Aug. 04, 2023
In Part 2 of our focus on Oil Seals, we examine common reasons for industrial oil seal failure and what can be done to address such problems.
Industrial Oil Seals are used in various industrial applications. These seals help increase machine efficiency and productivity and help reduce maintenance time and costs. Depending on the type of seal, some can handle a wide temperature range.and have special properties such as resistance to abrasives, chemically compatible and having low wear. Oil Seals can be used in various industries such as chemical processing, oil and gas, pharmaceutical, general industry, hydrocarbon processing, and so on.
Like any other mechanical component, Industrial Oil Seals can also be susceptible to failure. Some of the top reasons that can lead to Industrial Oil Seal failure and how these can be solved are as follows:
1. Failure mode: Excessive Lip Wear
The lip edge is severely worn, and the worn surface appears dull and rough.
Image by NOK.
Cause: Insufficient Lubrication
This is due to insufficient lubrication, which has led to increased friction and as a result, abnormally high wear. The amount of lubricant applied was below the specified level and therefore, did not reach the sealing lip.
Solution: Add lubricant up to the specified level before operating again.
2. Failure mode: Oil seal deformation
The oil seal is damaged causing lip deformation.
Image by NOK.
Cause: Inappropriate assembly
This problem can occur when the inside diameter of the Oil Seal is too small. The oil seal may also have been deformed due to an inappropriate assembly jig or wrong installation tools being used.
Solution: To fix this issue, use the right tools and improve the assembly jig.
3. Failure mode: Lip hardening
The lip wear band is smooth and glossy. The entire sealing lip is hardened and cracks appear.
Image by NOK.
Cause: Abnormally high temperature
This problem occurred because the oil temperature near the sealing lip exceeded the heat-resistance limits of the rubber.
Another reason could be that the oil temperature exceeded the design temperature limits due to application condition changes.
Solution: Investigate the cause of failure and take the necessary measures to prevent future temperature spikes.
If the oil temperature exceeds the design temperature limits, choose a seal with a better heat-resistant lip material, for example, changing from nitrile rubber (NBR) to acrylic rubber (ACM), or acrylic rubber (ACM) to fluorocarbon rubber (FKM).
Do take note that a change in lip material also means the oil resistance will be changed.
4. Failure mode: Collapse or tearing of sealing lip
The sealing lip gets scraped or collapsed or the flexible part is torn.
Cause: Improper shaft chamfer or incorrect tools being used during assembly. Another reason for this can be high pressure directed at the flexible part.
Solution: To fix this problem, chamfer the shaft to the correct size, choose the correct assembly tool, and apply grease to the chamfered area before assembly. Also, choose an oil seal suitable in handling high pressures. Proper material handling is also key.
5. Failure mode: Garter spring disconnected
One of the most critical problems that have been reported with regards to Industrial Oil Seals is that the garter springs out of the groove.
Cause: This can occur because 1) the chamfer does not have the correct angle or 2) it can be due to incorrect assembly with grooves that are not deep enough.
Solution: If your problem was because of 1), you may use a mounting sleeve, or properly chamfer the shaft. Apply grease to the chamfered area before assembly. For failure mode 2), you need to assembly the unit correctly by aligning the shaft and housing bore. If required, choose another design or use a spring with a smaller diameter.
Want to Learn More About Oil Seal?
SLS distributes a wide range of oil seals for a variety of industries. Our sealing solutions are specially tailored to your industry. Our engineers have expertise in recommending seals for the petrochemical, oil and gas, and manufacturing industries, among others. We partner with a range of brands like NOK, Garlock and Economos to provide our customers with the best selection available.
It’s no secret that seals play a critical role in ensuring proper function of rotary systems, but designers may not be aware of just how many factors can affect seal performance. The good news is that every factor can be mitigated to a significant degree, greatly reducing the risk of seal failure.
