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Common Quality Problems In SMC Material Process

Jun 20, 2020

MC material molding process is one of the highest production efficiency in the FRP/composite molding process. The SMC molding process also has many advantages, such as: accurate product size, smooth surface, good appearance and size repeatability of products, complex structures can also be formed at one time, and secondary processing without damaging products, etc. However, undesirable defects will also occur during the SMC molding process, mainly in the following aspects

(L) Shortage:

The lack of material means that the SMC molded parts are not completely filled, and the production parts are mostly concentrated on the edges of the SMC products, especially the roots and tops of the corners.

Cause Analysis:

(a) Low discharge volume

(b) Poor fluidity of SMC materials

(c) Insufficient equipment pressure

(d) The curing is too fast.

Production mechanism and countermeasures:

① After the SMC material is plasticized by heat, the melt viscosity is large. Before the crosslinking and curing reaction is completed, there is not enough time, pressure, and volume to fill the mold cavity with the melt.

② The storage time of the SMC molding material is too long, and the styrene volatilizes too much, which causes the flow performance of the SMC molding material to decrease significantly.

③ The resin paste is not saturated with fibers. During molding, the resin paste cannot drive the fiber to flow and cause material shortage. The most direct solution to the lack of materials caused by the above reasons is to remove these molded materials during cutting.

④ Insufficient feeding amount causes shortage of material. The solution is to appropriately increase the amount of feed.

⑤The molding material is packed with too much air and a lot of volatiles. The solution is to increase the number of exhausts properly; increase the feeding area burps appropriately to clean the mold for a certain time; increase the molding pressure appropriately.

⑥ Pressing is too late, the molding material has been cross-linked and cured before filling the cavity. ⑦The mold temperature is too high, and the crosslinking and curing reaction is in advance.

(2) Stomata.

There are regular or irregular small holes on the surface of the product, and the production parts are mostly at the top and middle thin wall of the product.

Production mechanism and countermeasures:

①The SMC molding material is packed with a large amount of air and has a large volatile content, and the exhaust is not smooth; the thickening effect of the SMC material is not good, and it cannot effectively expel the gas. For the above-mentioned causes, it can be effectively controlled by a combination of increasing the number of exhausts and cleaning the mold.

②The feeding area is too large, and it can be controlled by appropriately reducing the feeding area. In the actual operation process, human factors may also cause trachoma. For example, if the pressure is too early, the gas wrapped by the molding material may not be easily discharged, resulting in surface defects of pores on the surface of the product.

(3) Warpage deformation.

The main reason is the uneven curing of the molding material and the shrinkage of the product after demoulding