Failure and Diagnosis

 

Oil Seals Failure and Diagnosis

 

Often, when parts such as oil seals fail prematurely they are replaced and returned under warranty; however, in most cases the seal itself isn’t the reason the failure has occurred. In this guide, we will take you through the causes and how to avoid premature leaks and failures in the future.

Lip Leakage Diagnosis

If the lip has worn out then this is often caused by the seal not being sufficiently lubricated before installation causing abnormally high temperature, the presence of foreign matter, disproportionate internal pressure or an excessively rough shaft surface. Similarly if when removing a seal, if the lip has hardened and there are visible cracks, you can be sure that this has again been caused by abnormally high temperatures, excessive internal pressure or insufficient lubrication. The cause for the abnormally high wear has occurred due to friction as the amount of lubricant was below the specified level and therefore did not reach the seal lip. Alternatively, insufficient lubrication can come from dry-wear conditions because the vehicle’s oil levels are low. Another sign of this is if the lip wear band is smooth and glossy.

Alternatively, if the lip has softened, then the main cause of this is the lip having the incorrect material required for the application. In order to prevent this from reoccurring make sure the correct seal is sourced for the specific application before installation.

If you notice the lip of the seal has worn unevenly then this is due to cocked seal installation or an excessive shaft offset. As before, both should be checked during installation but crucially before the vehicle is out on the road.

Installation errors tend to be a big factor in automotive parts failing prematurely. This is apparent if you can see that the lip of the seal is scratched, caused by improper assembly, improper handling, an incorrect shaft chamber or the presence of foreign matter entering the seal. The scratches are often caused by being assembled over burrs or other defects in the shaft chamber, the lip coming into contact with sharp metal parts during transit or storage or if the seal was handled with gloves contaminated with metal particles.

As stated improper handling can be a factor in causing a seal to fail prematurely, the tell-tale sign is the seal lip being swollen or soft. The swelling is caused by the lip being soaked in solvents or petrol before installation. Alternatively, if when removing a seal you see the fit trace is disconnected locally then the seal could have been deformed because of an improperly designed assembly jig or a gap in the press-fit occurred due to rough handling.

However, although problems during fitting can contribute to the part failing, other issues may be the key factor. If the lip’s waist (flex area) is broken, then this can be because of improper assembly but can also triggered by excessive internal pressure. Similarly if the lip is turned-under, the lip edge is severely worn and the wear band is concave then this is connected to an incorrect shaft chamber, improper assembly and excessive internal pressure meaning the oil seal area exceeded the maximum pressure it was originally designed for. To prevent this reoccurring, identify the maximum pressure for the seal and check it is compatible with the vehicle. However, if the lip edge is severely worn but there are circumferential grooves on the wear band then the cause is that the shaft finish was rougher than the specified range again this can be prevented by sourcing the correct part for the specific application.

Similarly, if the lip edge is severely worn and there are grooves or indentations on the surface. Foreign matter can affect the seal in many ways whether the cause is due to a shaft or seal that has been contaminated with foreign particles being used or the contaminants were embedded in the seal lip. The cause can be triggered when the seal is assembled in the presence of dirt and/or dust causing the contaminants to become embedded in the sealing lip. In addition, if the seal or the housing was assembled with silicone, the sealant will have contaminated the shaft or seal.

If, when removing a seal the garter spring has become disconnected then this has likely been caused by an incorrect shaft chamber or improper assembly, checking the installation can ensure you and you customers are happy with the finished job.

However, if there isn’t an obvious fault with the oil seal, the cause is often difficult to diagnose, but before you prematurely condemn a good seal first check if the shaft is scratched or the diameter is incorrect, if the shaft rotational direction does not match the helix on the seal, there is excessive shaft offset or runout, the shaft is worn or the seal has been installed incorrectly.

Press-Fit area leakage diagnosis

Below we identify four common causes of premature leaks due to incorrect handling/installation.

If the oil seal is cocked then this can be caused by an improperly sized bore diameter, incorrect shaft chamber or improper assembly jig.

