The Technical Hub
O-Ring Calculator
This interactive calculator assists engineers with selection of O-ring and hardware dimensions, and to form the basis of an O-ring installation.
Chemical Compatibility Checker
This interactive guide will help you choose a seal material based on existing compatibility test results of known chemicals and elastomers.
Interactive Engineering Calculators
Click here for volume, mass and compression set values for O-rings and rotary seal and hydraulic cylinder calculations.
Unit Converter
Our interactive conversion tools allow engineers to switch between units of measurement when preparing engineering calculations.
Engineering Tables
Our reference tables provide cross reference information for surface finish, metal hardness and polymer hardness measurement units.
Surface finish requirements for static and dynamic sealingWhat is hardware surface finish? Any surface can look (and even feel) perfectly smooth. However, look closely enough with high magnification and all surfaces will have a degree of fluctuation and a topography that looks similar to a mountain range or the surface of the moon. The roughness of a surface is generally linked to the way a surface is produced or machined, and any subsequent processes such as coating or platings. Ra (metric) is the unit of measurement for surface hardware finish. Ra simply, is the mean roughness; the average calculated from the peak heights and valley depths. A surface that is mostly spiked can have the same Ra value as one that is mostly troughed, but each could have a very different impact on seal performance. Surface finish measuring equipment is capable of tracing a surface finish using a diamond tipped stylus or non-contact 3D laser scanning. Static and dynamic sealing applications will have different requirements for seal finish. Measuring and analysing the hardware surface finish is important to ensure the correct conditions and no leakage occurs. If a seal application is static, and is sealing a low molecular size gas such as helium, for example, then a very smooth surface is preferable. For some dynamic applications, it can be critical for either seal friction, or wear life, that the interface between the seal and the hardware is well lubricated. Specifying the right surface finish for the hardware components that contact a seal can be complex and daunting. Our expert team advise our customers on the relevant parameters, with consideration to what is important for the given application. We ensure the optimum finish is fully specified to achieve right-first-time seal performance. Find out how our expert quality engineers and inspectors ensure the highest level of quality assurance HERE
Are all elastomers the same?Elastomer rubbers look very similar - but are they all the same? With many different base groups and recipe formulations, there's a huge range of elastomer materials suitable for applications with varying temperature ranges and chemical media compatibility. It's critical to the seal performance to make the right choice. There are number of factors to consider, these include: Material hardness Elastomer material hardness can impact assembly loads, seal friction and extrusion resistance. Softer seal compounds can be used effectively against rough hardware surface finishes, as the softer rubber can better accommodate surface imperfections (especially when sealing low pressure gas). Harder compounds will have greater wear resistance in dynamic applications. Chemical compatibility Unlike PTFE seals (where there are very few chemicals that will attack and breakdown the material) elastomer seal materials have to be carefully selected. It's important to ensure properties are not affected by any fluids or gasses that the seals come into contact with. Temperature range Outwardly, elastomer rubbers seem straightforward, but the technology can be complex. Material groups often have well published temperature ranges. For example, the silicone family is able to reach -100°C (or even lower with special grades), and perfluoroelastomer (FFKM) grades are able to withstand 320°C (or even higher for short durations). Whilst guidance can be given on maximum temperature capability for any specific elastomer grade, this is often in a benign air environment. Therefore the chemical impact of being exposed to hot fluids in the sealing application should be considered. For information about our extensive product range, see HERE
The importance of engineering tolerancesTolerances are present in every man-made item. It is practically impossible to repeatedly manufacture something to an exact size or specification. In seal manufacturing, it's important to understand which tolerances impact performance and by how much. This will ensure a system is optimized for overall performance, and whole-life product cost. Considerations for tolerances include the seal material and the hardware for sealing installation.
Seal material, polymer and metal seals
Almost all polymer seal materials contain multiple ingredients. For PTFE and polyurethanes this is typically 2 or 3 different elements. Additionally, for an elastomer material, as many as 30 different ingredients can be used in the recipe. In machined seals, polymer seal materials tend to have high rates of thermal expansion. Together with their relative softness, this makes it difficult to maintain the same level of tolerance that can be achieved when machining metal components.
Hardware tolerances
When designing hardware for seal installation, engineering tolerances are sometimes more obvious, and certainly where engineers can focus some attention. A stack-up of tolerances for many applications should be considered. Together with tolerances of the assembly such as concentricity or misalignment (especially for dynamic sealing applications). Other considerations include bearing wear and the resulting increase in misalignment or runout as the equipment approaches the end of it’s target life.
Why are engineering tolerances important for sealing systems?
Every application starts from a nominal condition, and the maximum and minimum tolerance conditions should always be considered. Even in seemingly straightforward applications, it's important to ensure the seal is continuing to operate within it’s ideal set of conditions. Click on the link for information about our engineering, design and innovation service, click on this link HERE Use our interactive tools HERE
Elastomer manufacturing moulding processesHow is it manufactured? A question we get asked in the seal design process, but perhaps not considered often enough. How a rubber seal is produced can affect a number of things; the cost, the material choice...even how a part should be designed. All of these can have a significant impact on the performance of the seal in application. Let's take a look at the three main manufacturing methods for moulding elastomer seals. Compression Moulding This is the most simple method of converting a piece of rubber into a finished seal product. First, the rubber compound is mixed and prepared. The material has a stiff and non-elastic consistency (like thick dough). From this dough we produce a rubber blank (also known as a pre-form) by either cutting, punching or extruding cord. These blanks are normally a little bigger than the finished part (normally based on weight) will be placed into a metal moulding tool. The tool (in its simple form) is in two halves with the final product shape cut into the metal. This is known as the mould cavity. Injection Moulding This manufacturing process is often used to produce plastic components, but for rubbers, the temperatures are switched. A warmed rubber is injected into a hot tool, as the force required to inject uncured rubber is much greater than what’s required to push molten plastic into a chilled mould. Otherwise the equipment and principles remain similar. Transfer Moulding This is a variation on compression moulding. It uses the same hydraulic compression presses, but this tooling is a little more sophisticated (and consequently a little more expensive). Comparing the three most common methods of producing an elastomer seal, it's clear that evaluating how the part is going to be made, is key to ensuring the technical and commercial success of the seal in the application. Read more about our engineering, design and innovation service HERE
Polyurethane as a seal materialThe foam in your armchair. The strap on your wristwatch. The wheels on a supermarket shopping trolley and beyond; Polyurethane certainly has a diverse range of uses since its invention almost 85 years ago. Aside from day-to-day products; it is also a highly capable and versatile sealing material - and an option that is often overlooked.
What is Polyurethane?
This material is rubber, plastic, rigid and flexible. Polyurethane covers a group of materials; plastic polymers produced by the combination (or synthesis) of di-isocyanates with polyols and a chain extender. This makes Polyurethane an excellent seal material.
How are Polyurethane materials manufactured?
There is a one and two-step process to manufacturing polyurethane.
One-step process
This is when a compound containing multiple hydroxyl groups (called a polyol), is mixed with highly reactive low molecular weight chemicals (isocyanate), and a chain extender (low molecular weight diols or diamines). Consequently, the result is a random copolymer with a physically cross-linked irregular molecular structure.
Two-step process
In a two-step process, the polyol and isocyanate are mixed first to produce a pre-polymer. This is mixed with the chain extender to produce a block copolymer with more regular molecular structure. Although this often results in improved and more consistent material properties, there is a slightly higher production cost.
Why is Polyurethane a good seal material?
Evidently, when formulated appropriately, Polyurethane does produce an impressive set of material properties that make it an ideal material for sealing products. Consequently, its flexible, with very high abrasion resistance, tensile strength and stiffness. The tensile and tear strengths are typically 3-5 times higher compared to rubber seal materials. Although it lacks the chemical resistance and temperature capability of PTFE, it is compatible with mineral oils. There is more information on polyurethane as a seal material HERE You will learn more about our range of materials HERE
Why the focus on PFAS?PFAS is a blanket term used to describe Poly- and Per- fluoroalkyl substances. There are currently around 10,000 substances in existence that fit this description, with potentially more variants still yet to be produced. Some are already known to be harmful to human and animal health and the environment (such as PFOA and PFOS), and these specific PFAS are already controlled under legal restrictions. But in February 2023, The European Chemical Agency (ECHA) published a regulatory proposal to further restrict the manufacture, placing on the market, and use of all PFAS within the EU.
