The engineering label FKM is a designation, a term that describes a group of durable fluoro rubbers. Branded as Viton, the synthetic material is a capable gasketing rubber. Consider the superior high and low-temperature resistance properties here, the aptitude for enduring the kind of chemical attacks that would quickly lay waste to a standard gasketing solution. FKM endures, even when corrosive fluids attack.
Hangs Tough When Caustic Fluids Attack
Classed by American engineering groups as a specialized fluoroelastomer category, FKM compounds are designed to provide outstanding material durability. The ASTM (American Society for Testing and Materials) appraised synthetic holds firm and functions without issue when a contained fluid is boiling hot or freezing cold. Corrosive solvents and caustic chemicals pass through the gaskets without eating away the rubber. Even ozone can’t undermine the toughened properties of fluoropolymer seals, nor can the lubricating or hydraulic oils that are known to cause seal fatigue.
Loaded with Upper-Limit Endurance
Granted, most gasket families are fabricated from the ‘right stuff,’ but this gang of rugged rubber compounds can’t match the elastomeric characteristics of Viton, a known FKM. For this synthetically enhanced polymer form not only resists such challenges, it retains the original shape of the gasket. That’s an important feature. After all, gaskets can function when they’re exposed to caustic fluids, but few of these materials have the structural strength to entirely defeat such form-damaging influences. Exposed to such corrosive fluids, non-fluoride gaskets swell and distort. As for a comparable FKM compound, this synthetic sealing material won’t collapse.
Determining Specific Applications
Picture a Viton gasket handling 200°C of vessel boiled heat. Then, out in a cryonics facility, the same FKM gaskets are capably handling -40°C of super-chilled fluid. Meanwhile, aerospace applications employ these fluoroelastomers in their hydraulic systems and lubricant lines. The oil doesn’t impact the gasket, so high-altitude wing flap operations are safeguarded. Biofuels or regular fuels, chemical plants or oil refineries, the gasket material properties of an FKM based seal are well recognized. Still, as with any other polymer, there are different types of FKM on the market. Know specific flow conditions before sourcing a potential synthetic rubber product, one that’s based on this robust synthetic rubber.
FKM gasket material properties highlight some seal challenging applications. In aerospace technology, the fluoropolymer seals install as ideal high-altitude, cold climate gaskets. They also channel lubricating oils and hydraulic fluids. At the other end of the spectrum, FKM gaskets operate as high-endurance ‘O’ rings and general application seals in the most caustic industrial settings, even those that channel highly corrosive acids.
Even though the label may seem unfamiliar, PTFE gasket materials exist throughout the food sector. Sure, you’re not going to see PolyTetraFluoroEthylene promoted in many kitchen brochures, but what about Teflon? That’s just another label for this chameleon-like material, a brand name that’s well-known as a non-stick cookware coating. As for PTFE as a gasket material, what benefits make Teflon a superior flange sealant when the food industry comes calling?
PTFE Gasket Materials: Scouring for Benefits
Well, non-stick benefits aren’t relevant here, but what about a talent for temperature resistance? PTFE is fabricated to endure when the fluid temperature hits 200°C. Considering the elevated temperatures found in the various food industries, that’s an important property. Furthermore, the gaskets will maintain their key mechanical characteristics when they’re called into service in a freezer. Approximately minus 70°C of frigid cold won’t trouble a Teflon seal. Of course, several other gasket families are similarly gifted. What about chemicals, then? Aren’t corrosive chemical compounds an issue in this industry?
Dealing a Blow to Corrosive Compounds
If you’ve never considered the corrosive conditions in the numerous food industries, now would be a good time to start. Sure, there are caustic cleaning agents aplenty, but they’re not the compounds you should be worrying about. There are acids in fruits, plus more acids in the blood and soft tissues that break free of various animal products. If time has its way, those relatively weak fluids will break down a substandard gasket. PTFE seals endure, even when a concentrated acid or alkali seeps into the waste discharge line. Incidentally, this could be a pressure vessel construct, this scenario described here. After all, pressure vessels raise the boiling temperature of water, which means the contained food cooks faster. If that seal is sustained, no matter the pressure, temperature, or acidity of the contents, then all pathogens are killed as the dish concludes cooking in no time at all.
