Oil Seals: The Structure, Functions, And Types Of Oil Seals

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

With spring type Secures stable sealing performance.

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

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

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

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.

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:

Oil Seals 101 – Part 1

What is an Oil Seal?

Oil seals, also referred to as shaft seals, are widely used to prevent the leakage of medium (such as oils and grease) along a rotating shaft. This leak prevention is primarily achieved by the sealing element which can be made from a wide range of materials that are chosen according to each application. They are commonly used in gearboxes, hydraulic cylinders, and related components.

Purpose of an Oil Seal

An oil seal is designed to perform three major functions: to prevent lubricants from leaking outside the seal even under high pressure, to act as a barrier to retain the lubricating oil, and to prevent dirt and other contaminants from entering the unit.

Shop for Oil Seals

Construction of an Oil Seal

Oil seals normally consist of three basic components: the sealing element, the metal case, and garter spring.

1. Sealing Element

The sealing element makes up the interior of the oil seal, and the materials commonly used are:

a. Nitrile Rubber (NBR) – this is the most commonly used material. It has good heat resistance properties and has good resistance to salt solutions, oils, hydraulic oils, and gasoline. Operating temperatures are recommended from -40 to 248⁰ F (-40 to 120 deg.C). Nitrile also functions well in a dry environment, but only for intermittent periods. The disadvantage of this material is poor chemical resistance.
b. Polyacrylate Rubber (PA) – also known as acrylic rubber, this material has better heat resistance than nitrile. PA is also recommended for a high surface speed environment. Operation temperatures are recommended from -4 to 302⁰ F (-20 to 150⁰ C). Polyacrylate rubber should not be used with water or in temperature below -4⁰ F (20⁰ C).
c. Silicone Rubber (SI) – these compounds operate effectively in a broad temperature range of -58⁰ F to 356⁰ F (-50 to 180⁰ C). Silicone rubber is a leading choice for its resistance to both low temperatures and heat. The high lubricant absorbency of the material minimizes friction and wear. These oil seals are usually used as crankshaft seals. Silicone has poor resistance to hydrolysis and should not be used in oxidized or hypoid oils.
d. Fluorocarbon Rubber (FKM) – is widely known under the Chemours (formerly Dupont™) trade name of Viton® and offers the best resistance to chemicals and superior performance to high temperatures.

2. Metal Case

The metal case is the exterior (or frame) of the oil seal, the principal function of which is to give rigidity and strength to the seal. The material of the case must be selected depending on the environment where the seals are to be used. Often the metal case is covered by the same rubber material used in the sealing element, which also helps seal the exterior of the oil seal in the housing bore. Common case material types are:

a. Carbon Steel – the most common material used in oil seals.
b. Stainless Steel – for applications that require resistance to water, chemicals, or corrosion. (Stainless steel metal cases are also recommended for many FDA applications.)

3. Garter Spring

The garter spring is located at the end of the primary sealing lip and used to apply pressure to the sealing lip against the shaft. Common garter spring material types are:

a. Carbon Steel – which is used in conjunction with regular lubricants.
b. Stainless Steel – which is used when resistance to water, seawater, and chemicals are involved.

What is Oil Seal | Purpose , types of Oil Seal , Advantages

What is Oil Seal | Purpose , Types of Oil Seal , Advantages

OIL SEAL

Oil seals, also known as shaft seals, are radial lip type seals which are primarily used for retaining lubricants in equipment having rotating, reciprocating or oscillating shafts. The rotating shaft application is most common.

An oil seal normally consists of three basic components: the sealing element, the metal case and the spring. The purpose of the sealing element is to stop the fluid from leaking between the shaft and housing. The metal case will give rigidity and strength to the seal while it is being held in the bore or recessed groove. The garter spring ensures constant pressure and maintains the radial force to the shaft, flattening the sealing edge to a defined width. The garter spring maintains the radial force exerted by the sealing lip around the shaft surface. All materials must be selected depending on the environment in which the oil seal will function.

The performance of these seals depends to a large extent on a suitable unit load being maintained at the seal-shaft interface. These seals withstand a pressure of 15PSI and their working depends on parameters like shaft diameter, shaft speed, working temperature, service conditions, etc

Oil seals or shaft seals are an integral part in any rotating and moving part assembly. Oil seals find great deal of usage in gearboxes, hydraulic cylinders, etc. The usage of the seals in areas concerned with motion also earns them a name of “Dynamic Oil Seals.”

The purpose of the oil seals is

To act as a physical barrier retaining the lubricating oil where it is bound to be.
To prevent thelubricating oil from leaking outside even under high pressure of the oil.
To act as a barrier and prevent dirt, contamination and other external entities from entering the system containing the lubricating oil.

Constructional Aspects of an Oil Seal:

1. The oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal.

2. The outer skin is made of nitrile rubber and various other materials which are used based on the requirement.

3. The spring on the lip of the oil seal tends to provide support to the lip and prevents the lubricant from leaking outside and also prevents the entry of contaminants from outside.

TYPES OF OIL SEAL

Double Lip Oil Seals

In this an auxiliary lip is provided along with the regular sealing lip. The additional dust lip protects the main sealing lip against dust and other fine solid contaminants and therefore this type is recommended for use in polluted environments. To achieve a long lifetime a suitable lubricant between the two sealing lips should be applied.

Advantages:
– Good static sealing
– Compensation of different thermal expansion
– Reduced risk of fretting corrosion
– Effective protection against air side contaminants
– Higher bore surface roughness is allowed
– Installation in split-housings
– Modern lip design provides low radial forces

Duplex Oil Seals

Sometimes, two different kinds of fluids leak from one chamber to another and gets mixed up. Here, this type comes as a boon. This is a metal inserted duplex type oil seal recommended on such assembly where mix-up of two different fluids is to be prevented.

Oil Seals without Spring

This type of oil seal can withstand only low speed and friction. It is recommended in places where thick fluid or grease is to be sealed. This is not recommended for difficult applications.

Material:

Oil seals are made out of nitrile synthetic rubber with steel stiffener rings. Other rubbers such as viton, silicon, neoprene or poly acrylic can be used for specific applications. The stiffener rings may be stainless steel or brass where highly corrosive fluids are to be sealed. Springs are generally made of spring steel to IS: 4454:Gr.ll or from stainless steel or bronze for corrosion resistance

Type A Oil Seals

Sealing of lip type seal is normally a result of an interference fit between the flexible sealing element, usually augmented by spring pressure and a shaft. Fluid retention is based on the precise amount of lip contact pressure. In most lip seals, increased fluid pressure in the sealed area causes lip contact pressure on the shaft to increase.

Advantages:
– Good static sealing
– Compensation of different thermal expansion
– Reduced risk of fretting corrosion
– Higher bore surface roughness is allowed
– Installation in split-housings
– Modern lip design provides low radial forces

Type B Oil seals

This is almost similar to that of ‘A’ type seal. But this has the metal case placed outside. When the housing is rough, temperature is high and working conditions are severe, this type is preferred.

Type C Oil seal

Type ‘C’ oil seal has an additional cup inserted into the outer cup of ‘B’ type. The supplementary metal inner ring provides a superior stiffness. This type is recommended for use in heavy polluted environments. As the static sealing between housing and metallic shell is limited, low viscosity media can “creep”.

Advantages:
– Very good fitting stability avoiding pop-out of the seal
– Modern lip design provides low radial forces
– Superior radial stiffness, especially for very large diameters
– Cost effective for expensive elastomer materials
– Suitable for use in combination with axial seal

Material used for Oil Seal :

Based on the application of the oil seal, the outer skin layer tends to differ. Here are some types of the materials used for the outer skin of the oil seal.

1. Nitrile rubber – The commonly used material for oil seals

2. Silicone – Used in specific applications where only light loads are applied.

3. Poly acrylate

4. Fluroelastomer also popularly known as Viton. – The high temperature resistant material used in places where temperature is more than 120 Degree Celcius.

5. PolytetraFluroEthylene (PTFE)

The oils seals require certain prerequisites to be maintained for their proper working. They are as follows:

a) The shaft on which the oil seal is to be mounted should be ground with the surface finish or surface roughness between 0.2 to 0.8 Microns. It is best for the shaft to be hardened atleast to 40 – 45 HRc in order to prevent groove formation on the shaft due to the pressure exerted by the spring.

b) The area where the oil seal is seated is to be plunge ground in order to prevent wear grooves that normally tend to wear out the lip of the oil seal at a faster rate.