Oil Seals (Part 1): The structure, functions, and types of oil seals

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:

We offer quality sealing and cost-effective oil seal designs that help keep equipment running longer while reducing downtime. Through our comprehensive selection we provide oil seals with short lead times and with a variety of designs for use in many common and more challenging industry applications. When selecting an oil seal, it is important to know what sort of design is needed, and we have outlined a few of the more common elements below.

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Standard Sealing LIP Designs

Our oil seals have many different available lip designs, with some being simple and others complex, due to their special application. However, the most common industry lip standards are described below:

• (single lip):  This design uses a garter spring and generally seals against internal media in lower pressure applications.  The single lip is not recommended for use in applications in which the environment contains dirt or contaminants.
• (double lip): This design is also used with a garter spring and consists of a primary lip for sealing against internal media in lower pressure applications.  The secondary (also known as the auxiliary lip) provides additional protection from dust and dirt.
• (dual or twin lip):  This design consists of garter springs and two identical primary lips that are usually used to separate two liquids. The space in between these two lips must be lubricated with grease or something similar.
• (single lip):  This design has NO spring and is generally used for sealing a non-pressure medium, such as grease or protecting against dirt.
• (double lip): This design has NO spring and is generally used for sealing a non-pressure medium, such as grease and is used to protect against dirt as well as internal and external media.

Standard Sealing CASE Designs

We offer oil seals in many various case designs from the most simple to the most challenging applications. Below are just a few of the most commonly used case designs for most sealing applications:

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

Metal Case Finishes & Treatments

Oil seals with outer metal cases may include finishes or treatments that are 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 that is usually a yellowish-green color), a Color Painted edge, and a grinded-polished edge.

Oil Seal Style Selection (Common Types)

Combining both the lip and case types explained above, it is easy to assemble the Global O-Ring and Seal (GOR) types as indicated in the following examples:

Type SC: Single lip w/spring, rubber covered O.D.
Type TC: Double lip w/spring, rubber covered O.D.
Type SB: Single lip with spring, metal O.D.
Type TB: Double lip with spring, metal O.D.
Type SA: Single lip w/spring, reinforced metal O.D.
Type TA: Double lip w/spring, reinforced metal O.D.

Factors in Oil Seal Selection

Our oil seals are available in both inch and metric sizes and are selected as follows:

• Type: Combination of lip design and case type.
• Shaft Diameter: The outside diameter of the shaft where the seal will operate (sometimes referred to as the I.D. of the oil seal)
• 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)
• Width (or Depth): The depth of the bore (also known as the width or height of the seal). Note: When the width of the seal is not strictly specified, the depth of the bore is usually made big enough so a seal might be replaced by a wider one.
• Sealing Lip material
• Any special materials or considerations, such as stainless steel for the case and/or spring
• Any special treatment or finish such as painted, polished edge, etc.

Oil Seal Designs From Global O-Ring and Seal

Global O-Ring and Seal offers a full line of oil seal designs in all industry standard sizes. If you are a distributor or purchaser who may have need for our oil seal products, contact us today to speak with one of our technical sales associates, request a no-obligation quote, or place an order online from our extensive inventory.

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Did you miss the first part in our series? Be sure to click here to read part one.

PRESIDENT/OWNER:
Bill has served in the sealing industry for more than 25 years, and founded Global O-Ring and Seal nearly 10 years ago.

HTCL

(Anti-clockwise)

HTCR

(Clockwise)

HTGW

(Bi-direction)

OSC

Single lip, Garter spring loaded, designed for housing / bore rotated used.

OTC

Twin lips, Garter spring loaded, designed for housing / bore rotated used.
Sealing identical to Type OSC, with an extra lip to excluded foreign matter from Auxiliary lip.

SEC

TCA

TCN

TCV

KA3J

TCJ

Twin lips, garter spring loaded, rubber covered outer with PTFE cover on the main lip.

SBG

Single lip with garter spring loaded, combines the advantage of reliable static sealing by the elastomeric component with secure seating of metal part on outer case.