By fully understanding the importance of installation, the potential for contamination, the amount of friction within the system, the mating surfaces involved, the shaft dynamics and the fluid conditions, designers can select a seal that will function for the maximum time possible. We’ll examine each factor in detail.
A seal’s lip is key to making sure seal wear is low. The right amount of lubricant under the lip keeps friction/wear low without resulting in a leak. Today’s sophisticated seal lips are designed to do just that, but this functionality adds a degree of complication to installation.
First, seal lips (whether rubber or polytetrafluoroethylene [PTFE]) tend to be fragile.
If the geometry of the seal’s installation is not ideal, the seal lip may be damaged or even turned inside out during installation.
Second, the seal lips’ small size means they are relatively easy to install backward, pushing fluid in the wrong direction.
Fortunately, both problems can be solved by paying close attention to the following during installation:
Ensure that seals do not go into the system at an angle (a cocked seal). Ensure that ideal conditions exist during seal installation to avoid damaging the seal lip.
Insert a step in the installation process during which the seal is checked: Is this the right seal lip for this system? Is it facing the correct direction for the media to be sealed? Is it being installed so that the shaft rotation is in agreement with any directional pumping features of the seal?
In rotary systems, it’s common to have a seal near a ball bearing or other rotary bearing. Debris in the system usually migrates toward the bearing, causing further debris to come off the bearing and damaging the seal.
Changing the system fluid usually doesn’t fully alleviate this problem because the bearing acts as a deterrent to full flushing of the contaminant. This tends to settle near the seal.
To reduce the chance of seal failure due to contamination, consider the following factors:
Make sure all system elements are fully cleaned before assembly. Pay special attention to small metal debris from the machining process.
Conduct frequent checks on the oil in the system to determine the level of contamination. If the level is high, perform a thorough flushing of the system.
Whenever replacing a bearing in a rotary pump, replace the seal as well. It may have been exposed to contaminants and could be prone to failure.
Because heat within a rotary system does not dissipate in the same way as in a linear system, both the shaft surface and the area around the seal have a tendency to experience higher temperatures.
This can lead to fluid breakdown, damaged shaft material, and degraded or brittle seal lips.
The solution may lie in changing some or all of the materials involved. In other words, a situation with a significant amount of friction may call for changing from a rubber seal to a higher temperature rubber or PTFE material, hardening the shaft or changing to a higher viscosity fluid.
Designers may also want to consider fluid flow.
More lubricant between the seal and the shaft can reduce the temperature, as can a heat-conductive housing designed to get heat out of the seal area as quickly as possible.
The finishing process on the shaft within a rotary system can be essential to proper function. First, there should be no burrs or sharp edges that could damage the seals during installation. Second, unless precautions are taken, a microscopic screw pattern can be embedded in the shaft finish, creating a micro-pump that inadvertently directs fluid. The solution is to use plunge grinding rather than traditional grinding and ensure that there is no angle to the machining marks.
In addition, surface finish of the shaft should be matched to the seal type and material.
A finish that is too rough will cause the seal to wear quickly, while too fine a finish will not allow lubricant to be retained under the lip, resulting in higher friction.
Any anomaly within the shaft’s movement can be hazardous to seal function. For example, a less-than-ideal bearing allows the shaft to shift, putting undue wear on the seal. Likewise, if a shaft is not properly aligned when assembled, one section of the seal will be more compressed than the other sections. The compressed section will show high wear while the uncompressed section will be prone to leakage.
Axes that don’t line up can cause a problem as well, since shaft wobble causes one portion of the seal to be compressed with every rotation, resulting in high levels of material fatigue.
The answer lies in the design first and foremost: ensuring that everything in the finished product will line up exactly.
Precise machining and proper positioning of the bearing within the shaft are also important to prevent seals from failing due to uneven compression.
The position of the seal in a rotary system (tucked behind a bearing) means there is a minimal amount of fluid interchange. Fluid being sheared off the seal lip to prevent leaks just compounds the problem. Under ideal conditions, the fluid is thin enough to lubricate the system without becoming so thin that it leaks.
