Oil seals are rotary shaft seals that close a gap between stationary and moving components and prevent lubricant to escape and thus stop contamination through the clearance. There are different types of oil seals that fit a different application and surroundings and are made out of different materials. The right material and type of oil seal is determined by the application and the medium that will be used with the oil seal.

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Norm design

The DIN standard specifies dimensions and requirements for materials, marking, use and installation of rotary shaft lip seals used for retaining fluid or grease in unpressurized equipment, or equipment with a low differential pressure, that has rotating shafts. DIN defines standards for rotary shaft lip type seals for automobiles.
 

The standard oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal. The outer part is made of rubber or metal - based on the requirement and the application of the oil seal. The spring on the lip of the oil seal provides support to the lip and prevents the lubricant from leaking outside and also prevents contaminants from entering.

The oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal. The outer part is made of rubber or metal - based on the requirement and the application of the oil seal. The spring on the lip of the oil seal provides support to the lip and prevents the lubricant from leaking outside and also prevents contaminants from entering.

Tip for greasing oil seals with dust lips: If oil seals with fixed dust lips are being used, the space between the sealing lip and the dust lip may also be filled entirely with grease. The medium to be sealed will dissipate the heat.

A garter spring is a coiled steel spring that is connected at each end to create a circular shape. It maintains the radial force exerted by the sealing lip around the shaft surface.

Types of oil seals

The most commonly used oil seals in most applications are rubber cased or metal cased oil seals.

Metal Cased Oil Seals

Metal-cased oil seals are used when installed to a housing bore made of the same material. This allows for equal contraction and expansion of the materials during operation, preventing leakage from occurring. Typically metal-cased seals are more cost efficient than rubber seals.

Rubber Cased Oil Seals

Rubber-cased oil seals are the most common oil seal execution, used when a metal-cased seal has the potential to fail (for example because of thermal expansion). Oil seals with a rubber case cannot rust, in contrast to oil seals with metal cases. Moreover, oil seals with a rubber case can seal a lightly damaged housing much better than metal cased oils seals. In high temperatures and high pressures, fast expanding rubber can provide a tight fit and more stable sealability.

The most commonly used type is type R. This type has a carbon steel insert and has rubber outside diameter. The rubber gives a good sealing capability, even when the housing is not fully in tolerance. The sealing lip with spring provides interference on the shaft for effective sealing. The outside diameter, with inner metal reinforcement case, allows press-fitting in the housing, with sufficient interference on the rubber to provide static sealing.

Oil Seal Buying Guide

Are you looking to keep your machinery free from any unwanted leakages but aren't sure which rotary shaft seal is right for your needs? This guide will provide you with everything you need to know in order to select the right one for your application.

Oil seals, which are also known as rotary shaft seals, fluid seals or grease seals, play an important role in closing down the gaps between moving and stationary elements of mechanical equipment.

By preventing lubricants from escaping, they protect key components of machinery from being damaged by leaks of various fluids. Everything from car engines to assembly machines use these oil seals to remain free from any harmful interactions that can cause serious and expensive damage to any of their critical parts.

There are a wide range of oil seals to select from for any number of uses, so this guide will break down the most common seals to help you choose the right one for whatever piece of machinery you are working on.

What are rotary shaft seals?

Rotary shaft or oil seals are placed between moving and stationary pieces of machinery to ensure that contaminants, moisture, corrosive materials and abrasives do not damage the various components. They can also prevent unwanted mixing of fluids, including water and oil combining within a machine.

How are Oil Seals made?

First, an elastomer, most often nitrile, is vulcanised to a metal ring. This creates a stiffening effect that includes a specialised metal tension spring directly behind the sealing lip, keeping the oil seal firmly in place against the moving part.

Oil Seal Materials

There are many different materials used to manufacture oil seals.

Leather Oil Seals ' Leather Seals, also known as Type L Oil Seals, are most common in components that are subject to dirt and poor lubrication. Since they come pre-lubricated and are able to absorb fluids, leather oil seals are able to provide sealing properties in conditions that synthetic rubber is unable to.

Synthetic Rubber Oil Seals ' Styrene Butadiene Rubber oil seals, or just SBR oil seals, offer strong resistance to abrasions and lesions, making them an ideal seal for fast-moving machinery. With the ability to withstand extreme temperatures with its heat-aging qualities, they can be used in outdoor components. They are also seen as more cost-effective oil seals than natural rubber.

Nitrile Oil Seals ' Nitrile oil seals, which is the commonly used term for acrylonitrile-butadiene rubber seals, is a very good general-purpose option due to the flexibility of use across a variety of components. The resistance is strong against fats, hot water, gasoline, mineral oils, grease and animal oils, making them the most often-used oil seals. They do not have a wide temperature range, making them a poor choice for machinery that can see extreme changes in temperature.

Viton Oil Seals ' A synthetic rubber and fluoropolymer elastomer, Viton is used to make oil seals that provide resistance in both high temperature, up to 250°C and low compression set components. They also offer a high resistance to chemicals and abrasions, so they can be used in elements that regularly interact with petroleum and solvents.