What are the consequences for seal manufacturers?
A broad ban on all PFAS would have a significant and direct impact on European industries and businesses that manufacture products using these substances. This will have consequences globally. One particular concern is the fluoropolymers material group. These elastomers could be caught in any blanket ban of PFAS without any exemption. These materials are essential in a wide variety of applications in many industries. These include food, medical, pharmaceutical, clean energy, semiconductor, electronics, oil & gas, chemical, automotive and electric vehicle industries. These fluoropolymers include materials used in high performance sealing solutions, such as PTFE and PVDF plastics, and FKM, FFKM and FVMQ elastomers.
What's the problem?
There is substantial scientific evidence showing fluoropolymers demonstrate unique characteristics that mean they do not pose significant risk to the environment. Additionally, no risk to human health as they’re not bio-available, toxic or mobile. They do not dissolve in or contaminate water, or generate microplastics, therefore cannot enter or accumulate in a person’s bloodstream. They meet the criteria specified by the Organisation for Economic Cooperation and Development (OECD) as “polymers of low concern” as they present no significant toxicity concerns, and do not degrade into other PFAS chemicals. Fluoropolymers far outperform other sealing materials in countless applications. To put it simply; they seal tighter, last longer and survive harsher application environments considerably better than any other available materials. Fluoropolymers add irreplaceable value to society, and contribute significantly to environmental sustainability
What do we do?
We fully support restricting the use of PFAS chemicals that are known to be harmful to our health or our environment; but we believe grouping all PFAS within a restriction would be a mistake. Fluoropolymers do not have the toxicological and environmental profiles of other PFAS. Additionally, prolonged existence alone is not justification to restrict a substance under REACH. We already work proactively to ensure the products we put to market are safe, compliant with legislation, and utilise the latest sustainability developments. This is to minimise our impact on the environment – during manufacture, in use and at end-of-life. As a company with high environmental, social and governance standards we will continue to do so, whenever and whatever new legislation comes into force. However, we believe the sealing industry, it’s many customers, end users and society as a whole, need specific derogations and exemptions for fluoropolymers (free of any time limitations) to be included in any legislation covering PFAS substances. As we have done, we strongly encouraged any individual or organisation that may be impacted by a ban to engage with ECHA. This would be during their consultation period on this proposed restriction (which ended on 25th September 2023). To learn more about our key industries and our sealing solutions, read HERE
Seals for cryogenic applicationsCryogenic sealing means controlling or sealing a media at very low temperatures. This process can be complex and advanced, and spans a range of markets; from pharmaceutical, chemical and refrigeration, to automotive and electronics.
What are low temperatures for seals?
A typical industrial sealing system operates in the realms of a stable temperature rating. This is often sufficient for elastomer seals to cope with most of the time. For example, a general pump application running at -20°C to +80°C in air or water would be perfectly suitable for a sealing solution manufactured in nitrile (NBR) elastomer. However, if that temperature specification dropped to -196°C in liquid Nitrogen, the overall sealing solution would need adapting dramatically. Therefore, a more advanced polymer solution is needed. This is because general elastomer groups such as NBR, FKM, & VMQ are not suitable to perform at very low temperatures. This is due to the chemistry of the elastomers at a molecular level. All elastomers need a particular chemical makeup to be able to withstand a temperature range of the application required. However, many global elastomers on the market are not rated much more below -70°C. This means they’re not a viable choice for cryogenic applications with temperatures way below -70°C (often requirements reach below -196°C).
Types of cryogenic sealing solutions
Specialised sealing solutions are required for cryogenics conditions. Our engineers utilise a range of more advanced seal polymers to solve the most demanding and critical application setups. PTFE has an outstanding temperature rating of -260°C to +260°C and low friction characteristics. It is also regularly used in conjunction with a metal spring energiser. The spring energiser acts to maximise the sealing force at the seal contact points and to maintain a tight seal. This is the case even when the very low temperature conditions are attempting to contract the seal away from the mating surfaces. Other common polymers suitable are UHMPWE and PTCFE for more specific applications.
Our seals for cryogenic applications
We offer a range of cryogenic sealing solutions for various markets and applications including; pumps, engines, couplings, cylinders and many more. Read about our full range of engineered materials HERE
Why use 2-Shot moulded seals?2-Shot moulding is a manufacturing process that allows the co-polymerisation of hard (or soft) plastics and thermoplastic elastomers (TPE’s). We use the 2-Shot manufacturing approach to deliver engineered parts that perform a critical sealing function.
What is 2-Shot moulding?
A 2-Shot mould is designed with a top and bottom cavity. During the moulding process the first material is injected into the top cavity and the mould opens and rotates. The first material is then injected into the top cavity again, while the second material is injected into the bottom cavity simultaneously. The mould then opens and the parts are ejected from the bottom cavity; the mould rotates again and the whole process is repeated. 2-Shot moulding is not considered a brand new method of manufacturing. In fact it has been used for years to produce items that we see and use every day. Toothbrushes, tools, kitchen utensils and toys are but a few examples of multi-shot moulding being used to produce relatively cheap items in large production quantities.
Why do we use 2-Shot Moulding?
Previously, manufacturers of high volume metal or plastic- to- rubber component assemblies have processed them via chemical or mechanical bonding, and by using adhesives or over-moulding. Examples of the types of markets that lend themselves to these types of sealing products are Automotive, Life Sciences and Aerospace & Defence. Although these production methods may achieve the final assembly requirement, the many different processes involved are lengthy, costly, and can be fraught with problem areas that require stringent controls. A failure in any of these areas will result in poor quality parts, therefore often deeming these methods unsuitable for critically engineered components.
Why do we use 2-Shot Moulding?
When designing a new 2-Shot moulded product (or replacing an existing assembly part) our engineers review each application parameter carefully, and utilise years of sealing experience and materials expertise alongside the latest 3D modelling technologies and FEA simulation programs before presenting a seal proposal. This allows us to anticipate and analyse the finest details of mould performance, and means we can adjust our seal design to ensure our customers receive the highest level of performance possible from our engineered 2-Shot seal solution. The result means we supply our customers with high integrity parts with a powerful molecular bond, reduced production cycle times (as many additional processes are removed from the production line) and comprehensive cost reductions as all parts are produced in a single manufacturing tool (meaning reduced running costs and the removal of pre and post moulding processes).
2-Shot moulding is not just a way of manufacturing simple, high volume parts. Our application engineers are always breaking norms and pushing design limits to consider more creative ways of producing high performance engineered sealing solutions to meet our customer requirements.
Read more about our 2 shot mouldings HERE
Why use PTFE seals?Polytetrafluoroethylene (PTFE) is a thermoplastic polymer that can be used in a variety of sealing applications; it is particularly suitable where the application conditions exceed the parameters of elastomeric seal use, but are not as highly demanding as applications that require the use of metal seals.
What is PTFE?
Discovered accidentally in the DuPont™ laboratory in Jackson, New Jersey, USA in in 1938. The molecular structure of PTFE is based on a linear chain of carbon atoms which are completely surrounded by fluorine atoms. The carbon-fluorine bonds are among the strongest occurring in organic compounds. As a result PTFE has thermal stability across a wide temperature range. It’s high melting point (342 °C) and morphological characteristics allow seal components made from virgin PTFE to be used continuously at service temperatures of up to 260 °C, and with the addition of fillers – up to 300°C. It has the unique ability to resist material degradation, heat-aging and alteration in its physical properties during temperature cycling. Alongside this rare combination of material characteristics PTFE also has unlimited shelf life.
Why use PTFE seals?
Notably PTFE demonstrates extraordinary chemical resistance: the intrapolymer chain bond strengths preclude reactions with most chemicals, thereby making it chemically inert at elevated temperatures and pressures with virtually all industrial chemicals and solvents. Only a few media (some molten alkalis) are known to react with PTFE seals making them the perfect sealing solution for highly aggressive chemical applications. PTFE also has the lowest friction coefficient of any known solid; it has self-lubricating capabilities which offers continuous dry running ability in dynamic sealing applications and has superb stick/slip capabilities.
