Which side of an oil seal faces the oil?

One of the main principles of power transmission is consistent lubrication. Shaft seals play a hugely important role in this. Imagine a situation involving a shaft-mount reducer – electric motor prime mover, driven by belts, motion controlled by a torque arm – with an improperly seated seal. A blown-out input shaft seal is a nightmare situation, necessitating an entire breakdown and reassembly, not to mention re-aligning and re-tensioning the belts.

The oil seal is our first line of defense in regards to keeping lubrication inside the reducer. It might also be described as the last line of defense – keeping contaminants outside the reducer where they belong. The average seal is incredibly simple in design – made up of a case, a lip or lips, and frequently a garter spring. Of course, some are exponentially more intricate and are manufactured with unusual materials, but the majority are straightforward.

The care taken during the installation process will pay off by allowing the seal to work quietly and operate efficiently behind the scenes of your application.

Prepping for Oil Seal Installation

Before you begin the installation process for any power transmission component, the first goal is making sure everything is clean and free of any material flaws such as nicks, burrs, scratches, dents, et cetera. Most of these components have very tight tolerances, so maintaining this accuracy is important in their performance. This is especially critical for oil seals because of their function.

Begin with a thorough inspection of all involved surfaces: shaft sealing surface and housing bore, seal lip(s), and outside diameter. Maintaining the integrity of the sealing lips is “Priority 1″. The slightest tear or nick can develop into a more significant issue during operation.

Over time, the seal lip(s) will wear a shallow groove into the shafting due to the pressure the seal imposes upon it. Visible scoring on the shaft indicates a genuine possibility that the seal will not perform as well as intended. The potential for lubricants leaking out and particulates working their way through the seal drastically increases when placed over a worn location.

There are a few options to remedy this situation:

• Using a spacer to move the seal forward is a possibility, assuming there is enough room in the housing bore to allow a shift. Ideally, the seal outside diameter (OD) should be in full contact with the housing.
• There are also shaft repair sleeves that can add a “new surface” to the shaft. Measuring a few thousandths of an inch in thickness, they cover shaft flaws so the seal can make proper contact with the surface.
• Probably the least appealing solution is to either replace or refinish the shafting. In some cases, this is not possible; in others, it could benefit the application in the long term.

Which option is best? This decision is left entirely to you. Whatever solution you choose, the seal needs a proper fit to function.

With the application cleaned and the components ready, you’ll begin your installation.

Oil Seal Installation

Many seals come with a garter spring, found within the backside of the seal. It provides contracting pressure against the sealing surface. Making sure the spring seats correctly within the seal is an excellent first step.

Next, apply a small amount of grease to the seal lip(s) and the area of the shaft in contact with the seal.  When using a double-lip seal, fill the small cavity between the two lips with grease as well. This both protects the lips during initial installation and break-in, and also acts as another barrier keeping contaminants out. When installing rubber-coated seals, apply lubricant to the outside diameter as well. This will help prevent the seal from rebounding or backing out from its mounting place.

Orient your seal the same way as the initial install. The sealing lip should face the lubricant that requires sealing. The second lip on a double lip oil seal is intended as a dust lip. The seal must be installed at a 90°, or perpendicularly, to both the shaft and housing bore. This is an issue in cases where the housing does not have a counterbore or shoulder the seal can seat up against.

When a seal is angularly misaligned – or cocked on the shaft – an irreversible process begins. Excessive pressure on one section of the seal, when not installed properly, can cause the spring to become dislodged or the seal to heat up and become brittle through excessive wear, both leading to a premature failure.

Some Tools Required During Installation

In situations where the shaft has splines or an integral gear on the end, you’ll want to take precautions. These gears and splines often have very sharp edges that are quite detrimental to the seal’s integrity. You may use an installation sleeve that will allow the seal to slide past these hazards undamaged.

The last step involves the actual pressing-in of the seal. There are tools and tool kits available that can help with seal installation. Their biggest benefit is that they apply a very uniform force to the seal case, eliminating the possibility of the seal seating in any way other than flush.

If these specific tools aren’t available, it’s entirely possible to correctly seat an oil seal in its housing using a hammer. Ideally, this hammer will be plastic or rubber due to it’s more forgiving nature. Using this and a strike plate that covers the entire seal will lend you accuracy while driving it in. The downside to this method is the inability to drive the seal any further than the strike plate will allow.

The small little oil seal has an outsized role in power transmission.

Proper techniques and diligence during oil seal installation will result in what seems like an unremarkable situation – a component holding its lubrication. When something you’ve installed works effectively and quietly, you know you’ve done it right.

Want to find an oil seal or shaft repair sleeve for your application? Visit the Durus website.

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.

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 6194-1 and JIS B 2402-1.
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 6194-1 1)

JIS B 2402-1 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: