It takes a specially designed gasket material to keep low-temperature fluids in check in cryogenic freezers. A normal seal will freeze solid when such arctic climates are encountered. At that point, jointing brittleness ensues, the issue is likely compounded by ice-saturated creep, and the high-performance substance ends up crumbling. All is not lost, for there are gasket materials that thrive in cryogenic freezers. First, however, what is cryogenics?
According to a reputable engineering resource, cryogenics is the division of science that deals with extremely cold applications. Think of an engineering system that operates below -150°C, and then add liquefied gas to that image. Specialized refrigerants, liquid nitrogen, and a host of other bitterly cold applications, they all fall under this umbrella term. Despite the frosty nature of these equipment usage domains, the ancillary components employed here look just like a middle of the road freezer system. Only, the pipes are carrying liquefied gases, not a partially chilled refrigerant. In light of the rock-bottom thermal state maintained within these pipes and fittings, we need gasket materials that can withstand this chill factor.
Cryogenic Freezers: Selecting Gasket Materials
Advances in polymer engineering have extended the operational temperature range of many advanced plastics families. Despite the kind of temperature extremes that can freeze gases in their tracks, these polymers remain ductile. Furthermore, the selected gasket material won’t contract drastically as the temperature descends perilously low. Polytetrafluoroethylene (PTFE) is often recruited when this usage domain calls for a sealing family that maintains its finest operating characteristics. Branded as Teflon, this synthetic fluoropolymer is known to be a reliable jointing solution, one that’s used in the aerospace industry and those laboratory situations that rely on extremely low temperatures. Tungsten carbide, another capable cryogenics sealing solution, proves there are several options available, including a number of cermets. Fabricated from ceramic and sintered metals, this latter group is defined as a reinforced composite group. Why, though, are these composites making headway as cryogenics gasketing products?
To answer that question, we have to look beyond gasket material ductility and those thermal contraction effects that weaken the seals within a cryogenic system. Curiously, these fluids are classed as poor lubricators. They’re ‘sticky,’ in that the icy boundaries around the gasket cause face adherence issues. Like that time someone’s finger got stuck to the surface of a freezer’s inner housing, the extreme cold creates a dry-stick effect. Fortunately, the selected glass-filled composites and their just as capable Teflon branded gaskets are designed to defeat this phenomenon.
What are water pump gaskets? Are they fundamentally different from other sealing products? Absolutely, especially when those gaskets are employed in situations that imbue water with added energy. For example, a vehicle water pump gasket handles high temperatures and a coolant load, whereas a marine pump seal resists the encroachment of salt. Back to the main query, just what does this gasket type do for a water pump?
Bookends the Inlet and Discharge Ports
In simple terms, water pump gaskets seal the flange segments that hook the pump to the inlet and outlet pipes. If water is drawn by a positive displacement mechanism, such as a volute impeller, it’s the job of this seal pair to ensure the coupling between the pump and those ports is tight. Expect the seal to be manufactured from a fairly rigid elastomer, especially if the gasket in question is bound for an application that uses hot water.
Weighing Fluid Medium Variables
Water is like a blank sheet of paper; we can change it in so many ways. Car water pumps are mixed with coolants while their marine cousins pass a salt-saturated outflow. HVAC water pumps add pressure and greater temperature extremes to the mix. Therefore, the chosen seal material obviously has to match a chosen application. In pressure-sensitive usage fields, the selected material exhibits greater mechanical strength, plus a knack for surviving compressive tightening forces. Other water pump gaskets add chemical corrosion resistance or an intelligently imbued material characteristic that’s designed to resist a specific compound, like salt.
Uniquely Qualified Gasketing Solutions
A uniform pressure pairs with a certain thermal curve to bully a standard pipe seal as it lays between two flange faces. Okay, a change in fluid state or a transient pressure spike pushes that same seal to its design limits, but those limits will normally hold. Water pump gaskets are a little different. They’re positioned around a mechanically dynamic area, a work zone that churns the water and injects it with centrifugal energy. Surrounded by fastener openings and a wide flange face, plus some gasketing sealant, the seal holds firm despite the internal stresses generated inside the pump.
