Extrusions are discharged through special die assemblies. The elastomers are loaded into extrusion machines, heated and forced at pressure, then they slide through the die section, where they’re shaped into a desired cross-sectional outline. Continuing outwards, like toothpaste from a tube, the die-profiled extrusions assume many functional shapes, including those that have edge trims.
A Side-On Viewpoint
Viewing this gasketing medium from the side, we see its extruded profile. In one case, the synthetic rubber has been heated and pressed through an ‘H’ shaped die. There’s a curved notch on the lower half of the rubber lining, plus a subtly different notch located on the top section. Picture this material formed into a framing shape or a ring. For a custom-fabricated gasket, it precisely fits two mating surfaces because the die was perfectly profiled. For a glazing seal, the material stretches slightly when panes of glass slot into place. And that profile, the ‘H’ shape, isn’t alone. Indeed, there are limitless options here, including U-channel extrusions and hollow-tubed variations.
Extrusions: The Different Types
Materially, neoprene and EPDM rubber gaskets dominate the industry. Silicone variants and Viton alternatives are also available. Whatever the material choice, it must suit its application. Utilizing a die insert, the extrusion equipment profiles the tubular or flat-formed material lengths. U-shaped channels are squared or squeezed into ovals. For tubing seals and D-shaped inserts, there are die plates to accommodate those profiles, too. Essentially, there’s a limitless number of extrusion shapes available, each of which satisfies one of a thousand applications. However, there are material limitations and client parameters to regulate the material/shape selection process. Let’s look at those now.
Shaped By Material Limitations
Unlike geometrical shaping, this form-fitting approach depends on the application domain. For example, glazing extrusions, ones used in the automotive industry, should always source weather and UV resistant rubbers. Likewise, an extruded gasket, perhaps destined to suit some high-altitude aerospace application, won’t satisfy a client if it can’t retain its gasket-compressing capabilities when the temperature turns icy cold. Indeed, unlike pipe face gaskets, extrusions are more geometrically intricate, so a capacity for keeping that shape when attacked by the harshest environmental and/or mechanical forces ranks high here, especially when a potential seal discontinuity represents a substantial application or user hazard.
This is a second but equally relevant branch of the gasketing tree. Instead of die cutting entire shapes from a sheet, the material is pressed by a hydraulically powered piston through a toughened die. Heat and pressure are the driving forces here, and they produce some amazingly feature-rich, cut-to-length seals and gaskets. Arguably more flexible than their ring-shaped gasketing peers, extrusions assume countless cross-sectional profiles.
Full face gaskets are wide enough to cover an entire flange. That means the ring starts at the edge of the flange face, moves in towards the internal pipe diameter, and thus covers the whole seal surface. Securing bolts pass through the gasket, so there’ll be bolt holes included on the die-cut material. Talking of materials, Viton is the selected base here, with its fluoroelastomer-backed features dispensing heat-resisting resilience.
Outstanding Mechanical Performance
Applications include processing constructs that carry pressurized petroleum-based fluids. In large-scale pipes, oil refinery zones and fuel depot sections convey corrosive oils and fuels. In here, Viton type full face gaskets retain their sealing characteristics when they’re exposed to high pressures. Similarly, in chemical processing environments, the ring gaskets, compressed by circles of tightened fastener bolts, refuse to be impacted by dynamic state changing events, as encountered in catalyst-rich processing plants.
Heat Resistance Applications
Heat exchangers use streams of pressurized steam to warm independently connected heating networks. Stack and tube configurations channel the steam in, the second stream of cooler water is warmed, and the system works its heat exchanging magic. Thanks to Viton’s high-temperature capabilities, full-face gaskets made from the fluoroelastomer perform grandly in boiler-side applications. If the steam is super-pressurized or carrying hundreds of degrees of thermal energy, it just won’t matter; the bolt-tightened Viton sealed flanges will safely and surely channel the super-hot (+200°C), super-pressurized fluid. Granted, a regular Viton gasket can also manage high-temperature fluids, but blowout dangers are more likely when these seals are selected. To manage high temperatures and higher pressures, the design engineer opts for a stronger, more resilient solution. And that’s where Viton full-face gaskets enter the scene.
