by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Auto molding PTFE seals and seats offer a wide variety of benefits, especially for high-volume production runs. In this blog post, we cover some background on both PTFE and auto molding (also known as compression molding) and discuss why this particular manufacturing process is often preferred by engineers for both seals and ball valve seats.

PTFE for Seals and Ball Valve Seats

One of the popular materials for both seals and ball valve seats is PTFE, often referred to by its trade name Teflon. PTFE has extremely low friction, is self-lubricating, and exhibits no stick-slip behavior. It is also known for its outstanding chemical resistance and wide operating temperature range. PTFE offers a wide temperature range, good stress recovery, and excellent dimensional stability. In addition, PTFE is hydrophobic and non-wetting.

PTFE has been found an ideal material for ball valve seats and seals for a wide variety of applications and industries. It is well known for its excellent performance in harsh environments involving extreme temperatures, high pressures, and corrosive media. Furthermore, PTFE is available in FDA-approved grades.

Auto Molding PTFE Seals and Seats

Auto molding, also known as compression molding, is a versatile and commonly used manufacturing method for polymers, including PTFE. In this process, a pre-heated, carefully measured polymer charge that consists of granules, a putty-like mass, or a preform (whose size and shape are similar to the final part) is placed into the bottom half of a heated mold. 

The top half of the mold is then closed and pressurized via a hydraulic ram to compress the polymer charge and force it to flow through the mold. Heat and pressure are maintained until the part has cooled. At that point, the part is removed from the mold.

The molds themselves are machined from steel and account for factors such as shrinkage, molding compound flow, ejector pins, and the size and positioning of channels. Molds typically comprise the main cost in auto molding.

Advantages of PTFE Auto Molding for Seals and Seats

There are a variety of advantages for PTFE auto molding for high-volume production runs compared to other manufacturing methods such as injection molding and machining

  • Cost-effective
  • Minimal waste
  • Consistent, precision components
  • Avoid issues found in injection molding and machining

Cost-Effective

There are several ways that PTFE auto molding (or compression molding) can be cost-effective. For example, the essential equipment and tooling are not as expensive as other options such as CNC machining or injection molding. The heating requirements are also significantly less than injection molding, which means less energy is required to make parts–and PTFE injection molding does require high temperatures. The tooling for auto molding, especially when it comes to high volume production runs, involves two-part molds that, depending on part size, can be configured to manufacture multiple seats or seals at once. 

The costs of the molds primarily depend on the geometric complexity of the component. For example, high tolerances, difficult geometries, undercuts, and similar design factors are the primary cost source. And depending on the size of the design and the capacity of the auto molding equipment, it may be possible to mold two or more parts simultaneously.

Minimal Material Waste

A dual benefit of auto molding PTFE components is the amount of plastic used. A carefully measured charge of softened PTFE is used in compression molding, and there is minimal waste of material. Machining is considered a material removal process where excess material is cut away to generate the final part, leading to wasted material. 

Material waste is especially obvious for conical geometries when significant material must be removed. This, however, is never a problem with auto molding, which means material costs are going to be much less for medium to high volume production runs. More expensive engineering polymers such as virgin and filled PTFE can lead to noticeable cost savings, especially in the cast of high-volume production runs.

Avoids Issues Found in Other Methods

Auto molding results in components with far more consistent mechanical properties than the injection molding process. Because the mold is kept at a predetermined temperature until the part has cured, it avoids the issues with warping that come with a non-uniform cooling rate. Auto molding also avoids sink marks, ejector pin marks, excessive flash, and unfilled sections.

Compared to machining, auto molding avoids the issues that can develop in machined polymer parts, such as localized heat build-up, internal stresses, and tolerance issues arising from deflection rather than cutting. Machining plastics depends heavily on the stiffness of the part being molded instead of the stiffness of the cutting tool (as is the case with metal machining).

Also, note that auto molding works exceptionally well for PTFE blends with additives such as glass, carbon, graphite, and others.

Conclusion

For high-volume production, one of the best options for manufacturing PTFE seals and seats is auto molding. If you are interested in evaluating your options for PTFE seals, seats, or gaskets, contact the specialists here at Advanced EMC. We can help you every step of the way, from material selection to testing to manufacturing. 

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