Also known as grease seals, rotary shaft seals, or fluid seals, oil seals play a pivotal role in mechanical equipment. They are often overlooked because they are a small part of the machine, but when these oil seals fail, the consequences can be huge, like seal leakages that are costly to fix.
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From assembly machines to car engines, oil seals prevent any harmful damage from occurring, which is why you must choose the right oil seal with the highest quality. There are many kinds of oil seals, all of which have several uses.
This article will guide you through the most common factors you should look for when buying oil seals to help you choose the right one for the machinery you’re working on.
Improper installation and poor-quality oil seals are some of the reasons that pieces of machinery get damaged. When choosing an oil seal, consider the following factors.
The temperature range of the seal elastomer should match the temperature range of where you’ll install the seal. For example, high-temperature and high-pressure environments need more durable rubber, like Viton. If the oil seal is exposed to extreme temperatures outside of the elastomer’s range, the sealing lip may harden, break, and crack.
The oil seal’s material matters, as it can determine how well it performs depending on its use. Sealing elements can come in leather, silicone, synthetic rubber, Viton, nitrile, and polyacrylate. Nitrile is good for general purposes, as it’s flexible and resistant against oils, hot water, and gasoline. However, it doesn’t do well in extremely high temperatures. Meanwhile, silicone oil seals lessen wear and tear by absorbing lubricants. They have a wide temperature range and high thermal resistance, too.
Understanding the compression requirements of your components is important. Most ordinary oil seals are designed for very low-pressure applications (about 8 psi or less). If the intended application has high pressure, you should consider choosing an oil seal ideal for high pressure or changing to a pressure-free structure.
The oil seal shouldn’t suffer from spiraling or abrasions. As such, you should consider the maximum allowable shaft speed, runout, type of oil seal material, type of fluid being sealed, and housing bore and shaft concentricity before buying an oil seal.
Close shaft and bore tolerances should be present if you want the best seal performance. It would be best to consider the shaft’s vibration, eccentricity, and end play.
You must align bore and shaft centers because misalignment can shorten the oil seal’s life cycle due to the excessive wear concentrated on only one side of the sealing lip.
It would be best if you kept runout to a minimum. When the center of rotation moves, it’s usually caused by a shaft whip or bearing wobble. When you add misalignment, then you’ll face a greater problem. Contrary to common practice, installing flexible couplings won’t correct misalignment, which is why you need the right oil seal to prevent all these issues from arising.
The quality of the oil seal affects its service life. The higher the quality, the longer the lifespan, reducing wear and tear and increasing your ROI through lower maintenance costs. While wear and tear issues are inevitable, you should mitigate them by using materials that last long. Here, the first step to ensuring quality oil seals is purchasing from a reputable oil seal supplier.
When shafts have a Rockwell (RC) hardness of 30 or more, you can expect the oil seal to have a longer seal life. For shafts exposed to more abrasive contamination, your oil seal should handle RC 60.
You can tell that you have effective sealing if the shaft surface finish is in excellent condition. Sealing performance is greatly influenced by the spiral lead and the direction of the finish tool marks.
You’ll get the best sealing results when the shafts are ground or polished with concentric (no spiral lead) finish marks. If the shaft can’t help but have spiral finish leads, they should lead toward the fluid when the shaft rotates.
Oil or lubricants play a significant role in improving the oil seal’s performance. You should choose a lubricant compatible with the seal lip elastomer material and the right viscosity for the application. Incompatible lubrication can result in the wearing out of the oil seal.
An example of a lubricant you can use is Permatex Anti-Seize Lubricant, a highly refined blend of graphite, aluminum, and copper lubricants.
Oil seals come in various sizes, styles, and materials. Hence, it can be challenging to pick the right type for your needs. Use the factors above to guide you throughout your oil seal selection process. If you’re looking for top-of-the-line oil seals, Simplex is a premier distributor of oil seals and premium industrial and engineering parts in the Philippines. Visit our shop today to get started!
In Part 1, we explained the structure, functions, and types of oil seals.
Oil Seals (Part 1): The structure, functions, and types of oil seals
Oil seals come in various shapes to fit the machines and substances to be sealed.
For this reason, when designing a machine, it is important to select the oil seal that is right for that machine.
That's where this column comes in.
We will explain the key points for selecting the oil seal that is right for your machine.
Oil seals come in a wide range of types, and they also have various sizes.
When selecting the right oil seal for your machine from among these many varied types of oil seals, the following two criteria are very important.
