Current location：Home > Products and Services > Oil Seal Technical Information > Key Points To Check When Oil Seal Leaks | Main Reason | Failure Mode | Reason | Countermeasures |
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 Excessive wear on the lip - insufficient lubrication |
 The lip end is severely worn and the worn surface has lost its luster.
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· Since the lubricating oil used is below the specified amount, the oil cannot return to the lip part, so it slides in a dry state and causes abnormal wear. · The structure near the oil seal is poor, and the oil cannot return to the lip part. (Example) Due to splash lubrication, the oil cannot return within a few minutes after starting. |
· Refill the lubricant to the specified amount before operation. · As an emergency measure, you can use a double-lip seal and apply grease between the two lips. · As a permanent measure, you can change the structure near the oil seal to make the oil return to the lip well. |
| Lip wear is too large - there is a foreign object stuck |
 The lip end is heavily worn, with "stripes" and "dents".
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·Since there are chips attached to the shaft and oil seal in use, the chip powder is stuck at the lip. ·Dust and sand are attached to the shaft and oil seal, but they are still used, and they are stuck at the lip. ·Liquid sealant is attached to the lip and shaft, but they are still used, and they are stuck at the lip. ·When the machine is painted, there is paint attached to the lip and shaft, but it is still used, and it is stuck at the lip.
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·Do not allow dust and sand to get on the oil seal and shaft during assembly. ·Use lubricating oil when cleaning the machine. |
| Excessive wear on the lip - high internal pressure |
 The lip end is worn and has a "dent".
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·The pressure of the oil seal part exceeds the design value. |
·Use pressure-resistant oil seals instead. ·Set up vent holes to create a pressure-free structure. |
| Lip wear is too large - shaft surface roughness is too large |
The lip end is heavily worn, with circumferential "stripes" on the wear surface. |
·Because the surface roughness of the shaft used is coarser than the specified Ry0.8~2.5μm, abnormal wear occurs. |
·Use full corundum sandpaper (about #240) to correct the surface roughness of the shaft to Ry0.8-2.5μm. The corundum sandpaper must not move in the axial direction. ·Replace the shaft with the specified surface roughness. |
| Partial wear on the lip - large eccentricity in installation |
 The sliding width of the lip is uneven on the circumference, and the positions of the minimum width and the maximum width are roughly symmetrical.
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·The center of the shaft and the cavity is installed and operated in a displaced state. ·The shaft is operated in a state of bending in one direction. |
· Improve the concentricity accuracy between the shaft and the cavity. · Improve the strength (i.e. stiffness) of the shaft "bending". |
| Partial wear on the lip - tilted installation |
 The sliding width of the lip is uneven on the circumference, and the positions of the minimum width and the maximum width are roughly symmetrical. In addition, the sliding width of the sealing lip and the dustproof lip are opposite in size.
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· The inner diameter of the cavity is smaller than specified, and it has never been fine-machined, so the oil seal is barely driven in, and the oil seal is installed at an angle. · The cavity is not chamfered, it is not suitable, the oil seal is barely driven in, and the oil seal is installed at an angle. · The assembly fixture is tilted, so it is installed at an angle. |
·Use a cavity of specified size. ·Chamfer the cavity to the appropriate size. ·Improve the assembly fixture. |
| Lip hardening - abnormally high temperature |
 The sliding part of the lip is smooth and shiny, the entire lip is hardened, and cracks occur on the lip.