Focus on dry coatings
The advantages of using PTFE in sealing applications are; functionality at high and low temperatures, dynamic sealing with high wear capabilities, high pressure sealing (using combinations of PEEK back-up rings) and compatibility with highly aggressive chemical combinations. Our range of PTFE seal products include back-up rings, rod and piston seals, slipper seals and spring energised seals in a wide variety of sizes. Materials depend on application requirements but we offer a wide range from Virgin PTFE or including filler combinations of MoS2, glass, carbon, carbon fibre, graphite, and bronze. These characteristics make PTFE seals perfect for the demanding applications involved in Oil & Gas, Aerospace, Automotive and Chemical Process markets (to name but a few) and Ceetak’s engineering team are experienced in the design of PTFE sealing solutions to meet the complex specifications these types of application demand. Read our overview and more detail about PTFE seals HERE
Why use metal seals?The use of metal seals as an engineered sealing solution is appropriate where it is not possible to use elastomeric or polymer seals due to extremely demanding application requirements. For example, these could include applications with extremely high temperatures (300°C upwards) and pressures, intense radiation, cryogenic conditions or highly aggressive chemicals.
How do metal seals work?
The metal seal concept is based on plastic and elastic deformation of the seal during compression which creates a sealing interface. The metal seal is compressed in the cavity on average about 20% of its original free height. The force generated through compression of the ring produces a high contact stress at the seal/cavity interface. This force is then supplemented by the pressure-energisation force which rises in proportion to the increase in differential pressure inside the seal cavity.
What types of metal seal are there?
There are three types of seal energisation; self, spring and pressure energisation. By design metal C-rings are self-energising due to the good spring back characteristic of the C-shaped profile. Additionally, they can be used in internal, external and axial pressure conditions. The different base material characteristics and heat treatments, along with material thickness, and cross section of the seal also determine the compressive load. This is directly related to the sealing level achieved and is known as “self-energisation”. Spring energised seals have excellent spring back properties and are typically used to improve leakage rates by increasing the load on the sealing interface. All metal seals can use system pressure to generate a hydrostatic load to obtain the highest level of sealing possible; this is known as pressure energisation. At high pressures this becomes an advantage and allows the design of metal seals for applications of 25,000 PSI and above.
Ultimate seal performance
Once the metal seal profile and material has been selected depending on the application, there are a variety of platings and coatings available. These can modify the surface properties of the seal to create a malleable outer surface layer. Typically precious metals such as gold and silver are used for plating, but many other options are available with two common ones also being Tin or PTFE. This layer ensures optimum sealing despite any mating surface imperfections. The plated or coated layer also reduces coefficient of friction so the seal can slide and bed down during initial compression. Consequently, this prevents galling. As well as providing better physical properties to the seal, coatings and platings are chosen to withstand high temperatures and aggressive (often corrosive or oxidizing) environments. There are ever changing industry demands and fast paced technology developments – particularly from customers in the Oil & Gas, Aerospace & Defence and Automotive markets. Therefore, we are challenged daily with applications where the boundaries are being pushed to the absolute limit. We have designed metal seals into F1 car exhaust systems, subsea repeaters, oil and gas production valves as a few examples; the capabilities of high performance metal seals is endless. Working with the latest developments in materials, platings and manufacturing technology; our engineering team design the sealing solutions to meet the complex specifications these types of application demand. Learn more about metal seals HERE
Why use Push-in-Place gaskets?Where a seal groove follows an irregular path or profile, a common sealing solution is to design a custom Push-In-Place (PIP) gasket that has the same profile as the centre line of the groove, simply drops into place and is retained by the features of its own design.
Gasket sealing overview
There are many ways to seal the static join between two components. This could be to keep fluids inside a cavity or to keep fluids or contaminants out of a device or assembly. The options can vary from simple O-rings, moulded elastomer gaskets and flat sheet style materials, to liquid gaskets (or RTV’s). As with all sealing applications, the optimal sealing solution is designed by first reviewing the application conditions. These include temperature, pressure, fluid exposure etc; and other variables such as life requirement, equipment serviceability and seal compression set should all be considered. Arguably though, compared to other sealing applications, when designing face, cover or flange sealing solutions it is imperative to consider the packaging requirements and assembly issues of gasket sealing options. The need to avoid or seal around bolt holes (or other retaining/clamping devices), together with optimizing hardware wall sections or depths can play a very important part in choosing the most suitable gasket sealing technique.
What are Push-in-Place gaskets?
With the right combination of application conditions, an o-ring style approach to sealing may be the most appropriate. O-rings tend to require relatively shallow grooves compared to their cross section in one half of the assembly, and in cases where the groove is round in plan view – they can be a good solution. However, in cases where the groove follows a more irregular path or profile (frequently referred to as a “racetrack”) the O-ring can sometimes pop out in places – often where the two housing parts are being brought together. A common solution is to design a custom moulding that has the same profile as the centre line of the racetrack groove and simply drops into place. A similar approach is used when the application or hardware constraints steer the design towards a gasket that has a greater cross section depth compared to the width; this would typically be designed so the centre line of the gasket matches the centre line of the groove plan profile – again so that it drops easily into place. An inherent problem with gaskets that can drop into place is that often, they easily drop out of place too. If the component needs to be inverted, or has the potential for rough handling during assembly then the gasket may become partially or fully dislodged from the groove, which results in a badly sealed interface. The best solution to this issue is to incorporate retention pips or bumps in the gasket design, a solution known as Push-In-Place (PIP) gaskets. These require a distinct force to put them into the groove, and as a result require more than just gravity to get them out of the groove.
Why use Push-in-Place gaskets?
There are other less effective solutions for tricky groove sealing, such as the use of a sticky grease, or the use of an adhesive. These can bring compatibility and health and safety issues to consider. Additionally, it carries the risk that any contaminant could keep the gasket off the surface that it is supposed to be sealing against. Therefore, the integrity of the seal can be severely compromised as a result. Neither of these approaches can be recommended, and instead the use of retention pips is a safe and secure way of ensuring the gasket remains in the groove. To determine the optimum number, size and position of the retention bumps, Finite Element Analysis (FEA) is used. This ensures they provide sufficient squeeze to prevent the gasket being easily dislodged. Additionally, it is important there’s no overfilling the groove space with seal material or interfering with the seal compression footprint against the hardware faces. The bumps can be strategically positioned to control any distortion of the gasket under pressure or temperature conditions. For example, low temperature conditions can shrink the gasket and tighten the radius it adopts around a bend in the racetrack profile. This can reduce the seal compression locally and potentially create a leak path.
Correct positioning
By positioning retention bumps at either end of the bend, the thermal contraction can be controlled to minimize the risk of leakage. Effective retention ensures that if the part needs to be inverted (which could be the preferred assembly method for practical reasons) or is subject to rough handling – the gasket remains correctly located in the groove. For large gaskets this is normally the most effective solution. On smaller gaskets (particularly those located well inside the periphery of the assembly), there is a significant risk of a dislodged gasket being totally undetected unless using a PIP gasket design. It’s possible to include tell-tale signs on a gasket design. For example, if a part of the elastomer gasket protrudes sideways through a gap in the housing wall, the presence of the gasket can be checked. This would be either with the human eye or an automated vision system. However, this does not ensure correct seating all around the gasket length, and cannot be used for internal gasket locations. In these cases a missing or badly fitted gasket would only be discovered during post-build testing, or even worse with a machine failure at a customer.
Further considerations
If included at the design stage, the small additional tooling and material costs associated with a PIP gasket are negligible compared to the costs of an impossible assembly scenario, strip and re-build costs on the assembly line, or the consequential costs associated with failure of an assembly once delivered to a customer. More information on PIPs and gaskets can be found HERE
Perfluoroelastomers in valvesIs it time to re-visit using perfluoroelastomer seals in your valves? First developed by DuPont™ in the late 1960s, perfluoroelastomers (or FFKMs), are now widely known and understood in a variety of markets. But for those that may be less familiar with these high performance materials, here is a quick recap...
What are perfluoroelastomers (FFKMs)?
