Summary

• Oil seals comprise three core components – the sealing element (or lip), the metal case, and the optional garter spring, each contributing to the seal’s functionality and effectiveness.
• Choosing an oil seal involves evaluating multiple factors, including design, application needs, shaft diameter, bore diameter, sealing material, and environmental considerations.
• Regular maintenance, including proper lubrication, routine inspections, and scheduled replacements, ensures the longevity and reliability of oil seals, enhancing overall machine efficiency.

Introduction

In the mechanical world, where machinery and equipment make the earth move and gears rotate, the oil seal is an important component. Oil seals, or shaft seals, are a crucial part of various industrial equipment and applications, ensuring that lubricants don’t escape and contaminants don’t enter. While they may seem simple, their construction, design, and application are anything but. This in-depth guide aims to help you understand the essential role of oil seals, their construction, the various designs available, and key factors to consider when selecting one for your application.

Purpose of an Oil Seal

An oil seal serves three crucial purposes within any machinery. First, it prevents the leakage of lubricants or fluids outside the seal, even under high pressure. This function ensures the effective operation of equipment, as sufficient lubrication is a key requirement for the smooth functioning of machinery. Second, it retains the lubricating oil within the machinery. This retention function reduces the need for constant maintenance or re-lubrication, saving time and resources. Third, the oil seal acts as a barrier against contaminants. It prevents dirt, dust, and other potential contaminants from entering the machinery, protecting sensitive parts from damage or wear.

Construction of an Oil Seal

The construction of an oil seal is a testament to meticulous engineering. Each oil seal primarily comprises two core components: the sealing element and the metal case. The collaboration of these parts brings about the seal’s functionality and effectiveness. A garter spring may also be included as an available feature, providing an extra layer of operational support.

Sealing Element

The sealing element, also known as the sealing lip, forms the interior of the oil seal. Various materials can make up the lip depending on the application’s specific needs. Below are some commonly used materials:

• Nitrile Rubber (NBR): This is the most frequently used material for sealing elements, boasting good heat resistance properties and resistance to salt solutions, oils, hydraulic oils, and gasoline. Its recommended operating temperature range is from -40 to 248°F (-40 to 120°C). Nitrile functions adequately in a dry environment but only for intermittent periods.
• Polyacrylate Rubber (PA): PA is a go-to material for high surface speed environments as it has better heat resistance than nitrile. It performs optimally within a temperature range of -4 to 302°F (-20 to 150°C). It is incompatible with water or temperatures below -4°F (20°C).
• Silicone Rubber (SI): A popular choice for its resistance to low and high temperatures (-58 to 356°F, or -50 to 180°C). Silicone rubber has high lubricant absorbency, which reduces friction and wear, making it ideal for crankshaft seals. However, it is unsuitable for oxidized or hypnoid oils due to its poor resistance to hydrolysis.
• Fluorocarbon Rubber (FKM): Also known as Viton®, this material offers excellent resistance to chemicals and performance at high temperatures. It’s highly esteemed for its exceptional durability and heat resistance.

Metal Case

The metal case serves as the oil seal’s exterior or frame, providing rigidity and strength to the seal. The case material selection depends on the environment in which the seal will operate. Often, the same rubber material used in the seal element covers the case to help seal the exterior of the oil seal in the housing bore.

• Carbon Steel:  The most common material for oil seal cases, suitable for use with standard lubricants.
• Stainless Steel: Ideal for water, chemicals, or corrosion resistance applications. Stainless steel cases are also suitable for many FDA applications.

Oil seals with outer metal cases may include finishes or treatments applied to the outer edge to aid in rust protection, identification, and sealing of scratches or imperfections in the housing bore. Common finishes applied to the outside edge of metal O.D. oil seals include plain (a bonding agent of usually a yellowish-green color), a color-painted edge, and a grinded-polished edge.

Garter Spring

When included, the garter spring applies pressure to the sealing lip against the shaft, ensuring a tight seal. The choice of material, like that of the case, largely depends on the environment of use.

Garter springs are generally used when the lubricant is oil, as it provides the necessary downward force to maintain a tight seal. However, when grease is the lubricant, garter springs can often be eliminated. Due to its low viscosity, grease doesn’t require as much downward force to maintain an effective seal.

Standard Sealing Lip Designs

Oil seals come with various lip designs, each serving a unique purpose and suitable for different applications. Let’s discuss the most common industry-standard lip designs:

• Single Lip: This design features a garter spring and primarily seals against internal media in low-pressure applications. It’s not ideal for environments with dirt or contaminants.
• Double Lip: Like the single lip design, this design uses a garter spring with a primary lip that seals against internal media in low-pressure applications. The secondary (or auxiliary) lip offers extra protection from dust and dirt.
• Dual or Twin Lip: This design features two identical primary lips and a garter spring, typically used to separate two liquids. Lubricating the space between the lips with a grease or similar substance is essential for this lip design.
• Single Lip, No Spring: This lip design, which does not include a spring, is mainly used for sealing a non-pressure medium, such as grease, or protecting against dirt.
• Double Lip, No Spring: This design is also springless and is generally used to seal non-pressure media like grease. It protects against both internal and external media.

Standard Sealing Case Designs

Beyond the variety of lip designs, oil seals also come in various case designs, each serving a unique role. Here are some of the most common ones:

• Type A: An outer metal case with a reinforced plate for structural rigidity. It’s ideal for shafts when the diameters exceed 150mm, smaller shafts that need extra strength, or when used with special rubber compounds.
• Type B: An outer metal case generally used on shafts with diameters under 150mm and bore housing materials made of steel or cast iron. It provides a firm and accurate seal in the housing but may limit the static sealing on the outer diameter (O.D.).
• Type C: A rubber-covered metal case that can be useful on any size shaft. The rubber prevents rust & corrosion and shields against damage during assembly. This design is suitable for soft alloy, plastic housing materials, or replacement in environments with minor damage to the housing surface.

Factors in Oil Seal Selection

Selecting the right oil seal involves comprehensively evaluating your application’s needs and conditions. Below are the key factors to consider when choosing an oil seal:

1. Type: The combination of lip design and case type you select will determine the overall design of the oil seal.
2. Shaft Diameter: The outside diameter of the shaft where the seal will operate (sometimes referred to as the I.D. of the oil seal)
3. Bore Diameter: The inside diameter of the bore housing where the seal will operate (sometimes referred to as the O.D. of the oil seal)
4. Width: The thickness or width of the oil seal is another critical dimension that impacts the fit and functionality of the oil seal.
5. Sealing Material: The material used in the seal lip should be resistant to the operating temperature range, chemicals, lubricants, and pressures in your application.
6. Environmental Factors: Consider external factors such as exposure to dirt, water, and other contaminants, temperature fluctuations, chemical exposure, and shaft speed. For example, oil seals that must withstand high-speed rotational motion, high-pressure conditions, or extreme temperatures require more durable and resilient materials.
7. Lubrication: The lubrication used in the application will affect the choice of sealing material. The material must be compatible with the lubricant to prevent degradation and ensure the seal’s longevity.
8. Spring Material: The choice of garter spring material is also crucial as it must resist environmental factors such as exposure to water, chemicals, etc.
9. Application Requirements: The specific requirements of your application are critical to making the right choice. For example, if the seal is for a food processing machine, it must meet FDA standards.

Failure Modes of Oil Seals

It is crucial to understand that oil seals, like any other mechanical component, are subject to failure over time. The key to minimizing downtime and enhancing operational efficiency is recognizing the signs of oil seal failure and understanding its reasons. Here are some common failure modes:

• Excessive Wear: This is often a sign of regular friction between the seal lip and the shaft, usually resulting from inadequate lubrication or a rough shaft surface finish.
• Hardening or Cracking: Exposing oil seals to high temperatures for extended periods may cause the sealing material to harden or crack. This breakdown compromises the seal’s effectiveness and can lead to leakage.
• Chemical Erosion: If the seal material is incompatible with the chemicals or lubricants used in the machinery, it can degrade over time, leading to seal failure.
• Improper Installation: Incorrect oil seal fitting can cause immediate or premature failure. This improper fit can be due to many reasons, such as damage during installation, misalignment, or using the incorrect size.
• Excessive Pressure: Exposing an oil seal to pressure beyond its design parameters can result in seal deformation.

Maintenance and Inspection of Oil Seals

Proper maintenance and regular inspection are vital for prolonging the service life of oil seals and preventing unplanned downtime. Here are some tips:

• Regular Lubrication: Ensuring adequate lubrication will minimize friction and prevent wear and tear on the seal. Use only compatible lubricants as per the seal material to avoid chemical erosion.
• Routine Inspections: Schedule regular inspections of the oil seals to spot any signs of failure, such as leakage, hardening, or visible wear. Catching issues early can prevent minor problems from escalating into significant failures.
• Proper Cleaning: Dirt, grime, and debris can damage the sealing surface, leading to leaks. Regular cleaning of the seal and surrounding areas can help prevent this.
• Monitor Operating Conditions: Keep track of pressure levels, temperatures, and shaft speed. Excessive fluctuations can signal something wrong and potentially harm the oil seal.
• Replacement: Even with impeccable maintenance, oil seals won’t last forever. Understanding the typical lifespan of the oil seal type and material used in your machinery will help you plan for timely replacements.

Conclusion

Oil seals are integral components in a range of machinery and equipment, playing a vital role in keeping lubricants in, contaminants out, and machinery operating efficiently. Understanding the design, materials, and selection factors of oil seals can help you make an informed choice regarding your industrial needs. The reliability, longevity, and efficiency the right oil seal can bring to your machinery is priceless.

