Interested in learning about injection molding? Discover more about it here.
Compression molding is a time-tested, widely used molding process for thermosetting (TS) plastics. Compression molding manufacturers use the technique for applications such as phonograph records, rubber tires and polymer matrix composite parts.
The process, illustrated below for TS plastic, has the following basic steps:
Compression molding for thermoplastics steps: (1) load the charge, (2) and (3) compress and cure the charge between the mold halves, and (4) open the mold halves and remove the part from the cavity
A molding compound’s initial charge can take a variety of forms, such as:
Preheating methods include:
The latter technique is borrowed from injection molding and serves to meter the amount of the charge.
Compression molding presses are vertically oriented and contain two platens to which the mold halves are fastened. There are two types of actuation the presses use:
A hydraulic cylinder usually powers the presses. Compression molding manufacturers can design a cylinder to provide clamping capacities of up to several hundred tons.
Compression molding molds are typically simpler than their injection molding counterparts. However, there are some differences:
Manufacturers must make provisions for heating a mold. They usually accomplish this using:
Compression molds are classified as:
Materials used for compression molding include:
Items commonly made using TS plastic moldings:
Advantages of compression molding for the respective applications include:
The greatest disadvantage for the respective applications is a longer cycle time, which leads to lower production rates when compared to injection molding.
The custom transfer molding process uses a thermosetting charge, or preform, that manufacturers load into a chamber immediately ahead of the mold cavity to preheat it. The equipment then applies pressure to force the softened polymer to flow into the heated mold, where it cures.
Transfer Molding Processes
There are two transfer molding processes:
1. Pot transfer molding: The charge is injected from a “pot” through a vertical sprue channel into the cavity
2. Plunger transfer molding: A plunger injects the charge from a heated well through lateral channels in the mold cavity
Both processes produce scrap called “cull” during each cycle. The leftover material forms in the lateral channels and the well’s base. The sprue in the pot transfer is also scrap material. Because polymers are thermosetting, manufacturers cannot recover the scrap.
(a) Pot transfer molding, and (b) plunger transfer molding. Cycle in both processes is (1) charge is loaded into pot; (2) softened polymer is pressed into mold cavity and cured; and (3) part is ejected.
Sinotech brings you excellent compression and transfer molded parts at competitive rates. Our specialists are dedicated to managing your important project on-site and delivering parts at lower prices while providing the excellent quality, services and terms you expect from a domestic supplier. We invite you to view our motor catalog.
Contact Sinotech today to discover more about our processes. We’d love to hear about your project.
联系客服