10 Things to Consider When Buying Oil Seal Companies

Oil Seals By: Angelo Ting/MINERAL CIRCLES BEARINGS

 

In any mechanical manufacturing company, optimal performance and long service life are vital to your products’ success in the market. No matter how much we go deeper in considering the brand and in deciding which one would last longer than the other, it’s also significant to at least put into consideration the importance of maintenance and preventive measures.

If there is any component that is underappreciated within a mechanical assembly or a bearing assembly, it would be the oil seal. Due to its relatively inexpensive cost, the importance of oil seals is often being overlooked and neglected. However, being a game changer in a bearing assembly, one must know the benefits it contributes in keeping your machine in perfect shape.

Often called a rotary shaft seal, oil seals purposely serve to close the gap between stationary and moving components. When properly installed, oil seal’s  main job is to retain or separate fluids. Furthermore, it also helps in preventing lubricants from escaping the gauge as well as it prevents foreign contaminants from moving in through the clearance. Seals also serve to prevent intermixture of two fluid mediums such as oil and grease . An oil seal that fails and create seal leakage, enables abrasives and corrosive moisture apart from allowing sediments to enter your machine.

Bearing manufacturers stress the importance of selecting the right seal for your machine for each has its own distinct differences. The selection of the right seal is crucial for the maintenance and integrity of a given application due to some situations wherein not all are fit to work on some machines.

Failure to follow common application best practices potentially results in costly mistakes or worse, system or machine failure.

 

What are the benefits of Oil Seals ? Is it cost-effective?

Aside from keeping your machines in its best shape, oil seal has so much to offer than what’s mentioned above. Some of these are as follows:

 

• Prevent the entry of foreign contaminants
• Prevent seal leakage
• Maintain a bearing’s lubricity

Oil seals work like glue between two elements: a stationary and moving component. Their function is to remove the spaces between such elements to ensure both components resist non-lubricity. This is especially important in a precision bearing. Any non-lubricated contact from both the seal and other elements can lead to a catastrophic failure. This will result to seal damage and ultimately, extended maintenance downtime.

Oil Seals also serve as a prevention method ensuring that no foreign objects such as dirt and soil enter your equipment. Since seals are employed in a variety of applications (from industrial to automotive), an effective seal must maintain a high-impenetrable degree of exclusion when it comes to contaminants or foreign objects that would aggravate the performance of your machineries.

However, in some cases when you have been caught up in a situation such as seal failure while it’s under the process of filtering out contaminants, possible event such as excessive mechanical strain may be introduced resulting in mechanical failure.

In addition to the list of positive things it does to our mechanical applications are:

• Ability to perform in extreme environments
• Long shelf life
• Easy assembly
• Low friction properties
• Increased strength properties to work in stressful environments

Applications of oil seals

Oil seals play a major role in mechanical assemblies. Their strength and flexibility allows them to be used in numerous industries (any automotive or industrial application that has a rotating and moving part assembly) such as gearboxes, electric motors, industrial pumps, fans, and customized equipment.

In particular, oil seals are utilized in mechanical environments that must function under extreme pressure. This concept often applies to temperatures in which oil seals must operate. With its high degree of flexibility and use in various industries, oil seals must be able to work optimally in temperate conditions of – 70°C and +260°C.

Oil seals must also work in extreme fluid environments in which the risk of foreign contaminant is great. While most oil seals appear in the traditional ‘o-ring’ shape, oil seals can be manufactured to the specifications of each application. This means there’s a sealing solution for any uniquely designed equipment.

According to your requirements, the types of oil seals you can select from include:

• Single and double lip oil seals
• Metal cased, external, and internal orientated oil seals
• Spring-energized oil seals.

Choosing the right oil seal

Before an oil seal is installed, considerations must be made with regard to the type of application parameters  that it must function within. Considering these variables and factors ensures the right one is installed. A sound replacement affords mechanical longevity and proper functionality.

When selecting the right oil seal for your application, nine factors must be taken into consideration. Top bearing companies, designers, and maintenance engineers have specified the nine factors as:

• Shaft speed
• Temperature
• Pressure
• Shaft hardness
• Shaft surface finish
• Concentricity
• Shaft and bore tolerances
• Runout
• Lubricant

 

 

These nine factors will also determine the right materials that your oil seals should be made of as wrongful selection can result in  failure, including excessive internal pressure on the seal itself, premature wear, lip hardening, cracks, and swelling.

Over time, this damage can incur massive costs.-particularly if such issues are not promptly addressed.

While there are a variety of oil seals to select from, it’s important to choose the right profile for the application. This not only guarantees optimum performance for the applications but it also ensures a safe working environment for years to come.

If you are in need of further information or a professional advice,  contact  our sales specialists at +971-4-886-5100 or send an e-mail to export@mcb.ae.

 

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

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 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

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: