Guide to Oil Seals for Your Application

Oil seals, also known as rotary shaft seals, are critical components in machinery and equipment, used to prevent the leakage of lubricants and block contaminants from entering mechanical systems. Selecting the right oil seal is essential for maintaining the efficiency and longevity of your machinery. This guide will provide an overview of oil seals, their types, materials, and key considerations to help you choose the right oil seal for your application.

htob contains other products and information you need, so please check it out.

Understanding Oil Seals

1. Definition and Function

Oil seals are mechanical devices designed to close the spaces between stationary and moving components in mechanical equipment. They prevent lubricants from leaking out and contaminants such as dirt, dust, and moisture from entering the system.

2. Key Components of Oil Seals

Sealing Element: Typically made of elastomeric material, this part makes direct contact with the shaft to provide the sealing function.

Metal Case: Provides structural stability and maintains the shape of the seal.

Garter Spring: Ensures that the sealing lip maintains consistent contact with the shaft, enhancing the seal's effectiveness.

Rubber Skeleton Oil Seal

Types of Oil Seals

1. Single Lip Seals

Application: General-purpose sealing where the primary function is to retain lubricant and exclude contaminants.

Advantages: Simple design, cost-effective, and easy to install.

2. Double Lip Seals

Application: Environments where additional protection from contaminants is required.

Advantages: Extra sealing lip provides additional defense against dirt and debris.

3. Dual Spring Seals

Application: High-pressure and heavy-duty applications.

Advantages: Two garter springs provide enhanced sealing force, making them suitable for more demanding conditions.

4. PTFE Seals

Application: Harsh chemical environments, high temperatures, and high-speed applications.

Advantages: Exceptional chemical resistance, low friction, and high-temperature tolerance.

TC TG SC NBR FKM Oil Seal

Materials for Oil Seals

1. Nitrile Rubber (NBR)

Characteristics: Good resistance to oils, fuels, and other chemicals. Suitable for temperatures between -40°C to +120°C.

Applications: Automotive, general industrial use.

2. Fluoroelastomer (FKM)

Characteristics: Excellent high-temperature resistance up to +200°C and superior chemical resistance.

Applications: Aerospace, chemical processing, high-temperature applications.

3. Silicone Rubber

Characteristics: High-temperature resistance, good flexibility at low temperatures.

Applications: Food and beverage industry, extreme temperature conditions.

4. Polyurethane (PU)

Characteristics: High wear resistance, excellent mechanical properties.

Applications: Hydraulic systems, applications with high abrasion.

5. Polytetrafluoroethylene (PTFE)

Characteristics: Outstanding chemical resistance, low friction, high-temperature tolerance.

Applications: Aggressive chemical environments, high-speed applications.

Selecting the Right Oil Seal

1. Identify the Operating Environment

Temperature Range: Select a material that can withstand the operating temperatures of your application.

Chemical Exposure: Ensure the seal material is compatible with any chemicals it will be exposed to.

2. Determine Shaft and Bore Dimensions

Inner Diameter: Match the inner diameter of the seal with the shaft diameter.

Outer Diameter: Ensure the outer diameter fits snugly into the bore.

3. Assess the Rotational Speed

High-Speed Applications: Consider seals with low friction and high heat resistance, such as PTFE seals.

4. Consider Pressure Requirements

High-Pressure Systems: Choose seals designed to handle higher pressures, like dual spring seals or PTFE seals.

5. Evaluate Lubricant Compatibility

Lubricant Type: Ensure the seal material is compatible with the lubricants used in your system.

Installation and Maintenance Tips

1. Proper Installation

Tools: Use appropriate tools to avoid damaging the seal during installation.

Guidelines: Follow manufacturer guidelines for best results.

2. Regular Inspection

Monitoring: Periodically check for signs of wear, leakage, or damage.

Replacement: Replace seals as necessary to prevent machinery breakdowns.

3. Lubrication

Sealing Lip: Properly lubricate the sealing lip during installation and operation to reduce wear and improve performance.

4. Cleanliness

Environment: Maintain a clean environment during installation and operation to prevent contaminants from damaging the seal.

Conclusion

Oil seals work by squeezing and retaining lubricant in a thin layer between the lip and the shaft. Perfect sealing is ensured by the hydrodynamic action of the rotating shaft, which in turn produces a slight pump action.

As earlier said, oil seals perform some functions that ensure the functionality of mechanical equipment and extend their lifespan. And how they do this is by retaining lubricants at all cost and not making them escape no matter how high the pressure of the machine is.