Water pump gaskets, as anyone can guess, are found in every industrial and commercial sector. Even cars have water pumps so that the engine runs cool. HVAC rooms are positively loaded with belt-driven variants, then there are marine pumps driving water through outboard engines so that a svelte boat can skip across a lake surface. It’s absolutely imperative that these gaskets are installed properly, for water leaks can cripple all of these applications.
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.
Few mechanical breakdown events engender as much dread in a car owner’s heart as a blown head gasket. Located between the engine block and the cylinder head compartment, this mechanically-essential seal is responsible for containing the internal combustion process, plus all of those explosively rising and falling cylinder parts. It’s because of these stress factors that this gasket doesn’t leak, it blows. What are the causes of blown head gaskets?
What is A Head Gasket?
As we briefly explained a moment ago, this is the all-important engine seal that contains internal combustion stress. When the engine block is mated to the cylinder head, this geometrically complex gasket is fitted between the two core engine parts as a seal. If you were to look at it, you’d see a row of cylinder apertures, plus an accompanying series of smaller holes. The latter array of openings exists to deliver the engine lubricant and a coolant. If this primary seal were to be breached, what would happen? Well, engine compression ratios drop like the proverbial stone if the gasket leaks. Furthermore, the once isolated lubricants and coolants leak and mix. From here, the engine overheats, it spits out clouds of smoke, and there’s an increased risk of permanent engine damage.
The Causes of Blown Head Gaskets
If we know the causes, we can avoid them. For instance, those two engine halves are forged from strong alloys. Still, even the smallest manufacturing difference can alter the way one of those segments reacts to stress. If combustion cycles do produce heat, the thermal energy is making the metal expand and contract. Mechanical creep hits the head gasket hard, especially if it’s made from an overly rigid material. The result of this expansion effect is head gasket fatigue, which means a blown head gasket is imminent. Head bolt overtightening is the other culprit here, with the bolt pressure over compressing the head gasket material. Engine assembly expertise rectifies this latter problem by applying the correct torque to each bolt and installing each one in the right sequence.
Substandard head gasket materials don’t react well when placed under pressure. The segment marrying stress, perhaps done out of sequence, over compresses the seal and introduces a weak spot. Meanwhile, a poor lubrication fluid or low coolant level causes rapid expansion and contraction cycling, a repeating event that’s felt as a mechanical creep effect. Have the engine serviced by an expert, someone who will install a high-quality head gasket correctly. On top of that provision, avoid high-temperature cycling effects by using a superior lubricant and a properly topped coolant reservoir.
Strong chemicals will eat into poorly selected gaskets, make no mistake about that. Sure, that joint seal has been designed to handle high temperatures and intense pressures, but the clock is ticking. The deteriorating material will fail. A chemically resistant gasket doesn’t suffer from such issues. It retains its toughened outlines and its sealing duties, no matter how corrosive the chemical attack. Still, not all corrosion-resistant gaskets are created equal.
Chemically Compatible Gaskets
The following elastomers and metals are robust substances, but that durability factor doesn’t necessarily mean much, not when the reactive properties associated with a particular chemical compound are known to target that particular material. With that fact in mind, the correctly selected gasket type uses a compatibility model to avoid corrosive action, as imposed on a pipe or fitting joint. Just to illustrate that point, most oils and fuels are seemingly harmless. If someone rubs an oil drop between two fingers, no harm is done. However, those same oils have a very different effect on rubber gaskets. Seal deterioration is likely, as is the likelihood of a nasty leak. Nitrile, EPDM, and Viton gaskets are designed to counteract that material deterioration effect.
Chemical Resistance Charts
Material deterioration effects progress differently, depending on the composition of the chemical medium. Fuels corrode certain elastomers, as do the oils we mentioned earlier. Even vegetable oils and vehicle lubricants can corrode non-compatible gasket rubbers. Hybrid materials, including elastomer-bonded cork seals, are one solution to this best gasket selection puzzle, but the preferred approach is to use data sheets and chemical resistance charts. Like a unique fingerprint, these substance resistivity documents provide details on which rubbers and metals work best with particular fluid stream types. From dust ingress protection to strong acid and alkali protection, the information assures seal compatibility.
