Vulcanized materials are exposed to high-temperatures and special additives. Essentially, these curatives function as cellulose binding agents. In gasket processing, the process adds tensile strength to the hard, durable rings, plus mechanical resistance. The treated gaskets endure when strong compressive forces are applied, and they’re equipped to deal with material damaging abrasive actions. Let’s look at some common usages for these vulcanized products.
Defining Material Characteristics
Take a closer look at a table full of vulcanized rubber gaskets. Some are thicker than others, so they’re rated to handle compressive flange stress. Also, on the same desk, there are coloured and graded vulcanized materials. In plain terms, the source fibre varies from one grade to the next. For instance, cotton pulp is a common fibre type, as is wood pulp and other cellulose-rich substances. Durable by nature, the gaskets are pressed, calendered, and dried until they suit a nominated application.
Electrically Graded Seals
Known as “fish paper” by industry insiders, this thin vulcanized material is dimensionally stable. Proven as an extremely flat gasketing solution, the die cut substance is commonly used as an arcing shield and dielectric. This time around, instead of pressurized fluids, the application base evokes images of electrical substations, of high potential differences and dangerous electrical charges. Cut to shape, the vulcanized fibre forms the insulation on high voltage transformer coils and grid distribution insulation.
Commercial Grade Gaskets
Made almost entirely of crushed cellulose, the sheet material arrives laminated in plastic. The homogenized material won’t separate, not even in water, and it’s a natural fit for the petrochemical sector. Lacking chemical resins, the gaskets are hard and chemically pure. Taking those two features into account, the seals slot into place on automobile fuel and lubricating systems, solvent storage facilities, and petrochemical processing plants. For further material strength, the fibres can be blended with cork granules.
Motor vehicle engines kick out great quantities of mechanical energy. Cylinders rise and fall, crankshafts spin, and drive trains engage wheels. In the cylinder heads, die cut vulcanized fibre gaskets contain the lubricating oil and intense kinetic forces. Back at the electrical transformer, similar energies are in motion. This time around, however, its electrical power, not kinetic energy, that’s testing the sealing strength of the gasket. After all, the cooling medium inside that transformer is oil, a fluid that would compromise most other electrical dielectrics and insulators.
Employed heavily in the automotive and electrical industry, vulcanized fibre gaskets are also used as high-strength petrochemical seals and machine cylinder gaskets. Expect to see them in their sealed plastic bags as red rings, although they also come in several other colours.
Caustic chemicals cause strong materials to smoke and sizzle. Even vulnerable metals experience fatigue and corrosion when a particularly concentrated alkali or acid attacks. If corrosive chemicals can eat durable metals, what chance does a gasket stand of enduring such an attack? To answer that question, read on and learn about the specialized sealing materials that are capable of enduring these aggressive chemical attacks. Let’s begin with sulphuric acid.
Polytetrafluoroethylene is known as Teflon by most. It’s a synthetic polymer that’s equipped with a good-to-moderate acid and alkali resistance feature. Modified PTFE adds exotic fillers to the fluoropolymer backbone so that the soft gasketing material gains mechanical strength.
Ethylene Propylene Diene Monomer
Although EPDM is vulnerable to oil-based fluids, it’s a good candidate for a chemical processing system that’s loaded with salts, acids, and alkalis. For that reason, an engineer clearly wouldn’t select this material as a petrochemical sealer, but the selection process would quickly skip to EPDM if the chemical base was an aggressive chemical. Incidentally, PTFE envelopes are known to further reinforce the capabilities of this gasket material.
This neutral element doesn’t react to the presence of strong chemicals. Instead, the exfoliated flakes withstand high pressures, temperature extremes, and caustic chemical loads. However, graphite is a soft material, which means it won’t perform well when large compressive forces are applied. To solve this issue, steel inserts or wires are added to the carbon base.
Adopting Metal Gaskets
When polymers and fibres don’t work, metal gaskets take up the slack. However, there are countless options here, and some metals will react unfavourably when they’re attacked by a specific chemical. For example, copper and brass are both superior choices, but they will fail if the liquid stream contains an oxidizing agent. Steel is another option, but some ferrous-heavy gaskets are known to corrode when super-heated oxidizing fluids are at hand. Select an alloy that won’t corrode or harden when a selected chemical base receives a heat-induced kick.
Then there are the composites, the gaskets that mix-and-match these different materials. EPDM is a logical choice as a harsh chemical seal, but the ring of material works better when it’s covered in a PTFE envelope. Certain rubbers are moderate chemical resistors, but they gain strength when they’re bound with aramid fibre. Likewise, carbon flakes are mechanically soft but chemically inert. Just add metal to the flexible graphite to equip the gasket with strength. Glass-reinforced Teflon or metal, alloy or metal-reinforced polymer, the materials all defy the oxidizing effects of strong chemicals. But remember, this feature can only be demonstrated if the chemical stream is known.