Polyacrylate Oil Seals ' Mostly selected for automotive and transmission uses, polyacrylate seals are able to withstand fuel, oil, ozone, sunlight and weather when used. With cars exposed to all these different fluids and elements, they are the perfect choice. However, they should not be used in low temperatures, as their flexibility weakens when cold.

Silicone Oil Seals ' Designed to absorb lubricants in order to lessen wear and friction, silicone rotary shafts also offer high thermal resistance and a large temperature range. But, they do not handle abrasions well or interact with oxidized oils.

PTFE Oil Seals ' A relatively new and exciting oil seal, the use of polytetrafluoroethylene means that they can withstand dry or unlubricated operations. With a massive thermal range of  -130ºC to +200ºC and a strong resistance to chemicals, they are considered to be the future of rotary shaft seals.

How to Choose the Right Oil Seal

There are several key factors to consider when you are selecting the oil seals for your next project to ensure that you protect your machinery from immediate and long-term damage.

Pressure ' Many oil seals can only withstand low-pressure applications, so understanding the compression set of your components is key.

Temperature ' Just like pressure, the temperature that your oil seal will be operating in must be known so that you can choose one that can withstand the heat or cold. PTFE have the widest range of temperature, making them useful for machines who can see usage in extreme weather or elements.

Shaft Speed ' Considering the speed that the shaft will be moving, the runout, the housing bore and the type of oil being sealed is vital to making sure you select an oil seal that will not suffer from abrasions or spiralling.

Fluid Types ' Various oil seals are able to withstand interactions with oils, fuels, grease, water and more. Knowing what type of fluid the rotary shaft seal will be in constant contact with will ensure the longevity of the seal and surrounding components.

Lubricant Amount ' Seals will always perform best when lubricated, however in some machines there are more likely to be dry spells. For these cases, selecting a leather or PTFE seal will be beneficial, as both can operate with less lubrication than others.

Replacing a critical component

can be difficult to get right, especially if you do not have the original machine specifications. Thankfully, there are a few ways to identify oil seals; from their design, size and material. As there are hundreds of different oil seals available on the market, this guide will cover the four most common design types. Typically available with either a single or double lip, in Nitrile or Viton Rubber Material.

Oil Seal Single Lip vs Double Lip

Firstly, the oil seals covered in this guide classify the single lip as the inner diameter at the bottom of the component. The single lip is vital to the function of the seal by containing the oil, grease or lubricant. The only difference between a single and double lip is the additional rubber lip on the top of the oil seal which helps prevent dust or dirt from coming close to the shaft. Identifying the oil seal lip can be misinterpreted with a visual inspection alone. For or this reason, you should press along the inner diameter at the top of the seal, if you feel a ridge with a slight movement or give it is highly likely you have a double-lipped oil seal.

Identify Oil Seal Design

1. Type A ' Rubber Covered Lip Seals

Fully covered outer diameter for excellent sealing. This oil seal is fully enclosed in a rubber material and is the most widely used type of oil seal. Great resistance to thermal cycling, temperatures and different chemical resistance.

2. Type B ' Metal Outer Diameter Oil Seals

Economic metal outer diameter for standard applications. This is an economical oil seal where the metal is exposed on one side and offers a closer fitting between the oil seal and housing or bore. Due to this, it has limited use with sealing thin liquids or gases.

3. Type C ' Reinforced Metal Insert Oil Seals

The same design as type B with an additional inner case for greater structural rigidity. This type of oil seal is typically used in heavy-duty engineering machinery or large diameter sized seals

4. Type F ' Stainless Steel Garter Spring

The same design as type A with corrosion protected metal case and stainless-steel garter spring. Suitable for use with a wide range of fuels and chemicals.

 Machines play a crucial role in keeping our world functioning efficiently. We depend on them heavily to ensure that everything runs smoothly. This dependence often leads us to concentrate on the larger parts of these machines. However, we should recognize the smaller yet vital components like oil seals. These seemingly minor parts are key to maintaining a machine's efficiency. Oil seals keep lubricants inside the machinery as protectors and block out harmful contaminants. Their straightforward but essential function is vital for the seamless operation of our machines.

That's why choosing proper sealing for a railcar component, an automobile, or a heavy type of machinery helps keep them running properly without any failures. And that's where the magic of measuring and understanding different oil seals typescomes in. It's not just about picking any seal; it's about finding the perfect fit for your needs. 

So, let's dive into this blog to understand how to measure and select the ideal oil seal for your machinery. 

What are Oil Seals? 

Oil seals, also known as shaft seals or lip seals, are critical components in machinery used to seal pressurized systems, maintain lubricants, and exclude contaminants. These seals are often made of nitrile rubber, silicone, or polytetrafluoroethylene (PTFE), providing the flexibility and durability needed to keep a tight seal under varying conditions. An oil seal has a metal casing to keep it firm and a sealing lip to prevent fluid loss. 

They are frequently used in automotive, industrial, and manufacturing applications, critical to machine smooth and efficient operation. Elements such as the material's compatibility with the fluid and the temperature range of the seal determine the efficacy of oil seals. 

