Seal Lubrication Process – Why It’s Important

Carbon can wear down due to abnormally high abrasives.

One often overlooked measure to ensure that a mechanical seal can function at its peak efficiency is to properly lubricate the seal. A properly lubricated seal is important because if a seal is not lubricated, it can lead to break-downs of pumps, as well as other potential damages to parts and machines which utilize mechanical seals. When a seal is properly lubricated, however, then it will be much more reliable and lead to fewer breakdowns. Fortunately, “Lubrication related failures are the most preventable type of machinery failures. With sufficient attention to details, they should be rare events. It is normally through the neglect of lubricants and lubrication systems that equipment fails prematurely.”1 Lubrication is also necessary “for proper mechanical seal installation. Lack thereof can damage o-rings or rubber bellows on the seal, causing them to tear, or roll.”2 As for what lubricant may be considered best, it is highly advised to “refer to the manufacturer’s recommendation”3 when selecting an appropriate lubricant.

Oil lubricants can be quite useful in lubrication processes because oil can help with sealing. “At the same time as it lubricates and cools, the lubricating oil also acts as a sealing agent, preventing the lubricant from flowing out and the entry of external contaminants.”4 Typically, “Mineral oils are the most commonly used industrial lubricants due to their relatively low cost.”5 At times, grease is preferred as a lubricant. Grease is usually used as a lubricant in “lower speed applications (1800 rpm or less).”6 Here at EMC, we are experts at lubricating seals and we would be more than happy to assist you with your seal lubrication needs!

 

Why Do O-Ring Seals Need Lubrication?

Why Do O-Ring Seals Need Lubrication?

Lubricating an O-ring is an important part of the assembly line process as it can help protect an application from abrasion or scuffing damage. Applications that are constantly in motion are prone to this wear over time. The addition of a lubricant can extend the operating life of the O-ring by creating a barrier film over its surface. This barrier film can also help reduce leakage by filling the asperities between the metal surface and the O-ring seal.

 

These benefits can be seen in Nye’s Case Study, featuring KOSME, a company that designs and manufactures a full range of bottling and beverage line equipment for filling, labelling, and stretch blow molding. The company was looking to replace an existing grease with an H1 incidental food contact product to lubricate the O-ring seals of a pneumatic cylinder. The cylinder is a rotating piece of equipment that requires all seals to survive hundreds of thousands of cycles. The seals are made of EPDM elastomer and require good material compatibility from a lubricant. KOSME reached out to our Channel Partner in Italy, Technolube Seal, to find a compatible grease.

Tecnolube Seal recommended Fluorocarbon Gel 880FG & 885FG to KOSME for evaluation as they are two H1 certified lubricants that provide excellent water and oxidative resistance over a broad temperature range. Both products were tested to make sure each eliminated stick-slip friction on the cylinders. The cylinders were lubricated with the 880FG and 885FG and cycled for several hundred thousand repetitions. Following testing, the cylinders were evaluated for smoothness (no stick-slip) and wear on the seals. Each product was subjected to an accelerated aging test to ensure the seals would last the expected life time of the application.

 

 

 

Product Chemistry Temp
Range (°C) Water Washout
(60 minutes @40°C) Copper Corrosion
(24 hrs @ 100°C) FLUOROCARBON GEL 880FG Dimethyl Silicone/PTFE -40 to 200 0.25% 1b (Slight tarnish) FLUOROCARBON GEL 885FG Dimethyl Silicone/PTFE -40 to 200 1.74% 1b (Slight tarnish)

 

 

Fluorocarbon Gel 880FG & 885FG passed all test requirements, confirming the lubricants prevent stick-slip friction and wear throughout the lifespan of the O-ring. KOSME chose to use both products to lubricate and protect the seals. These products are now specified in for the first fill on each filling machine.

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.