Like with the lip leakage diagnosis if the oil seal is problem free, check if there is a scratched or an improperly sized bore or excessive bore surface roughness. Similarly if the seal OD is damaged or chafed the bore is often the cause. Ensure you check if there is an improper sized bore diameter, incorrect shaft chamber or improper assembly jig before installation.

All the causes mentioned can be avoided if the correct steps are taken when assembling, ordering and fitting a part.

Head over to www.corteco.com/en/products/sealing/ to view our oil seals range. 

This article can also be found online at CAT magazine. 

Oil Seals (Part 3): Handling of seals and seal failure causes and countermeasures

In Part 2, we explained how to select the right oil seal.

Oil Seals (Part 2): How to select the right oil seal

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 beforehand. Therefore, this column will explain the handling of seals, seal failure causes, and their countermeasures.

 

1. Oil seal storage, handling, and mounting

Carelessness in seal handling may cause seal failure. For this reason, it is necessary to take care to perform appropriate storage, handling, and mounting.

1) Storage

Table 1 shows the main points of seal storage.

Table 1: The main points of seal storage

No. Main points to be aware of Remarks 1 Keep at room temperature (max. 30°C) and humidity 40 to 70% on average. See Figure 1. 2 Avoid direct sunlight and electrical devices that emit ozone. 3 Do not hang them (to prevent lip deformation and failure). 4 Store in a tightly sealed container and protect from contaminants such as dust and sand. 5 If storing for a long time, use the ones with the earliest manufacture date first.

 

 

Figure 1: Storage method and conditions

 

2) Handling

Table 2 shows the precautions for handling oil seals.

Table 2: Precautions for handling oil seals

No. Main points to be aware of 1 When carrying, avoid excessive impact. 2 When opening the wrapping with a sharp object such as a knife, do not damage the seals. 3

Do not leave seals out on a table (to prevent the adhesion of contaminants).

4 Do not hang them (to prevent lip deformation and failure). 5 Use kerosene for cleaning.
N.B.
Using abrasive cleaners, solvents, or the like will negatively affect the rubber material.

 

3) Mounting

Table 3 shows the precautions for mounting oil seals.

Table 3: Precautions for mounting

No. Main points to be aware of Remarks 1 Before mounting, confirm that there is
• no dirt,
• no foreign particles, and
• no damage
on the seals. Prevents the entry of foreign matter 2 Feed (apply) lubricant for pre-lubrication (initial lubrication).
• Use clean lubricant for the lip.
• Use clean grease between the main and minor lips (see Figure 2).
See the list below for recommended grease. Prevents heavy wear on lip 3 Recommended grease to be used (applied) between the main lip and the minor lip:
• Soft grease (small penetration)
• Small penetration change by temperature
• Wide serviceable temperature range
• Lithium base type N.B.
Avoid using the following combinations of rubber and grease, as they may cause the rubber to deteriorate or harden
Ex. 1: Silicone base grease
for silicone rubber seals
Ex. 2: Urea base grease
for fluoric rubber seals 4 When the seal is mounted in a cold area, it should be warmed up and its lip flexibility restored before mounting. 5 When the structure is such that the component is mounted on the shaft with an interference fit, reducing the lip contact surface shaft dimensions to be roughly 0.2 mm smaller than the bore diameter of the component helps prevent damage on the shaft surface (see Figure 3). Prevents abnormal contact between the lip and the shaft 6 When the seal is pressed into a housing bore, use a pressing jig and mount it perpendicularly to the shaft and avoid failures such as scuffing on the fitting surface (see Figure 4). Prevents fitting surface failure
Prevents oil seal lifting (spring back) on the rubber O.D. wall 7 If the shaft has a spline, keyway, or holes,
• use a seal-protecting jig (see Figure 5)
• If a seal-protecting jig cannot be used,
round the edges of the spline/keyway and apply sufficient grease to the area in question before carefully mounting. Prevents lip failure when the oil seal passes above the shaft 8 If mounting a long shaft,
or if mounting heavy housing,
use a guide jig to center the seal and shaft and prevent failure resulting from the part of the seal knocking against the shaft (see Figure 6). Prevents failure caused by contact with the shaft 9 If removing the oil seal, use a new oil seal and spacer so the sealing edge doesn't overlap with the trace of the previous lip (see Figure 7). Prevents abnormal contact between the lip and the shaft