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·The oil temperature near the sealing lip rises due to various reasons and exceeds the heat resistance limit of the rubber. ·The oil temperature rises and exceeds the heat resistance limit, which is different from the temperature and conditions set during design. |
· Investigate the cause and prevent the temperature from rising. · Use an oil seal with a lip material that has good heat resistance. (Example) Nitrile rubber (NBR) → Acrylic rubber (ACM) |
| Lip and mouth hardening - high internal pressure |
The lip sliding width is wide, shiny, and cracked. |
·The pressure exceeds the pressure limit of the oil seal. |
·Use pressure-resistant oil seals instead. ·Equip with vent holes to create a pressure-free structure. |
| Lip hardening - insufficient lubrication |
The sliding part of the lip is smooth and shiny, and cracks occur on the sliding surface of the lip, or when pressed with fingers. In addition, there are many cases where hardening occurs only on the sliding surface. |
· Because the lubricant used was outside the specified amount, the lip had less oil and insufficient lubrication. · Because it was splash lubrication, the lip had less oil and insufficient lubrication. |
·Add the specified amount of lubricating oil and operate again. ·As an emergency measure, you can use a dustproof oil seal and apply grease between the two lips. ·As a permanent measure, change the structure near the oil seal and splash oil sufficiently. |
| Softening of the lip - unsuitable lip material |
The lips and mouth area swell and soften. |
· The wrong lip material was selected for the lubricant used, so the lip swelled. · The seal was soaked with cleaning fluid and gasoline. After cleaning, there was liquid attached to the seal and it was left as it was, causing swelling. |
· Use oil seals that do not swell the lip material according to the lubricant used. · Use oil that does not swell the lip material. · Do not clean the oil seal. |
| Lip and mouth damage-poor assembly |
With visible damage on the lip end. |
· When the oil seal passes through the keyway and spline, it contacts the sharp edge and causes damage. · The chamfered part of the shaft has "burrs" and "flash", and it is damaged by assembling it as it is. |
· Install covers on the keyway and spline shaft to prevent them from being damaged. · Remove "burrs" and "flash". |
| Lip and mouth injuries - improper use |
Visually detectable damage on the lip end |
· When transporting and storing the oil seal, sharp metal parts come into contact with the lip, causing damage to the lip end. · When handling the oil seal with gloves covered with cutting chips, the lip end is damaged. |
· Improve the handling and storage methods. · Do not touch the lip end. |
| Lip damage-bad shaft chamfer |
With visible damage on the lip end. |
·The chamfer size and angle of the shaft end are incorrect, causing the lip end to get stuck on the shaft end, causing damage. |
· Correctly chamfer the shaft. |
| Lip and mouth injury-foreign body stuck in the mouth |
There is foreign matter attached to the end of the lip, and there is a "pit" on the sliding part of the lip. |
· When using a shaft with chips attached, the chips get stuck at the end of the lip. · When using a part with metal powder attached, the metal powder gets stuck at the end of the lip. · When using a shaft and oil seal that have been placed in a dusty place for a long time, foreign matter gets stuck at the end of the lip. |
·Cleaning machine |
| Lip flip-shaft chamfer defect |
With respect to the direction in which the oil seal is inserted into the shaft, a portion of the lip portion is turned in the opposite direction. |
·The chamfer size and angle of the shaft end are incorrect, causing the lip end to get stuck on the shaft end, causing damage. |
· Make sure the chamfer size and angle of the shaft are correct, and apply grease to the chamfer during assembly. |
| Lip flip-up-bad assembly |
With respect to the direction in which the oil seal is inserted into the shaft, a portion of the lip portion is turned in the opposite direction. |
·Due to the non-concentricity between the shaft and the cavity, the assembly is rough and the lip part is turned over. |
·Make the shaft and the cavity concentric and pay attention to assembly. In this case, apply grease to the shaft end. |
| Lip and mouth inversion-high internal pressure |
 There is a partial or complete inversion on the circumference of the lip.
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·Due to abnormal high pressure during operation, abnormal force is applied to the lip, causing the lip to flip. |
· Improved to a pressure-free structure. · Use a pressure-resistant oil seal. |
| Lip waist damaged - poor assembly |
There are cracks on the lips and waist. |
·During assembly, the lip is crushed, causing cracks in the waist. |
·Make the shaft and cavity concentric and pay attention to assembly. |
| Lip waist damage - excessive internal pressure |
 There are cracks on the lips and waist.
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· During the pressure test (air tightness test) after assembly, the pressure was too high, causing cracks in the waist of the oil seal. · During operation, a pressure higher than the designed pressure occurred, causing cracks in the waist of the oil seal. |
· Do not use a pressure test that exceeds the oil seal pressure resistance specification during inspection. · Use a pressure-resistant oil seal instead. · Use a structure that does not generate excessive pressure. |
| Spring falls off - shaft chamfer is bad |
The spring has partially or completely fallen off. |
·The chamfer size and angle of the shaft end are incorrect, causing the lip to get stuck at the shaft end and the spring to fall off. |
· Make sure the chamfer size and angle of the shaft are correct, and apply grease to the chamfer and assemble. |
| Spring falls off - bad assembly |
The spring has partially or completely fallen off. |
·Due to the non-concentricity between the shaft and the cavity during assembly, the assembly was rough, causing the spring to fall off. |
·Make the shaft and the cavity concentric and pay attention to assembly. In this case, apply grease to the shaft end. |
| Deformation of oil seal - poor assembly |
 The oil seal deforms and the sliding width of the lip changes at the deformed part.