They are essentially highly or fully fluorinated compounds with a fluorine content above 75%, and they offer outstanding chemical resistance. Generally better than all other elastomer types, FFKMs are often referred to as having the resistance of PTFE but in elastomer form. The term “universal” chemical resistance is commonly used; although it’s not strictly true as we will learn shortly. Unlike PTFE, the molecular make-up of FFKM includes crosslinks (or spring-like elements). This is contrast to just a backbone of carbon-carbon atoms surrounded by protective fluorine atoms. These crosslinks are what give the FFKMs their crucial elastic behaviour (in other words returning quickly to their original shape after being deformed). But the crosslinks are also a drawback as they can be a weak point for a chemical attack. Different crosslinking systems can be used when developing FFKMs and the choice will determine the high and low-temperature capabilities. Compounds developed for extreme high-temperatures (up to around 325oC) generally have a less broad chemical resistance. This is in comparison to the lower temperature grades (up to 225oC). Similarly, FFKMs developed to have excellent resistance to specific fluids (such as amines or high-temperature steam) can have limitations of low-temperature capability or compression set. As a result, there is no universal material that covers all application criteria bases.
A variety of grades
Previously the number of perfluoroelastomer grades was less prolific than other elastomer types such as FKM, EPDM, and NBR. However more than 50 years of technical developments have created a range of FFKM grades for specific and challenging applications. These are particularly in chemical process, oil and gas, semiconductor, and aerospace industries. Additionly, options with a hardness range of 65 to 90 durometer, and versions that meet international standards or specifications for food, medical, CPI, and oil & gas applications means the portfolio of FFKM-based compounds available to engineers is now substantial. In addition to technical developments, manufacturers and compounders have also been addressing the only real drawback of FFKM materials; the cost. They are difficult and time-consuming base polymers to manufacture. With a relatively low volume production base and sometimes lengthy processing times, FFKM seals carry a high financial premium over FKM seals. Even several times greater than FKM itself has over NBR. In recent years, there’s been more focus on making general-purpose grade FFKMs with broader temperature and chemical resistance capabilities more financially attainable. The initial procurement costs remain high compared to less capable elastomer bases. The overall cost of ownership may now be more appealing than it was twenty or even ten years ago. The ability of FFKM seals to survive for much longer in applications where exposure to a variety of fluids (perhaps wider than originally specified) is possible. This considerably reduces unplanned costs associated with maintenance and downtime.
Focus on dry coatings
The cost of unscheduled maintenance and repair in pump and valve equipment can be high in any industry, but exceptionally so in petrochemical, oil & gas, and semiconductor. When these costs are fully considered in the overall lifetime of a product, the initial price of seals in a valve is considered relatively minor, but it can still be a barrier in the material selection process. With both technical and commercial developments in recent times FFKM materials now compare more favourably against other materials for static, or low-duty dynamic applications in valves. In applications where persistent and sporadic issues keep coming back to cause problems, they are now a more financially attainable choice of material to avoid re-work, overhaul, downtime, customer dissatisfaction, and ultimately, more costs. Read more about FFKM as a suitable sealing material HERE
Seals for valve applicationsValves are imperative for isolation and control functions, and can be found in a broad range of industries such as Oil & Gas, Water & Wastewater, Food & Beverage and Hydraulics & Pneumatics. We supply seal products into valve applications in a variety of styles including ball, gate, flap, plug, butterfly, spool, check and solenoid valves.
Characteristics of valve sealing
There are many challenges involved in valve application sealing. Conditions and application parameters can vary with temperature extremes from cryogenic up to 325°C, and pressures up to 1000+ bar. We need to carefully consider the materials to suit all fluid compatibility required. Often the seal design requires low breakout friction and offers no stick-slip following prolonged static periods when the valve is not used. Alongside this, customers require long service life and minimal maintenance. Valve styles include ball, gate, flap, butterfly, spool, check and solenoid valves. Also different types of actuation include manual, pneumatic, hydraulic and electro-mechanical. Different areas of the valve demonstrate different sealing requirements.
Valve sealing areas Actuation
There are a range of sealing solutions to suit the variety of actuation types employed with valves. This includes diaphragms for pneumatic actuation, rotary and linear hydraulic and pneumatic seals, and gaskets and O-rings. Seal materials are available to suit all ranges of temperatures and media associated with the actuator and any external contaminants it encounters.
Body bonnet joint
This is a static sealing location that can often be sealed with an O-ring (a wide range of materials are available to satisfy fluid compatibility). However dependent on the fluid, pressures and temperatures, metal seals can be more suited to the application. Additionally, housing deflection under pulsating system pressures may worsen compression set sealing issues. Therefore, a custom gasket design could be potentially more suitable than an O-ring. For subsea valves, a sealing solution capable of handling alternating pressure regimes and multiple media types may be required.
Stem
A critical and dynamic sealing location with often demanding requirements. Depending on the application of the valve, the seals used here may see frequent dynamic operation and will require a long wear life. In other cases, the valve may be static for long periods and then require operation with minimal break-out friction forces. In all cases, reliable sealing is paramount.
Seat body
Valve seats are often mounted in a housing or carrier which has a sealed interface within the valve body and in these cases it can be a critical location to seal correctly. Dependent on the design, the seal location may be subject to upstream or downstream pressures at various points. In some cases fluid flow through the valve can pull or wash-out seals from their grooves if they are not designed to prevent this. As pressure conditions change with valve operation, the seals here may be required to withstand small (but sometimes frequent) movements of the carrier without sticking or wearing.
Valve Seat
A wide variety of elastomers and engineered polymer materials can be moulded or machined to suit valve seat components. Bonded rubber to metal or rubber to plastic seals can provide bespoke solutions. These offer benefits in terms of space envelope, component count or ease of assembly.
Design & Development for valve sealing applications
Our engineering team understand the application demands associated with valve sealing and can support our customers with the design of seals for every position within the valves. We provide a complete design service; from initial seal geometry and profile choice, to material selection and prototyping, through to final production. This is utilised with our seal design experience and materials expertise, alongside technology such as 2D/3D CAD and FEA analysis. These simulate performance before finalising each individual seal design. We are familiar with the requirements of individual markets and their valve applications. Our seals are manufactured in materials with approval requirements such as NORSOK M-710, ISO23936-2, NACE, WRAS and FDA. For more on our design and engineering service, see our dedicated page HERE
3D printing for seals3D printing has developed significantly and now performs a crucial role in many applications. 3D printed products vary from fully functional to purely aesthetic applications; with the most common application being for manufacturing. Here we discuss how our engineers use 3D printing to demonstrate a seal concept.
What is 3D printing?
3D printing is typically the more common name used for additive manufacturing. This process involves the construction of a three dimensional shape that is designed and generated from a computer aided design program (or CAD). The most typical process used for 3D printing is FFF (Fused Filament Fabrication) or FDM (Fused Deposition Modelling). The FDM process uses a continuous filament of a thermoplastic material that is then deposited onto the 3D print bed, creating layer by layer and gradually building up the structure of the 3D model. This is the process we commonly use to create our design and development range of 3D printed models and seal prototypes.
What material is suitable for 3D printing?
The materials used for 3D printing must of course be compatible with the process – these include a range of thermoplastic grades. Typical suitable material grades include; Polylactic acid (PLA), Acrylonitrile Butadiene Styrene (ABS), Thermoplastic Polyurethane (TPU), Nylon and Polypropylene (PP). The most common grade we use for 3D printing is PLA – for its great strength and stability. We’ve also adapted our design process to use more TPU based material grades, as it loosely demonstrates the same properties as elastomer grades and is better for using in prototype programmes where mechanical fit in groove is tested.
Why use 3D printing for seals?
3D printing can be used for a variety of designs and seal types; from O-rings, gaskets and lip seals – to grommets, multi shot mouldings and large seal assemblies. There are many benefits of using 3D printing during the initial design stages of a project. The rapid turnaround means that a simple seal design can be produced in around 15 minutes, and even more complicated parts can be manufactured in the same day. We can even print the application housings and it’s the perfect way to demonstrate to an engineer what they can expect from a seal part in terms of shape and fit for hardware without the lead time and cost of cutting a prototype tool for moulded parts. One example of this is by quick turnaround of gasket designs typically to suit automotive applications or similar critical markets. Our engineers can design the concept and then 3D print a rapid prototype of a gasket to suit a 3D printed gauge groove. This further demonstrates to the customer that the seal has been fit checked for installation and builds further confidence in the design recommendation. Our engineers combine the 3D print with FEA simulation reports to offer a fully engineered sealing solution. Learn more about our design and simulation service HERE
Tools
O-Ring Calculator
This interactive calculator assists engineers with selection of O-ring and hardware dimensions, and to form the basis of an O-ring installation.