 

 

 

Figure 2: Pre-lubrication for seals with minor lip



 

Figure 3: Recommended shaft profile and machine construction to avoid damaging shaft surface



 

 

Figure 4: Recommended seal press-fitting jig



 

 

Figure 5: Seal protecting jig for spline, keyway, holes on shaft



 

 

Figure 6: Guide jig for inserting of long shaft into seal bore



 

Figure 7: Avoid old seal lip track



 

For a more detailed discussion of seal handling, please see the following:
Oil seal storage, handling, and mounting

2. Seal failure causes and countermeasures

Leakage from the seal can be broadly divided into "leakage from lip" and "leakage from seal fitting area."
Figures 4 and 5 show the types of failure and the appearances of "leakage from lip" and "leakage from seal fitting area" respectively.
 

Table 4: Failure (leakage from lip)

No. Failure Appearance 1 Damage on sealing edge 2 Lip turned backward 3 Missing spring 4 Lip hardened 5 Lip softening

 

 

6 Heavy wear on shaft

 

 

7 Heavy wear on lip 8 Lip uneven wear 9 Rough face and streaks on lip 10 Tear at seal heel bottom 11 Lip deformation

Reduction of tightening interference due to rubber hardening

12 Lip face contact 13 Lip tear 14 Blister on lip

Table 5: Failure (leakage from seal fitting area)

No. Failure Appearance 1 Peeling, scuffing on O.D. wall 2 Damage on O.D. wall 3 Deformation 4 Seal inclined mounting 5 Oil seal fall-out

Tables 6 and 7 show the major failure types, their causes, and countermeasures against them.


 

Table 6: Seal failure causes and countermeasures (leakage from lip)

No. Failure Causes Countermeasures 1

Damage on sealing edge

 

1) Sharp edge or burrs on shaft chamfer
2) Shaft spline or keyway
3) Entry of foreign matter
4) Poor handling

• Remove burrs and polish
• Use shaft-protecting jig (see Figure 5)
• Clean surrounding components
• Improve manner of handling

2

Lip hardened

1) Temperature exceeded seal service temperature range
2) Poor lubrication
3) Excessive inside pressure happened

• Change rubber material to high-temperature-proof rubber
• Improve lubricating method and lubricant supply volume
• Apply high-pressure-proof seal or breather (vent)

3

Heavy wear on shaft

1) Entry of foreign matter
2) Chemical wear due to high temperature or excessive-pressure additives
3) Poor lubrication
4) Stick slip

• Attach prevention device for entry of foreign matter
• Take countermeasure to prevent high temperature and change lubricants
• Improve lubrication on lip including pre-lubricating (improve quantity of lubricant or lubricating method)

4

Heavy wear on lip

Excess heat generation due to
1) Poor lubrication
2) Running under conditions beyond specifications

a) Excess peripheral speed
b) Excessive inside pressure

• Improve lubrication
(change machine structure)
• Examine cause of heat source
• Change rubber to heat-proof rubber
• Apply high-pressure-proof seal or breather (vent)

5

Blister on lip

Expansion of agglomeration of high-temperature oil entering into the sliding surface

a) Deterioration of lubrication
b) Mirror finish on shaft surface
c) Higher peripheral speed
d) Higher lip radial load

• Improve lip lubrication
• Correct shaft surface finish
• Reduce lip radial load of oil seal

Table 7: Seal failure causes and countermeasures (leakage from seal fitting area)

No. Failure Causes Countermeasures 1 Damage on O.D. wall

1) Burrs on housing bore
2) Damage or blowholes on housing bore

• Remove burrs and chips
• Repair housing bore to eliminate damage and blowholes

2 Oil seal fall-out

1) Larger housing bore
2) Smaller oil seal O.D.
3) Improper oil seal press-fit position
4) Deformation of housing

• Use appropriate housing bore diameter
• Correct the oil seal press-fit position
• Improve housing rigidity

 

For details of failure causes and countermeasures, please see the following:

Seal failure causes and countermeasures

To identify the causes of seal failure and take proper measures, it is critical to observe the seal lip closely and evaluate the failure in all respects, such as shaft surface roughness, contaminants, and lubrication.