The densely woven carbon and fluorine atoms present a united front. In other words, that non-stick surface does not break down. This feature ensures biological inertness, so the food streaming across the PTFE gasket is not tainted or spoiled, no matter how tortured that sealing product becomes. Run a finger down those properties, past food neutrality, temperature and chemical resistance, and superior compressibility. Those features and functions make Teflon a natural choice for many industries, but it’s the food industry that really benefits from those material attributes. Finally, there are ‘filled’ Teflon variants, products that tune these food industry properties so that its food handling capabilities are maximized.
What factors affect gasket performance when that product is utilized in a high-pressure vessel? Think about it for a moment. Imagine a horizontally oriented storage unit and the seals that secure a discharge port or an access hatch. What’s the first thing we notice when these rounded ports come into view? It’s the encircling ring of bolted fasteners, a feature that somehow influences the maximum variable pressure threshold of the gaskets.
Explaining Pressure Variability
Constants are welcome elements in any engineering discipline. They’re nice and easy to predict. Unfortunately, there are typically score of variables in motion at any given moment when a real-world engineering event is underway. Furthermore, if the engineered systems are responsible for a fluid, then the variable number swells as strange dynamic forces have their way. In high-pressure vessel design, rolled sheet metal panels and welded seams contain those dynamic forces, with a series of auxiliary fittings and pipes also channeling the fluid load when the liquid is moved elsewhere. Gaskets are the glue that hold the access plates and flange connectors securely in place on and around the storage vessel. How, then, do these seals react to the pressure variables we’ve briefly summarized so far?
Maximum Variable Pressure Ratings and Gasket Behaviour
As described earlier, one of the more immediate performance factors is identified on sight. It’s the mechanically applied torque, the pressure applied on the gasket material by the ring of fasteners. That steely band of bolts is perceived as a bolt load versus gasket load issue, a relationship that alters the elastic properties of the seal. Dependent on bolt torque, the stress placed on the port seal material will also plastically deform the gasket and produce a subsequent shift in the gasket’s spring index. Do these hampered performance features mean danger is in the air? Yes, to be absolutely blunt, the material changes will create an opportunity for a sealing defect. Picture a pressure increase. The gasket compresses, which it should, but if its maximum variable pressure rating isn’t satisfactory, then its compromised plasticity attribute will stop the seal from ‘springing’ back after the loading event has passed.
Leakage occurs if the gasket can’t vary its shape to accommodate this maximum variable pressure feature, so the selected material must be elastically and plastically designed to ensure full dimensional expansion after the fluid loading event has elapsed. By design, there are engineering equations that establish a required mutability feature within the sealing material. They add fastener load, material type, fluid pressure characteristics, and other pressure vessel-related criteria to complex formulas so that the seal always performs at its adaptable best.
How does the term ‘High-Pressure Vessel’ impact gasket design? For openers, this is an engineering scenario that implies a substantial stress factor. The pressure, if it were to be released, would be dangerously high, perhaps even explosively destructive. If that pressurized fluid is to be reliably contained at each and every vessel seam, capable gasket materials must be employed then correctly installed. What exactly are the best materials for this job?
Choose Metallic Strength
Strong elastomers equipped with a fluoropolymer backbone compress and then hold their shape when the upper end of the medium pressure scale is realized. Equally resilient carbon seals and mineral fibre inserts provide adequate jointing properties when they’re moderately stressed, plus they retain their strength when the fluid temperature climbs high. For true high-pressure resistance, however, it’s metal that gets the recruitment call. Pure metal rings, alloy gaskets with graphite inserts, and even specially profiled ceramic-packed rings fill this gasketing family with metallurgically established durability. Let’s check out those solid metal gasket materials.