Chemical Compatibility Checker
This interactive guide will help you choose a seal material based on existing compatibility test results of known chemicals and elastomers.
Interactive Engineering Calculators
Click here for volume, mass and compression set values for O-rings and rotary seal and hydraulic cylinder calculations.
Unit Converter
Our interactive conversion tools allow engineers to switch between units of measurement when preparing engineering calculations.
Engineering Tables
Our reference tables provide cross reference information for surface finish, metal hardness and polymer hardness measurement units.
Articles
Surface finish requirements for static and dynamic sealingWhat is hardware surface finish? Any surface can look (and even feel) perfectly smooth. However, look closely enough with high magnification and all surfaces will have a degree of fluctuation and a topography that looks similar to a mountain range or the surface of the moon. The roughness of a surface is generally linked to the way a surface is produced or machined, and any subsequent processes such as coating or platings. Ra (metric) is the unit of measurement for surface hardware finish. Ra simply, is the mean roughness; the average calculated from the peak heights and valley depths. A surface that is mostly spiked can have the same Ra value as one that is mostly troughed, but each could have a very different impact on seal performance. Surface finish measuring equipment is capable of tracing a surface finish using a diamond tipped stylus or non-contact 3D laser scanning. Static and dynamic sealing applications will have different requirements for seal finish. Measuring and analysing the hardware surface finish is important to ensure the correct conditions and no leakage occurs. If a seal application is static, and is sealing a low molecular size gas such as helium, for example, then a very smooth surface is preferable. For some dynamic applications, it can be critical for either seal friction, or wear life, that the interface between the seal and the hardware is well lubricated. Specifying the right surface finish for the hardware components that contact a seal can be complex and daunting. Our expert team advise our customers on the relevant parameters, with consideration to what is important for the given application. We ensure the optimum finish is fully specified to achieve right-first-time seal performance. Find out how our expert quality engineers and inspectors ensure the highest level of quality assurance HERE
Are all elastomers the same?Elastomer rubbers look very similar - but are they all the same? With many different base groups and recipe formulations, there's a huge range of elastomer materials suitable for applications with varying temperature ranges and chemical media compatibility. It's critical to the seal performance to make the right choice. There are number of factors to consider, these include: Material hardness Elastomer material hardness can impact assembly loads, seal friction and extrusion resistance. Softer seal compounds can be used effectively against rough hardware surface finishes, as the softer rubber can better accommodate surface imperfections (especially when sealing low pressure gas). Harder compounds will have greater wear resistance in dynamic applications. Chemical compatibility Unlike PTFE seals (where there are very few chemicals that will attack and breakdown the material) elastomer seal materials have to be carefully selected. It's important to ensure properties are not affected by any fluids or gasses that the seals come into contact with. Temperature range Outwardly, elastomer rubbers seem straightforward, but the technology can be complex. Material groups often have well published temperature ranges. For example, the silicone family is able to reach -100°C (or even lower with special grades), and perfluoroelastomer (FFKM) grades are able to withstand 320°C (or even higher for short durations). Whilst guidance can be given on maximum temperature capability for any specific elastomer grade, this is often in a benign air environment. Therefore the chemical impact of being exposed to hot fluids in the sealing application should be considered. For information about our extensive product range, see HERE
The importance of engineering tolerancesTolerances are present in every man-made item. It is practically impossible to repeatedly manufacture something to an exact size or specification. In seal manufacturing, it's important to understand which tolerances impact performance and by how much. This will ensure a system is optimized for overall performance, and whole-life product cost. Considerations for tolerances include the seal material and the hardware for sealing installation.
Seal material, polymer and metal seals
Almost all polymer seal materials contain multiple ingredients. For PTFE and polyurethanes this is typically 2 or 3 different elements. Additionally, for an elastomer material, as many as 30 different ingredients can be used in the recipe. In machined seals, polymer seal materials tend to have high rates of thermal expansion. Together with their relative softness, this makes it difficult to maintain the same level of tolerance that can be achieved when machining metal components.
Hardware tolerances
When designing hardware for seal installation, engineering tolerances are sometimes more obvious, and certainly where engineers can focus some attention. A stack-up of tolerances for many applications should be considered. Together with tolerances of the assembly such as concentricity or misalignment (especially for dynamic sealing applications). Other considerations include bearing wear and the resulting increase in misalignment or runout as the equipment approaches the end of it’s target life.
Why are engineering tolerances important for sealing systems?
Every application starts from a nominal condition, and the maximum and minimum tolerance conditions should always be considered. Even in seemingly straightforward applications, it's important to ensure the seal is continuing to operate within it’s ideal set of conditions. Click on the link for information about our engineering, design and innovation service, click on this link HERE Use our interactive tools HERE
Elastomer manufacturing moulding processesHow is it manufactured? A question we get asked in the seal design process, but perhaps not considered often enough. How a rubber seal is produced can affect a number of things; the cost, the material choice...even how a part should be designed. All of these can have a significant impact on the performance of the seal in application. Let's take a look at the three main manufacturing methods for moulding elastomer seals. Compression Moulding This is the most simple method of converting a piece of rubber into a finished seal product. First, the rubber compound is mixed and prepared. The material has a stiff and non-elastic consistency (like thick dough). From this dough we produce a rubber blank (also known as a pre-form) by either cutting, punching or extruding cord. These blanks are normally a little bigger than the finished part (normally based on weight) will be placed into a metal moulding tool. The tool (in its simple form) is in two halves with the final product shape cut into the metal. This is known as the mould cavity. Injection Moulding This manufacturing process is often used to produce plastic components, but for rubbers, the temperatures are switched. A warmed rubber is injected into a hot tool, as the force required to inject uncured rubber is much greater than what’s required to push molten plastic into a chilled mould. Otherwise the equipment and principles remain similar. Transfer Moulding This is a variation on compression moulding. It uses the same hydraulic compression presses, but this tooling is a little more sophisticated (and consequently a little more expensive). Comparing the three most common methods of producing an elastomer seal, it's clear that evaluating how the part is going to be made, is key to ensuring the technical and commercial success of the seal in the application. Read more about our engineering, design and innovation service HERE
Polyurethane as a seal materialThe foam in your armchair. The strap on your wristwatch. The wheels on a supermarket shopping trolley and beyond; Polyurethane certainly has a diverse range of uses since its invention almost 85 years ago. Aside from day-to-day products; it is also a highly capable and versatile sealing material - and an option that is often overlooked.
What is Polyurethane?
This material is rubber, plastic, rigid and flexible. Polyurethane covers a group of materials; plastic polymers produced by the combination (or synthesis) of di-isocyanates with polyols and a chain extender. This makes Polyurethane an excellent seal material.
How are Polyurethane materials manufactured?
There is a one and two-step process to manufacturing polyurethane.
One-step process
This is when a compound containing multiple hydroxyl groups (called a polyol), is mixed with highly reactive low molecular weight chemicals (isocyanate), and a chain extender (low molecular weight diols or diamines). Consequently, the result is a random copolymer with a physically cross-linked irregular molecular structure.
Two-step process
In a two-step process, the polyol and isocyanate are mixed first to produce a pre-polymer. This is mixed with the chain extender to produce a block copolymer with more regular molecular structure. Although this often results in improved and more consistent material properties, there is a slightly higher production cost.
Why is Polyurethane a good seal material?
Evidently, when formulated appropriately, Polyurethane does produce an impressive set of material properties that make it an ideal material for sealing products. Consequently, its flexible, with very high abrasion resistance, tensile strength and stiffness. The tensile and tear strengths are typically 3-5 times higher compared to rubber seal materials. Although it lacks the chemical resistance and temperature capability of PTFE, it is compatible with mineral oils. There is more information on polyurethane as a seal material HERE You will learn more about our range of materials HERE
Why the focus on PFAS?PFAS is a blanket term used to describe Poly- and Per- fluoroalkyl substances. There are currently around 10,000 substances in existence that fit this description, with potentially more variants still yet to be produced. Some are already known to be harmful to human and animal health and the environment (such as PFOA and PFOS), and these specific PFAS are already controlled under legal restrictions. But in February 2023, The European Chemical Agency (ECHA) published a regulatory proposal to further restrict the manufacture, placing on the market, and use of all PFAS within the EU.