Oil Seals Types

1.Rotary Shaft Seals: These seals protect bearings from impurities and prevent lubrication leakage in rotating machinery parts. They guarantee that the machine's moving components run smoothly and last long.

2.Hydraulic Seals: Hydraulic seals are often used in hydraulic cylinders and designed for high-pressure settings. They protect fluid systems by preventing fluid leakage at excessive pressure.

3.Axial Seals: Axial seals are important components in pumps and valves since they are used largely for axial motions. They offer excellent sealing in applications where pieces move parallel to the seal axis.

4.Static Seals: These types of seals are Ideal for circumstances when the sealing pieces move very little or at all. Static seals keep a seal in place while stationary, avoiding leakage in fixed joints.

5.Custom Seals: When regular seals fail to suit the unique needs of a particular application, custom seals are the go-to answer. They are custom-made to match specific dimensions and circumstances, producing excellent sealing performance.

Understanding these oil seals types is essential to choose the perfect one for your machines. 

Measuring Oil Seals

The accuracy of measuring oil seals is paramount. Here's a step-by-step guide:

• Measurement of Diameter:

-Inner Diameter (ID): To determine the seal's inner diameter, measure across its interior. This ensures the seal can adequately fit onto the shaft it's designed to protect.

 ' Outer Diameter (OD): To find the seal's outer diameter, measure across the exterior of the seal. This dimension is critical for ensuring the seal fits appropriately within the hole or housing in which it is installed.

These dimensions are critical for ensuring the seal fits securely and efficiently in its intended location, resulting in maximum performance and protection.

• Width Measurement:

Simply measure the width of the seal from one edge to the other. This width ensures the seal fits correctly in its allotted housing area. This dimension must be correct for the seal to function effectively and offer the necessary protection.

• Type of Sealing Lip:

Determine whether the seal has a single or double lip. This feature is significant because it affects how the seal works against the surface it is sealing. A single lip is easier, and seals in basic settings; on the other hand, a double lip seal provides enhanced protection and is better suited for demanding environments where extra sealing is necessary. Numerous reputable suppliers of aftermarket parts in India offer high-quality oil seals for various needs.

• Material Composition: 

Determine the seal's substance, which might be nitrile, silicone, or Viton. The material determines how effectively the seal can withstand various temperatures and chemicals. Each material has strengths and is suitable for specific conditions, so choosing the right one is crucial for the seal's effectiveness.

Selecting the Right Oil Seal

After measuring, you must select the appropriate type of seal for your needs. Bear in mind:

• Operating Conditions: Consider the temperature, pressure, and general environment where the seal will be employed. These criteria have a significant impact on the seal selection.
• Shaft Speed: Think about how quickly the shaft rotates. Different speeds may necessitate different types of seals for optimal performance.
• Fluid Type: The type of fluid encountered by the seal is critical. This determines the best seal material for compatibility and durability.

There are various oil seals types available to suit different needs, but selecting the appropriate oil seal is crucial for your machine's performance. 

Installation Tips

Proper installation is just as important as selecting the appropriate seal. Here are some basic guidelines to follow:

• Cleanliness is Key: Ensure the seal and its housing are clean and debris-free before installation. This helps to guarantee a perfect fit and seal.
• Handle with Care: Sharp tools should be avoided during installation as they might harm the seal.
• Lubricate Before Installing: Before installing the seal, apply a small lubricant coating on it. This simplifies installation and improves seal performance.

Many top rubber products manufacturers in India now make user-friendly oil seals, frequently including installation guidelines. However, it is still advisable to have professionals perform the inspections and repairs to ensure everything is done correctly.

Maintenance and Replacement

Inspection and replacement of worn oil seals are critical for preventing leaks and contamination in machinery. Consider the operational environment, as severe temperatures might accelerate wear. Adhering to a standard replacement plan and preserving maintenance records increases equipment lifespan and dependability.

Read More ' Things you should know before buying rubber oil seals .

Get High-Quality Oil Seals from Sujan Industries 

Understanding how to measure and select the properoil seals is critical for maintaining the integrity and performance of machinery. A good oil seal does more than just prevent leaks and keep out contaminants; it also helps extend the life of your machinery, reducing the need for repairs and avoiding costly downtime. Investing time in selecting the right seal is a smart move that pays off in the long run. 

For high-quality oil seals and rubber products, Sujan Industries is your go-to answer. We offer a range of top-notch products tailored to meet your specific needs. Known for their quality and commitment to excellence, contact our expertsfor durable and practical sealing solutions.

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

'

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.)

'

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.

'

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.

'

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.

'

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.

'

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.

'

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.

'

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

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Want more information on d type skeleton oil seal? Feel free to contact us.

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 ' 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

' Spring code

No code: without minor lip

A: with minor lip

' Lip type code

No code: without minor lip

A: with minor lip

' 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. ' 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 248' 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 302' F (-20 to 150' C). Polyacrylate rubber should not be used with water or in temperature below -4' F (20' C).
• c. Silicone Rubber (SI) ' these compounds operate effectively in a broad temperature range of -58' F to 356' F (-50 to 180' 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: :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.

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