Criterion 1: It should be appropriate for the machine's usage environment and the operating condition that is being demanded of the oil seal
Criterion 2: It should be easy to acquire replacement oil seals and it should facilitate maintenance/inspection of the machine
If these criteria are met, damage of the machine can be reduced, the time needed to replace the oil seals when performing repairs can be shortened, and the machine can be used for a longer period of time.
In this way, selecting the appropriate oil seal will lead to machine design that is economically superior!
In general, oil seals should be selected in the order of priority indicated in Table 1.
However, when you actually select the oil seal to use, the most important factors are past success history and points of improvement, so it is not necessary to follow this order to the letter.
Table 1: The order of priority for selecting oil seals
No. Examination item 1 Seal type 2 Rubber material 3 Metal case and spring material
Select your oil seal type according to Table 2.
Table 2: How to select the seal type
No. Examination item Flowcharts 1 O.D. (outside diameter) wall material Figure 1 2 Necessity of spring Figure 2 3 Lip type Figure 3
Figure 1: O.D. (outside diameter) wall material
Figure 2: Necessity of spring
Figure 3: Lip type
＜Seal selection example＞
Based on the above flowcharts, the oil seal type that meets the requirements shown in Table 3 would be the type code MHSA or HMSA shown in Table 4.
Table 3: Requirements
No. Requirements 1 Housing Made of steel, one solid design, housing bore surface roughness 1.8 μmRa 2 Substance to be sealed Grease 3 Pressure Atmospheric 4
Shaft surface speed
(peripheral speed)
6 m/s 5 Air-side condition Dusty
Table 4: Type of selected seal
Type 1 Type 2 O.D. wall material Rubber O.D. wall Metal O.D. wall Necessity of spring Spring required Spring required Lip shape Minor lip required Minor lip required
Type (type code)
For a more detailed discussion of seal types and type codes, please see the following:
The rubber material used in the oil seal should be selected based on the operational temperature and substance to be sealed.
Table 5 lists the major rubber materials along with their operational temperature ranges.
Note that it is necessary to check the compatibility with fluids.
＜N.B.＞
Extreme pressure additives are compounds added to the lubricant. They are activated by heat and chemically react against rubber, which deteriorates rubber properties. For this reason, it is necessary to check for compatibility with rubber materials.
Table 5: Major rubber materials and their operational temperature ranges
Rubber material
(ASTM*1 code) Grade Features Operational temperature range (°C) Compatibility with fluids
Nitrile rubber (NBR)
Standard type
Well-balanced in terms of resistance to abrasion and high and low temperatures
-30～
100
Necessary to check compatibility with fluids
(See *2)
Fluids
• Fuel oil
• Lubricating oil
• Hydraulic fluid
• Grease
• Chemicals
• Water
High- and low-temperature-resistant type Highly resistant to both high and low temperatures -40～
110
Hydrogenated nitrile rubber (HNBR)
Standard type
Compared with nitrile rubber, superior in resistance to heat and abrasion
-30～
140
Acrylic rubber (ACM)
Standard type High oil resistance and good abrasion resistance -20～
150
High- and low-temperature-resistant type Improved low temperature resistance and same level of heat resistance as the standard type -30～
150
Silicone rubber (VMQ)
Standard type Wide operational temperature range and good abrasion resistance -50～
170
Fluoro rubber (FKM)
Standard type The most superior in resistance to heat, and good abrasion resistance -20～
If you are looking for more details, kindly visit Auto Oil Seal.
180
Notes
*1 ASTM: American Society for Testing and Materials
*2 For more details on fluid compatibility, please see the following:
Rubber materials, operational temperature ranges and their compatibility with fluids
The metal case and spring material used in the oil seal should be selected based on the substance to be sealed.
Table 6 shows how to select the metal case and spring materials.
Table 6: Selection of metal case and spring materials
Substance to be sealed Material Metal case Spring
Cold rolled carbon steel sheet
(JIS* SPCC)
Stainless steel sheet
(JIS* SUS304)
High carbon steel wire
(JIS* SWB)
Stainless steel wire
(JIS* SUS304) Oil ○ ― ○ ― Grease ○ ― ○ ― Water × ○ × ○ Seawater × × ○ Water vapor × ○ × ○ Chemicals × ○ × ○ Organic solvent ○ ○ ○ ○
Notes
* JIS: Japanese Industrial Standard
✓: Compatible
✗: Incompatible
―: Not applicable
Oil seals can show good sealing performance in combination with properly designed shafts and housings.
Table 7 shows the shaft design checklist.
