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.