The technological process of SMC production mainly includes resin paste preparation, pasting operation, fiber cutting, sedimentation and impregnation, resin thickening and other processes. The technological process is as follows
(1) Feeding: add a specified amount of material into the mold as required, and the amount of feeding directly affects the density and size of the product. If the feeding amount is large, the rough edge of the product is thick, the dimensional accuracy is poor, it is difficult to demould, and the mold may be damaged; If the feeding amount is small, the products are not compact, the gloss is poor, and even lead to material shortage and waste products.
(2) Closed mold: even if the male mold and female mold are closed after feeding. When closing the mold, first use fast, wait for Yin, and change to slow when the male mold is in quick contact. The operation method from fast to slow is conducive to shortening the non production time, preventing the scratch of the mold, and avoiding the raw materials in the mold groove from being brought out by the air due to too fast mold closing, and even causing the displacement of the insert and the destruction of the forming rod. After the mold is closed, the pressure can be increased to heat and pressurize the raw material.
(3) exhaust: when molding thermosetting plastics, moisture and low molecular substances are often released. In order to eliminate these low molecular substances, volatile substances and air in the mold, after the plastic reaction in the mold cavity of the plastic mold has been carried out for an appropriate time, the mold can be released for a very short time. Exhaust operation can shorten the curing time and improve the physical and mechanical properties of the products, so as to avoid delamination and bubbles in the products; but exhaust too early, sooner or later, too early Fail to achieve the purpose of exhaust; If it is too late, the gas cannot be discharged because the material surface has been solidified.
(4) Curing: the curing of thermosetting plastics is to maintain for a period of time under the molding temperature, so that the polycondensation reaction of the resin can reach the required cross-linking degree, so that the products have the required physical and mechanical properties. Plastic with low curing rate can also be cured temporarily when the product can be completely demoulded, and then use post-treatment to complete the whole curing process; To improve the utilization of equipment. The molding curing time is usually the pressure holding time, generally ranging from 30 seconds to several minutes, most of which are not more than 30 minutes. Too long or too short curing time will affect the properties of products.
(5) Demoulding: demoulding is usually completed by ejector rod. For products with molding rods or some inserts, special tools should be used to remove the molding rods first, and then demould.
(6) Mold purging: after demoulding, the mold cavity and mold surface are usually purged with compressed air. If the fixture on the mold is tight, it can also be cleaned with a copper knife or brush, or even with a polishing agent brush.
(7) Post treatment: in order to further improve the quality of products, thermosetting plastic products are often post treated at higher temperatures after demoulding. After treatment, the plastic can be cured more completely; At the same time, reduce or eliminate the internal stress of the product, reduce the moisture and volatile matter in the product, which is conducive to improving the electrical performance and strength of the product