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·The oil seal is deformed due to incorrect assembly fixture of the oil seal. |
·Improved assembly fixture. |
| The oil seal is normal, but there is damage or dents. |
·There are visible "damage" and "dimples" on the sliding part of the shaft. |
· Place a gasket on the oil seal to move the sliding position a little. · Perform correction processing on the damaged area. |
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| Oil seal is normal - shaft directionality |
·A shaft processed by a lathe was used. ·The feed was hung during finishing with a grinding wheel and emery paper. |
·Use emery paper (#240) to correct the sliding part between the shaft and the lip without feeding. ·Change the processing method. (Use the method of finishing without feeding in the axial direction.) |
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| Oil seal is normal - shaft eccentricity |
· Due to abnormal bearing, the eccentricity of the shaft is larger than the design value. · The eccentricity of the shaft in the mechanism is large, and a universal oil seal is used. |
·Replace the bearing. ·Replace with a special oil seal that can withstand larger eccentricity. |
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| Oil seal is normal - shaft is worn |
·Dust and swarf adhere to the oil seal during installation. ·Lubricating oil deteriorates and foreign matter is mixed in. ·Foreign matter enters from the outside and gets stuck in the sliding part. ·Nonferrous metal shaft is used. |
· Clean the machine and place a gasket on the oil seal during assembly to move the sliding position. · In situations where the amount of dust is light, use an oil seal with a dust lip and attach a dust cover. · Use appropriate shaft material. |
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| The oil seal is normal - the installation direction is reversed |
·Wrong installation during assembly. |
·Install with the sealing lip pointing toward the sealing medium. |
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| Oil seal tilted installation |
[Before removing the oil seal] Visual inspection shows that the oil seal is tilted relative to the cavity and shaft. [After removing the oil seal] The contact of the oil seal mating part is uneven. |
· The inner diameter of the cavity hole is smaller than the specified size, and it has never been fine-machined. The oil seal is barely driven in, and the oil seal is installed at an angle. · The cavity is not chamfered, it is not suitable, the oil seal is barely driven in, and the oil seal is installed at an angle. · The assembly fixture is tilted, so it is installed at an angle. |
· Use the specified cavity hole inner diameter size. · Chamfer the cavity hole surface to the appropriate size. · Improve the assembly fixture. |
| Deformation of oil seal |
 There is a partial interruption in the traces of matching
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· Due to incorrect assembly of the oil seal fixture, the oil seal is deformed. · Due to local deformation during use, the oil seal is installed and a gap occurs in the mating part. |
·Improve the assembly jig. ·Be careful not to drop or hit hard objects when using. |
| The oil seal mating part is squeezed or stuck |
[After the oil seal is removed] There is "damage" or "squeezing" of the rubber in the axial direction of the oil seal mating part. |
·The inner diameter of the cavity hole is smaller than the specified size, and it has never been finely processed. The oil seal is forced into it, and the oil seal is installed at an angle, which eventually causes damage to the fitting part. ·The cavity is not chamfered, which is not suitable. The oil seal is forced into it, and the outer periphery of the oil seal is damaged. ·When the oil seal is installed in a state where the parallelism between the oil seal assembly fixture and the cavity is not achieved, the fitting part of the oil seal is "squeezed". |
·Use the specified cavity hole inner diameter size. ·Chamfer the cavity hole surface to the appropriate size. ·Make the parallelism between the oil seal assembly fixture and the cavity meet the requirements. |
| Oil seal is normal |
The lip end is heavily worn, with circumferential "stripes" on the wear surface. |
· When installing the oil seal, foreign matter such as swarf powder adheres to the inner surface of the cavity hole and the oil seal mating part, causing "damage" to the inner surface of the cavity hole. · Because the "burrs" on the chamfered part of the cavity hole surface were not removed, "damage" occurred on the inner surface of the cavity hole when the oil seal was installed. · The inner surface of the cavity hole is too rough. |
·Apply a thin layer of liquid sealant to fill the "damage" and pits on the inner surface of the cavity hole. But be careful not to let the liquid sealant adhere to the lip of the oil seal and the shaft. ·When disassembling the oil seal, check whether there are "burrs" on the chamfer of the cavity hole. If there are burrs, remove them with emery paper and apply liquid sealant to the inner surface of the cavity hole. ·Emergency treatment: Apply liquid sealant to the inner surface of the cavity hole. |
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