 

3. Conclusion

In this month's column, "Handling of seals and seal failure causes and countermeasures," we conveyed the following points:

1) Carelessness in the storage, handling, and mounting of oil seals may cause seal failure. For this reason, you must take sufficient care in storage, handling, and mounting. A jig should also be used in mounting oil seals.

2) Leakage from the seal can be broadly divided into "leakage from lip" and "leakage from seal fitting area," and various types of failure are categorized according to their appearance.

 

To identify the causes of seal failure and take proper countermeasures, it is critical to observe the seal lip closely and evaluate the failure in all respects, such as shaft surface roughness, contaminants, and lubrication.

 

 

3 Reasons for Oil Seal Failure and Their Solutions Discussed

3 Reasons for Oil Seal Failure and Their Solutions Discussed

 

Oil Seals

Jul 04, 2019

The oil and gas industry is one of the most challenging industries due to adverse conditions and demands involved. A few engineered components such as oil seals are required to perform in these adverse conditions, where they may be exposed to various extreme conditions. Although most of these seals are precision designed for a long-term performance, they may fail due to several reasons. This post gives a brief insight into the challenges that the seals are exposed to, and explores various reasons behind their failure.

 

An Overview on the Challenges Endured by Gas and Oil Seals
Mechanical seals are always designed in adherence to the conditions of a particular application where they may be used. Oil and gas seals are designed to resist the following:

Aggressive Corrosive Chemicals

Sour Gas (H2S)

Decomposition

Explosive Conditions

Extreme Pressures and Temperatures

Analyzing the Top 3 Reasons for Failure of Oil Seals and Corrective Actions
Like any regular mechanical seal, oil seals fail due to several reasons or one of these reasons. Here, the failure reasons are also followed by their solutions.

Chemical Attack: As said, the oil seals are exposed to several types of chemicals. The seal may exhibit a variety of signs ranging from cracking, blisters, and discoloration to a change in hardness levels. Why does this happen? The material of your seal is not compatible with the chemicals it is being exposed to. This chemical attack will affect its cross-link density, increasing or decreasing it. The seal material becomes hard and brittle when this cross-link density increases and becomes softer when the cross-link density decreases.

Solution: Selection of the right sealing material is important for ensuring the compatibility of the seal with chemicals. This chemical incompatibility leads to chemical attacks, which accelerate at high temperatures or pressures. So, check the compatibility of the elastomer seal material before choosing it for your application.

Extrusion and Nibbling: At times, the oil seals may have a chipped or nibbled appearance. In extreme cases, the surface of these seals may peel on its own, thereby lending it a shaved appearance. What is the cause of extrusion and nibbling? Stress induced by high pressure is one of the main reasons for extrusion and nibbling. This stress widens the clearance gap between the mating edges, where the seal may get entrapped, and it leads to severe physical damage.

Solution: Many industry experts suggest using backup devices to avoid the formation of clearance gaps between the mating edges. The selection of a properly sized oil seal is also important to avoid extrusion and nibbling.

Out-gassing: This is one of the common causes of oil seal failure, which happens due to the volatility of any of the constituents of the elastomer. These constituents may be the part of elastomer formulation, or gases may get trapped in the elastomer during the process of molding. Although the oil seals may not show any visual indications of out-gassing, at times they may shrink due to extreme out-gassing. The out-gassed molecules may cause contamination in wafer processing in several semiconductor applications, and also it can affect vacuum performance in industrial applications.

Solution: Use the materials that are rated to the temperature of application. Also, ensure that the elastomer used is free from volatile ingredients such as waxes, plasticizers, and so on. Both these will help you avoid the chances of outgassing.

The above mentioned are only the top three causes of oil seal failure; however, there can be several other reasons for the same. In addition to these solutions, it is important that you source these seals from some trusted manufacturer such as SSP Seals. The company provides customized oil seals in different specifications to its clients in the oil and gas industry.

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