The other way oil seals work is by stopping outboard materials that can damage the machine or contaminate its lubricant. The outboard materials that the oil seal will need to stop depend on the application. However, the most common kinds are dirt, moisture, and the particles produced during manufacturing.

Standard petroleum oil has a lifespan of 30 years at 86 degrees Fahrenheit if it’s not 

contaminated with moisture or any other particle. But the same oil will only last for a month at 212 degrees Fahrenheit if it’s contaminated with little water. This is why the function of an oil seal is very evident whenever it’s used.

Simple modifications to breathers and sight glasses can be beneficial, but shaft seals are just as important in this process. Labyrinth-type seals are common devices for contaminant exclusion, and when properly maintained, they can greatly influence the reliability of the components in which they are installed.

A comparison of various seal materials (Ref. Seal & Survive, Seal School Handbook)

A seal’s function is multifaceted. Not only is it attached to a machine to keep particles and outside contaminants from getting in, but it also must keep what is inside the machine - whether it is oil, process fluid or a barrier fluid - inside.

One study by Exxon Mobil showed that the amount of oil lost is four times the capacity of the machine. The need for minimizing leakage while prolonging the machine’s operating life is more critical today, as the demands for reliability and the penalties for failure continue to rise.

Standard lip seals will limit certain contaminants from entering and restrict some leakage, but they are subject to failure, especially in systems with high pressure or extreme ambient conditions. One limiting factor of these types of seals is the construction material, with each elastomer having its own strengths and weaknesses.

What Is A Labyrinth Seal?

The basic concept of labyrinth seals is to reduce contaminant ingression not only by restricting the clearance through which particles enter but also by creating areas of turbulent flow to exclude contaminants. These types of systems provide better particle exclusion and less lubricant leakage than standard lip seals, which contact the shaft and rub the surface during operation.

Lip Seals vs. Labyrinth Seals

Shaft seals must be properly selected and maintained. Some seals do a good job of retaining oil or grease but do a lousy job of excluding contamination. Lip seals are a prime example, particularly the ones that are only directed inward. These types of seals tend to wear after a period of time because they make rubbing contact with the shaft. Eventually, the seals no longer function well from the standpoint of both oil retention and contaminant exclusion.

Lip Seal                            Labyrinth Seal

On the other hand, a labyrinth seal is non-contacting, so it will not have the wear-out condition. These seals are excellent for excluding particle contamination and moisture, even if there’s a spray of water nearby. So both oil retention and contaminant exclusion are at a much higher level of performance compared to contacting mechanical seals and lip seals.

Of course, the disadvantage of using labyrinth seals is that they are more expensive. Generally, you will need to retrofit these on the equipment and will incur the cost of their installation. However, labyrinth seals will last longer and perform better.

Labyrinth seals are constructed in multiple pieces. One piece, known as the stator, is affixed to the machine and remains stationary. The other piece, called the rotor, is attached to the shaft and rotates with the motion of the system. The two pieces interlock to effectively seal out the majority of contaminants while holding in the lubricant or process fluid.

These types of seals are non-contacting, which means that the two opposing faces do not touch each other. They are also considered frictionless, as the rotor and stator are separated by a very small gap. In many instances, this gap can be as small as 0.003 inches, which equates to roughly 76 microns. This may sound like a large opening in comparison to the 1-micron lubricant film inside a rolling-element bearing, but because of the path that the contaminant must take to actually reach the bearing, this gap is more than adequate.

All contaminants trying to enter the bearing housing must go through the seal’s maze (labyrinth) of turns and angles in order to reach the bearing. On the path through all of these turns, particles are constantly subjected to centrifugal forces due to the rotational motion of the shaft, and only a very small number make it through the entire length of the seal.

Types of Labyrinth Seals

A variety of different labyrinth seals are available, from bronze and stainless steel to plastic. The construction of the seals may even change between brands, with some employing magnets and others simply using O-rings to provide the necessary seat for the housing and shaft. However, they all operate on the same principle and must be properly installed to work correctly.

When looking for options to boost reliability and minimize bearing failures, consider the seals that are in use. In areas of high airborne particulate matter or heavy washdown areas, a labyrinth-style seal can help limit the ingress of contaminants and prolong machine life. With proper lubrication and contaminant-exclusion devices, many bearings can come close to achieving their design life.

How to Protect Stored Gearboxes with Labyrinth Seals

• Spray shaft extensions with a suitable dry film or similar preservative.

• For gearboxes with non-contact labyrinth seals, use internal vapor-phase rust protective coating instead of complete oil fill. Both oil wet and non-oil wet surfaces are protected by vapor-phase rust inhibitors.

