The group of oil seals used in dynamic applications include radial shaft seals that seal a rotating shaft around its circumference. They are also known as lip seals, but in this blog we will use the term oil seals.

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Usually, these oil seals are used to seal lubricating oil or grease and contain it within the application, so that moving parts such as bearings are continually supplied with enough lubrication. However, such seals are also used for sealing other liquids, gases, and solids, such as powders or granules.

All are fitted with a spring to preload the sealing lip. All these types are for non-pressurised or low-pressure applications up to 0.5 bar for diameters of a limited size. For diameter of 500 mm or more, the maximum pressure is 0.1 bar. For higher pressures, special types or PTFE lip seals can be used.

ERIKS type M (type B according to the DIN standard) has a single metal casing and rubber sealing lip. Since the casing is made of metal, it must be fitted in a well-finished, undamaged groove. Large volumes of oil seals with metal casings are often cheaper, which is why they are often used as original equipment in machines. However, if an oil seal has to be replaced, types with a rubber exterior (type R or RST) are easier to fit. Type MST is similar to M and commonly used. The difference is the dust lip in the MST oil seal that prevents dust and dirt reaching the sealing lip, and extends its service life in dusty environments.

ERIKS type GV (type C according to DIN) is equivalent to type M, but is a heavy-duty version with a double metal casing. This can be a useful solution with larger diameters in more demanding applications. There is also a version of this type with a dust lip; the GVST (type CS according to DIN).

ERIKS type R (type A according to the DIN standard) is identical in shape to type M, but has a rubber outer case with metal reinforcement on the inside. The rubber creates a good seal in the housing, even if the housing has suffered minor damage or is not in its best condition for other reasons. The RST version has a dust lip. These types are often chosen to replace a type with a metal outer case because they are easier to install and can cope with minor damage to the groove, such as scratches.

ERIKS also supplies the types GR and GRST. These are virtually identical to the types R and RST, except in this case the metal inner ring is also completely encased in rubber. ERIKS uses FKM rubber here as standard, so these seals are ideal for use in acidic environments.

An overview of the different standard types of oil seals and their main characteristics is shown below.

Outer case

• Metal

The metal used in the outer case of oil seals is usually made of carbon steel. Upon request, and depending on quantities, a different type of steel (such as stainless steel) can be used.

• Rubber or rubber fabric

The quality of the rubber or rubber fabric used to make an outer case is the same as the quality of the rubber sealing lip. Fabric reinforced rubber is, as the name suggests, rubber reinforced with a fabric.

Spring

Standard springs are made of carbon steel. We use stainless-steel springs for our GR and GRST oil seals made from FKM rubber. In some rare cases, an O-ring is even used as a spring element. Standard PTFE lip seals are not fitted with springs.

Sealing lip

The sealing lip is always made of a rubber or synthetic material. For oil seals with a rubber outer case (R, RST, GR, GRST), the rubber quality of the sealing lip and the outer case are the same.

The material of the sealing lip is chosen according to the liquid to be sealed and the rotational speed. For larger shafts, an NBR sealing lip can cope with surface speeds of up to 10-12 m/s, while an FKM lip is suitable for speeds of up to 35-38 m/s. 

Nitrile Butadiene Rubber (NBR, nitrile)

NBR, also known as nitrile rubber or nitrile, is the most popular material for an oil seal because of its good resistance to many oils and greases, such as mineral grease and hydraulic oil. Depending on their composition, synthetic oils and greases, such as those based on glycol, can damage NBR rubber materials. Depending on the amount of glycol, a PTFE lip seal may be the best choice. NBR is also unable to cope with contact with acids and solvents. The rubber is suitable for oil and grease at temperatures from -35 °C to 100 °C.

Most ERIKS oil seals, such as the types M, MST, R and RST, are made of NBR as standard.

Fluorine rubber (FKM, Viton™)

FKM or FPM, which is in well-known brand Viton™, can withstand higher liquid temperatures of up to 180 ˚C. FKM is highly resistant to strong acids and bases, as well as to synthetic oils and greases. Glycol-based oil and grease, however, can also damage FKM.

Because of the higher temperature resistance of FKM, this material is also chosen for applications where higher speeds play a role, which raise the temperature at the sealing lip considerably. Usually, using FKM will result in a longer life than using NBR. This compensates the higher price of FKM compared to NBR, as an FKM does not have to be replaced as frequently. The low temperature resistance of standard FKM is limited to -15 ˚C.