A Chemical Compatibility Primer
If nitrile gaskets perform well when aggressive hydrocarbons are carried in-pipe, then EPDM is the next favoured member of this synthetic rubber group. Ethylene propylene diene monomer, is an excellent outdoor chemical seal, with its UV-resistant polymer base acting as a superior open-air pipe jointing product. Nitrile, on the other hand, is every bit as popular as EPDM, but its chemical resistance fingerprint makes the material a preferred gasketing solution in vehicles, in the car engines that carry corrosive hydrocarbons. Curiously, of all the singular materials on the market, few are rated to handle every conceivable chemical type, which is why special bindings and coatings are making headway into every engineering branch, even those that add high temperatures and pressures to the fluid mix. One example of this approach is a PTFE (Polytetrafluoroethylene) coating, a synthetic fluoropolymer that maintains chemical resistance while allowing the base gasket polymer to retain its mechanical traits.
A medium-grade flexible gasket compresses well and handles high temperatures, but it may not resist a certain acid or fuel type. Bonded with a PTFE coating, the hybrid product gains a newly augmented measure of chemical resistivity. Meanwhile, tried and true synthetic rubber gaskets, nitrile and EPDM among them, target nominated chemical compounds as long as the correct chemical resistance chart has been properly interpreted. Finally, tough Viton gaskets and spiral wound metal composites excel when pressure extremes drive those caustic fluid streams, although the latter product must use a ring alloy that doesn’t chemically react with the chemical medium.
Gaskets divide into two discrete classes when they’re employed in automotive applications. There are the passive areas where the seals protect passengers and driver. They’re the door gaskets and window seals, products that are formed from extruded lengths of weatherized rubber. What about the active seals, though, the common gaskets that manage engine and exhaust fluids?
Extraneous System Seals
The coolant in a car lays dormant. When the ignition circuit sparks life into the engine, that fluid rapidly heats as it recirculates around the engine and absorbs mechanically-generated heat. It’s in here that water-glycol resistant seals withstand the heat without ageing prematurely. Meanwhile, the gruelling conditions throughout the oil distribution system generate a corrosive environment. Fortunately, cork and cured nitrile automotive gaskets resist the impact of aromatic hydrocarbons while creating a formidable barrier that blocks oil leaks.
Engine Gasket Solutions
Head gaskets are one example of the automobile engine seal, then there are intake manifold seals, exhaust manifold gaskets, seals for the engine block, the oil pan, and much more besides. Compressed by torque-heavy tools, the engine segments clamp tightly down on these parts so that the internal combustion chamber maintains its explosive cycle. If that measured air/fuel mix is to be compressed and combusted, this rugged seal family needs some heavy-duty sealing characteristics, just like the super-tough industrial pipe gaskets we’ve been describing in other articles. With that thought in mind, expect a head gasket and its associated engine seals to be manufactured from thin layers of heat-treated steel. More accurately, those bonded layers are likely fabricated as composite parts, as die cut inserts that are layered with an elastomeric coating.
All around a vehicle, common gasket types fill every conceivable application. They’re in the electronic control modules as cable protection inserts. Oil-bathed transmission systems use cork gaskets and compressed fibre seals. Whatever the application, the material exists to meet the need, be it a super-hot coolant stream or a channeled supply of engine oil. Down in the depths of the engine, geometrically shaped gaskets allow the passage of cylinder heads, so they’re die cut and manufactured from layers of composite material, from steel, copper, and from a wear-resistant rubberized coating. Of course, should a weatherized window seal crack, the extruded material simply leaks rainwater. However, if that engine head gasket fails, the combustion cycle is compromised, plus there’s a possibility of a nasty fluid contamination scenario, which is why even the most common vehicle gasket is built according to a stringent manufacturing methodology.