The following serves as a guideline in the choice of material for
elastomeric seals such as o-rings, gaskets and diaphragms. There can never
be one size fits all when it comes to the choice of an o-ring for specific
applications. Depending on the industry, sealing products may be subject to
varying degrees of abuse. Generally, the elastomeric material that these
products are made of are expected to function even at elevated temperatures
while in contact with corrosive chemical media. Design criteria will also
have to consider factors as ozone degradation with prolonged weather
exposure. The most common material grades that are used in its manufacture
are as below:
1) NBR Rubber
Nitrile rubber has extraordinary mechanical properties and that is the reason that it is been used in an extensive range of applications. Nitrile rubber, or NBR, is not suitable for use in applications where exposure to weathering is expected because it suffers degradation as a result of ozone attack. Resistance to wearing as well as abrasion is outstanding, and nitrile rubber is unique in its ability to return to its original form upon the release of a sustained loading. This characteristic of NBR material is termed as low compression set, and is a critical factor to be considered as any changes in dimensions would have an adverse effect on joint seal integrity. NBR rubber is also referred to buna N and Nitrile, and is chemically known as acrylonite-butadiene copolymer. A common use of NBR elastomeric material is for the manufacturing of o-rings and seals for use in hydraulic cylinders in hydraulic equipment manufacturing. This is due to its excellent resistance to the abuse of wear and abrasion.
Buna N, NBR and Nitrile rubber are the generic terms that refer to the acrylonitrile-butadiene copolmer. A sector of industry where the use of NBR rubber seals is commonplace include hydraulic equipment manufacturing, as in hydraulic cylinders. Properties of NBR include excellent resistance to abrasion and wear, the ability to undergo loading without permanent deformation (low compression set) and good tensile characteristics. Its superior mechanical characteristics makes it ideal for use in many applications, though it lacks resistance to ozone attack.
2) EPDM (ethylene-propylene)
The elastomeric material of choice in the automotive manufacturing industry is EPDM, or ethylene-propylene. Typical performance requirements of sealing parts like o-rings and gaskets in automotive components factor in resistance to substances and fluids like greases, alkalis, ketones and hydraulic fluids. EPDM material can resist high temperature and aggressive media, while continuing to perform to expectations.
A seal design engineer will need to factor in varies concerns like service conditions, change of service environments, the ability of the seal to withstand thermal and chemical conditions for sustained durations in operations, as well as cost efficiency when it comes to choosing the right elastomeric material for the seal. There is also the possibility of over-engineering a seal and incurring unnecessary expenses.
Brake systems and components in automotive manufacturing uses EPDM as a material of choice for sealing applications. Ethylene-propylene compounds gives reliable performance under conditions of elevated temperature, and they are highly resilient to exposure to corrosive media like greases and mild acids, alcohols, alkali substances and ketones.
3) Viton (Fluorocarbon)
Fluorocarbon (FKM) seals are characterized by their high performance for sealing applications where exposure to ultraviolet degradation, ozone and weathering is expected. FKM material also has desirable properties like low compression set and low volume swell, which are critical factors to consider in join seal design. Volume swell is the change in volume of a material as a result of absorption of chemical fluid into the sealing component, and the effect is more pronounced when the seal is subject to high pressure. Volume swell will adversely affect the properties of the sealing material, and can cause extrusion of the material. FKM material is commonly found in applications in the aircraft industries, oilfield equipment manufacturing and petrochemicals industries.
Temperature extremes, chemical corrosiveness, ozone and UV resistance and mechanical properties like low compression set and gas permeability resistance are the advantages of using fluorocarbon or FKM seals. Because of its versatility, Viton is a commonly specified material for use in an extensive range of applications. Industries where FKM is used include, but are not limited to, that of the aerospace, oil and gas, petrochemicals and more.
4) FFKM Perfluoroelastomers
The high-end in sealing technology with the most demanding in performance criteria is perhaps found in semiconductor chip manufacturing. Seals and o-rings come into contact, or are exposed to highly aggressive chemicals. In addition, temperature extremes encountered in the production subject seal parts to excessive abuse. Perfluoroelastomers is the ultimate compound that satisfies the requirements in such harsh working conditions.
The top of the range elastomeric material which is used for sealing applications in the most severe and demanding environments during manufacturing processes is perfluoroelastomers (FFKM). Perfluoroelastomers are used where no other elastomeric material will do the job. Extreme heat and contact with harsh chemical media are conditions that are common in oilfield applications and semiconductor processes. The ability to resist rapid gas decompression (RGD), also known as explosive decompression, is unique in perfluoroelastomers due to its high resilience and durability. Explosive decompression is a phenomena commonly found in oil and gas extraction processes, where the sudden release of high pressure gases or liquefied gases causes the expelling of absorbed gases within the elastomeric seals and o-rings, in a manner which damages the seal. Perfluoroelastomers are also specified for their exceptional ability to withstand extreme thermal and chemical environments.