This is a difficult balance, given that the lack of fluid interchange means fluids tend to break down over time. Thus, it’s important to check fluid conditions regularly for a number of factors:
excessive air in the system, which can cause air bubbles around the seal
high moisture content in the air around the pump, which can cause water content in the fluid to increase beyond normal values
oil level (Seal failure due to low oil levels is common.)
When we talk about fluid condition, we come full circle in terms of reasons for seal failure. When fluid conditions aren’t optimal, the bearings may wear prematurely. This causes the bearings to become unaligned with the shaft, which in turn causes debris that can damage the seal.
Oil seals are used on the final drive motor axle to keep the gear oil for the planetary gear set or bearings from mixing with hydraulic oil. These seals are vital to the operation and performance of your final drive motor -- and learning how they can fail is essential.
Here are a few other Shop Talk Blog topics you might find helpful:
Oil seals are another key component in your final drive motor. They have a lip spring that closes the tension on the shaft to create a 1-way seal as the hydraulic side is the pressure side. This keeps the fluid from flowing past the seal into the gears or bearings, depending on the application.
Oil seals can wear out in two ways: one is due to aging, and the other is caused by wear. Aging results from a chemical process that causes elastomeric seals to become brittle over time.
You may notice this when you’ve had a seal packaged and on your shelf for a long time. When you open the packaging and start to install it, it is brittle and cracks or splits. This is natural aging and is unavoidable. Aging also occurs while an oil seal is in service.
The speed at which aging accelerates is related to temperature: exposure to high temperatures speeds up the chemical process behind aging. When seals become brittle and fail before they should, thermal aging is usually the cause.
Oil seals naturally experience wear, and even the highest quality seals will wear out. For rotary seals, the lip comes in contact with a rotating shaft. Factors such as shaft finish, shaft hardness, contamination, and regular use play a role in the lip of the oil seal becoming too worn to keep the hydraulic fluid and gear oil separate. Seals like the one shown below (which is a face seal, however) will introduce serious, expensive contamination into your final drive motor.
This is a great video from The Mountaineer Mechanic that shows the correct process of replacing an oil seal on a pretty good sized Caterpillar. When installation is done improperly, however, it will contribute to seal failure. Here are some of the ways that improper installation can occur:
Installing seals in the wrong direction, which defeats their purpose
Using the wrong tools, which can damage seals or compromise their ability to seal
Damaging the seals, which shorten their useful life and create paths for leakage
Sharp corners in the seal groove, which can create paths for leakage
You'll notice that some of these mention leakage paths. Something as simple as a nick or crimp in the seal lip usually leads to a leak. And all t
hese factors can impact seal performance by accelerating the natural wear process.
You'll notice that some of these mention leakage paths. Something as simple as a nick or crimp in the seal lip usually leads to a leak. And all t
Oil seals must be compatible with the hydraulic fluid and gear oil used in your final drive. For example, Teflon seals resist otherwise problematic chemicals, but EPDM rubber isn’t very compatible with mineral-based oils. Likewise, if seals fail too quickly, but heat or poor installation isn’t the problem, there may be a chemical compatibility issue.
Pulling a seal that looks torn up will usually be normal wear or improper installation. If the seal is cracked or split, it will be either aging (natural or thermal) or poor chemical compatibility.
Here at Texas Final Drive, we know that seal failure has serious repercussions and can damage your final drive motor. Any time we open up a final drive, we replace the oil seals -- and the seals that we use in all our reman or repaired final drives are of OEM quality. And our replacements are not outdated seals that are ready to crack -- we don't hang onto expired seals.
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FOUNDED IN 1993
China SBT Oil Seal is an international company integrating design, research and development, production and processing.
No. 68, Hua'an Street, Renze District, Xingtai City, Hebei Province, China
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Won many honorary certificates through a number of patented inventions