Global O-Ring and Seal offers over 50,000 unique oil seals with 215,000 cross-referenced part numbers for OEMs and Manufacturers. To find a part you need, search for the OEM/Manufacturer part number alone, and the oil seal matching the part number will be displayed. If you don’t have a part number, visit our online store and use the filter options to find the oil seal you are interested in. If you are unsure which oil seal is right for your application, please contact us and speak with a sales representative to discuss your best options.

If you deal with rotatory shaft equipment, you would probably be having rubber seals in your mechanical assembly. For any manufacturing company, optimal functionality, efficiency, and long service life are essential to your success in the market. A component that is majorly underappreciated within a machine assembly, would be oil seal. 

Shaft seals are used to prevent lubricant leaks like oil or grease and protect machinery from dirt, dust, and water—which makes them invaluable to industrial operations. In this post, we will dive deeper into oil seals and discuss everything that one must know, such as what it is, how it works, types, applications, and what to keep in mind when buying oil seals. 

What are rubber oil seals? 

Rubber oil seals are placed between moving and static parts of mechanical equipment to prevent damage caused by moisture, contaminants, etc. Also known as rotatory shaft seals, grease seals, fluid seals, lip seals, and dirt seals; oil seals play an important role in closing the gaps between moving and stationary parts of machines. 

Their main purpose is to retain or separate fluids from mixing and escaping the gauge, as well as stop moisture, abrasives, corrosive materials, and foreign contaminants from entering the parts, thereby ensuring maximum machine efficiency. Moreover, shaft rubber seals help prevent lubricant leakage at high pressure, for instance, when the machine is working at an extremely high pace. 

How does rubber oil seal work? 

Oil seals work by retaining lubricant in a thin layer between the lip and the shaft. These seals are attached to the bearing, with their lip pressing against the rotating shaft and the casing resting against the housing to hold the seal in place. 

Oil seals perform some functions that ensure functionality at all costs and they do this by retaining lubricants at all costs and not making them escape no matter how high the pressure is.  Whenever an oil seal fails, it creates seal leakage allowing abrasives, corrosive moistures and sediments to enter machines. Oil seals are especially used in equipment that has rotating, oscillating, and reciprocating shafts – pumps, pistons, etc. 

Different types of seals offered by rubber products manufacturers in India include – Single and double lip oil seals, metal cased, external and internal oriented oil seals, and spring-energized oil seals and you can pick the one that best suits your industry requirements. 

Applications of Oil Seals 

Practically, all machine equipment including assembled machines, car engines, and PTFE machined parts use these oil seals to prevent harmful interactions that could possibly result in damaged parts. They are used in the assembly of Elevators, conveyor belts, engines, grinding mills, pipelines, wind turbines, and more. 

When equipment is under high pressure, lubricants tend to escape, and dry parts clash. Oil seals help prevent this by sealing holes where lubricants can leak out. rubber seals are designed to offer optimum sealing performance and extreme durability even under high-peripheral speed. They are lightweight, compact, and exhibit high self-lubricating properties. Oil seals are manufactured with high-grade materials and last long without showing any signs of hardening, softening, or aging. 

Moreover, oil seals are widely used throughout the aerospace industry in both space exploration and aviation applications. Sujan Industries manufactures all aircraft rubber items including O-rings, Gaskets, Seals, Pistons, Grommets, Washers, and Protective Boots & Bellows. In the aviation sector, pneumatics and hydraulics are used to operate components like landing gear and wing flaps. Rubber gaskets are needed in these systems to keep dust and air out while ensuring aircraft components run effectively.

How to Choose the Right Oil Seal 

Picking the right type of oil seals is crucial for the proper functioning of machines because in some situations not all types can fit to work on certain machines. 

There are quite a few factors to put into consideration when you’re choosing the right oil seal for your machine. Some of these factors include – dimensions, pressure, temperature, type of fluid, lubricant, shaft speed, shaft and bore tolerance, and more.

The capacity of oil seals to handle different intensities of pressure varies with their composition and application, so it is important to understand the compression set of your equipment. Just like the pressure, the temperature that your oil seal will be operating in must be known to be able to choose one that can withstand the working temperature. 

Likewise, different types of fluids like grease, water, oil, fuels, etc. will come into contact with oil seals. So, knowing what type of fluids will be in constant contact with oil seals will help you choose the one capable of withstanding the surrounding conditions. When we talk about lubricants, seals always perform well when lubricated, however, in some machines there are dry spells.  If you are a supplier of aftermarket parts in India or a user looking for oil seals in the aerospace industry, your search might end with Sujan Industries. 

Wrapping Up

Oil seals are critical to a machine’s functionality. A machine’s oil seals are critical to its functionality. Picking the right seal for your machine is vital as it not only guarantees the optimum performance of applications but also ensures a safe working environment for years to come. With so many rotary shaft seal options available, it can be hard to know which one to choose for your machine! Contact us today to speak to one of our experts and pick the best one for you.

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.