Rubber Compression Molding is one kind of elastomer rubber molded process, also which heat up strips of rubber compound (pre-forms) or mixed silicone rubber raw material (free-flowing granular form or a viscous material) in heated mould cavity & chamber in aim to fabricate desired elastomer rubber products by hydraulic press machines.
Compression Molding of rubber strip compound provide a surplus of material to be placed in the cavity, in aim to all cavities filled. Once in place, the mould is then closed, applying both heat and pressure to the rubber raw material (thermoplastics and thermoset resin) and allowing it to fill the cavity. When the cavity is filled, excess pre-form material spills out into overflow grooves. Following this step the rubber is then demolded, usually by hand, leaving us with the molded rubber product.
Rubber Compression Moulding process is also called vulcanization process, is performed at a mold temperature of 350 °F and mold pressure of 100 psi (180 °C and 700 kPa) with curing time about 3mins
Compression Molding Advantages
Removal of the rubber flash (edge) from a molded silicone rubber parts & product can be accomplished in a number of ways. Depending on the material, part size, tolerance demands and quantity deflashing methods commonly include
Transfer molding is a combination of compression molding and gumstock material pushed into a mold under low pressure. Silicone Transfer Mold also called as a simplified rubber injection mould, or an advanced compression mold. There is a pot on the top plate and a ram above the pot. This mold pot is used to contain pre-measured rubber raw material and transfer it to the cavities throug pot runner and sprues.
Raw material silicone rubber are measured and put into the pot. Then mold close. The raw material will tranfer to cavities under high pressure and temperature.
Rubber Injection Molding
Rubber Injection Molding as one of the most efficient rubber molded ways, which is a process that heats the rubber by placing the rubber matterial under significantly more pressure per square inch of cavity surface in molding. Rubber Injection molding is different from plastic molding process where the material are cooled under less pressure.
The injection and injection transfer molding’s high effeciency is mainly because of the material preparation stage. Different from compression molding, injection molding need to mix the materials in bulk and then strip them into continuous approx 1.25 inches wide and 0.375 inches strips. And then the strips are fed into a screw, and the screw will control the appropriate predetermined amount of rubber material to fill the barrel.
Rubber Injection Mold's Benefits
Injection Molding’s Material preparation time is short. Do not need operator to place material in cavities one by one.
Injection Molding’s cure time is short. Becasue the injection screw pre-heats the material before it into cavities, which process decreases the material’s viscosity, so the mateiral can flow into cavities easily.
Rubber Injection Molded’s parts with higher precision and less rubber flashings.
Rubber Injection Molding is suitable for overmolded components
Rubber Injection Molding is an economical process for high volumes and higher precision requirement components.
Minimal material waste compared to Transfer Molding
Transfer Molding's Advantages
Transfer Molding with shorter production cycle compared to Compression Molding.
Transfer Molding can achieve closer dimensional tolerance then compression molding.
Transfer Molding's Defects
Transfer Molding is waste material.
Large amount of flash will occur in the pot after curing, which add more material cost to unit price.
Transfer Molding's mold cost is higher compared to compression mould.
Silicone Transfer Injection Molding is more complex than compression molding, so the mold investment is higher. But it is cheaper than plastic or LSR injection molding.