Gasket material must always be matched to the media being sealed. If the fluid and gasket are incompatible, the joint will almost certainly fail prematurely, with costly consequences.
Selecting the right material for an application can be complicated. The risk of chemical attack must always be considered, along with operating temperature, environment and pressures or loads. Some materials swell when exposed to certain fluids, others become brittle or soften, and a few may even dissolve.
When it comes to resisting corrosion and chemical attack, the most versatile gasket material is PTFE, better known as Teflon.
Chemical Resistance of PTFE
PTFE consists of long chains of carbon, with each carbon atom linked to two atoms of fluorine. These carbon-fluorine bonds are so strong as to be almost unbreakable, which makes it resist attack by almost every other chemical, from oils and acids to water and most alkalis. In fact, only fluorides and molten alkali metals (like lithium, sodium, and potassium) will ever attack or corrode PTFE.
Other Properties of PTFE
Besides unrivaled chemical resistance, properties of PTFE making it an important gasket material are:
- Wide temperature range (-450°F to 620°F)
- Soft, conforms readily to rough or irregular surfaces
- Available in FDA-approved grades
In addition, though of limited value for gaskets, PTFE has a very low coefficient of friction.
However, PTFE will creep under load, and lacks good elastic recovery. These limitations are addressed by using filled grades of PTFE. These are stronger, but are not available for food or medical applications.
Alternatives to PTFE Gasket Material
Two other materials with excellent chemical resistance and other good gasket properties are silicone and FKM/Viton. These remain flexible over wide temperature ranges and resist attack by most chemicals other than strong alkalis. (FKM is also vulnerable to ketones like acetone.) However, they have better elastic recovery than PTFE, making them the smarter choice in some applications.
Your Source for Gasket Material
If you need to seal against an aggressive chemical, it’s vital to choose your gasket material wisely. Contact our specialists at 1-800-747-7661, or by using this inquiry form.
