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FRP Mold Production-mold Gel Coat

Jun 29, 2020

When manufacturing FRP molds, first choose high-quality mold gel coat. As the surface layer of the mold, the gel coat of the mold requires the cured surface to be dense, with certain strength and hardness. However, due to the influence of the resin matrix of the mold gel coat, the added auxiliary materials, quality control, etc., the final product quality indicators such as leveling, defoaming, viscosity, thixotropy, etc. of the mold gel coat are very different. The gel coat layer produces different defects. Such mold gel coats have higher requirements on the skills of operators during construction, which is reflected in the fact that on-site personnel must adjust accordingly according to the actual situation during construction. High-quality mold gel coat should be spray-type gel coat, with low viscosity, high thixotropy, good defoaming and leveling, and stable curing characteristics. In order to achieve the above purpose, in addition to the use of excellent matrix resins in mold gel coats, it is necessary to add leveling and defoaming substances to improve the leveling and defoaming properties of mold gel coats, but note that these substances are small molecules The substance does not participate in the reaction. At the same time, because of the presence of the solvent, it may cause the appearance of pinholes. Therefore, it is necessary to choose efficient leveling and defoaming additives to avoid the introduction of excessive small molecule substances with a large amount of addition. Therefore, high-quality mold gel coat should be selected and spraying method should be adopted, which can effectively reduce the pinhole in the mold gel coat layer.

        Secondly, the curing system of the mold gel coat is also one of the factors prone to pinholes. Disproportionate accelerators and initiators will be left in the gel coat after the mold gel coat gel coat is cured, and pinholes will form after the mold gel coat gel coat surface is demolded. Excessive curing system or excessively high temperature may cause the gel time of the mold gel coat gel coat to be shortened too much, so that the air brought into the mold gel coat gel coat during the application process cannot escape in time, resulting in the mold gel coat gel coat A large number of micro bubbles exist, and pinholes are formed on the surface of the mold gel coat. When the amount of mold gel coat is small, it is easy to cause disproportionate or excessive addition due to measurement errors. Therefore, it is recommended to use pre-accelerated gel coat. The proportion of accelerator added is more accurate, and the gel time is more stable and reduced. The number of bubbles introduced when stirring the accelerator. It is also easy to control the gel time. Once the over-thick mold gel coat gel coat is sprayed, the bubbles brought in during the operation of the high-thixotropic mold gel coat will not easily escape, often forming pinholes in the gel coat. The proper amount of initiator and accelerator, reasonable gel time, and uniform thickness of the mold gel coat can effectively reduce the pinhole. The quality of the initiator will also affect the quality of the mold gel coat. The high-quality initiator contains less hydrogen peroxide, and less water molecules are generated when the resin polymerization is initiated, thereby improving the curing degree of the mold gel coat and reducing the probability of defects such as pinholes. So as to effectively improve the surface quality such as surface hardness and surface density.

        In the construction of mold gel coat, the surface of the model, the operating environment, the operating method, etc. will also lead to the appearance of pinholes to varying degrees. First of all, as the mold of the mold-product model, the surface quality will directly affect the surface quality of the mold. Loose and rough surfaces are not conducive to the formation of a good gel coat surface. Due to the large surface area of the loose and rough surfaces, it is not conducive to the discharge of tiny bubbles during the construction of the gel coat. For loose and rough surfaces, surface treatment must be used to improve the density and hardness of the surface, so as to improve the surface finish. Secondly, when the model is put into use, the environmental cleanliness of the environment will also cause adverse effects. For example, if dust in the air falls on the surface of the model or falls on the surface of the mold during the gel coat spraying process, there will be hidden quality problems. The cleanliness of compressed air is one of the causes of pinhole defects. Clean and clean air must be used to avoid the generation of pinholes caused by water and gasoline drops.

        Improper construction methods of mold gel coat will also cause pinholes. The chance of pinholes in spray mold gel coat is less than that of hand brush mold gel coat. The main spray mold gel coat has low viscosity, uniform spray construction thickness, easy to control, and more Conducive to the discharge of bubbles. When spraying, it should be carried out in time after the mold release treatment on the surface of the model is completed to avoid the contamination of the release layer. When spraying, the first layer of the first pass should be thinly sprayed, with an interval of 1 to 2 minutes between each layer, so as to facilitate the mold gel coat The bubbles in are discharged. Reduce pinholes. Selecting a mold gel coat with good thixotropy and low viscosity is a necessary condition for fewer pinholes. A good mold gel coat has excellent defoaming and leveling properties. When the viscosity of the mold gel coat is too large, it is best not to use solvents (benzene Ethylene, acetone, etc.). Because the small molecules of the solvent will volatilize to form bubbles, increasing the possibility of pinholes in the gel coat, the best way is to increase the ambient temperature and the temperature of the gel coat to reduce the viscosity of the mold gel coat. Air temperature and environmental conditions: 18℃~30℃ temperature, 35%~65% relative humidity are the best conditions for mold gel coat spraying, too low temperature, too high viscosity of mold gel coat is not conducive to the discharge of bubbles in gel coat, the temperature is too high The gel time of the high-mold gel coat is too short, and the bubbles in the mold gel coat are already gelled without being discharged. These can cause pinholes.

  In summary, the production of pinhole-free molds should be solved from the aspects of the surface of the model, the mold gel coat material and the curing system, operating environment, and construction methods. We can't completely rely on the improvement of a certain aspect, and expect to get an ideal mold surface without pinholes. As one of the important tooling equipment for FRP production, the quality of the surface quality directly affects the quality and production efficiency of the product. A good mold surface can reduce a lot of product post-processing manpower and material resources, shorten the work process, and save the operation The site improves production efficiency, improves the working environment, and reduces labor intensity.

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

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