate layers in the future can be increased, and each time you lay 3 to 5 layers , Until the FRP mold is laid to the expected strength requirement.

    4.2 RM method

    In the process of laying the middle layer, we use one felt and one cloth that is chopped mat, and the process of overlapping gingham cloths. Two layers of gingham cloth are used to lay the interlayer. The shear force between the layers is very poor: the chopped mat is used for paving and cutting. , Its fiber line is short, the force direction performance is not concentrated, and it has a large amount of glue. In view of their respective advantages as a complement to their respective shortcomings, the RM method is used to promote the penetration of resin fibers and increase the moment between fiber cloth layers to obtain the best results.

    4.3 45° laying method

    The bending force, top force and torsion force of glass fiber are very poor, and it has only a strong tensile 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 adding 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, one fiber at the right angle is just under 90° bending force and the other is torsion, both of which are in the worst condition of stress. Therefore, the right angle on the product or mold structure Use the 45° laying method to make the two fibers at right angles to form 120°. At this time, we add light pre-stress in the operation process to make the force of the fibers tighten and the product structure stress Get better play.

     Due to business benefits, many manufacturers rush to demold the mold after a short curing time after the mold is laid, and then grind it with sandpaper with water and immediately put it into production after polishing. At this time, the FRP mold is in a state of incomplete curing, the FRP mold has not yet the best strength, the resin has not fully reacted, the stress caused by the shrinkage and deformation of the FRP mold material has not been released, and the product is produced The influence of the heat on the mold will gradually reveal the problems in strength and durability, surface finish, deformation, etc., and then the gel coat, surface texture, and even the gel coat cracks, the layer is white and internally injured, and the mold is warped as a whole. Therefore, the post-curing treatment of the glass fiber reinforced plastic mold is very important. After a constant temperature of 80 ℃ for 3 to 4 hours, the stress caused by the shrinkage deformation of the glass fiber reinforced plastic mold at different angles in the structural modeling can be buffered and released. A complete reaction is obtained at a constant temperature of 80°C, so that it can be demolded in the best state.

     In addition to being more user-friendly, the grinding and polishing of the mold is a key factor that is the quality of the water sandpaper in the water grinding process. A good water matte paper can achieve twice the result with half the effort (now we use water matte paper in addition to MT, there are also Japan, England, Italy, the United States, and the most common is the use of South Korean Eagle Ball brand sandpaper). 600~800# should be used at the beginning of the water mill process. If the mold is too rough, use 400# first. Because I started to use too thick water matte paper, its sand marks were very coarse. The final water scrub time will be much longer. Every time you have to remove the last sand marks, until 1500~2000#, there are no traces of water sand at all. This is a very patient and meticulous process, and it will not start until the process can meet the process requirements. polishing. Use No. 1 polishing water to coat all the molds to be polished. Use wool polishing disc for polishing. Pay attention to the turning of the polishing disc. According to the turning of the polishing disc, bring the polishing water in to achieve the polishing effect. The polishing disc cannot be thrown out of the polishing water. The effect is labor-intensive, time-consuming, and material-consuming. After this process is completed, the mold basically appears shiny. We use No. 3 polishing water again, and we must also pay attention to the above problems. Since the No. 3 polishing water itself has a sealing agent, the following procedures are much simpler (Note: (1), (3) Two grades of grinding and polishing water from American Megiya company).

     Semi-permanent high-efficiency mold release water PMR, it is a better mold release agent, but in the use process should pay attention to adopt some necessary processes, that is, after the mold is polished, PMR must be applied first, and then the coating will be thin. Brush it clean without leaving water marks, because it is difficult to brush it clean after letting it dry. After applying it once or twice, wait for half an hour and then start waxing. According to the waxing process requirements, a new mold It needs to be played several times. Brush very clean every time. This is a very important process requirement. Conversely, waxing first and then applying PMP is meaningless. Finally, we have started to try a new high-efficiency mold release water FREKOTE. From the trial, in addition to having a good mold release effect, low-molecular substances are less volatile. The advantage of no damage to the gloss of the mold is very obvious, but the mold must be fully cured and high-gloss mirror.

     In order for us to make better the process of making FRP molds, it is necessary to carry out tracking management on the number of FRP molds. Sum up the gaps and make continuous improvements to ensure the quality of FRP molds.

Source:https://www.up-resin.com/

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