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What is Compression Molding?

What is Compression Molding?

Compression molding is a process of silicone molding products, and the raw materials need to be mixed and cut manually. The molding temperature reaches to 180 Celsius degrees. This process uses the temperature and pressure of a hydraulic compression molding machine to vulcanize the silicone through the mold, and the mold structure is usually 2 plates, an upper plate and a bottom plate.

Compression molding is usually cost-effective, high yielding and widely used. It's most commonly used for single-color silicone products  and have a great advantage for orders with multi-color and small quantities. It can also be used for products of two-color and dual-hardness silicone products, while the structure is inflexible and restricted. Also, for silicone overmolded with plastic or metal by compression molding process, it requires the overmolded parts temperature resistant shall reach 180 Celsius degrees without deformation.

What is Compression Molding CSR

With a pair of upper plate and bottom plate, depends on product's structure, there might be 3 plates or 4 plates, the cycle time for vulcanization and the mold returning is much longer than Liquid Injection Molding. The raw materials can either be put into the base plate for compression molding, or to be extruded for injection.

Compression Molding Process

At our factory, for custom silicone products, the compression molding processes are as below. 


Raw Materials Preparing → Rubber Mixing → Cutting → Compression Molding→ Inspection →Secondary Vulcanization→  Deflashing→ Inspection → packaging

1. Raw material preparation

The silicone raw materials purchased are all in blocks, usually milky white. At this time, the raw material cannot be directly subjected to compression molding, and it is necessary to add a vulcanizing agent or coloring agent. In the preparation of raw materials, the ingredients must be weighed according to the formula. In order to make the raw rubber and the compounding agent evenly mix with each other, it is necessary to process some materials, such as, fluorescent powder, conductive agent, color master batch.

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2. Rubber Mixing

According to the product requirements, the raw materials and the vulcanizing agent and other additives required are put together, and mxied by the rubber mixing machine. For 20KGS solid silicone material, the general rubber mixing time is about 30 minutes, depending on the weight of the rubber raw materials and the roller gap, the mixing time may be longer.

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3. Cutting

The prepared silicone material is cut to the proper size. Place the cut raw materials on the shelf for a period of time. Leaving it for around 8 hours (PE film protection on both the front and back sides of the raw materials to ensure the silicone materials keep clean).

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4. Compression Molding

While in compression molding, the worker needs to weigh the silicone material, then place the right material into the mold, after the compression mold close, the machine starts heating, venting, holding, and molding.

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5. Inspection

After molding, our quality inspectors will check each product for dirty or missing edges, missing materials, pollution products, broken products, etc. They will take away the defective products and send the qualified products to the next process. For silicone molded products, defective products can only be disposed of as scrap and cannot be put into secondary use.

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6. Secondary Vulcanization

No matter the product needs to be food grade or not, for all custom silicone products processed by vacuum compression molding, we'll do the post curing after inspection, so to eliminate odors and low molecular, which makes the product truly non-toxic.


6. Deflashing

For qualified products, our production team will remove the burr, for sure, the flash will be within in the tolerance required as the corresponding drawing.

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7.Surface treatment

If the product needs to do the surface treatment, for example, UV light treatment, oil spraying, laser engraving, the product will be processed after inspection.

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8. Inspection

The compression molding silicone products are inspected for the last time to pick out the defective products, and the qualified products will be packed.

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9. Packaging

To ensure that the surface of the product is clean, we will use the air-gun to remove the dust, then packing, and put it into the warehouse.

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Before shipment, our quality inspectors will inspect the products for shipment to ensure that there are no problems with the random inspection, the the custom compression molding silicone products can be arranged for shipment.

Compression Molding Silicone Gasket Production Flow

Taking the production processed of food grade water bottle silicone gaskets as an example, here is the Video for checking. 


Custom Compression Molding Silicone Products

Yejia Silicone, as the professional manufacturer of custom silicone products, is experienced in compression molding, liquid injection molding and silicone overmolding. We've produced custom silicone products by compression molding for over 20 years, at the beginning, we mainly produced silicone keypads, silicone keyboard covers and other flexible silicone parts. Nowadays, we can not only produce silicone gaskets, silicone bottle sleeves, silicone protective covers, silicone watch band and other consumer silicone products, but also high precision medical silicone components by compression molding, for example, wound drainage ball.

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If you're looking for compression molding supplier for custom silicone products, please feel free to contact us. We'll reply to you within 24 hours.