Polytetrafluoroethylene (PTFE, Teflon®)

PTFE, which is used in the well-known brand Teflon®, is less commonly used, but it is the preferred material for specific rotating seals in the chemical, food and pharmaceutical industries. This material is notable for having a very low frictional resistance and the best chemical resistance. It can also withstand a very wide range of temperatures in these types of seals; -80 ˚C to 200 ˚C. The shafts on which oil seals with PTFE lips are used require a harder and finer finish. Something like an axle sleeve can also be used to meet this requirement.

EPDM

EPDM oil seals are less common. They are used in solvent, hot water and steam applications, EPDM resists low temperatures down to -50 °C and UV radiation well. Some types of EPDM are also suitable for higher temperatures up to +150 °C. EPDM oil seals are usually available upon request.

VMQ (silicone)

VMQ, also known as silicone, is also used for oil seals, but this is less common because the mechanical strength of VMQ is low and this material has poor wear-resistance This makes it less suitable for dynamic applications, but it can withstand fairly low and high temperatures from -60 °C to 200 °C. Many types of VMQ are also suitable for contact with pharmaceutical and food products, so VMQ is an option worth considering. VMQ oil seals are usually available on request.

Types of Oil Seal Materials / Material Selection Guide for Oil Seals

Material Chart for Oil Seals

Oil Seals are also known as a Rotary Shaft Seal, shaft seal, lip seal, elastomeric lip seal or any variation of these. It is a simple device for excluding dust, dirt, water or any other contaminant whilst retaining lubricant in rotary shaft equipment. Generally, it has been developed as a means of protecting the bearings of rotating shafts.

Below is the chart for oil seal Materials selection:

Temperature range: between -10°C and +205°C (intermittent/compound specific between -20°C and +250°C)

Applications: Aflas® are created from an exceptional Fluoroelastomer (FKM), which is resistant to steam, petroleum oils, amine corrosion inhibitors, and hydrogen sulphide.

Resistant to: Steam, Petroleum Oils, H2S

Temperature range: between -55°C and +135°C

Applications: Carboxylated Nitrile (XNBR) oil seals are created from a low-temperature tolerant compound, also has an excellent abrasion resistance.

Resistant to: Water, Petroleum Oils

Temperature range: between -20°C and +205°C or between -45°C and +230°C (intermittent/compound-specific)

Applications: FKM Fluorocarbon oil seals distinguish a great resistance to solvents and petroleum oils. They are, therefore, great for high-temperature installations and have present low compression set attributes. Additionally, they are adapted for use with large chemical exposure and hard vacuum applications.

Resistant to: Transmission Fluids, Gasoline, Petroleum Oils

Temperature range: between -55°C and +205°C (dependant on core material)

Applications: FEP oil seals are an excellent option for static and slow intermittent dynamic applications. FEP is interfered by a poor memory at low temperatures. FEP is, however, very tough, a chemically inert polymer that has a spectacular working scope.

Resistant to: Majority of chemicals

Temperature range: between -60°C and +180°C (intermittent/compound specific up to +200°C)

Applications: Fluorosilicone (FVMQ) oil seals incorporate a good low and high-temperature persistence of Silicone (VMQ) and Fluorocarbon’s resistance to solvents, oil, and fuel. It also presents great resistance to gasoline and petroleum oils.

Resistant to: Gasoline, Petroleum Oils

Temperature range: between -30°C and +170°C (intermittent/compound specific up to +190°C)

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Applications: Oil seals produced from Hydrogenated Nitrile (HNBR) present superior sour gas and petroleum oils resistance. Due to an extensive temperature range of Highly Saturated Nitrile, it happens to be most preferable material in Oil Industries.

Resistant to: H2S, CO2, Petroleum Oils

Temperature range: Buna-N between -40°C and +135°C (intermittent up to +150°C); Low-Temp between -65°C and +120°C

Applications: Nitrile (NBR) is currently the most extensively used elastomer in the Fluid Seal Industry. Furthermore, Nitrile oil seals incorporate exquisite reluctance to hydraulic oils, water, silicone greases, petroleum-based oils and fluids, and alcohols. Nitrile presents great stability of working attributes such as high tensile strength, high abrasion resistance, and low compression set combined with low cost.

