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.