SMC materials frequently encountered problems in the molding process and their treatment methods(1)

Everyone knows that the SMC molding process has many advantages, such as: accurate product size, smooth surface, good product appearance and size repeatability, complex structure can also be molded at one time, and secondary processing does not need to damage the product. It can be said that the SMC material molding process is the most efficient one in the glass fiber reinforced plastic/composite material molding process. However, in the SMC molding production process, bad defects will also appear, leading to defective products, which are mainly manifested in the following aspects:
1. Material shortage:
Lack of material refers to the fact that the SMC molded parts are not completely filled, and the generated parts are mostly concentrated on the edges of the SMC products, especially the roots and tops of the corners.
Cause Analysis:
(a) The discharge amount is small,

(b) The fluidity of SMC material is poor,

(c) The equipment pressure is insufficient

(d) The curing is too fast.
Generation mechanism and countermeasures:
①After the SMC material is plasticized by heat, the melt viscosity is large. Before the cross-linking and curing reaction is completed, there is not enough time, pressure, and volume to fill the mold cavity with the melt.
②The storage time of the SMC molding material is too long, and the styrene volatilizes too much, resulting in a significant decrease in the flow properties of the SMC molding material.
③The resin paste is not soaked into the fiber. The resin paste cannot drive the fiber to flow during molding, resulting in material shortage. For the shortage of materials caused by the above reasons, the most direct solution is to remove these molded materials when cutting materials.
④Insufficient feeding amount causes material shortage. The solution is to increase the feeding amount appropriately.
⑤There is too much air and a lot of volatile matter in the molding material. The solution is to appropriately increase the number of vents; appropriately increase the feeding area and burp the mold for a certain period of time; appropriately increase the molding pressure.
⑥The pressure is too late, and the molded material has completed cross-linking and curing before filling the mold cavity. ⑦If the mold temperature is too high, the cross-linking and curing reaction will advance, so the temperature should be appropriately lowered.

2. Stoma
There are regular or irregular small holes on the surface of the product, most of which are produced at the top and middle thin walls of the product.

Generation mechanism and countermeasures:
① The SMC molding compound contains a large amount of air and the volatile content is large, and the exhaust is not smooth; the thickening effect of the SMC compound is not good, and the gas cannot be effectively driven out. The above causes can be effectively controlled by a combination of increasing the number of vents and cleaning the mold.
② If the feeding area is too large, 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 pressurization is too early, it may be difficult for the gas wrapped in the molding compound to be discharged, resulting in surface defects such as pores on the surface of the product.