8.2 Failure analysis and suggestion 8.2.1 I.D. leakage
Primary causes R o u g h s h a f t s u r f a c e
Failure mode
Excessive lip wear and traces on the lip circumferential direction. Shaft surface roughness
exceed Ra= 0.2-0.8um and lead to excessive wear.
l I n u b s u r i f c f i Excessive lip a c t i wear i e o n n t L gH i Excessive lip i h p W i n wear. t e e r a n r a l p r e s s u r e
C o n t a m i n a n t s
L i p h a r d e n
Causes
Improper lubrication can cause accelerated shaft wear
Suggestion Finish the shaft to surface roughness to Ra= 0.2-0.8 um
Change the shaft which the surface roughness is acceptable.
Check lubricant compatibility with lip and quantity of lubricant reaching seal. Use pressure type seal
The internal pressure exceed Design a vent in the application to the seal limit. release the pressure.
Excessive lip Shaft and seal don’t wear. Nicks, contaminated by dust or mud scratches or cuts during installation. Dust and mud adhere between at lip contact shaft and lip that causes lip area. wear, nicks, scratchers or cuts Add a dust lip design in the at lip contact area. application.
Lip harden and l I n has crack. u b s u r i f c f i a c t i e o i n n t
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Lubrication is not enouth that Supply lubrication oil exceeding cause dry running. the seal level.
t e m H t u p i Lip harden and r e e g r h has crack. a H i Contact width is p g r h e i large and lip is s n s u t e r r harden and have e n a l
crack.
Primary causes
E c c e n t r i c W e a r
S o f t e n i n g o r s w e l l i n g
S e a l c o c k i n g
Failure mode Asymmetric contact between lip and shaft.
The temperature exceed the rubber heat-resistance limit.
The internal pressure exceed Design a vent in the application to the seal limit. release the pressure. Causes
I m p Lip soften or r o p swelled. e r l i p m a t e r i a l
r m I T e e m p a r a r o v o s r p a e a i n l e r Tears in lip area l i p
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Suggestion
Use proper installation tool. Seal installation. Check installation force to insure complete installation. Insufficient or improper bore Provide proper amount and lead chamfer. in angle for chamfer Excessive seal interference with rubber O.D. seal.
Check bore I.D. and seal O.D. for proper dimensions.
Poor initial alignment.
Review design and assembly operations and rovide accurate alignment.
Asymmetric P o contact between o r a lip and shaft. l i g n m e n t
Change the rubber to good heat-resisitance material. Use pressure type seal
Seal manufactured with high Review production quality data radial wall variation. and adjust process. Volume change of material very high.
Refer to elastomer physical data and check fluid. Check elastomer/fluid Reversion. compatibility specifications. Review teardown procedure and Exposure to solvent used elastomer compatibility during teardown. specifications. Check for possible exposure to Operational contamination of unspecified media coming in fluid being sealed. contact with seal. Review teardown and seal Caused during disassembly or removal methods and check removal. tools used.
p H r i e g s h s u i n r t e e r n a l
I n v e r t e d L i p
S p r i n g f a l l o f f
I m p c r h o a p m e f r Whole or e r s h a f lip t i n I m inversed. s t a p l r l o a p t i e o n r i n H r t i e g e s r s n h u a r e l I m p c r h o a p m e f r e r s h a f t
Incorrect chamfer size and part of angle. Lack of proper concentricity assembly. Circumferential tear behind lip.
Whole or part of Incorrect chamfer size and spring fall off. angle.
i n I m s t a p l r l o a p t i e o n r
Primary causesI
L i p D a m a g e
Circumferential tear behind lip.
Lack of proper concentricity assembly. Failure mode
m p c r h o a m p e f r e r s h a f t i n I m s t a p l r Lip damage visually. l o a p t i e o n r l i I p m c p o o r n p t a e c t r
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Causes Incorrect chamfer size and angle.
Look behind lip at base for circumferential tear caused by pressure or fatigue.
Adjust the chamfer size and angle, and smear lubricant on chamfer when intallation. Adjust the concentricity and smear lubricant on chamfer when intallation. Look behind lip at base for circumferential tear caused by pressure or fatigue. Adjust the chamfer size and angle, and smear lubricant on chamfer when intallation. Adjust the concentricity and smear lubricant on chamfer when intallation. Suggestion Adjust the chamfer size and angle, and smear lubricant on chamfer when intallation.
The chamfer has burrs causing lip damage when Cut the burrs. installation. Lip contacts sharp bodies Prevent contacting seal lip when assembling or during assembling and transporting. transporting.
C o n t a m i n a n t s
S e a l d i s t o r t
Contaminants packed in seal area
I m Seal distorts that r p o change the p e r contact width. i The improper installation tool that n Improve the installation tool. s t cause seal distorts. a l l a t i o n d S e h f a e f c t t
N o w e a r o n s e a l l i p
Failure of auxiliary lip
Look for cut or damaged auxiliary. Look for auxiliary lip worn excessively.
R o t a t i n g d i r e c t i o n
Shaft surface has defect visually. Processed shaft in a lathe had directional when rotating the shaft. (x63)
Use plunge grinding to change property of direction.
Poor alignment of shaft. O f f s e t W r o n d g i r i e n c s t t i o a l n a l t i o n
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Change contact position between shaft and lip.
Change to the seal that can bear poor alignment. Make sure the shaft and bore is concentric.
Wrong installation direction. Turn seal oil side toward to oil.
Primary causes N o w S e h a a r f t o w n e s a e r a l l i p
Failure mode
Causes
Suggestion
Contaminants attached on the seal or shaft when assembling the seal. Lubrication went bad and mixed contaminants. Contaminants entering the lip that caused wear.
Prevent mud and dust contaminate shaft and seal when assembling the seal.
Causes
Suggestion
Avoid overusing the lubricant. Have a dust lip design.
8.2.2 O.D. leakage
Primary Failure mode causes S e a l d i Seal distort s t o r t
C o c k e d s e a l
S e l w a i e s d t g g e i h t l y
Improper installation tool causing the seal distort. When the seal distort on certain location.
Use the proper installation tool. Prevent the seal dropping or impacting.
Before removing Bore dimension is too small to the seal, the seal install the seal that causes seal Use the suitable bore size. seal cock can be cock. seen by eyes. o bore chamfer that causes Chamfer the bore. seal damage during installing.
After removing the seal, there is eccentric wear on the lip. Bore damaged, seal O.D. rubber extruded or damaged.
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Use the improper installation Use the proper installation tool. tool.
Bore I.D. is too small to install the seal that causes seal Use the suitable bore size. damaged. o bore chamfer that causes Chamfer the bore. seal damage during installing.
Installion tool is not parallel with the bore that causes the seal extruded. Primary causes
Failure mode
N o w e a r o n s e a l l i p
Causes
Suggestion
Contaminants attach the bore Avoid contaminant attaching on and seal O.D and damaged the the bore and seal during bore surface during installing. installing. Assembly bore surface has pits or too rough.
Pay attention to surface roughness.
Bore chamfer has burrs that cause the bore surface damaged.
Trimming the burrs of the bore chamfer.
Remark: Some materials above are adopted from RMA.
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Require the installion tool is parallel with the bore.