Table 7: Shaft design checklist
No. Examination item Major points to confirm Remarks 1 Material Use one of the carbon steels for machine structural use, low-alloy steel, or stainless steel. Soft materials (brass and so on) are not suitable. 2 Hardness Shaft hardness should be at least 30 HRC. In usage conditions where wear can occur easily because of dust or contaminated oil, hardness should be 50-60 HRC. 3 Shaft diameter tolerance This should be h8 (seals are designed to suit shafts with a tolerance of h8). 4 Shaft end chamfer "Provide a chamfer on the shaft end.
(This prevents failure during mounting.)" See Figure 4. 5 Surface roughness and finishing The shaft surface to be in contact with the lip should be finished to
0.1 to 0.32 μmRa and 0.8 to 2.5 μmRz
and the lead angle to no greater than 0.05°. (There is a risk that the lead marks will impede the sealing performance of the oil seal: see Figure 5.)
Nominal shaft diameter
d1, mm d1-d2, mm を超え 以下 ― 10 1.5 min. 10 20 2.0 min. 20 30 2.5 min.
Figure 4: Shaft end chamfer
a) Good finished surface
(no lead marks) b) Undesirable finished surface
(visible lead marks)
Figure 5: Shaft surface with and without lead marks
Table 8 shows the housing design checklist.
Table 8: Housing design checklist
No. Examination item Major points to confirm Remarks Material Steel or cast iron is generally used as the housing material.
Aluminum alloys and resin (materials with a large difference between the linear expansion coefficients) demand sufficient consideration (as there is a risk of failure due to the increased clearance with the oil seal at high temperatures). 2 Bore diameter tolerance 1. If the nominal bore diameter is 400 mm or less:
H7 or H8
2. If the nominal bore diameter exceeds 400 mm:
H7 3 Bore inlet chamfer Provide an appropriate chamfer with rounded corners.
(This facilitates mounting.) See Figure 6. 4 Shoulder diameter
(if the housing bore has a shoulder) Set appropriate shoulder diameter. See Figure 7. 5 Bore surface roughness 1. For metal O.D. wall type:
0.4 to 1.6 μmRa,
1.6 to 6.3 μmRz
2. For rubber O.D. wall type:
1.6 to 3.2 μmRa,
6.3 to 12.5 μmRz
(Firmly affixes the oil seal and prevents leakage through the seal O.D.)
Nominal seal width
b, mm
B1 min.
mm L
mm Over Up to ― 10 b + 0.5 1.0 10 18 1.5 18 50 b + 0.8
Figure 6: Recommended housing bore chamfers (shouldered bore)
Nominal seal O.D.
D, mm
F
mm Over Up to ― 10 D - 4 10 18 D - 6 18 50 D - 8
Figure 7: Recommended housing shoulder diameters
When the total eccentricity is excessive, the sealing edge of the seal lip cannot accommodate shaft motions and leakage may occur.
Total eccentricity is the sum of shaft runout and the housing-bore eccentricity.
Total eccentricity, shaft runout and housing-bore eccentricity are generally expressed in TIR (Total Indicator Reading).
A) Shaft runout
As shown in Figure 8, shaft runout is defined as being twice the eccentricity between the shaft center and center of shaft-center rotation trajectory.
Figure 8: Shaft runout
B) Housing-bore eccentricity
As shown in Figure 9, housing-bore eccentricity is defined as being twice the eccentricity between the housing-bore center and shaft rotation center.
Figure 9: Housing-bore eccentricity
The allowable total eccentricity is the maximum total eccentricity at which the sealing edge can accommodate shaft rotation and retain adequate sealing performance. The oil seal's allowable total eccentricity is affected by the design of the oil seal, the accuracy of the shaft, and the operating conditions.
For details on shaft and housing design, please see the following:
Examples of allowable total eccentricity for oil seals
Oil seal performance is affected by not only the type and material of the selected oil seal, but also a variety of other factors, such as operating conditions, total eccentricity, rotational speed, the substance to be sealed, and lubrication conditions.
Figure 9 shows items relating to oil seal characteristics.
Figure 9: Items relating to oil seal characteristics
No. Item Content Major factors 1 Sealing property Lip pumped volume
(the volume of oil, etc., pushed back at the lip contact area per unit of time) • Shape
(hydrodynamic ribs)
• Rotational speed
• Oil viscosity, etc. 2 Oil seal service life Wear on the rubber material
Loss of lip sealing function • Operational temperature
• Total eccentricity
• Rotational speed
• Substance to be sealed
• Lubrication conditions, etc. 3 Lip temperature Temperature rise due to sealing edge friction heat because of the shaft rotation • Rotational speed, etc. 4 Allowable peripheral speed When shaft rotation is extremely fast, the sealing performance deteriorates. • Total eccentricity
• Rubber material
• Seal type, etc. 5 Allowable internal pressure Internal pressure is a factor that may deteriorate seal performance. • Total eccentricity, etc. 6 Seal torque The seal torque is large. • Lip radial load
• Lubricating oil
• Rotational speed
• Shaft diameter, etc.