What are the consequences for seal manufacturers?
A broad ban on all PFAS would have a significant and direct impact on European industries and businesses that manufacture products using these substances. This will have consequences globally. One particular concern is the fluoropolymers material group. These elastomers could be caught in any blanket ban of PFAS without any exemption. These materials are essential in a wide variety of applications in many industries. These include food, medical, pharmaceutical, clean energy, semiconductor, electronics, oil & gas, chemical, automotive and electric vehicle industries. These fluoropolymers include materials used in high performance sealing solutions, such as PTFE and PVDF plastics, and FKM, FFKM and FVMQ elastomers.
What's the problem?
There is substantial scientific evidence showing fluoropolymers demonstrate unique characteristics that mean they do not pose significant risk to the environment. Additionally, no risk to human health as they’re not bio-available, toxic or mobile. They do not dissolve in or contaminate water, or generate microplastics, therefore cannot enter or accumulate in a person’s bloodstream. They meet the criteria specified by the Organisation for Economic Cooperation and Development (OECD) as “polymers of low concern” as they present no significant toxicity concerns, and do not degrade into other PFAS chemicals. Fluoropolymers far outperform other sealing materials in countless applications. To put it simply; they seal tighter, last longer and survive harsher application environments considerably better than any other available materials. Fluoropolymers add irreplaceable value to society, and contribute significantly to environmental sustainability
What do we do?
We fully support restricting the use of PFAS chemicals that are known to be harmful to our health or our environment; but we believe grouping all PFAS within a restriction would be a mistake. Fluoropolymers do not have the toxicological and environmental profiles of other PFAS. Additionally, prolonged existence alone is not justification to restrict a substance under REACH. We already work proactively to ensure the products we put to market are safe, compliant with legislation, and utilise the latest sustainability developments. This is to minimise our impact on the environment – during manufacture, in use and at end-of-life. As a company with high environmental, social and governance standards we will continue to do so, whenever and whatever new legislation comes into force. However, we believe the sealing industry, it’s many customers, end users and society as a whole, need specific derogations and exemptions for fluoropolymers (free of any time limitations) to be included in any legislation covering PFAS substances. As we have done, we strongly encouraged any individual or organisation that may be impacted by a ban to engage with ECHA. This would be during their consultation period on this proposed restriction (which ended on 25th September 2023). To learn more about our key industries and our sealing solutions, read HERE
Seals for cryogenic applicationsCryogenic sealing means controlling or sealing a media at very low temperatures. This process can be complex and advanced, and spans a range of markets; from pharmaceutical, chemical and refrigeration, to automotive and electronics.
What are low temperatures for seals?
A typical industrial sealing system operates in the realms of a stable temperature rating. This is often sufficient for elastomer seals to cope with most of the time. For example, a general pump application running at -20°C to +80°C in air or water would be perfectly suitable for a sealing solution manufactured in nitrile (NBR) elastomer. However, if that temperature specification dropped to -196°C in liquid Nitrogen, the overall sealing solution would need adapting dramatically. Therefore, a more advanced polymer solution is needed. This is because general elastomer groups such as NBR, FKM, & VMQ are not suitable to perform at very low temperatures. This is due to the chemistry of the elastomers at a molecular level. All elastomers need a particular chemical makeup to be able to withstand a temperature range of the application required. However, many global elastomers on the market are not rated much more below -70°C. This means they’re not a viable choice for cryogenic applications with temperatures way below -70°C (often requirements reach below -196°C).
Types of cryogenic sealing solutions
Specialised sealing solutions are required for cryogenics conditions. Our engineers utilise a range of more advanced seal polymers to solve the most demanding and critical application setups. PTFE has an outstanding temperature rating of -260°C to +260°C and low friction characteristics. It is also regularly used in conjunction with a metal spring energiser. The spring energiser acts to maximise the sealing force at the seal contact points and to maintain a tight seal. This is the case even when the very low temperature conditions are attempting to contract the seal away from the mating surfaces. Other common polymers suitable are UHMPWE and PTCFE for more specific applications.
Our seals for cryogenic applications
We offer a range of cryogenic sealing solutions for various markets and applications including; pumps, engines, couplings, cylinders and many more. Read about our full range of engineered materials HERE
Why use 2-Shot moulded seals?2-Shot moulding is a manufacturing process that allows the co-polymerisation of hard (or soft) plastics and thermoplastic elastomers (TPE’s). We use the 2-Shot manufacturing approach to deliver engineered parts that perform a critical sealing function.
What is 2-Shot moulding?
A 2-Shot mould is designed with a top and bottom cavity. During the moulding process the first material is injected into the top cavity and the mould opens and rotates. The first material is then injected into the top cavity again, while the second material is injected into the bottom cavity simultaneously. The mould then opens and the parts are ejected from the bottom cavity; the mould rotates again and the whole process is repeated. 2-Shot moulding is not considered a brand new method of manufacturing. In fact it has been used for years to produce items that we see and use every day. Toothbrushes, tools, kitchen utensils and toys are but a few examples of multi-shot moulding being used to produce relatively cheap items in large production quantities.
Why do we use 2-Shot Moulding?
Previously, manufacturers of high volume metal or plastic- to- rubber component assemblies have processed them via chemical or mechanical bonding, and by using adhesives or over-moulding. Examples of the types of markets that lend themselves to these types of sealing products are Automotive, Life Sciences and Aerospace & Defence. Although these production methods may achieve the final assembly requirement, the many different processes involved are lengthy, costly, and can be fraught with problem areas that require stringent controls. A failure in any of these areas will result in poor quality parts, therefore often deeming these methods unsuitable for critically engineered components.
Why do we use 2-Shot Moulding?
When designing a new 2-Shot moulded product (or replacing an existing assembly part) our engineers review each application parameter carefully, and utilise years of sealing experience and materials expertise alongside the latest 3D modelling technologies and FEA simulation programs before presenting a seal proposal. This allows us to anticipate and analyse the finest details of mould performance, and means we can adjust our seal design to ensure our customers receive the highest level of performance possible from our engineered 2-Shot seal solution. The result means we supply our customers with high integrity parts with a powerful molecular bond, reduced production cycle times (as many additional processes are removed from the production line) and comprehensive cost reductions as all parts are produced in a single manufacturing tool (meaning reduced running costs and the removal of pre and post moulding processes).
2-Shot moulding is not just a way of manufacturing simple, high volume parts. Our application engineers are always breaking norms and pushing design limits to consider more creative ways of producing high performance engineered sealing solutions to meet our customer requirements.
Read more about our 2 shot mouldings HERE
Why use PTFE seals?Polytetrafluoroethylene (PTFE) is a thermoplastic polymer that can be used in a variety of sealing applications; it is particularly suitable where the application conditions exceed the parameters of elastomeric seal use, but are not as highly demanding as applications that require the use of metal seals.
What is PTFE?
Discovered accidentally in the DuPont™ laboratory in Jackson, New Jersey, USA in in 1938. The molecular structure of PTFE is based on a linear chain of carbon atoms which are completely surrounded by fluorine atoms. The carbon-fluorine bonds are among the strongest occurring in organic compounds. As a result PTFE has thermal stability across a wide temperature range. It’s high melting point (342 °C) and morphological characteristics allow seal components made from virgin PTFE to be used continuously at service temperatures of up to 260 °C, and with the addition of fillers – up to 300°C. It has the unique ability to resist material degradation, heat-aging and alteration in its physical properties during temperature cycling. Alongside this rare combination of material characteristics PTFE also has unlimited shelf life.
Why use PTFE seals?
Notably PTFE demonstrates extraordinary chemical resistance: the intrapolymer chain bond strengths preclude reactions with most chemicals, thereby making it chemically inert at elevated temperatures and pressures with virtually all industrial chemicals and solvents. Only a few media (some molten alkalis) are known to react with PTFE seals making them the perfect sealing solution for highly aggressive chemical applications. PTFE also has the lowest friction coefficient of any known solid; it has self-lubricating capabilities which offers continuous dry running ability in dynamic sealing applications and has superb stick/slip capabilities.