Resistant to: Water, Petroleum Oils & Fluids, Hydraulic Oils

Temperature range: between -20°C and +150°C

Applications: Polyacrylate oil seals have superior high-temperature resistance than that of Nitrile. Therefore, they are ideal for high surface speed oil applications.

Resistant to: Freon, Petroleum Oils

Temperature range: between -15°C and +85°C (intermittent/compound specific between -50°C and +100°C)

Applications: Polyurethane oil seals are used in high-stress hydraulic applications, in which highly pressured compounds are exposed to wear. Polyurethane, however,  presents a great high abrasion resistance qualities and high tensile strength.

Resistant to: Hydraulic Oils, Petroleum Oils

Temperature range: between -60°C and 250°C (special grades up to +300°C)

Applications: Silicone (VMQ) oil seals present a high lubricant absorbency. It minimizes wear and friction in certain applications.

Resistant to: Number of Acids, Petroleum Oils

Temperature range: between -50°C and +327°C (intermittent up to +350°C; compound specific)

Applications: Simriz® oil seals are created of an elastomer, which has the widest chemical resistance our of all elastomer materials. They incorporate all the elasticity and sealing strength of an elastomer and chemical resistance similar to that of FEP (Fluorinated Ethylene Propylene).

Resistant to: Majority of chemicals

The above information had been derived from numerous sources and the ratings are therefore intended as a guide only. Users must test under their own operating conditions to determine the suitability of any compound in a particular application and temperature.

M Barnwell Services is the UK’s largest independent stockist, manufacturer, and distributor of fluid sealing products and services. For more information about Barnwell O Rings click here, or to download a brochure click here.
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E & OE. M Barnwell Services endeavours to make sure all the content is correct. Information has been gained from manufacturing partners.

A Guide to Select Oil Seals for Your Industrial Application

A Guide to Select Oil Seals for Your Industrial Application

An oil seal is a type of seal used in various industrial equipment to close the gap between its moving and non-moving components. These oil seals help prevent lubricant leakage at high pressures and block foreign components from entering the machinery. With such an important role to play, these oil seals must be chosen carefully. This post discusses the types of oil seals and also guides you through the important factors to choose an appropriate oil seal for your industry.

Types of Oil Seals – Based on Materials 

There is a wide range of seals to select according to the type of material. Some of the types of oil seals are as follows:

• Rubber Oil Seals:

Rubber seals are the most common types of sealing solutions preferred for tight sealing. Rubber seals are corrosion resistant and are used in both high and low-pressure applications. Nitrile, polyacrylate, Viton®, silicone, and polytetrafluoroethylene are a few common types of rubber materials used for this purpose. Each material possesses the typical capability, so, you must choose the rubber material carefully for your application.

Rubber seals are the most common types of sealing solutions preferred for tight sealing. Rubber seals are corrosion resistant and are used in both high and low-pressure applications. Nitrile, polyacrylate, Viton®, silicone, and polytetrafluoroethylene are a few common types of rubber materials used for this purpose. Each material possesses the typical capability, so, you must choose the rubber material carefully for your application.

• Metal Cased Oil Seals:

These seals feature stamped metal cases with an elastomer bonded sealing lip. Carbon steel is the metal used for making the case. The case protects the lip seal during installation. Metal encased seals are generally used for high-pressure or high-temperature applications.  

These seals feature stamped metal cases with an elastomer bonded sealing lip. Carbon steel is the metal used for making the case. The case protects the lip seal during installation. Metal encased seals are generally used for high-pressure or high-temperature applications.

• Leather Oil Seals:

These seals possess good running properties and are generally preferred for abrasive applications. The seals are usually used for shafts that possess surface roughness higher than rubber seals.

These seals possess good running properties and are generally preferred for abrasive applications. The seals are usually used for shafts that possess surface roughness higher than rubber seals.

7 Important Factors to Consider When Choosing Oil Seals

With varieties of seals available, choosing the right seal for application can be a daunting task. The following factors will help make the right selection. 