For a more detailed discussion of seal characteristics, please see the following:
Seal characteristics
When selecting the oil seal that is right for your machine, it is important that the oil seal be appropriate for the requirements of the usage environment and that it be easily acquired for replacement.
In this month's column, "How to select the right oil seal," we conveyed the following points:
1) Oil seal shape and material should be selected based on the housing, substance to be sealed, pressure, rotational speed, total eccentricity, and air-side conditions.
2) Oil seals can show good sealing performance in combination with properly designed shafts and housings.
3) Oil seal performance is affected by not only the type and material of the selected oil seal, but also a variety of other factors, such as operating conditions, total eccentricity, rotational speed, the substance to be sealed, and lubrication conditions. For this reason, diligent care is required in oil seal selection.
In order for the sealing property of the oil seal you selected to really shine, attention needs to be paid to how it is handled.
In the event of seal failure, it is necessary to take effective countermeasures.
We will cover these points in the next column, "Oil Seals (Part 3)".
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:
When lubricant begins leaking from hydraulic equipment, sumps or pumping systems, the chances are that the incorrect hydraulic seals were selected, installed poorly, maintained improperly or the wrong seals are being used for the application at hand.
However, the good news is that with an understanding of the factors that make for long seal life, most of these issues can be resolved. The other part of this is the importance of redefining the procedure for the selection of hydraulic seals.
Evaluating Factors when Selecting Seals
There are several variables to consider when oil seals need to be chosen. All need to be considered by maintenance engineers and designers.
Factors Involving the Shaft
The surface finish of the shaft onto which it will be installed will determine how effectively a seal can do its job. The best results in terms of sealing can be achieved when the shaft is ground or polished with concentric finish marks. The efficiency of the seal will be affected by the direction of finish marks, as well as the spiral lead. Any use of shafts with spiral leads should lead toward the fluid during rotation of the shaft.
The hardness of the shaft is another important factor. Shafts with RC hardness of 30 or more should expect longer seal life. Shaft hardness should be increased to RC 60 where the seal will be exposed to contamination considered to be abrasive.
Shaft speed is determined by the finish of the shaft and the amount of runout, as well as the concentricity of the shaft, housing bore and type of oil seal material as well as the type of fluid that the seal is preventing from leaking out of the equipment it’s installed on.
Additional Factors
Another factor is the temperature of the location where the seal is going to be installed. Care should be taken to ensure that the temperature at the site of installation will not exceed the range of the seal’s elastomer.
The pressure the seal will be placed under also affects which type of seal is chosen. Typically, most oil seals have been designed for very low-pressure applications of 8 psi or less. Any pressure higher than this will require the installation and use of some kind of pressure relief solution.
The centres of the bore and shaft need to be aligned. If they are not, this will result in the loss of seal life due to more wear on one side of the lip than on the other.
Continuous lubrication is one of the key factors to ensuring long seal life. Seals should be lubricated continuously using oil of the right viscosity for the application. But viscosity is not enough; the oil also needs to be compatible with the elastomer material of the seal’s lip. This is one of the most important ways to ensure a seal works as it should, and also involves the consideration of what kinds of additives will be used and whether or not a synthetic lubricant is being applied.
Where runout is concerned, as little as possible is the ideal if the goal is to extend seal life. When movement exists and the centre of rotation, shaft whip or bearing rotation is usually the cause. If misalignment is also present, this exacerbates the problem. There is also a myth that misalignment can be compensated for by installing flexible couplings. This will not fix the issue.
The presence of close tolerances of shaft and bore will ensure optimal seal performance. However, these are not the only factors; the vibration, eccentricity and end play of the shaft will also affect the performance of the seal.
When it comes time to purchase new seals, the importance of selecting the correct one cannot be underestimated, but this is what tends to occur more often than not, and what ultimately leads to premature and frequent seal replacement.
What is Oil Seal:
The oil seal is an essential component used in various machinery and equipment to prevent the leakage of lubricating oil and other fluids. It plays a crucial role in maintaining the efficiency and durability of the mechanical system it is applied to. Made from high-quality materials such as rubber, metal, or a combination of both, the oil seal is designed to withstand extreme temperatures, pressure, and chemical exposure, making it suitable for a wide range of applications across industries.
One of the primary functions of an oil seal is to retain the lubrication within a machine, ensuring smooth and efficient operation. By creating a barrier between moving parts, it prevents oil from escaping and contaminants from entering the system, thereby reducing friction and wear. This not only extends the lifespan of the machinery but also contributes to its optimal performance.
