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How to avoid the pinhole problem of FRP mold

Aug 29, 2019

Gel coat

First of all, choose high-quality fiberglass mold rubber coat.

As the surface layer of the mold, the cured surface is required to be compact, with a certain strength and hardness. Due to the influence of resin matrix, added accessories and quality control, the final product quality indexes such as leveling, defoaming, viscosity and thixotropy are very different, and there will be different defects in the coating layer. This kind of rubber coat has higher requirements for the skills of the operators during the construction, which is reflected in the fact that the site personnel must adjust accordingly according to the actual situation. The high quality fiberglass mould rubber coat should be spray coating, 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 resin, leveling and defoaming substances need to be added to improve the leveling and defoaming properties of the rubber coat, but note that these substances are small molecular substances that do not participate in the reaction. At the same time, because of the presence of solvent, it may lead to the emergence of pinholes, so it is necessary to choose efficient leveling and defoaming aids to avoid the use of more addition and the introduction of excessive small molecular substances. Therefore, we should choose high-quality fiberglass mold rubber coat, using spraying method, so that we can effectively reduce the pinhole in the mold rubber coating layer.

Secondly, the curing system of rubber coat is also one of the factors which are easy to produce pinholes.

After the rubber coat is cured, the excess part remains in the rubber coat, and the pinholes are formed after the demoulding of the rubber coat surface, the out-of-proportion promoters and initiators will remain in the rubber coat after curing and the excess part will remain in the rubber coat after curing. Excessive curing system or too high temperature can easily shorten the gel time of the rubber coat, so that the air brought in the application process can not escape in time, resulting in the existence of a large number of micro bubbles in the rubber coat, and pinholes are formed on the surface of the rubber coat. When the amount of rubber coat is small, it is easy to cause the addition amount to be out of proportion or too much due to the error of measurement, so it is suggested to use pre-promoting rubber coat, the addition ratio of accelerator is more accurate, and the gel time is relatively stable. The number of bubbles is reduced when the accelerator is stirred. It is also easy to control the gel time. A spray too thick rubber coat, in the process of operation in the high thixoplastic rubber coat brought in the bubble will not be very convenient to escape, often forming the pinhole in the rubber coat. Proper amount of initiator and accelerator, reasonable gel time and uniform coating thickness can effectively reduce the pinhole. The quality of the initiator will also affect the quality of the rubber coat. The high quality initiator contains less hydrogen peroxide and less water molecules when the resin polymerization is initiated, which improves the curing degree of the rubber coat and reduces the probability of pinhole and other defects. In order to effectively improve the surface hardness and surface density and other surface quality.

Gel coat2

In the construction of rubber clothing, the surface of the model, operating environment, operating methods and so on will also lead to the emergence of pinholes to varying degrees. First of all, as the mould of fiberglass mould-product model, the surface quality will directly affect the surface quality of fiberglass mould. The loose and rough surface is disadvantageous to form a good rubber coating surface, because the loose and rough surface area is not conducive to the discharge of small bubbles in the process of rubber coating construction. The loose and rough surface must be treated to improve the density and hardness of the surface in order to improve the finish of the surface. Secondly, when the model is put into use, the degree of air cleanliness of the environment will also cause adverse effects, such as the dust in the air falling on the surface of the model or falling on the surface of the fiberglass mould together in the process of rubber coating spraying, which will cause quality risks. The clean degree of compressed air used for respraying is one of the reasons for pinhole defects. Clean and clean air must be used to avoid pinholes caused by water gasoline droplets and other pollution.

The improper construction method of rubber coat will also cause pinhole, the probability of pinhole produced by spraying rubber coat is smaller than that of hand brush rubber coat, the viscosity of main spraying rubber coat is low, the thickness of spraying construction is uniform and easy to control, which is more beneficial to the discharge of bubbles. When spraying, it should be carried out in time after the demoulding treatment of the model surface is completed, and the pollution of the release layer should be avoided. When spraying, it should be sprayed thinly on the first layer, with an interval of 1 to 2 minutes between each layer, so as to facilitate the discharge of bubbles in the rubber coat. Reduce pinhole production. The choice of good thixotropism, low viscosity is a necessary condition for less pinholes, a good rubber coat has excellent defoaming and leveling, when the viscosity of fiberglass mold coating is too high, it is best not to use solvents (styrene, acetone, etc.) to dilute. Because the small molecules of the solvent will volatilize to form bubbles, the best way to increase the possibility of pinholes in the rubber coat is to increase the ambient temperature and the rubber coating temperature to reduce the viscosity of the rubber coat. Air temperature and environmental conditions 18 ℃ to 30 ℃ temperature, 35% to 65% relative humidity are the best conditions for rubber coating spraying. Too low temperature and too high viscosity are not conducive to the discharge of bubbles in the rubber coat, and the gelation time of the rubber coat with too high temperature is too short. In the gummed coat, the bubbles are gelled without being discharged. All of these can lead to the production of pinholes.

To sum up, the manufacture of non-pinhole FRP mould should be solved as a whole from many aspects, such as the surface of the model, mold glue coating material, initiation and curing system, operating environment, construction method and so on. Can not rely entirely on a certain aspect of improvement, and expect to get an ideal die surface without pinholes. As one of the important tooling equipment in FRP production, the surface quality of the mould directly affects the quality and production efficiency of the product. A good mold surface can reduce a lot of manpower and material resources after the product, and shorten the work flow.The operation site is saved, the production efficiency is improved, the working environment is improved, and the labor intensity is reduced.