Compression, Extrusion, and Injection Molding Explained

In the industrial field, rubber is used to create coatings for tools as well as for other parts. Rubber has endless benefits, such as its durability and strength. It can form a composite component by bonding to nearly any material and can be morphed into complicated structures.

Here at Mark Tool, we create custom molded rubber using the following three processes:

Compression Molding

While this is one of the oldest methods for polymer processing, it still carries many benefits. It’s inexpensive and creates little waste, all the while being suitable for manufacturing intricate larger parts.

Compression molding has four stages:

1. First, a high strength, temperature-controlled metal mold is custom-created to produce a rubber product that’s designed to fit specific dimensions.
2. The uncured rubber is then pre-formed to a specific shape and weight that mimics the end product.
3. The pre-formed rubber is placed into the metal mold and forcefully enclosed so that it contacts all areas of the mold. Pressure and heat allow the rubber to move about the entire cavity to form the final product.
4. After the rubber is cured, pressure is released and the custom molded rubber product is ready for removal and use.

Extrusion Molding

This type of molding is used for products like hoses and pipes that have a fixed, cross-sectional profile. Extrusion molding involves using pressure to force a mixed elastomer or rubber compound through a die that is built like the end product--sort of like squeezing toothpaste out of its tube.

Extrusion comes in two forms:

• Cold feed- The unheated rubber compound is fed into the extruder at room temperature.
• Hot feed- The rubber compound is preheated before processing. This is an older method that is rarely used anymore.

The final step in extrusion includes stretching the material to straighten it, then letting it cool into  a solid shape.

Injection Molding

Injection molding is typically associated with thermoplastics and is one of the most cost-effective ways to produce custom molded rubber.

This process forces heated rubber into a highly pressurized mold cavity and involves six different stages:

1. Like compression molding, the first step is creating the metal mold.
2. After the mold is created, a fixed amount of uncured rubber elastomer is fed into the temperature-controlled injection barrel, further heated by a screw-like plunger that’s inside the barrel.
3. Rubber begins to build up in the front of the screw, forcing it backward. The pressure then causes the screw to dip forward and push the rubber through a system of gates, feed runners, and sprues that heat the compound further.
4. The heated mold cures the rubber and the screw gets ready for the next shot.
5. The heated mold is closed by an injection press that applies pressure to keep it shut during the curing and injection cycles.
6. The rubber cools and hardens to the mold’s contour.

These three molding processes are what allow us to create any type of custom molded rubber for your specific project. Contact us today to request a quote!