Oil seals are commonly used in automotive applications, including engines, transmissions, and axles. They are responsible for keeping the lubricants contained within these systems, protecting them from dirt, debris, and moisture. By doing so, they prevent corrosion, premature wear, and potential damage to the sensitive internal components. This ensures consistent performance and improved fuel efficiency, enhancing the overall reliability of vehicles.
Oil seals are available in various types and sizes to accommodate different applications. Common types include radial lip seals, axial seals, and rotary shaft seals. Radial lip seals are the most widely-used type and are often installed around rotating shafts to prevent the passage of fluid along the shaft. Axial seals, on the other hand, are mainly used to seal against axial movement and retain fluids within a cylinder or housing. Rotary shaft seals are designed for applications where the shaft is rotating or oscillating.
When selecting an oil seal, it is essential to consider factors such as the operating environment, temperature range, pressure conditions, and the type of fluid being sealed. Choosing the appropriate seal material is crucial to ensure compatibility and longevity. Common materials include nitrile rubber (NBR), fluoroelastomer (FKM), polytetrafluoroethylene (PTFE), and silicone. Each material has its own unique properties, such as resistance to oil, chemicals, high temperature, or abrasion.
When it comes to sealing solutions, oil seals play a crucial role in preventing fluid leakage and the ingress of contaminants in various industrial components, machinery, and equipment. Amongst the wide array of oil seals available, the TB and TC oil seals are two popular options. Although they serve a similar purpose, understanding the key differences between these seals is essential to ensure optimal performance and compatibility with your application. In this product description, we will explore the characteristics, features, and applications of both TB and TC oil seals, providing you with the necessary information to make an informed decision.
TB Oil Seal Overview: TB oil seals, also known as single-lip seals, are designed to provide effective sealing capabilities while maintaining low levels of friction. They typically consist of a metal case, a sealing lip made of elastomeric material (such as nitrile rubber), and a garter spring reinforcing the seal's sealing lip. The metal case offers stability and easy installation, while the sealing lip prevents fluid leakage by making direct contact with the shaft.
Advantages and Applications of TB Oil Seals: TB oil seals offer several advantages, making them suitable for various applications. Some key advantages include: 1. Cost-effectiveness: TB oil seals are known for their affordable price point, making them an economical choice for industrial applications. 2. Flexibility: The elastomeric material used in TB seals ensures flexibility, enabling effective sealing even with slight shaft misalignments or irregularities. 3. Wide Temperature Range: Most TB oil seals can operate efficiently across a broad temperature range, making them suitable for both high and low-temperature applications. 4. Versatility: TB seals are available in different sizes and materials, allowing customization for specific requirements. 5. Common Applications: TB oil seals find extensive use in automotive engines, gearboxes, transmissions, and various rotating shaft applications.
TC Oil Seal Overview: TC oil seals, also known as dual-lip seals, are an advanced version of TB seals. They consist of two sealing lips, a primary sealing lip facing the fluid to be contained, and a secondary sealing lip acting as a dust lip to prevent the entry of contaminants. Similar to TB seals, TC seals also comprise a metal case and a garter spring reinforcing the sealing lips.
Advantages and Applications of TC Oil Seals: TC oil seals offer additional benefits compared to TB seals due to their dual-lip design. Some advantages include: 1. Enhanced Protection: The dual-lip construction of TC seals provides superior sealing performance by effectively preventing the ingress of both fluids and contaminants, ensuring longer service life for the components they protect. 2. Increased Reliability: TC seals exhibit improved resistance to wear, reduced friction, and extended longevity due to the dual-lip design and the added protection against external influences. 3. Versatility: TC seals are available in a wide range of materials, including various elastomers and reinforced designs, ensuring compatibility with numerous demanding applications. 4. Suitable for Harsh Environments: The enhanced sealing mechanism of TC seals makes them ideal for applications exposed to extreme temperatures, high pressures, or chemically aggressive environments. 5. Common Applications: TC oil seals are commonly used in hydraulic systems, industrial pumps, heavy machinery, and other critical equipment that demand superior protection against contamination and fluid leakage.
Differences between TB and TC Seals: The key difference between TB and TC seals lies in their sealing mechanism. While TB seals have a single sealing lip, TC seals feature an additional secondary lip that acts as a dust lip. This secondary lip provides enhanced protection against contaminants and extends the seal's overall efficiency and lifespan. Additionally, due to their dual-lip design, TC seals often have slightly larger dimensions compared to TB seals. This difference in design makes TC seals a preferred choice in applications where contamination prevention is crucial or in demanding environments that require superior sealing performance.