Focus on dry coatings
The advantages of using PTFE in sealing applications are; functionality at high and low temperatures, dynamic sealing with high wear capabilities, high pressure sealing (using combinations of PEEK back-up rings) and compatibility with highly aggressive chemical combinations. Our range of PTFE seal products include back-up rings, rod and piston seals, slipper seals and spring energised seals in a wide variety of sizes. Materials depend on application requirements but we offer a wide range from Virgin PTFE or including filler combinations of MoS2, glass, carbon, carbon fibre, graphite, and bronze. These characteristics make PTFE seals perfect for the demanding applications involved in Oil & Gas, Aerospace, Automotive and Chemical Process markets (to name but a few) and Ceetak’s engineering team are experienced in the design of PTFE sealing solutions to meet the complex specifications these types of application demand. Read our overview and more detail about PTFE seals HERE
Why use metal seals?The use of metal seals as an engineered sealing solution is appropriate where it is not possible to use elastomeric or polymer seals due to extremely demanding application requirements. For example, these could include applications with extremely high temperatures (300°C upwards) and pressures, intense radiation, cryogenic conditions or highly aggressive chemicals.
How do metal seals work?
The metal seal concept is based on plastic and elastic deformation of the seal during compression which creates a sealing interface. The metal seal is compressed in the cavity on average about 20% of its original free height. The force generated through compression of the ring produces a high contact stress at the seal/cavity interface. This force is then supplemented by the pressure-energisation force which rises in proportion to the increase in differential pressure inside the seal cavity.
What types of metal seal are there?
There are three types of seal energisation; self, spring and pressure energisation. By design metal C-rings are self-energising due to the good spring back characteristic of the C-shaped profile. Additionally, they can be used in internal, external and axial pressure conditions. The different base material characteristics and heat treatments, along with material thickness, and cross section of the seal also determine the compressive load. This is directly related to the sealing level achieved and is known as “self-energisation”. Spring energised seals have excellent spring back properties and are typically used to improve leakage rates by increasing the load on the sealing interface. All metal seals can use system pressure to generate a hydrostatic load to obtain the highest level of sealing possible; this is known as pressure energisation. At high pressures this becomes an advantage and allows the design of metal seals for applications of 25,000 PSI and above.
Ultimate seal performance
Once the metal seal profile and material has been selected depending on the application, there are a variety of platings and coatings available. These can modify the surface properties of the seal to create a malleable outer surface layer. Typically precious metals such as gold and silver are used for plating, but many other options are available with two common ones also being Tin or PTFE. This layer ensures optimum sealing despite any mating surface imperfections. The plated or coated layer also reduces coefficient of friction so the seal can slide and bed down during initial compression. Consequently, this prevents galling. As well as providing better physical properties to the seal, coatings and platings are chosen to withstand high temperatures and aggressive (often corrosive or oxidizing) environments. There are ever changing industry demands and fast paced technology developments – particularly from customers in the Oil & Gas, Aerospace & Defence and Automotive markets. Therefore, we are challenged daily with applications where the boundaries are being pushed to the absolute limit. We have designed metal seals into F1 car exhaust systems, subsea repeaters, oil and gas production valves as a few examples; the capabilities of high performance metal seals is endless. Working with the latest developments in materials, platings and manufacturing technology; our engineering team design the sealing solutions to meet the complex specifications these types of application demand. Learn more about metal seals HERE
Why use Push-in-Place gaskets?Where a seal groove follows an irregular path or profile, a common sealing solution is to design a custom Push-In-Place (PIP) gasket that has the same profile as the centre line of the groove, simply drops into place and is retained by the features of its own design.
Gasket sealing overview
There are many ways to seal the static join between two components. This could be to keep fluids inside a cavity or to keep fluids or contaminants out of a device or assembly. The options can vary from simple O-rings, moulded elastomer gaskets and flat sheet style materials, to liquid gaskets (or RTV’s). As with all sealing applications, the optimal sealing solution is designed by first reviewing the application conditions. These include temperature, pressure, fluid exposure etc; and other variables such as life requirement, equipment serviceability and seal compression set should all be considered. Arguably though, compared to other sealing applications, when designing face, cover or flange sealing solutions it is imperative to consider the packaging requirements and assembly issues of gasket sealing options. The need to avoid or seal around bolt holes (or other retaining/clamping devices), together with optimizing hardware wall sections or depths can play a very important part in choosing the most suitable gasket sealing technique.
What are Push-in-Place gaskets?
With the right combination of application conditions, an o-ring style approach to sealing may be the most appropriate. O-rings tend to require relatively shallow grooves compared to their cross section in one half of the assembly, and in cases where the groove is round in plan view – they can be a good solution. However, in cases where the groove follows a more irregular path or profile (frequently referred to as a “racetrack”) the O-ring can sometimes pop out in places – often where the two housing parts are being brought together. A common solution is to design a custom moulding that has the same profile as the centre line of the racetrack groove and simply drops into place. A similar approach is used when the application or hardware constraints steer the design towards a gasket that has a greater cross section depth compared to the width; this would typically be designed so the centre line of the gasket matches the centre line of the groove plan profile – again so that it drops easily into place. An inherent problem with gaskets that can drop into place is that often, they easily drop out of place too. If the component needs to be inverted, or has the potential for rough handling during assembly then the gasket may become partially or fully dislodged from the groove, which results in a badly sealed interface. The best solution to this issue is to incorporate retention pips or bumps in the gasket design, a solution known as Push-In-Place (PIP) gaskets. These require a distinct force to put them into the groove, and as a result require more than just gravity to get them out of the groove.
Why use Push-in-Place gaskets?
There are other less effective solutions for tricky groove sealing, such as the use of a sticky grease, or the use of an adhesive. These can bring compatibility and health and safety issues to consider. Additionally, it carries the risk that any contaminant could keep the gasket off the surface that it is supposed to be sealing against. Therefore, the integrity of the seal can be severely compromised as a result. Neither of these approaches can be recommended, and instead the use of retention pips is a safe and secure way of ensuring the gasket remains in the groove. To determine the optimum number, size and position of the retention bumps, Finite Element Analysis (FEA) is used. This ensures they provide sufficient squeeze to prevent the gasket being easily dislodged. Additionally, it is important there’s no overfilling the groove space with seal material or interfering with the seal compression footprint against the hardware faces. The bumps can be strategically positioned to control any distortion of the gasket under pressure or temperature conditions. For example, low temperature conditions can shrink the gasket and tighten the radius it adopts around a bend in the racetrack profile. This can reduce the seal compression locally and potentially create a leak path.
Correct positioning
By positioning retention bumps at either end of the bend, the thermal contraction can be controlled to minimize the risk of leakage. Effective retention ensures that if the part needs to be inverted (which could be the preferred assembly method for practical reasons) or is subject to rough handling – the gasket remains correctly located in the groove. For large gaskets this is normally the most effective solution. On smaller gaskets (particularly those located well inside the periphery of the assembly), there is a significant risk of a dislodged gasket being totally undetected unless using a PIP gasket design. It’s possible to include tell-tale signs on a gasket design. For example, if a part of the elastomer gasket protrudes sideways through a gap in the housing wall, the presence of the gasket can be checked. This would be either with the human eye or an automated vision system. However, this does not ensure correct seating all around the gasket length, and cannot be used for internal gasket locations. In these cases a missing or badly fitted gasket would only be discovered during post-build testing, or even worse with a machine failure at a customer.
Further considerations
If included at the design stage, the small additional tooling and material costs associated with a PIP gasket are negligible compared to the costs of an impossible assembly scenario, strip and re-build costs on the assembly line, or the consequential costs associated with failure of an assembly once delivered to a customer. More information on PIPs and gaskets can be found HERE
Perfluoroelastomers in valvesIs it time to re-visit using perfluoroelastomer seals in your valves? First developed by DuPont™ in the late 1960s, perfluoroelastomers (or FFKMs), are now widely known and understood in a variety of markets. But for those that may be less familiar with these high performance materials, here is a quick recap...
What are perfluoroelastomers (FFKMs)?
