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.
Moulded gaskets for an automotive applicationAn existing customer (an automotive manufacturer) approached our engineers with an application where they were experiencing failures of a seal designed and manufactured by another rubber seal provider.
The application
This moulded gasket is used within a valve housing in an automotive application. The competitor gasket experienced failure at the “T-junction” areas of the seal. Our customer had experienced chronic failures of their existing moulded gasket design at high temperatures and high pressures. The seal is required to perform under pulsating pressure of up to 50 Bar and temperatures of up to 150°C. Our engineers reviewed the existing gasket design and application conditions and recommended an increase in height of 0.40 mm. This was to increase the compression and improve the sealing function. Additional beads were also added to further stabilise the gasket in the groove.
The challenges
Prototype parts were manufactured from a single cavity soft tool and sent to the customer for in-house testing and validation. The prototype gaskets very nearly passed testing but did not quite reach the 50 Bar pressure requirement at 150° C (42 Bar reached). This was still a great improvement on the performance of the customer’s original gasket. Analysis of the customers test data and images of the tested parts, determined there were areas where the gasket was sliding in the groove and then shearing as the pressure pulsed. We resolved this issue by our engineers adding beads to the rear of the T-intersections of the gasket. This provided additional support and further stabilised the gasket at the high-pressure stress points in the groove, and reduced movement within the housing. The number of additional beads added needed to be balanced carefully with calculations on groove fill. Further development captured the cleanliness requirements and altered radii on the beads.
Customer satisfaction
The new design was approved, and the customer moved to production tooling stage and sample parts were produced to PPAP Level 3 for production. More information about our mouldings & gaskets on the link HERE
Special O-rings for an automotive applicationOur customer manufactures high performance oil and vacuum pump solutions, and approached our engineers with a new O-ring application for review.
The application
Our customer required an FKM (Viton™) 60 shore special O-ring. This is to meet Porsche material specification PN707 Class 2 (Oil), Class 5 (Fuel/FAME mix) and Class 12 (Blowby gas). This proved to be a very cost sensitive project with a short lead time. Additionally, we did not have an existing grade in our materials portfolio to meet this specialised O-ring specification.
The challenges
Our engineers reviewed the application and we provided two material options. The first is a lower cost grade of FKM (Viton™) A grade, and would possibly meet the Porsche specification required. The second material, a medium to higher cost FKM (Viton™) B grade that will definitely meet the specification. We supplied a quotation for the two material types. Additionally, the quotation included production tooling, PPAP Level 3 submission, testing for both materials and a pre-production batch of O-rings. The project was urgent and we were able to accommodate PPAP Level 3 grade O-rings for both materials to be manufactured from the same tool. Also, to save time we conducted material testing in tandem with the manufacture and preparation of the the production tool. The choice of compound to be used in the tool would be made on review of the results of material testing. On completion of the material testing, the customer reviewed the results with Porsche. The decision to produce O-rings from the FKM B grade was made.
Customer satisfaction
By this stage of testing, production tooling was complete, allowing manufacture of PPAP 3 samples and the pre-production batch to commence. Pre-production O-rings were supplied to the customer in the promised 12-week lead time together with PPAP Level 3 and PPAP 3 samples. See this link for more on our O-ring range and expertise: HERE
High speed Rotary seals for electric vehiclesThe electric vehicle industry is growing; global manufacturing and registrations of electric vehicles is increasing exponentially each year. Our engineers have extensive experience in designing seals for automotive applications, but we still find new challenges involved in sealing components within hybrid, hydrogen fuel and full battery powered electric vehicles.
The Application
Our customer has 30 years’ experience of providing pioneering technologies globally to the mobility industry. This established organisation is a supplier of powertrain solutions for electric and hybrid vehicles and traditional internal combustion power engines. The team of powertrain development experts approached our engineers for a high speed rotary seal. This is for the gearbox within an electric vehicle. The position of the rotary seal is needed between the wet transmission and dry e-motor, and pressed into a bulkhead housing. The sealing lip runs on the surface of the transmission rotor shaft. It is pressed radially by a tension spring onto the shaft, and requires a dust lip to provide protection against dirt and debris from the environment on the dry motor side. The shaft and housing dimensions, are all fixed and provided by the customer. These include full dimensional, surface finish, pressure, temperature and media specification for our engineers to review and propose a bespoke seal design.
Our sealing solution
The application media was a synthetic oil. This is relatively standard for an automotive application. However, because of the maximum working temperature, FKM (Viton) was the elastomer material to meet the required range. As with many applications within electric vehicle gearboxes, the shaft speed is particularly high at 8500 RPM. Typically with these high speeds, seal design needs to ensure minimal friction to ensure the service life required. Our application engineers designed a bespoke, double lipped spring energised seal. On the dry e-motor side, the rubber lip has been designed to act as a dirt and dust excluder. There is a slight clearance from the shaft to avoid friction which prevents damage to the seal, additionally any unnecessary wear to the rotary system as a whole. In the wet transmission side it is imperative that the oil is kept away from the e-motor with the same minimal friction requirements. Consequently, our engineers designed the seal with an inlaid PTFE lip with 15% graphite fill. It is energised with spring to ensure force to achieve ultimate shaft sealing performance. Read more about our rotary seals 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
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
Moulded gaskets for an automotive applicationAn existing customer (an automotive manufacturer) approached our engineers with an application where they were experiencing failures of a seal designed and manufactured by another rubber seal provider.
