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The Extrusion Molding Process

Extrusion Molding

Previously, on this blog we discussed two of the three processes used to create custom molded rubber productsinjection molding and compression molding. Today, we talk about the last process, extrusion molding.

What is extrusion custom rubber molding?

Extrusion molding is a manufacturing process used to make products that have a fixed cross-sectional profile such as pipes and hoses.

To create extruded rubber parts, a rubber compound or mixed elastomer is forced under pressure through a die that is shaped like the end product. The material is fed into an extruder, which is a cylindrical barrel that contains a helical screw.

You could liken extrusion to squeezing toothpaste out of the tube. When pressure is applied at the closed end, the paste is forced to flow through the open end, taking on the shape of the opening as it emerges.

In similar manner, the shape of the die used in extruding determines the shape of the tube. Based on the die used, extrusion rubber molding is capable of producing complex shapes (not unlike the way bakers use differently shaped nozzles to create fancy bands of icing for cakes). Shapes that can result from extrusion include T-sections, U-sections, square sections, I-sections, L-sections and circular sections.

There are two forms of extrusion, hot feed and cold feed.

In hot feed extrusion, the stock material being fed into the extruder is pre-heated prior to processing. In cold feed extrusion, the rubber compound is not heated but is fed into the extruder at room temperature. Hot feed extrusion is an older technology that is no longer used to any great extent.

Extrusion may be continuous, producing material as long as 60 ft or more, or semi-continuous producing many pieces.

Following extrusion, the material is stretched to straighten it, and then cooled to form a solid shape.

What are the advantages of using extrusion molding?

Extrusion molding provides the following advantages:

  • Continuous process can produce lengths of up to 60 feet;
  • Consistent cross-section results in the production of complex shapes;
  • High production volumes;
  • Low cost per pound of materials used;
  • Good for producing tube-shaped products such as pipes and hoses.

The two primary advantages of extrusion custom rubber molding are its ability to create very complex cross-sections, and to work materials that are brittle, because the material only encounters compressive and shear stresses.

Mark Tool is a leading manufacturer of custom rubber molded products including those made using an extrusion process. Contact us to learn more about we can meet your unique needs.

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