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Methods to improve the surface quality of hand laid FRP products

 Back to list Source: Yamakawa composite Release date: 09:30, May 12, 2019 Browse: -


FRP Simple molding, excellent performance, rich raw materials, has been more and more used in all aspects of the national economy. Hand lay glass fiber reinforced plastic process (hereinafter referred to as hand lay) has the advantages of less investment, short production cycle, low energy consumption, and can produce products with complex shapes, which occupies a certain market in China. However, the surface quality of hand laid FRP products is poor, which limits the promotion of hand laid FRP products to a certain extent. In foreign countries, the surface quality of hand pasted products is close to or up to grade A, which can be used as interior and exterior decoration parts of high-grade automobiles.

 Hand lay FRP


According to the characteristics of hand lay up process operation and raw materials, the main factors affecting the surface quality of products are as follows: ① resin processability; ② gel coat resin processability; ③ mold surface quality.

one resin The technological property of

Resin accounts for about 55-80% by weight in hand paste products. The properties of resin directly determine the properties of products. In the process of product production, the physical properties of resin determine the production efficiency and product quality. Therefore, the following aspects should be considered in the selection of resin:

(1) Resin viscosity

The viscosity of hand paste resin is generally between 170 and 117 CPS. The range of resin viscosity is wide, which is convenient for selection. However, due to the difference between the upper and lower limits of viscosity of the same brand of resin is about 100 CPS ~ 300 CPS, the viscosity will also change significantly in winter and summer.

By comparing the speed of resin impregnation with glass fiber, the foaming property of resin, the compactness and thickness of paste layer, it can be found that: The lower the viscosity of resin The faster the impregnation speed of glass fiber is The higher the production efficiency The porosity of the product is smaller The uniformity of product thickness is better However, when the temperature is high or the amount of resin is a little more, it is easy to flow glue (or control glue) conversely The speed of impregnating glass fiber is slow Low production efficiency High product porosity Poor uniformity of product thickness But glue control The phenomenon of glue flow is reduced

After many tests, The viscosity of the resin is 200-320 CPS at 25 ℃ It is the best combination point of surface quality, internal quality and production efficiency At this time, the viscosity of the resin is often reduced to a high value in the actual operation. There are usually two ways to achieve this: ① Dilute the resin with styrene Reduce viscosity ② Increase the temperature of the resin and the temperature of the environment to reduce the viscosity of the resin When the temperature is low, increasing the ambient temperature and resin temperature is a very effective way. In general, in order to ensure that the gelation of resin is not too fast, two methods are usually used.

(2) Gelation time

The gelation time of unsaturated polyester resin was 6-21 min (25 ℃, 1% MEKP, 0.5% cobalt naphthenate). If the gel is too fast, the operation time is insufficient, the product shrinkage is large, the exothermic concentration is easy to damage the mold and product; if the gel is too slow, it is easy to flow glue and solidify slowly, and the resin is easy to damage the gel coat layer and reduce the production efficiency.

The gelation time is related to the temperature and the amount of initiator and accelerator. When the temperature is high, the gelation time will be shortened and the amount of initiator and accelerator can be reduced. If too many initiators and accelerators are added into the resin, the color of the cured resin will become darker, or the product and mold will be burned due to the fast reaction, fast heat release and excessive concentration (especially for thick wall products). So, Hand paste operation is usually carried out in the environment above 15 ℃ At this time, the initiator It doesn't need a lot of accelerant Resin reaction (gel, curing) is relatively stable Suitable for hand paste operation.

The gelation time of resin is of great significance to the actual production, The gel time of the resin was 10-18 min at 25 ℃, 1% MEKP and 0.5% cobalt naphthalate Even if the operating conditions are slightly changed, the production requirements can be ensured by adjusting the amount of initiator and accelerator.

(3) Other properties of resin

① The defoaming property of resin is related to the viscosity of resin and the content of defoamer. When the resin viscosity is constant, the amount of defoamer determines the porosity of the product to a great extent. In actual production, accelerant is added to the resin When the initiator is stirred, more air must be mixed in If the defoaming property of resin is not good Before the gel in the air can not be discharged in time There must be more bubbles in the product High porosity Therefore, it is necessary to use the resin with good defoaming property, which can effectively reduce the bubbles in the product and reduce the porosity.

② Color of resin

At present, when FRP products are used as exterior decoration parts with high surface quality, high-grade paint is usually applied on the surface to make the surface of products colorful. In order to ensure the consistency of painting color on the surface of FRP products, the surface of FRP products is required to be white or light color. In order to meet this requirement, light color resin must be selected when selecting resin. Through the screening test of a large number of resins, the results show that the resin color value (APhA) Φ 84 can better solve the color problem after curing. At the same time, the use of light color resin can also easily find and discharge bubbles in the paste layer in time during the paste process, and reduce the occurrence of inconsistency in the color of the internal surface of the product due to the operation error in the process of pasting.