The application
This moulded gasket is used within a valve housing in an automotive application. The competitor gasket experienced failure at the “T-junction” areas of the seal. Our customer had experienced chronic failures of their existing moulded gasket design at high temperatures and high pressures. The seal is required to perform under pulsating pressure of up to 50 Bar and temperatures of up to 150°C. Our engineers reviewed the existing gasket design and application conditions and recommended an increase in height of 0.40 mm. This was to increase the compression and improve the sealing function. Additional beads were also added to further stabilise the gasket in the groove.
The challenges
Prototype parts were manufactured from a single cavity soft tool and sent to the customer for in-house testing and validation. The prototype gaskets very nearly passed testing but did not quite reach the 50 Bar pressure requirement at 150° C (42 Bar reached). This was still a great improvement on the performance of the customer’s original gasket. Analysis of the customers test data and images of the tested parts, determined there were areas where the gasket was sliding in the groove and then shearing as the pressure pulsed. We resolved this issue by our engineers adding beads to the rear of the T-intersections of the gasket. This provided additional support and further stabilised the gasket at the high-pressure stress points in the groove, and reduced movement within the housing. The number of additional beads added needed to be balanced carefully with calculations on groove fill. Further development captured the cleanliness requirements and altered radii on the beads.
Customer satisfaction
The new design was approved, and the customer moved to production tooling stage and sample parts were produced to PPAP Level 3 for production. More information about our mouldings & gaskets on the link HERE
Special O-rings for an automotive applicationOur customer manufactures high performance oil and vacuum pump solutions, and approached our engineers with a new O-ring application for review.
The application
Our customer required an FKM (Viton™) 60 shore special O-ring. This is to meet Porsche material specification PN707 Class 2 (Oil), Class 5 (Fuel/FAME mix) and Class 12 (Blowby gas). This proved to be a very cost sensitive project with a short lead time. Additionally, we did not have an existing grade in our materials portfolio to meet this specialised O-ring specification.
The challenges
Our engineers reviewed the application and we provided two material options. The first is a lower cost grade of FKM (Viton™) A grade, and would possibly meet the Porsche specification required. The second material, a medium to higher cost FKM (Viton™) B grade that will definitely meet the specification. We supplied a quotation for the two material types. Additionally, the quotation included production tooling, PPAP Level 3 submission, testing for both materials and a pre-production batch of O-rings. The project was urgent and we were able to accommodate PPAP Level 3 grade O-rings for both materials to be manufactured from the same tool. Also, to save time we conducted material testing in tandem with the manufacture and preparation of the the production tool. The choice of compound to be used in the tool would be made on review of the results of material testing. On completion of the material testing, the customer reviewed the results with Porsche. The decision to produce O-rings from the FKM B grade was made.
Customer satisfaction
By this stage of testing, production tooling was complete, allowing manufacture of PPAP 3 samples and the pre-production batch to commence. Pre-production O-rings were supplied to the customer in the promised 12-week lead time together with PPAP Level 3 and PPAP 3 samples. See this link for more on our O-ring range and expertise: HERE
High speed Rotary seals for electric vehiclesThe electric vehicle industry is growing; global manufacturing and registrations of electric vehicles is increasing exponentially each year. Our engineers have extensive experience in designing seals for automotive applications, but we still find new challenges involved in sealing components within hybrid, hydrogen fuel and full battery powered electric vehicles.
The Application
Our customer has 30 years’ experience of providing pioneering technologies globally to the mobility industry. This established organisation is a supplier of powertrain solutions for electric and hybrid vehicles and traditional internal combustion power engines. The team of powertrain development experts approached our engineers for a high speed rotary seal. This is for the gearbox within an electric vehicle. The position of the rotary seal is needed between the wet transmission and dry e-motor, and pressed into a bulkhead housing. The sealing lip runs on the surface of the transmission rotor shaft. It is pressed radially by a tension spring onto the shaft, and requires a dust lip to provide protection against dirt and debris from the environment on the dry motor side. The shaft and housing dimensions, are all fixed and provided by the customer. These include full dimensional, surface finish, pressure, temperature and media specification for our engineers to review and propose a bespoke seal design.
Our sealing solution
The application media was a synthetic oil. This is relatively standard for an automotive application. However, because of the maximum working temperature, FKM (Viton) was the elastomer material to meet the required range. As with many applications within electric vehicle gearboxes, the shaft speed is particularly high at 8500 RPM. Typically with these high speeds, seal design needs to ensure minimal friction to ensure the service life required. Our application engineers designed a bespoke, double lipped spring energised seal. On the dry e-motor side, the rubber lip has been designed to act as a dirt and dust excluder. There is a slight clearance from the shaft to avoid friction which prevents damage to the seal, additionally any unnecessary wear to the rotary system as a whole. In the wet transmission side it is imperative that the oil is kept away from the e-motor with the same minimal friction requirements. Consequently, our engineers designed the seal with an inlaid PTFE lip with 15% graphite fill. It is energised with spring to ensure force to achieve ultimate shaft sealing performance. Read more about our rotary seals 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
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.