• Commercial vapor phase rust inhibitors include products such as Ashland Oil, Tectyl 859A or Cortec VP corrosion inhibitor. Typically, add 5 percent of the oil volume. Some inhibitors require the oil/inhibitor mixture to be heated and agitated in order to perform effectively.

This method may only be good for about six months and should be renewed if the storage period is longer. Another disadvantage is that it may cause incompatibility and foaming problems when filled with the service oil. Flushing is recommended before putting the gearbox into service.

References

EG&G Sealol, “Seal & Survive,” Seal School Handbook, Revision 3.

Fitch, J.C., Scott, R., & Leugner, L. (), “The Practical Handbook of Machinery Lubrication - Fourth Edition.”

Inpro/Seal, “Bearing Isolators.”

Maintenance Technology (), “Beyond Predictive Maintenance.”

Neale, M.J., “Drives & Seals: A Tribology Handbook.”

About the Author

Oil seals are widely used as sealing devices for machines.

JTEKT's oil seals are described in our catalog, Oil Seals & O-Rings.
However, the catalog uses a large number of technical terms and is very long, so many people seem to have trouble handling it.

Therefore, this series of columns will summarize the following in order:
• The structure, functions, and types of oil seals
• How to select the right oil seal
• Handling of seals, and causes and countermeasures for oil seal failure

1. What are oil seals?

A wide range of sealing devices are used in various machines.
Sealing devices serve the following functions:

• Prevent leakage of sealed lubricant from inside
• Prevent entry of dust and foreign matter (dirt, water, metal powder, etc.) from outside

As shown in Figure 1, sealing devices come in two types: contact and non-contact.
Oil seals are among the major contact type sealing devices.

Figure 1: Types of sealing devices

Please see the following for the types of sealing devices for bearings.
How to Select the Right Bearing (Part 7): Components surrounding the bearing

2. Oil seal structure and functions

Oil seals come in various shapes to fit the machines and substances to be sealed.
Figure 2 shows the structure and the names of the various components of the most typical oil seal.
The functions of the various components are also indicated in Table 1.

Explore more:
Frequently Asked Questions About Cooling Towers

Contact us to discuss your requirements of TC Oil Seal. Our experienced sales team can help you identify the options that best suit your needs.

Figure 2: Typically shaped oil seal and component nomenclature

* "KOYO" is a registered trademark of JTEKT.

Table 1: The functions of the various components

No.

Name

Functions

①

Main lip The main lip is the most critical component of the seal.

Its sealing edge comes in full contact with the shaft surface in order to provide excellent sealing performance.
(See Figure 3.)

②

Minor lip The minor lip prevents the entry of dust and contaminants from outside.
Lubricant can be retained in the space between the main lip and the minor lip.

③

Sealing edge This refers to the component of the oil seal that makes contact with the shaft.
It is wedge-shaped to be pressed against the shaft surface and makes contact with the shaft to ensure sufficient sealing performance and suitability for operation at high peripheral speed.

④

Spring The spring supplements the tightening force (i.e., the lip radial load) to ensure enhanced sealing performance and tight contact between the shaft and the sealing edge.The spring also prevents the deterioration of main lip sealing performance caused by high heat or other such factors.

⑤

Metal case The metal case provides rigidity to the seal, helping it settle on the housing securely. It also ensures easy seal handling and mounting.

⑥

O.D. (outside diameter) surface The O.D. surface affixes the oil seal to the housing and prevents leakage , through the fitting area, of substances to be sealed, while excluding contaminants.

⑦

Fluid side face The front-end face of the seal is called the nose. The nose is made of rubber and forms a gasket seal when compressed on the housing shoulder.

⑧

Air side face The oil seal surface vertical to the center line of the shaft on the side that does not come in contact with substances to be sealed is called the back face.

Figure 3: Sealing function of main lip radial load
* "KOYO" is a registered trademark of JTEKT.

Figure 4 shows the features of a JTEKT oil seal.

Figure 4: JTEKT oil seal features

For more detailed information, please see the following:

Names and functions of seal components　

3. Seal types and numbering system

1) Common seal types and their features

Seals are classified by O.D. wall material, lip type, and whether they have a spring or not.
Major oil seals are specified in ISO -1 and JIS B -1.
Table 2 shows the common types of oil seals, while Table 3 shows the features of each type of oil seal.
Table 4 lists the JTEKT oil seal type codes and corresponding ISO and JIS standards.