They are essentially highly or fully fluorinated compounds with a fluorine content above 75%, and they offer outstanding chemical resistance. Generally better than all other elastomer types, FFKMs are often referred to as having the resistance of PTFE but in elastomer form. The term “universal” chemical resistance is commonly used; although it’s not strictly true as we will learn shortly. Unlike PTFE, the molecular make-up of FFKM includes crosslinks (or spring-like elements). This is contrast to just a backbone of carbon-carbon atoms surrounded by protective fluorine atoms. These crosslinks are what give the FFKMs their crucial elastic behaviour (in other words returning quickly to their original shape after being deformed). But the crosslinks are also a drawback as they can be a weak point for a chemical attack. Different crosslinking systems can be used when developing FFKMs and the choice will determine the high and low-temperature capabilities. Compounds developed for extreme high-temperatures (up to around 325oC) generally have a less broad chemical resistance. This is in comparison to the lower temperature grades (up to 225oC). Similarly, FFKMs developed to have excellent resistance to specific fluids (such as amines or high-temperature steam) can have limitations of low-temperature capability or compression set. As a result, there is no universal material that covers all application criteria bases.
A variety of grades
Previously the number of perfluoroelastomer grades was less prolific than other elastomer types such as FKM, EPDM, and NBR. However more than 50 years of technical developments have created a range of FFKM grades for specific and challenging applications. These are particularly in chemical process, oil and gas, semiconductor, and aerospace industries. Additionly, options with a hardness range of 65 to 90 durometer, and versions that meet international standards or specifications for food, medical, CPI, and oil & gas applications means the portfolio of FFKM-based compounds available to engineers is now substantial. In addition to technical developments, manufacturers and compounders have also been addressing the only real drawback of FFKM materials; the cost. They are difficult and time-consuming base polymers to manufacture. With a relatively low volume production base and sometimes lengthy processing times, FFKM seals carry a high financial premium over FKM seals. Even several times greater than FKM itself has over NBR. In recent years, there’s been more focus on making general-purpose grade FFKMs with broader temperature and chemical resistance capabilities more financially attainable. The initial procurement costs remain high compared to less capable elastomer bases. The overall cost of ownership may now be more appealing than it was twenty or even ten years ago. The ability of FFKM seals to survive for much longer in applications where exposure to a variety of fluids (perhaps wider than originally specified) is possible. This considerably reduces unplanned costs associated with maintenance and downtime.
Focus on dry coatings
The cost of unscheduled maintenance and repair in pump and valve equipment can be high in any industry, but exceptionally so in petrochemical, oil & gas, and semiconductor. When these costs are fully considered in the overall lifetime of a product, the initial price of seals in a valve is considered relatively minor, but it can still be a barrier in the material selection process. With both technical and commercial developments in recent times FFKM materials now compare more favourably against other materials for static, or low-duty dynamic applications in valves. In applications where persistent and sporadic issues keep coming back to cause problems, they are now a more financially attainable choice of material to avoid re-work, overhaul, downtime, customer dissatisfaction, and ultimately, more costs. Read more about FFKM as a suitable sealing material HERE
Seals for valve applicationsValves are imperative for isolation and control functions, and can be found in a broad range of industries such as Oil & Gas, Water & Wastewater, Food & Beverage and Hydraulics & Pneumatics. We supply seal products into valve applications in a variety of styles including ball, gate, flap, plug, butterfly, spool, check and solenoid valves.
Characteristics of valve sealing
There are many challenges involved in valve application sealing. Conditions and application parameters can vary with temperature extremes from cryogenic up to 325°C, and pressures up to 1000+ bar. We need to carefully consider the materials to suit all fluid compatibility required. Often the seal design requires low breakout friction and offers no stick-slip following prolonged static periods when the valve is not used. Alongside this, customers require long service life and minimal maintenance. Valve styles include ball, gate, flap, butterfly, spool, check and solenoid valves. Also different types of actuation include manual, pneumatic, hydraulic and electro-mechanical. Different areas of the valve demonstrate different sealing requirements.
Valve sealing areas Actuation
There are a range of sealing solutions to suit the variety of actuation types employed with valves. This includes diaphragms for pneumatic actuation, rotary and linear hydraulic and pneumatic seals, and gaskets and O-rings. Seal materials are available to suit all ranges of temperatures and media associated with the actuator and any external contaminants it encounters.
Body bonnet joint
This is a static sealing location that can often be sealed with an O-ring (a wide range of materials are available to satisfy fluid compatibility). However dependent on the fluid, pressures and temperatures, metal seals can be more suited to the application. Additionally, housing deflection under pulsating system pressures may worsen compression set sealing issues. Therefore, a custom gasket design could be potentially more suitable than an O-ring. For subsea valves, a sealing solution capable of handling alternating pressure regimes and multiple media types may be required.
Stem
A critical and dynamic sealing location with often demanding requirements. Depending on the application of the valve, the seals used here may see frequent dynamic operation and will require a long wear life. In other cases, the valve may be static for long periods and then require operation with minimal break-out friction forces. In all cases, reliable sealing is paramount.
Seat body
Valve seats are often mounted in a housing or carrier which has a sealed interface within the valve body and in these cases it can be a critical location to seal correctly. Dependent on the design, the seal location may be subject to upstream or downstream pressures at various points. In some cases fluid flow through the valve can pull or wash-out seals from their grooves if they are not designed to prevent this. As pressure conditions change with valve operation, the seals here may be required to withstand small (but sometimes frequent) movements of the carrier without sticking or wearing.
Valve Seat
A wide variety of elastomers and engineered polymer materials can be moulded or machined to suit valve seat components. Bonded rubber to metal or rubber to plastic seals can provide bespoke solutions. These offer benefits in terms of space envelope, component count or ease of assembly.
Design & Development for valve sealing applications
Our engineering team understand the application demands associated with valve sealing and can support our customers with the design of seals for every position within the valves. We provide a complete design service; from initial seal geometry and profile choice, to material selection and prototyping, through to final production. This is utilised with our seal design experience and materials expertise, alongside technology such as 2D/3D CAD and FEA analysis. These simulate performance before finalising each individual seal design. We are familiar with the requirements of individual markets and their valve applications. Our seals are manufactured in materials with approval requirements such as NORSOK M-710, ISO23936-2, NACE, WRAS and FDA. For more on our design and engineering service, see our dedicated page HERE
3D printing for seals3D printing has developed significantly and now performs a crucial role in many applications. 3D printed products vary from fully functional to purely aesthetic applications; with the most common application being for manufacturing. Here we discuss how our engineers use 3D printing to demonstrate a seal concept.
What is 3D printing?
3D printing is typically the more common name used for additive manufacturing. This process involves the construction of a three dimensional shape that is designed and generated from a computer aided design program (or CAD). The most typical process used for 3D printing is FFF (Fused Filament Fabrication) or FDM (Fused Deposition Modelling). The FDM process uses a continuous filament of a thermoplastic material that is then deposited onto the 3D print bed, creating layer by layer and gradually building up the structure of the 3D model. This is the process we commonly use to create our design and development range of 3D printed models and seal prototypes.
What material is suitable for 3D printing?
The materials used for 3D printing must of course be compatible with the process – these include a range of thermoplastic grades. Typical suitable material grades include; Polylactic acid (PLA), Acrylonitrile Butadiene Styrene (ABS), Thermoplastic Polyurethane (TPU), Nylon and Polypropylene (PP). The most common grade we use for 3D printing is PLA – for its great strength and stability. We’ve also adapted our design process to use more TPU based material grades, as it loosely demonstrates the same properties as elastomer grades and is better for using in prototype programmes where mechanical fit in groove is tested.
Why use 3D printing for seals?
3D printing can be used for a variety of designs and seal types; from O-rings, gaskets and lip seals – to grommets, multi shot mouldings and large seal assemblies. There are many benefits of using 3D printing during the initial design stages of a project. The rapid turnaround means that a simple seal design can be produced in around 15 minutes, and even more complicated parts can be manufactured in the same day. We can even print the application housings and it’s the perfect way to demonstrate to an engineer what they can expect from a seal part in terms of shape and fit for hardware without the lead time and cost of cutting a prototype tool for moulded parts. One example of this is by quick turnaround of gasket designs typically to suit automotive applications or similar critical markets. Our engineers can design the concept and then 3D print a rapid prototype of a gasket to suit a 3D printed gauge groove. This further demonstrates to the customer that the seal has been fit checked for installation and builds further confidence in the design recommendation. Our engineers combine the 3D print with FEA simulation reports to offer a fully engineered sealing solution. Learn more about our design and simulation service HERE
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Product Range
Our seal products range from simple static O-rings to complex and bespoke seal designs in specialist materials. Whatever your application, we have the seal product for you.