A Stronger Gasket: Alloys and Pure Metals
Picture metal seals as the ultimate high-pressure sealing solution. Sure, at least initially, the alloys seem too rigid and too unyielding, but all metals include a certain degree of elasticity. That slight amount of malleability acts just like the compression feature inside an elastomeric seal, except the feature is far more capable as a stress mitigation mechanism. Obviously, softer alloys have a strong presence here, with bronze and copper providing a fluid-resistant base, especially when the conveyed fluids have a corrosive ingredient. Higher up on the pressure spectrum, its aluminium and stainless steel that provide more strength, yet these alloys still have a slight amount of elasticity locked inside their structural form so that they perform superbly in their gasketing duties. Again, these strong yet slightly material-soft alloys are designed to handle intense fluid pressures and just as severe temperatures.
What could be better than solid steel as a gasket material when the fluid pressure is transferring massive quantities of stress? In place of that dense ring of metal, there are specially profiled metal gaskets, products that handle blow-out stress and transient pressure spikes, among other things. They use corrugated layers and grooves to manipulate the compressible characteristics of the seal. Jacketed variants push that principle in a different direction by adding special fillers, including graphite to the mix. Finally, consider spiral wound gaskets, a semi-metallic solution that uses one or more V-shaped inserts to centre the ring and add resilience to gasket materials for high-pressure vessels.
Synthetic fiber gaskets are imbued with specially tailored properties. A long list of man-made materials fills this category. They resist corrosive fluid attacks from specific acid strains, food types, or chemical compounds. Mechanically sound, the material structure of a calendered synthetic fiber is designed to withstand flange compression extremes and to handle large temperature fluctuations. With that being said, maybe we should take a closer look at this manufactured material.
What Are Synthetic Fibers?
Picture synthetic fibers as man-made materials, as the plastic and glass-based filaments that are built with a toughened molecular backbone. Fluoropolymer bonds and strong thermoplastic linkages create gasket sheets that deliver superior physical properties and custom-manufactured fluid handling traits. PTFE is a popular source for these synthetic strands, but there are many proprietary products, brand names that contain unique material characteristics. Cut by die cutting equipment, these synthetic filaments can be tailored to fit any conceivable sealing application.
Examining the Manufacturing Process
Special blends of rubber and aramid act as a structural framework for the exotic strands. They bind together to form long sheets, at which point they’re die stamped into synthetic fiber gaskets. Again, this process varies from one manufacturer to the next, but a binding agent is regarded a critical part of the manufacturing phase, for it bonds those toughened filaments in place. The sheets are loaded with a blend of graphite, glass, PTFE, and other synthetic filaments. The exact mix ratio is managed by the manufacturer so that the artificial material specifically accommodates a preordained fluid medium.
Synthetic Fiber Gaskets: Assorted Applications
If a data sheet filled with operational conditions impedes the adoption of a natural gasketing material, then synthetic fiber gaskets are on hand to take up the slack. Calendered and bonded to rubber or cork, these manufactured material seals serve the aerospace and automobile industry as fuel and lubricant-resistant seals. They exhibit excellent dimensional stability, even when the flange fastening pressure bears down with great compressive strength. A minor change in the formula, a substituted graphite base or man-made felt binding agent, is enough to alter a fluorocarbon stranded gasket group and its subgrouped product lineage so that the next iteration in the product inventory seals a solvent based fluid or a caustic chemical compound.
Every property assigned to a group of synthetic fiber gaskets is alterable. Controlled by the manufacturing process, the Teflon-strengthened bonds and their brand-determined siblings are endowed with a superior compressibility feature, plus a finitely adjustable filament base, one that can be intelligently adjusted to withstand any material type, pressure, or temperature variance. After the artificially manufactured strands are bonded to rubber or cork, the calendered sheets are readily cut up into ranks and rows of dimensionally stable gaskets.