Thermal Effects on O-Rings
Low Temperature Effects: Seals and o-rings behave in ways that can compromise their performance when under conditions of low temperature. Elastomeric materials, like most other materials, contract at low temperatures. A sealing component that is subject to low temperatures will experience a reduction in compression and subsequent failure due to leakage. Brittleness and lack of flexibility sets in when low temperature limits are exceeded, and failure of seals happen through hardening of the seal material and reduction of its ability to resist deformation. Low compression set, which is a desirable property of elastomeric material, is also compromised, resulting in the failure of a seal to return to its original dimensions upon the release of a sustained loading. Choosing the right material is crucial in effective seal design.
High Temperature Effects: The deterioration of o-rings and seals happens at elevated temperatures. High temperature causes the softening and swelling of seals and o-rings, resulting in greater friction in dynamic applications. High temperature also causes physical and chemical changes within the elastomeric material which become irreversible over extended service conditions. Volume changes, induced compression set as well as an increase in seal hardness are the results of material deterioration. Many elastomeric material are capable of withstanding elevated temperatures of up to 300 degrees F, with perfluoroelastomers at the high-end of performance at 600 degrees F for short duration exposures.
Rubber Components and Seals in Automotive Manufacturing
Since 1981, Gmors has been manufacturing o-rings of various sizes. rubber parts, seals and gaskets for the automotive industry. Applications are found in vehicle transmissions, air conditioning systems, brake and steering systems, clutch assemblies, engine gaskets, fuel and cooling systems seals and numerous other automotive parts.
Selecting the Right Elastomer for Your Application
The expected service environment is an important criteria in the selection of elastomeric seals. The following are important criteria to consider, but please contact our material specialists for free consultation.
1. Types of fuel to be sealed and the expected contaminants and additives.
2. Thermal conditions including highs and lows, and anticipated excursions to elevated temperatures.
3. Operating pressures including highs and lows, and rates of compression and decompression.
4. Static or dynamic application, and whether motion is rotary or reciprocatory.
5. O-ring sizes and tolerance within groove.
Cost effectiveness is a major consideration in selecting the right seal. An over-engineered seal that outperforms its corresponding parts or has a service life beyond its warranty period may add unnecessary costs to overall production. Generally, EPDM suffice for most typical applications where seals come into contact with heat and steam, but may not be suitable for applications at higher temperatures and when contact with corrosive fluids is expected. Unscheduled maintenance can be avoided along with costs savings because maintenance cost typically far outweighs the initial cost of the seal.
Automotive Powertrain Gaskets and Seals
Emissions control, extended periods of warranty as well as elevated service temperatures all leads to greater demands on the performance of elastomeric seals in engines and powertrain systems. Engines that run at higher temperatures along with aggressive lubricants all have deleterious effects on elastomeric materials.
Transmission systems in cars makes use of a combination of seals and o-ring sizes of various dimensions because their operation involves a complex set of movements. Gmors manufactures seals for automatic transmissions with reliability and durability meeting the performance criteria of vehicle drivetrains. The goal of automotive manufacturers is to achieve maintenance free drivetrain systems that fulfill a zero leakage requirement while working at high efficiencies.
Seal products used in automatic transmission include elastomeric parts like o-rings, lip seals, seals for fuel injectors and others. The ability to perform under different chemical environments at elevated temperatures without deterioration of physical properties is expected throughout the service life of the vehicle.
Power Steering Applications
Various sizes of o-rings and seals are used in the sealing of hydraulic rams, turning shafts and reciprocating rods for power steering applications subject to continuous abrasion. Sealing parts like reciprocating seals must resist constant wear and withstand high pressure in the hydraulic system during power steering operation.
Gmors designs and manufactures all sizes of o-rings and seals for the automotive industries to withstand a variety of fluid exposures under required operating temperatures. Important performance criteria like compression set, volume swell and abrasion resistance are all factored into the design.
Operating requirements for o-rings used in automotive applications may be specified for pressures up to 2000 psi, and temperature variation in the range of -40C to 200C. Contact fluids may be in the form of coolants, brake fluids, refrigerant, engine and compressor oil, transmission and power steering fluid.
Seals and gaskets
Viton© (FKM) fluoroelastomer is the preferred compound for the manufacturing of automotive engine seals, gaskets and o-rings sizes of varies dimensions because of its outstanding ability to maintain stability at high temperatures. Gmors produces seals and gaskets made from Viton©for use in car fuel injection and fuel pump applications. Rubber products that are custom molded to precise specification are also offered.
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