1. Lubricant: If choosing lubricated seals ensure they are continuously lubricated with oil that possesses appropriate viscosity required for the application and the lubricant is compatible with the elastomer material of seals.
2. Shaft Finishing: A good surface finishing of shafts gives a very effective oil sealing. The ground or polished shafts with concentric finish marks provide the best sealing that prevents leakage even during the shaft rotations. Hence, it is important to make sure that the shaft finishing is well maintained.
3. Shaft and Bore Tolerance: The seals must be strong enough to tolerate the pressure and vibrations caused by shaft and bores. The authenticity of metal and elastomer material is something that makes the shaft and bore tolerance possible. Therefore, check if the material meets these requirements before buying the seal.
4. Shaft Hardness: The life expectancy of a seal is measured on the basis of the hardness of its shaft. A shaft must possess a Rockwell hardness of 30 or above. When a seal is exposed to abrasive contaminants or high pressure, this RC hardness protects the seal from getting damaged. Hence, it is an essential factor.
5. Temperature: The temperature of the process should not exceed the temperature of the seal elastomer. Any increase or decrease in temperature may affect the sealing capability of the seal. Hence, it is an important point to be considered.
6. Pressure: Most seals are designed for applications where they may be subjected to pressures as low as 8 psi. However, if they are subjected to even low pressures then pressure relief must be ensured.
7. Shaft Speed: Shaft speed depends on many factors including shaft finish, its concentricity, the type of liquid being transferred, and the type of oil seal material. So each of these factors must be considered to achieve a maximum shaft speed. 

In addition to the above-given factors, sourcing high-quality seals from a trusted manufacturer are quite important.  SSP Seals provides high-quality

In addition to the above-given factors, sourcing high-quality seals from a trusted manufacturer are quite important. SSP Seals provides high-quality oil seals for industrial applications in automotive, oil and energy, and other sectors. The company can provide seals made of a wide range of materials including PTFE, Viton, Silicone, Nitrile, and so on.

Oil Seal Material Design Guide

Oil Seal Material Design Guide

Lip Materials

Nitrile Buna-N 70 durometer compound is the standard material for our seals and is recommended for a majority of common applications. Nitrile lip seals work well within the temperature range of -65°F to 250°F and provide compatibility with water and most common mineral oil and greases.

Polyacrylate compounds are recommended for higher temperature applications, ranging from -30°F to 300°F. They also work well with mineral oils, EP additives and greases. However, they offer poor sealing in dry running conditions and cost more than Nitrile.

Silicone compounds offer the widest range of normal operating temperatures ranging from -90°F to 340°F. However, they do not perform well in dry running conditions, and should not be used with EP compounds and oxidized oils.

Viton® compounds are premium lip materials offering the widest temperature range and chemical resistance. Viton® will handle temperatures from -40°F to over 400°F (-40°C to over 240°C).

Viton® will resist most special lubricants and chemicals that can destroy Nitrile, Polyacrylates and Silicones. Viton® is extremely resistant to abrasion and provides superior wear performance. Viton® works in dry running applications, but only for intermittent periods.

Graphite is available as an additive to any compound. Normally graphite is added at a 3% factor to aid in lubricity.

Case and Spring Materials

The cases and springs for our seal products are produced from carbon steel. In applications where corrosion resistance is important, either case or spring or both can be produced from stainless steel. In addition, rubber coated seals can provide the best resistance to corrosive environments in the most economical design. HYPALON® coating is an O.D. sealant which is available on any metal case design by customer request.

Lip, Case and Spring Tables

The following tables identify the most common lip and case designs. Additional, more complex designs are available for special applications; however, the lip and case designs below represent those which will fill the needs of most seal requirements.

Lip Design

The following designations indicate the configuration of the sealing members:

V = Single Lip  U = Triple Lip  K = Double Lip  D = Double Lip, Double Spring Loaded  S = Single Lip, Spring Loaded  WP = Wiper Lip Design  OB = Oil Bath (Prefix) O = External Seal Type WS = Wiper w/Bronze Scraper

Case and Spring Design

The following designations indicate the case type or any special features of the basic case designs. The designations for lip designs, attachment configuration and case style are then put together to indicate the specific seal type desired.

A = Double Case  N = Short Flex High Pressure Design  B = Lip Attached to End of Case Only  P = Flanged Case  C = Fully Rubberized Casing  Q = All Rubber Split Seal Design  E = Metal Reinforced Sealing Lip  SP = Other Special Feature  F = Special Fully Encased Design  X = Special Fitting Condition Design  G = Ridged Rubber Coated O.D.  Y = Indented Back Case  H = Reverse Case Style  Z = Rubber Covered Chamber J = Special Flanged Indented Case NOTE: Basic single case design has no designation M = Fully Rubberized Inner Case