What is Extrusion and Its Different Types?

13 December 2018

Extrusions are discharged through special die assemblies. The elastomers are loaded into extrusion machines, heated and forced at pressure, then they slide through the die section, where they’re shaped into a desired cross-sectional outline. Continuing outwards, like toothpaste from a tube, the die-profiled extrusions assume many functional shapes, including those that have edge trims.

A Side-On Viewpoint

Viewing this gasketing medium from the side, we see its extruded profile. In one case, the synthetic rubber has been heated and pressed through an ‘H’ shaped die. There’s a curved notch on the lower half of the rubber lining, plus a subtly different notch located on the top section. Picture this material formed into a framing shape or a ring. For a custom-fabricated gasket, it precisely fits two mating surfaces because the die was perfectly profiled. For a glazing seal, the material stretches slightly when panes of glass slot into place. And that profile, the ‘H’ shape, isn’t alone. Indeed, there are limitless options here, including U-channel extrusions and hollow-tubed variations.

Extrusions: The Different Types

Materially, neoprene and EPDM rubber gaskets dominate the industry. Silicone variants and Viton alternatives are also available. Whatever the material choice, it must suit its application. Utilizing a die insert, the extrusion equipment profiles the tubular or flat-formed material lengths. U-shaped channels are squared or squeezed into ovals. For tubing seals and D-shaped inserts, there are die plates to accommodate those profiles, too. Essentially, there’s a limitless number of extrusion shapes available, each of which satisfies one of a thousand applications. However, there are material limitations and client parameters to regulate the material/shape selection process. Let’s look at those now.

Shaped By Material Limitations

Unlike geometrical shaping, this form-fitting approach depends on the application domain. For example, glazing extrusions, ones used in the automotive industry, should always source weather and UV resistant rubbers. Likewise, an extruded gasket, perhaps destined to suit some high-altitude aerospace application, won’t satisfy a client if it can’t retain its gasket-compressing capabilities when the temperature turns icy cold. Indeed, unlike pipe face gaskets, extrusions are more geometrically intricate, so a capacity for keeping that shape when attacked by the harshest environmental and/or mechanical forces ranks high here, especially when a potential seal discontinuity represents a substantial application or user hazard.

This is a second but equally relevant branch of the gasketing tree. Instead of die cutting entire shapes from a sheet, the material is pressed by a hydraulically powered piston through a toughened die. Heat and pressure are the driving forces here, and they produce some amazingly feature-rich, cut-to-length seals and gaskets. Arguably more flexible than their ring-shaped gasketing peers, extrusions assume countless cross-sectional profiles.

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