What is the production process of smc products, let's learn more about it today.

1、Preparation before pressing

    (1)Quality inspection of SMC

    The quality of SMC sheet has a great influence on the molding process and the quality of the products. Therefore, it is necessary to know the quality of the material before pressing, such as resin paste formula, resin paste thickening curve, glass fiber content, glass fiber infiltrant type. Single weight, film peelability, hardness and quality uniformity, etc.

    (2)Cutting

    According to the structure and shape of the product, the location of the material to be added, the process decides the shape and size of the sheet cutting, makes the sample, and then cuts the material according to the sample. The shape of cutting is mostly square or round, and the size is mostly 40% to 80% of the projected surface area of the product. In order to prevent the contamination of external impurities, the upper and lower films are only removed before loading.

    (3) Preparation of equipment

    ①Familiar with the operating parameters of the press, especially adjust the working pressure and the running speed of the press and the parallelism of the table.

    ②Mold installation must be horizontal and make sure the installation position is in the center of the press table. Clean the mold thoroughly and apply mold release agent before pressing. Use clean gauze to wipe the mold release agent evenly before adding material so as not to affect the appearance of the products. For new molds, oil must be removed before use.

2、adding material

    (1)Determine the amount of material to be added

    The amount of material added to each product in the first pressing can be calculated according to the following formula amount of material added (g) = product volume (cm?0?6) X 1.8 (g) 

(2) the size of the material area to determine the material area, directly affect the degree of compactness of the product, the material flow distance and product surface quality. It is related to the flow and curing characteristics of SMC, product performance requirements, mold structure, etc.. Generally, the material addition area is 40%-80%, too small will lead to glass fiber orientation due to the flow is too long. Reduce the strength, increase the ripple degree, and even can not fill the mold cavity. Too large, it is not conducive to exhaust and easy to produce cracks inside the product.

(3) Charging position and method

    The position and way of charging directly affect the appearance, strength and orientation of the products. Usually, the charging position of material should be in the middle of the cavity. For non-symmetrical and complex products, the charging position must ensure that the material flow reaches all ends of the mold cavity at the same time during molding. The charging method must facilitate exhaust. When stacking multiple layers of sheets, it is best to stack the blocks in a pagoda shape with a small top and a large bottom. In addition, the blocks should not be added separately, as this will result in air entrapment and fusion zones, which will lead to a decrease in the strength of the product.

3. Forming

When the material block enters the mold cavity, the press moves down quickly. When the upper and lower molds match, the required molding pressure is slowly applied, and after a certain curing time, the product is formed. During the molding process, various molding process parameters and press operating conditions should be selected reasonably.

    (1) Molding temperature

    The temperature of molding depends on the curing system of the resin paste, the thickness of the product, the production efficiency and the complexity of the product structure. The molding temperature must ensure the smooth initiation and cross-linking reaction of the curing system, and achieve complete curing.

    Generally speaking, the molding temperature chosen for products with large thickness should be lower than that for thin-walled products, so as to prevent excessive heat accumulation inside the thick products at too high a temperature. If the thickness of the product is 25-32mm, the molding temperature is 135-145℃. And thinner products can be molded at 171℃.

    The increase of molding temperature can shorten the corresponding curing time; conversely, when the molding temperature decreases, it is necessary to extend the corresponding curing time. The molding temperature should be selected as a trade-off between the highest curing speed and the best molding conditions. It is generally believed that the SMC molding temperature is between 120-155 ℃.

    (2) Molding pressure

    SMC molding pressure varies with product structure, shape, size and the degree of SMC thickening. Simple shape products only need 5-7MPa molding pressure; complex shape products, molding pressure can be 7-15MPa. The higher the degree of SMC thickening, the higher the required molding pressure. The size of the molding pressure is also related to the mold structure. The molding pressure required for vertical parting structure mold is lower than that for horizontal parting structure mold. A mold with a smaller gap requires a higher pressure than a mold with a larger gap.

　　In short, the molding pressure should be determined by considering various factors. Generally speaking, SMC molding pressure is between 3-7MPa.

    (3) Curing time

    SMC curing time at molding temperature (also called holding time) and its nature and curing system, molding temperature, product thickness and color and other factors. Curing time is generally calculated by 40s/mm. For more than 3mm thick products, every 4mm increase, the curing time increased by lmin.

4、the operation of the press

    Since SMC is a fast curing system, it is very important to close the press quickly. If the press closes too slowly after adding material, then it is easy to appear on the surface of the product pre-curing patch, or produce a lack of material, or the size is too large. While achieving fast closing, the closing speed of the press should be carefully adjusted at the end of the press stroke to slow down the closing process and facilitate the exhaust.