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Seven steps of compression molding

Join Date: 2020-04-27

Compression Moulding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, while heat and pressure are maintained until the molding material has cured. The seven steps of compression molding are as follows

(1) Feeding: Add a specified amount of material into the mold as needed, and the amount of feeding directly affects the density and size of the product. If the amount of feed is large, the product has thick burrs, poor dimensional accuracy, and it is difficult to demold and may damage the mold; if the amount of feed is small, the product is not tight, the gloss is poor, and even a lack of material results in scrap.

(2) Mold closing: Even after the feeding, the male and female molds are closed. Use fast when closing the mold, wait for the negative, and change to the slow speed when the male mold is in quick contact. The operation method of quick first and slow second is helpful to shorten the non-production time, prevent the mold from scratching, avoid the raw material in the mold groove being taken out by the air due to too fast clamping, and even displace the insert and damage the molding rod. After the mold is closed, the pressure can be increased to heat and pressurize the raw materials.

(3) Exhaust: When molding thermosetting plastics, water and low-molecular substances are often released. In order to exclude these low-molecular substances, volatiles, and air in the mold, the plastic reaction in the mold cavity of the plastic mold can be carried out until the appropriate time. Exhaust the pressure to release the mold for a short period of time. Exhaust operation can shorten the curing time and improve the physical and mechanical properties of the product, avoiding the occurrence of delamination and bubbles inside the product; but exhausting too soon, sooner or later, not too early to the purpose of exhaust; too late, because the surface of the material has solidified gas can not be discharged.

(4) Curing: The curing of thermosetting plastics is maintained at the molding temperature for a period of time, so that the polycondensation reaction of the resin reaches the required cross-linking degree, so that the products have the required physical and mechanical properties. Plastics with a low curing rate can also be temporarily ended when the product can be completely demolded, and then use post-processing to complete the entire curing process; to improve the utilization rate of the equipment. Molding and curing time is usually pressure holding and holding time, generally ranging from 30 seconds to several minutes, most of which does not exceed 30 minutes. Too long or too short curing time will affect the performance of the product.

(5) Demoulding: Demoulding is usually done by ejecting the rod. Products with forming rods or some inserts should first use special tools to remove the forming rods, etc., and then demold.

(6) Mold blowing: After demoulding, usually use compressed air to blow the cavity and the mold surface of the mold. If the fixed objects on the mold are tight, you can also clean them with a copper knife or a copper brush, and even use a polishing agent .

(7) Post-treatment: In order to further improve the quality of products, thermosetting plastic products are often post-treated at a higher temperature after demolding. Post-treatment can make the plastic curing more complete; at the same time reduce or eliminate the internal stress of the product, reduce the moisture and volatiles in the product, etc., which is conducive to improving the electrical performance and strength of the product

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