Chemically Based Heat Exchangers
Since Viton features moderate low-temperature capabilities (-20°C), let’s stick with the synthetic rubber’s heat-biased applications. In the above paragraph, heat exchanger technology was discussed, but the usage domain was strictly limited to hot water. That’s a popular and essentially important industry, but heat exchangers are also employed in the chemical processing sector. Efficiently isolating two or more chemical phases, Viton seals resist this triple threat. They contain heat, retain their mechanical form when high pressures flow, and they also handle incredibly corrosive chemical reagents. That three-way threat exists in chemically-based heat exchangers, so Viton full-face gaskets are also on-hand to manage the multiple fluid hazards.
Skipping up a level, flanges assume raised faces. Meanwhile, flat-surface or full-faced gasketing applications demand a compressible but rigid material base. Cut with bolt holes, the fluoroelastomer isn’t weakened by those rings of fastening apertures. To the contrary, they function with reinforced heat and pressure resisting strength across countless industrial applications.
Low-pressure pneumatic systems employ less than 75-kPa of pump compressed air. That figure can climb as high as a several hundred kilopascal load. For hydraulic equipment, the design engineer can easily pop another zero on the end of that number, for these heavy-duty systems are often asked to handle thousands of kilopascals, and those kinds of fluid loads are unforgiving, at least when it comes to a leaky gasket.
Demystifying Fluid Mechanics
As a central premise, capable hydraulic and pneumatic gaskets are designed to keep compressed gasses and pressurized liquids within fluid power equipment. The equipment employs a closed loop, with the contained fluid forces conveying energy from pumps and reservoirs to onboard actuators. Those actuators include rod and piston devices, plus several branching families of force manipulating component classes. In fact, just like electrical equipment, a whole science has sprung up around fluid transmission technology. There are complex circuit elements in the systems, plus numerous feedback-controlled network forms, many of which are built to responsively turn small signals into proportionally larger mechanical actions.
Essential Qualities For Fluid Power Transmission Gaskets
Clearly, thanks to the immense contained pressures, a leaky gasket represents a major health hazard. From one point of view, the energy losses impact machinery. The gear becomes less responsive, an outrigger fails on a crane, there’s a chassis-toppling risk, and the boom of a heavy lifter could fail at the worst possible moment. More directly, tiny leaks act like invisible jets, which can send fluid rocketing towards an unprotected eye or someone’s skin. Forcefully ejected fluids can easily penetrate soft tissue and cause serious physical harm. Unfortunately, there’s no way around this danger, not without a high-quality gasketing series. Conforming to the irregular surfaces of a pneumatic or hydraulic tube interface or flange, quality gasket seals fill microscopically tiny mating surface voids. Installed correctly, though, o-rings and flat-faced gaskets stop fluid leakage effects in their tracks.
Unique among other equipment forms, hydraulic and pneumatic equipment handle huge loads, but they’re also built to function as clean closed loop systems. That’s a tough restriction to solve. No pollutants can enter from the outside, no oils or water, air or particulates. Meanwhile, hydraulic oils can be corrosive while pneumatic gasses suck in large quantities of system-corroding moisture. The selected gaskets can’t fail when they’re attacked by corrosive oils or parts-fatiguing water, nor can they break down if the fluid emulsifies. Heat and pressure, plus a slew of other system-impacting variables are waiting for their chance to damage the fluid seals, so high-quality gasket seals are a must-have feature.
When seeking low-temperature gaskets, coolroom designers use their engineering skills to select suitable materials. A conventional sealing material, although compressible and surface conformable, isn’t necessarily good enough here, not if it becomes brittle when the temperature drops below zero degrees Celsius. Clearly, then, as well as all of the normal, highly desirable material compressibility features, freezer gaskets require a little something extra.