③ Air dryness

In the case of high humidity or low temperature, the internal surface of the product is often sticky after curing. This is because the resin on the surface of the paste layer contacts with the polymerization inhibitor such as oxygen and water vapor in the air, so that there is a layer of incompletely cured resin on the inner surface of the product. On the other hand, it is easy to adhere dust on the inner surface and affect the quality of the inner surface. therefore When selecting resin Attention should be paid to the selection of air drying resin. For non air drying resin Generally, 5% paraffin (melting point 46-48 ℃) styrene solution can be added to the resin at 18-35 ℃ to solve the air drying property of the resin The dosage is about 6-8% of the resin.

2、 Gel coat resin

In order to improve the surface quality of FRP products, the surface of products generally needs a layer of resin rich layer with color. Gel coat resin is this kind of material. Gel coat resin improves the aging resistance of FRP products and provides a homogeneous surface for FRP products, which improves the surface quality of products. Generally, in order to ensure a good surface quality of the product, the gel coat thickness is required to be 0.4 ~ 0.6 mm. In addition, the color of gel coat should be mainly white or light color, and there should be no color difference between batches. Secondly, attention should be paid to the operation performance of gel coat: viscosity of gel coat and leveling property of gel coat. The most suitable viscosity for gel coat spraying is 6000cps The most direct way to measure the leveling property of gel coat is to spray a layer of gel coat on the local surface of the mould which has been demoulded if Gel coat There is a fisheye like shrinkage mark on the layer It indicates that the leveling property of gel coat is not good

The gel coat must be fully stirred before use. After adding the initiation system, it must be stirred quickly and evenly to achieve the best use effect. When spraying, if the viscosity is too high, appropriate amount of styrene can be added for dilution; if the viscosity is too small, spray thin and spray several times more. Besides, Spraying process requires that the spray gun is about 2cm away from the mold surface The compressed air pressure is appropriate The fan of the spray gun is perpendicular to the direction of the gun The spray gun fans overlap each other by 1 / 3 This can not only solve the process defects of gel coat itself, but also ensure the consistency of gel coat layer quality.

3、 Influence of mould on surface quality of products

Mold is the main equipment for FRP products molding. According to the material, mold can be divided into steel, aluminum, cement, rubber, paraffin, glass fiber reinforced plastic and other types. FRP mould It is easy to make glass and steel mold with low cost and easy maintenance.

The surface requirements of FRP mold and other plastic mold are the same, usually the surface of mold is one grade higher than the surface finish of product. The better the mold surface, the shorter the molding time and post-processing time of the product, the better the surface quality of the product, and the longer the service life of the mold. After the mold is delivered for use, in order to maintain the surface quality of the mold, the maintenance of the mold must be done well. Mold maintenance includes: cleaning mold surface, cleaning mold, repairing damaged parts, polishing mold. Mold maintenance timely and effective is the final starting point of mold maintenance, in addition, the correct maintenance method of mold is the key. The following table shows the different maintenance methods and corresponding maintenance results.

Different maintenance methods for different molds are as follows:

① New mould or mould not used for a long time

First of all, clean and check the mold surface, and repair the damaged and unreasonable parts of the mold. Secondly, clean the mold surface with solvent, and then polish the mold surface with polishing machine and polishing paste once or twice after drying. Then finish waxing and polishing three times continuously, then wax again, and polish again before use.

② Mold in use

First of all, the mold should be waxed and polished every three times, and the parts easy to be damaged and difficult to demould should be waxed and polished before each use. Secondly, a layer of foreign matter (possibly polyphenylene or wax) that is easy to appear on the mold surface for a long time must be cleaned up in time. The cleaning method is as follows: use cotton cloth articles dipped in acetone or special mold cleaning agent to scrub (too thick part can be gently scraped off with a force tool), and the cleaned part shall be demoulded according to the new mold.

③ In the broken mold

For the mold that can not be repaired in time, wax block and other materials that are easy to deform and do not affect gel coat curing can be used to protect the damaged part of the mold and continue to use. For those that can be repaired in time, the damaged part must be repaired first, and then cured, at least 4 people (at 25 ℃), and the repaired part must be polished and demoulded before it can be put into use.

The normal and correct maintenance of die surface determines the service life of die, the stability of product surface quality and the stability of production. Therefore, a good maintenance of the mold is necessary.

In a word, the surface quality of hand pasted products will be obviously improved by improving materials and technology and improving the surface quality of dies.

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[text label]: Hand laid FRP products

Editor in charge: Yamakawa composite Copyright: http://potmanhotpot.com/

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