Table 2 a): Common types of oil seals (with spring)

With spring Rubber O.D. wall Metal O.D. wall

Metal O.D. wall
(with a reinforcing inner metal case)

Without minor lip


Type code

With minor lip


Type code

Table 2 b): Common types of oil seals (without spring)

Without spring Rubber O.D. wall Metal O.D. wall

Without minor lip

Type code

With minor lip


Type code

Table 3: Features of each seal type

No.

Type

Features

1

With spring type Secures stable sealing performance.

2

Rubber O.D. wall type Provides stable sealing performance around the seal O.D. surface.

3

Metal O.D. wall type Ensures improved fitting retention between the seal O.D. and the housing bore.

4

Metal O.D. wall type (with a reinforcing inner metal case) Protects the main lip.

5

With minor lip type Used for applications where there are contaminants, such as dust and foreign matter, on the air side face of the oil seal.

Table 4: JTEKT oil seal type codes and corresponding ISO and JIS standards

JTEKT

ISO -1 1)

JIS B -1 2) MHS Type 1 HMS Type 2 HMSH Type 3 MH － HM － MHSA Type 4 HMSA Type 5 HMSAH Type 6 MHA － HMA －

Notes
1) ISO: International Organization for Standardization
2) 2) JIS: Japanese Industrial Standard

2) Special seal types and their features

JTEKT provides special seals for use in a wide variety of machines and applications.
Table 5 lists the major special seals, their shapes, and their features.

Table 5: The major special seals, their shapes, and their features

Name Type
(type code) Shape Features

Helix Seal

The hydrodynamic ribsa) provided in one direction on the air side face of the lip ensure higher sealing performance. Perfect Seal The hydrodynamic ribsa) provided in two directions on the air side face of the lip ensure higher sealing performance (higher sealing performance in both rotational directions of the shaft).

Super Helix Seal

The hydrodynamic ribsa) have a two-stepped rib configuration provided in one direction on the air face of the lip. Even if the first rib is worn out, the second rib comes into contact with the shaft surface, meaning that this type of oil seal ensures higher sealing performance. Seal with Side Lip A large side lip ensures prevention of entry of dust/water.

　　　　　　　　　　　　a)

Function of hydrodynamic ribs

For more detailed information, please see the following:

Special seal types and their features

3) Seal numbering system

Figure 5 explains the JTEKT seal numbering system.
Seal numbers consist of
　(1) the seal type code,
　(2) the spring code,
　(3) the lip type code,
　(4) the dimensional numbers, and
　(5) the special type code,
and Table 6 shows examples of each of these codes/numbers.

Figure 5: JTEKT seal numbering system



Table 6: Codes and numbers used in seal numbers

No. Code and number Example ① Seal type code (*)

MH: O.D. wall is a rubber material
HM: O.D. wall is a metal case
MH(S)H: O.D. wall is metal with a reinforced inner metal case

② Spring code

No code: without minor lip

A: with minor lip

③ Lip type code

No code: without minor lip

A: with minor lip

④ Dimensional numbers Shaft number 45: The seal suits the shaft diameter of ϕ45 mm. Housing bore number 70: The seal suits the housing bore diameter of ϕ70 mm. Width number 8: The seal width is 8 mm. ⑤ Special shape code

J: Additional code is added here as an identifier when two or more seals have exactly the same type codes and dimensional numbers.

Note: For seal type codes, see Table 2.

4. Example of the applications of seals

Oil seals are used in a great many machines.

1) Oil seals for cars

Oil seals are used in many areas around the car.
Figure 6 shows the places where each seal type is used.

Figure 6: Oil seals for cars

For more detailed information, please see the following:

Oil seals for cars

2) Oil seals for steel production equipment

Oil seals are used in a great many devices for steel production equipment.
Figure 7 shows the places where each seal type is used in a rolling mill.

Figure 7: Oil seals for steel production equipment (rolling mill)

For more detailed information, please see the following:

Oil seals for steel production equipment

5. Conclusion

Oil seals are one of the major contact type sealing devices.
• They prevent leakage of the lubricant or other sealed substance, and
• prevent entry of dust and foreign matter (dirt, water, metal powder, etc.) from outside.

Oil seals come in various shapes to fit the machine or substance for sealing.
For this reason, when designing a machine, it is important to select the oil seal that is right for that machine.
Next time, we will explain the key points to consider when selecting your oil seal.

If you have any technical questions regarding oil seals, or opinions/thoughts on these "Bearing Trivia" pages, please feel free to contact us using the following form:

Are you interested in learning more about Toyota Oil Seal? Contact us today to secure an expert consultation!