Elastomers are clearly malleable but not flimsy. They’re compressible, not fragile. You see, just because an elastic seal can deform, that doesn’t mean it’s mechanically weak. It’s the same with chemical resistance, a feature elastomer gasket materials possess in abundance. Stretchy cross-linked molecular chains deform and recover while they repel the effects of corrosive chemical attacks. However, to deliver enhanced seal compressibility features, tradeoffs are sometimes made.

A Balanced Set of Gasket Features

By tradeoffs, we’re talking about a loss of one material characteristic while a second property is enhanced. In gasket design, the compressibility factor ranks high, so other design characteristics can fall by the wayside. Well, this design faux pas cannot be permitted, especially on a seal that requires a balanced set of fluid containment attributes. For example, a high level of material compressibility is all very well, but it won’t help if a high temperature weakens the elastomeric bonds. Similarly, a deformable gasket isn’t much good if it lacks an all-important ability to resist harsh chemicals.

Utilizing the Right Elastomer

So the application in question uses high sealing energies, as applied by a series of encircling nuts and bolts, to squeeze an elastomeric gasket. The fluid rushing through the pipes isn’t likely to escape. Looking down the ingredients list of that fluid, however, it contains a corrosive acid. Mechanically sound or not, this caustic chemical will make short work of a seal that doesn’t feature a chemically resistant build. Generally speaking, EPDM and Viton based gaskets provide sound elastomeric resistance. Fluoroelastomers perform well when acids are around. Silicone gaskets, well, they’re more susceptible to acids, but they hold up well when attacked by oils. Likewise, nitrile and neoprene seals remain unaffected when oily substances attack.

Using Chemical Resistance Tables

Complex molecular chains stretch and recover when elastomer gaskets squeeze between two flanges. Importantly, while one part of the chain may stubbornly repel a lubricant or chemical reagent, a second linkage could weaken. Simply put, this is a tricky field of study. Making things worse, there are hundreds of different acids and oils, which will affect different gasket materials in different ways. To determine those effects, we need a chemical resistance table, a datasheet that contains a list of hundreds of chemicals. Running a finger down the table column, we can see how any single chemical will impact a chosen elastomer.

Elastomer science is ruled by hundreds of advanced bonding conventions. Cross-linked and deform-capable, the malleable materials react according to seemingly unfathomable physical laws. Check a gasket datasheet to see if it’s specced as a chemically resistant material. Which oils or acids does it specifically repel? For more information, contact the gasket manufacturer or grab a copy of a chemical resistance table.

Imagine the following unacceptable case study. An O-Ring is seated within an equally sized groove. What’s wrong with this picture? Well, the rubber won’t compress as it’s installed. Instead, the identically sized O-Ring and circular groove create a snug fit. An effective seal can never form. To create that seal, the cross-sectional width and depth of the ring must be sized so that it’ll compress as it’s installed, and here’s why.

Creating an Effective Seal

Generally speaking, it’s true, thicker rubber loops compress and produce better seals because they’re slightly larger than the hardware they’re entering. But engineers don’t work on general principles, which is why this squeezing effect requires intelligent management. Specifically, seal integrity is governed by what’s known as an O-Ring’s squeeze ratio. It’s a figure that’s expressed as a ratio. It can be found by comparing the amount of material deformation that takes place within a rubber ring as it’s pressed into its curving groove. In engineering terms, the free-state cross-sectional density and installation deformation volume are compared and expressed as a ratio.

Deform-Proficient Rubber Matrices

Looking deeper inside the rubber loop, the specially engineered elastomer is seen to gain energy as it’s compressed during the ring seating stage. The rubber matrices squeeze together and absorb energy. In response to this action, the material pushes outwards as it’s pressed into a smaller space. Those surfaces press hard against the hardware groove. In plain English, the rubber forms a formidable seal because that absorbed energy is seeking some kind of outlet. It’s this deformation factor, the inherent elasticity of the compressed O-Ring, that’s measured as a seal’s squeeze ratio. Importantly, by selecting the correct material and ensuring that the product comes with an intelligently selected cross-sectional density, the right O-Ring squeeze ratio is singled out each and every time.

More is better, at least that’s what people are taught. For engineering professionals, that’s not always true. An optimally rated squeeze ratio creates a solid seal. Pushed beyond a certain point, though, the sealing energy is transformed into stress. Friction and seal wear occur when such stresses abide. Worse still, pinch points weaken, the walls of the groove crack, and the seal becomes compromised. To sum up, if the cross-sectional thickness is too small, excess elastic stress causes too much material deformation. Sized to match the hardware groove, seal integrity is woefully inadequate. Finally, with too much squeeze, an overly thick O-ring will weaken, or the walls of the groove will crack. Overstressed, the pinched, worn or weakened seal creates tiny pathways, gaps where pressurized fluids will leak.