Sep. 25, 2024
The concept of sealing is the sealing line, an unbroken continuous band or area of contact between the seal and it’s mating surfaces, that will effectively and continually stop fluid movement from a pressurized area to an area of lower pressure. Anything that interrupts the sealing line, such as expansion, contraction, motion, shock, vibration, or contaminant migration across the sealing line, will create or increase leakage.
Static seals are those used in any application where there is no movement between mating surfaces. Common static seals are O-rings and gaskets. O-rings are effective seals because they will return to their original shape after deformation; however, because they are elastomers, O-rings will shrink up to 16 times as much as metals when the temperature drops. Therefore, some connections leak constantly at temperatures that are well below zero. Solutions to this problem are to use an O-ring of a larger diameter or to reduce the clearance gap between the mating surfaces.
Gaskets are the oldest sealing method still in use. Gaskets absorb the entire load across the mating surfaces, and the force required to crush the gasket and establish the sealing line can be very high. Under this constant preload, the gasket material will relax and creep, causing the entire joint to loosen.
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Dynamic seals are those used in systems where linear or reciprocating motion is part of the operation. Typical applications are hydraulic cylinder use. Every dynamic seal design is a compromise between the prevention of leakage (past the rod end) and the reduction of wear (in the area where the seal edges and rod surfaces meet). When selecting dynamic seals for these applications, friction, wear, system temperature, fluid viscosity, system pressure and fluid compatibility with the seal material, must be considered.
Contaminant particles in the fluid, or those carried into the system during cylinder rod retraction can cause serious sealing problems. Abrasive or embedded particles trapped between the seal and the reciprocating surface can gouge leakage paths in the rod or cylinder wall.
Several variables must be considered when selecting oil seals. There are nine factors that designers and maintenance engineers must evaluate when oil seals are specified.
Q | Does the maintenance group know the speed of the shaft to be sealed?
Logic: Shaft speed and effective sealing is a function of the shaft finish, run out, housing bore and shaft concentricity, the type of fluid being sealed and the type of oil seal material.
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Q | Does the maintenance group know the operating temperature?
Logic: The temperature range of the equipment in which the seal is installed must not exceed the temperature range of the seal elastomer material. See Chart 1 (next page).
Q | Is the maintenance staff aware of the pressures that the seals must withstand?
Logic: Most conventional oil seals are designed only to withstand very low-pressure applications, about eight PSI or less. If additional internal pressures are present or anticipated, pressure relief is necessary.
Q | Is the maintenance staff aware of the importance of the material hardness of sealed shafts?
Logic: Longer seal life can be expected with shafts having a hardness of Rc 30 or more. When exposed to abrasive contamination, the hardness should be increased to Rc 60.
Q | Is the maintenance group aware of the importance of sealed shaft surface finish?
Logic: The most effective sealing is obtained with optimum shaft surface finishes. The sealing effectiveness is directly affected by the direction of the finish tool marks and the spiral lead. Best sealing results are obtained with polished or ground shafts with concentric (no spiral lead) finish marks. If you must use shafts with spiral finish leads, they should lead toward the fluid when the shaft rotates, otherwise leaks will occur.
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Q | Is the maintenance staff aware of the importance of bore and shaft concentricity?
Logic: When the bore and shaft centres are misaligned, seal life will be shortened, because the wear will be concentrated on one side of the sealing lip.
Q | Is the maintenance group aware of the importance of shaft and bore tolerances?
Logic: Best seal performance is achieved when close shaft and bore tolerance are present. Other factors include shaft eccentricity, endplay, and vibration.
Q | Is the maintenance group aware of the importance of shaft run out?
Logic: Run out must be kept to a minimum. Movement of the centre of rotation is usually caused by bearing wobble or shaft whip. When coupled with misalignment, this problem is compounded. Contrary to popular belief and common practise, the installation of flexible couplings cannot correct or compensate for misalignment.
Q | Is the maintenance group completely familiar with and knowledgeable of the lubricants used in all equipment using seals?
Logic: Seals perform much better and longer when they are continuously lubricated with oil that has the correct viscosity for the application and that is compatible with the seal lip elastomer or O-ring material. Seal incompatibility, particularly with certain additives and some synthetic lubricants is important. It is also important to determine if the synthetic fluid being considered is compatible with any machine coatings or paint.
Synthetic polyglycols, polyalphaolefins, alkylated aromatics and diesters are generally compatible with the seal materials in See Chart 2 (above). One exception is Diester fluid, which is not compatible with neoprene or low nitrile content Buna N seals. Another exception is polyalphaolefins, which are not compatible with EPDM seal materials. If in doubt, contact the seal and synthetic lubricant manufacturers.
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L. (Tex) Leugner, author of Practical Handbook of Machinery Lubrication, is a 15-year veteran of the Royal Canadian Electrical Mechanical Engineers, where he served as a technical specialist. He was the founder and operations manager of Maintenance Technology International Inc. for 30 years. Tex holds an STLE lubricant specialist certification and is a millwright and heavy-duty mechanic. He can be reached at texleug@shaw.ca.
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.
Carelessness in seal handling may cause seal failure. For this reason, it is necessary to take care to perform appropriate storage, handling, and mounting.
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
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.
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
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.
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.
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Apr 12, 2024
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The lifespan of a tractor oil seal can vary depending on several factors, including the quality of the seal, the operating conditions of the tractor, and how well the seal is maintained. Generally, a tractor oil seal is designed to last for several thousand hours of operation under normal conditions. However, there are several factors that can affect its longevity.
Factors Affecting Tractor Oil Seal Lifespan
Quality of the Seal:
The quality of the PTFE oil seal itself plays a significant role in determining its lifespan. High-quality seals made from durable materials such as rubber or silicone are more likely to last longer than lower-quality seals.
Operating Conditions:
The operating conditions of the tractor, such as temperature, pressure, and the presence of contaminants, can impact the lifespan of the oil seal. Tractors operating in harsh environments or subjected to extreme temperatures may experience accelerated wear and tear on the seals.
Maintenance:
Regular maintenance and inspection of the oil seal are essential for prolonging its lifespan. Proper lubrication and ensuring that the seal is free from dirt, debris, and other contaminants can help prevent premature wear and leakage.
Seal Installation:
The correct installation of the oil seal is crucial for optimal performance and longevity. Improper installation, such as incorrect alignment or excessive seal compression, can lead to premature failure.
Signs of Oil Seal Failure
Oil Leaks:
One of the most common signs of OEM oil seal failure is the presence of oil leaks around the seal area. If you notice oil pooling or dripping from the seal, it may indicate that the seal is damaged or worn out.
Increased Oil Consumption:
A sudden increase in oil consumption without any noticeable leaks could be a sign that the oil seal is failing. As the seal deteriorates, it may allow oil to bypass and enter the engine or transmission, leading to higher oil consumption.
Loss of Lubrication:
If the oil seal fails, it can result in a loss of lubrication to critical engine or transmission components. This can cause excessive friction and wear, leading to further damage if not addressed promptly.
Conclusion
In conclusion, the lifespan of a tractor oil seal can vary depending on factors such as seal quality, operating conditions, maintenance, and installation. While a well-maintained and properly installed oil seal can last for several thousand hours of operation, it’s essential to monitor for signs of wear and failure and address any issues promptly to prevent damage to the tractor’s engine or transmission. Regular inspection and maintenance are key to maximizing the lifespan of tractor oil seals and ensuring reliable performance.
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China SBT Oil Seal is an international company integrating design, research and development, production and processing.
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Won many honorary certificates through a number of patented inventions
