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How to improve the quality of hand lay-up FRP? Look at the production process

Many friends who have encountered hand-made products complain about the quality stability. It is well known that hand lay-up workers are getting harder and harder, especially skilled technicians. Hand lay-up seems to be the simplest process. In fact, it is the process with the highest technical requirements for workers. People's emotions play a big role in the production process. The fluctuation of product quality is often caused by fluctuations in workers' emotions. How to circumvent these artificial factors? In addition to the selection of materials in the selection of materials, standardization and detailing in the production process, in order to avoid some artificial factors, thereby improving the stability of the product. Today, I will discuss with you how to standardize the production process of the hand lay-up process.


    First, preparation before production


    Site


    The size of the hand lay-up work site shall be determined according to the product size and daily output. The site shall be clean, dry and well ventilated. The air temperature shall be maintained between 15 and 35 ° C and the humidity shall be within 75%. After the finishing and refining section, it is necessary to provide a dust extraction and water spray device. Many domestic enterprises pay less attention to this point, the workshop environment is messy, product trimming and production are in the same area. On the one hand, dust will cause harm to workers' bodies, on the other hand, it will adversely affect the production process such as gel coat spraying. Therefore, having a good production site is very important.


    2. Mold preparation


    Preparations include cleaning, assembly, and release of mold release agents.


    3. Resin glue preparation


    When preparing, pay attention to two problems: 1 to prevent air bubbles from mixing in the glue; 2 the amount of glue should not be too much, and each dose should be used up before the resin gel.


    4. Enhancement material preparation


    The types and specifications of the reinforcing materials are selected according to the design requirements, and are generally cut in advance according to the size of the product.


    Second, paste and cure


    Plaster paste


    Hand layup paste is divided into wet and dry methods:


    1 dry layup


    Use the prepreg as the raw material, first cut the prepreg (cloth) according to the sample, heat and soften the layer, then close it to the mold layer by layer, and pay attention to remove the bubbles between the layers to make it dense. This method is mostly used for autoclave and bag forming.


    2 wet layup


    The reinforcing material is dipped directly on the mold, and is adhered to the mold layer by layer to eliminate the bubbles and make it dense. Generally, the hand lay-up process is mostly layered by this method. The wet layup is further divided into a gel coat layer paste and a structural layer paste.


    2. Hand paste tool


    Hand lay-up tools have a great impact on ensuring product quality. There are wool rolls, bristle rolls, spiral rolls and chainsaws, electric drills, polishing and polishing machines.


    3. Curing


    The curing of the product is divided into two stages: hardening and curing: from gel to curing, it usually takes 24 hours. At this time, the degree of curing reaches 50% to 70% (Baker hardness is 15), which can be demoulded and removed under natural environmental conditions. Curing for 1 to 2 weeks can make the product have mechanical strength, which is called aging, and its curing degree is more than 85%. Heating can promote the ripening process. For polyester glass reinforced plastic, heat at 80 ° C for 3 h, for epoxy glass reinforced plastic, the post-cure temperature can be controlled within 150 ° C. There are many methods for heat curing, small and medium-sized products can be heated and solidified in a curing oven, and large products can be heated by in-mold or infrared.


    Third, demoulding and trimming


    Demolding


    Demolding is required to ensure that the product is not damaged. There are several methods for demolding:


    1 ejection mold release


    The ejector device is pre-embedded on the mold, and the screw is rotated during demolding to eject the product.


    2 pressure release


    There is a compressed air or water inlet on the mold. When demolding, compressed air or water (0.2 MPa) is pressed between the mold and the product, and hammered with a wooden hammer and a rubber hammer to separate the product from the mold.


    3 large products (such as boats) demoulding


    Tools such as jacks, cranes and hardwood wedges are available.


    4 complex products can be manually demolded


    First, two or three layers of FRP are pasted on the mold, and after being solidified, they are peeled off from the mold, and then placed on the mold to continue to paste to the design thickness, and it is easy to be removed from the mold after curing.


    2. Trimming


    There are two types of trimming: one is size trimming and the other is patching.


    1 size trimming


    After the molding, the product is cut to exceed the excess part according to the design size, and generally has cutting piece cutting, water cutting, laser cutting, etc.;


    2 defect repair


    Including perforation repair, air bubbles, crack repair, hole reinforcement and so on.

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