Studying Seal Fracturing Events
If a freezer seal does harden and become inelastic, then the slightest amount of material expansion will be enough to cause a sealant crack. All it takes is one tiny crack. Such fractures grow, they propagate until they compromise energy-efficient freezers and coolrooms. It’s impossible to stop a material from expanding then contracting, and it’s impossible to eliminate compressibility stress. It’s also plainly impossible to eliminate door seal strain, as caused by a forcefully closed coolroom entryway. Spring-loaded door closers help, but the mechanical stress still works its way into the portal gasket. As for the other system seals, there’s just no avoiding the material-deforming forces that are pushing down on their stiffening forms.
Equipped With Freeze-Resisting Resilience
To be brutally honest, those gaskets must endure, even when the enclosure temperature dips far below freezing point. Logically, then, if the cold is unavoidable, what can be done to fix matters? There are heating elements of course, which are designed to protect door gasket elasticity. Better yet, though, system designers opt for gasket materials that feature low-temperature performance. In profile, the door gaskets mentioned earlier tend to be manufactured out of extruded silicone. Double or triple layered, the strip geometry conserves energy. As a heavily reinforced door closes, the folded silicone uses an air cushion to protect the compressible rubber so that it squashes evenly all around the door frame. Expect this material to function when the enclosure temperature drops as low as -60°C. Of course, few freezers and no coolrooms require this degree of ultra-low elastomeric performance.
Silicone and PTFE gasketing materials retain their squashable features, even when they’re used in cryogenic applications. For more conventional applications, however, soft PVC, nitrile, and other synthetics are acceptable. Other desirable features, ones that play a role in the decision-making process here, include pressure handling capabilities, tensile strength, and even an aptitude for accepting magnetically charged additives. Easy to clean, not impacted by popular cleaning chemicals, and unaffected by sudden temperature spikes, the chosen gasketing elastomer should also be die-cut congenial and extrusion tool friendly. Incidentally, since coolrooms and freezers contain oil-laden foodstuffs, the selected rubber should be as oil-resistant as it is low-temperature capable.
Acids and oils course like water through wide channels. And although the compounds aren’t as toxic as those found interred inside chemical processing plants, that doesn’t mean they can’t eat their way through a rubber gasket. That’s why the food industry can’t operate for long without food grade gaskets. Anything less, well, those corrosive fluids will eventually eat away their material bases.
Seal Materials That Frustrate Food Corrosiveness
Some rubbers deteriorate when they’re exposed to acids. Other materials, they break down when heavy oils are present. Granted, the fluids here are mildly acidic, and those oily fluids are nothing more than animal fat or vegetable oil. Still, in food grade applications, those seals are exposed to acids and oils 24/7, all year round. The liquefied foodstuff could also be hot or chilled, so the selected food grade gasket better provide plenty of chemical resistance strength.
Generally speaking, gaskets that are designed to satisfy the FDA (Food Drug Administration) standards and the FSANZ (Food Standards Australian and New Zealand) lack the additives that are commonly injected into most sealing products. But let’s leave this feature alone, just for the moment. The gaskets are die cut from sheets of silicone and nitrile, from modified PTFE and other food safe gasketing rubbers. Oftentimes, for maintenance and sanitizing reasons, the industry opts for a standardized style, a white or translucent sheeting material. Clearly, then, there are weighty issues in play.
Comprehensive Gasketing Solutions
The foodstuff in the pipes could be waste, could be some stringy residue, but it could also be headed for a jar or can, which then hits the highway on the back of a truck as it heads to market. As such, food grade rubber needs more than the system-beneficial chemical resistance feature mentioned earlier. Those seals must also guarantee a food safe build. Remember, pickling juices, vinegars, oils, and salts break down gaskets, but that action occurs slowly. This is what’s known as the food leeching effect. Going back to additives, the plasticizers and fillers touched upon in the previous paragraph, food safe gaskets cannot incorporate such additives, not if they’ll end up migrating into the edible stream.
Food safe and food-proof, the rubbers used in this mildly corrosive industrial and commercial application are designed to retain their fluid sealing features and elastoviscous characteristics, even when a strong vinegar, citric acid, or salt is conveyed. Beyond that key feature, of course, the rubber gaskets, be they nitrile or silicone, must be designed to neutralize the rubber leeching effect, for this is a consumables stream, a product that’s meant for human consumption.