Oct 25 32 Nibbling and Extrusion This type of O ring failure is common in dynamic applications such as piston seals hydraulic rods etc This type of failure may be introduced in static applications which are subjected to high pressure The most common symptoms may include a chipped appearance of the ring or leakageO rings with high modulus and hardness are better able to resist extrusion The higher the modulus of a material the greater the force required to stretch it Similarly the harder the material the greater its resistance is to indentation The following graph indicates conditions that result in O ring extrusion with and without back up rings
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O Ring Suppliers Kalrez Viton Silicone Gaskets SealsO Ring Groove Design Extrusion Limits An o ring is contained in a gland and forced to flow into the surface imperfections of the glands and any clearance gaps available to it An o ring can perform sealing by means of squeeze under low pressure conditions The extent of extrusion depends upon the hardness of O ring the pressure and the
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Feb 21 32 Diagnosing Damaged O Rings failure mode we see is the flattened o ring When a customer sent me a picture of a flattened o ring they were looking for a more compression set resistant material Extrusion is one of the most common types of O Ring failure When the internal systemic pressure of an application becomes too great the O Ring will frequently extrude into the clearance gap between mating parts In many instances this extrudate will be nibbled away causing a loss of material with seal failure quickly following
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84 Abrasion Failure Pattern Occurring primarily in dynamic seals involving reciprocating oscillating or rotary motion this failure pattern can be identified by a flattened surface on one side of the O ring O Ring Failure Trouble Shooting O ring seals often fail prematurely in applications because of improper gland design or compound selection This section is designed to provide the user with examples of common failure mod By correctly identifying the failure mode changes in the design or seal material can lead to improved seal performance
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Why do O rings fail A brief guide to O ring failure mod In high pressure applications the extrusion or nibbling may be held off on the high pressure side and only evident on the low pressure side The O ring often takes on the shape of the groove Cause pressure the primary cause of seal failure is extrusion of the seal material into the piston cylinder clearance The major factors affecting extrusion are fluid pressure seal hardness Figure 1 7 O ring Failure Figure 1 4 O ring Installed Parker O Ring Handbook Handbook Introduction 1 4 Seals Build With The Best
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prevent extrusion and eventual O ring failure pressure shocks should be anticipated and effectively dealt with in both seal selection and system design As required mechanical brakes or pressure relief valves may have to be built into the hydraulic system Illustration 46 Rod Diameter Piston Groove Diameter Bore Diameter PistonParker O Ring Handbook Abrasion Another rather common type of O ring failure is abrasion This usually is found only in dynamic seals subject either to reciprocating oscillating or rotary motion Possible causes of O ring abrasion are listed in Table 10 5 Figure 10 5 shows wear on an O ring Explosive Decompression Failure Analysis
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When the permissible extrusion gap for the pressure and temperature in application is exceeded back up rings may be used to prevent the seal pressing into the gap and causing extrusion damage and possibly even premature failure Figure 3 shows the O ring behaviour at different operating pressures and conditions In applications where the O Extrusion is one of the most common types of O Ring failure When the internal systemic pressure of an application becomes too great the O Ring will frequently extrude into the clearance gap between mating parts In many instances this extrudate will be nibbled away causing a loss of material with seal failure quickly following
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The pressure of the contained fluid transfers through the essentially incompressible O ring material and the contact stress rises with increasing pressure For this reason an O ring can easily seal high pressure as long as it does not fail mechanically The most common failure is extrusion through the mating partspressure the primary cause of seal failure is extrusion of the seal material into the piston cylinder clearance The major factors affecting extrusion are fluid pressure seal hardness Figure 1 7 O ring Failure Figure 1 4 O ring Installed Parker O Ring Handbook Handbook Introduction 1 4 Seals Build With The Best
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O ring seals often fail prematurely in applications because of improper design or compound selection This section is designed to provide the user with examples of common failure mod By correctly identifying the failure mode changes in the design or seal mended corrective actions Listed are the most common causes of seal failure For a complete listing of O ring failure modes obtain a copy of AIR Patterns of O ring Failure available from SAE INC Extrusion and Nibbling Failure Pattern Typical of high pressure systems this pattern can be identified by the many small bites nibbles taken
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element or simply adding anti extrusion devices typically called back up rings to the sealing element package Spiral failure Another failure mode usually associated with O ring type seals is called spiral failure as shown in Figure 5O Ring Troubleshooting Guide Application Specific Material and Design Support Fast Expert Quality Service Worldwide Inventory Network
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Home >O ring Seal Failure Analysis >Part 1 O ring and Seal Failure Part 1 Extrusion Over Compression and Spiral Failure Extrusion and/or Nibbling Description The o ring or seal develops ragged edges generally on the low pressure side which appear tattered Contributing Factors Excessive clearanc Excessive pressure Troubleshooting failures with O Ring due to oxidation installation lubrication and incompatible materials Phelps is a major manufacturer fabricator and distributor of Industrial Gaskets Compression Packing and Sealing Devices Established in to deliver the best performing fluid sealing products at competitive prices globally
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O ring seals often fail prematurely in applications because of improper design or compound selection This section is designed to provide the user with examples of common failure mod By correctly identifying the failure mode changes in the design or seal Avoiding common causes of O ring failure Use back up rings to prevent extrusion Use harder O ring elastomer Re check elastomer compatibility with system chemicals Increase rigidity and improve concentricity of metal components Break sharp edges of gland to a minimum radius of in
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