Key Questions to Ask When Ordering Automotive Oil Seal

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.

 

11 Factors to Consider When Buying Oil Seals

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.

 

1. Temperature

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.

 

2. Material

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.

 

3. Pressure

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.

 

4. Shaft speed

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.

 

5. Shaft and bore tolerances

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.

 

6. Concentricity

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.

 

7. Runout

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.

 

8. Quality

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.

 

9. Shaft hardness

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.

 

10. Shaft surface finish

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.

 

11. Lubricant

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.

 

Choose the Correct Oil Seal for Your Needs

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.

1. Criteria for selecting oil seals

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!

2. How to select the right oil seal

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

1) Seal type

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:

2) Rubber material

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

With competitive price and timely delivery, CDI sincerely hope to be your supplier and partner.

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&#;

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

3) Metal case and spring material

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

&#;
3. Shaft and housing design

Oil seals can show good sealing performance in combination with properly designed shafts and housings.

1) Shaft design

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 &#;&#;&#; &#;&#; &#; 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

2) Housing design

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

3) Total eccentricity

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

4) Allowable total 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

4. Seal characteristics

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

5. Conclusion

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:

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