Ord Overview 9 24 06
- 1. Parker Hannifin O-Ring Division Materials and Gland Design
- 2. Rubber Technology “Rubber” compounds are resilient (elastic) materials made from one or more cross-linked base polymers, reinforcing agents, processing aids, and performance-enhancing additives.
- 3. Polymers – Basic Information From Greek “Many Units” Polymers are long chains of repeating units. On the molecular level, they resemble extremely long spaghetti strands. Monomer = the unit that repeats in a polymer Isomer = Polymer made from one monomer Dimer or Copolymer = Polymer with two monomers Trimer or Terpolymer = Polymer with three monomers Polymers tangle themselves together like in a large bowl of spaghetti
- 4. Polymers – Basic Information Base polymer determines chemical resistance, rough temperature limits, and rebound resilience In some materials, the high and low temp limits can be modified by other compounding ingredients. Provides “baseline” for abrasion resistance, compression set resistance, permeability These can (and almost always are) modified – up or down – by other compounding ingredients.
- 5. Compounding – Cure Systems Polymer chains must be “glued” together (cross-linked) to achieve resilience and elasticity. Sulfur: simplest cure system, used in nitrile and EP Organic Peroxides: improved compression set in EP, improved compression set & high temp limit in nitrile, standard cure system for silicone. Bisphenol: best cure system available for fluorocarbon (specialty FKMs need to be peroxide-cured, but it’s not the first choice.) Others: specialty materials have special cure chemistry
- 6. Compounding - Fillers Reinforcing agents add mechanical strength and resistance to abrasion, permeation, and compression set Carbon black: standard for black compounds Silica: standard for non-black compounds Fillers lower the cost of a compound but reduce compression set resistance and elongation Carbon black: lower grades or excessive amounts provide no performance benefit for seals Clay: commonly used in “generic” seal compounds
- 7. Compounding - Plasticizers Oils and / or polymers used to lower the low temp limit of nitrile and make the material flow better (see Process Aids, next) Reduce resistance to compression set In “generic” materials, they are used to offset the hardening influence of high levels of filler Can extract into process fluids, resulting in seal shrinkage & hardening
- 8. O-ring Polymers Nitrile (NBR) Hydrogenated Nitrile (HNBR) Polyacrylate (ACM) Vamac (AEM) Neoprene (CR) Ethylene-Propylene (EPR, EPDM) Butyl (IIR) Polyurethane (AU, EU) Fluorocarbon (FKM) Tetrafluoroethylene-Propylene (TFE/P) Perfluoroelastomer (FFKM) Hifluor (FKM) Silicone (VMQ) Fluorosilicone (FVMQ)
- 9. Standard Nitrile (NBR) -30 F to + 250 F Recommended For General Purpose Petroleum Silicone Fluids Not Recommended For Ozone (Air) Ketones Automotive Brake Fluid Aircraft Brake Fluid Steam and Hot Water N0674-70 N1499-70 NA151-70 (8307) Most common seal material in the world.
- 10. Low Temp Nitrile (NBR) -70 F / -50 F to +180 F / +275 F Recommended For MIL Hydraulic Fluids MIL-STD-5606 General Purpose Petroleum Oils Silicone Fluids Not Recommended For Ozone (Air) Ketones Automotive Brake Fluid Aircraft Brake Fluid Steam and Hot Water N0304-75 N0756-75 MIL-STD-25732 AMS-R-83461
- 11. High Temp Nitrile (NBR) -25 F to +275 F Recommended For General Purpose Petroleum Silicone Fluids Not Recommended For Ozone (Air) Ketones Automotive Brake Fluid Aircraft Brake Fluid Steam and Hot Water N0951-75 N1210-90 Called “Low compression set” in Compound Offering.
- 12. High ACN Nitrile (NBR) -35 F to + 212 F Recommended For General Purpose Petroleum Silicone Fluids Gasoline Not Recommended For Ozone (Air) Ketones Automotive Brake Fluid Aircraft Brake Fluid Steam and Hot Water N1500-75 N0497-70 Called “Low Swell” in Compound Offering.
- 13. Carboxylated Nitrile (XNBR) -25 F to + 250 F Recommended For General Purpose Petroleum Silicone Fluids Wear / dynamic apps Not Recommended For Ozone (Air) Ketones Automotive Brake Fluid Aircraft Brake Fluid Steam and Hot Water N0750-80 N1090-85 NX352-70 (7727) Swells more in water than standard nitrile.
- 14. Hydrogenated Nitrile (HNBR) -25 / -40 F to + 300 F Recommended For R-134a Petroleum oils Silicone Fluids Air Hot water Not Recommended For Ketones Automotive Brake Fluid Aircraft Brake Fluid KB161-70 (21377) N1173-70 Similar to nitrile plus air (ozone) resistance.
- 15. Polyacrylate (ACM) -5 F to + 350 F Recommended For Petroleum oils Engine oil Power steering fluid Transmission fluid Silicone Fluids Air Not Recommended For Ketones Steam and Hot Water Low Temperature AA150-70 (12307) Only used in automotive market today.
- 16. Ethylene-Acrylic / VAMAC (AEM) -40 F to + 325 F Recommended For Petroleum oils Engine oil Power steering fluid Transmission fluid Silicone Fluids Air Not Recommended For Ketones Steam and Hot Water AE152-70 (12897) Swells more than standard polyacrylate.
- 17. Low Temp Polyacrylate (ACM) -40 F to + 325 F Recommended For Petroleum oils Engine oil Power steering fluid Transmission fluid Silicone Fluids Air Not Recommended For Ketones Steam and Hot Water Low Temperature A1111-70 Combines low swell of standard polyacrylate and low temp of Vamac.
- 18. Neoprene (Chloroprene – CR) -35 F to + 250 F Recommended For Refrigerants Ammonia High aniline point petroleum oils Weak / dilute acids Silicate ester lubricants Not Recommended For Ketones Phosphate ester fluids C1124-70 AMS 3209
- 19. Ethylene Propylene (EPR, EPDM) -65 F to + 300 F Recommended For Water and Steam Alcohols Ketones Automotive Brake Fluid Aircraft Brake Fluid Amines Air Not Recommended For Petroleum oils Di-Ester Based Synthetic Lubricants E1267-80 E0515-80 Good for practically anything that dissolves in water. NAS 1613
- 20. Butyl (IIR) -75 F to + 250 F Recommended For Water and Steam Alcohols Ketones Automotive Brake Fluid Aircraft Brake Fluid Amines Air Low permeation Not Recommended For Petroleum oils Di-Ester Based Synthetic Lubricants Short term resilience B0612-70 Excellent gas permeation resistance. Good rocket fuel resistance.
- 21. Polyurethane (EU, AU) -40 F to + 180 F Recommended For Petroleum oils Hydraulic Fluid Silicone Fluids Air Wear / Dynamic Apps Not Recommended For Ketones Brake Fluids Steam and Hot Water P0642-70 Parker Salt Lake makes thermoplastic urethanes that melt and can be re-used. They have even better wear resistance than “milleable” urethanes like P0642-70.
- 22. A-type Fluorocarbon (FKM) -15 F to + 400 F Recommended For Petroleum oils Silicone Fluids Acids (Black ONLY) Aromatic solvents Halogenated hydrocarbons Air Not Recommended For Ketones Steam and Hot Water Amines Low Temperature Automotive Brake Fluid Aircraft Brake Fluid V1164-75 V1226-75 V0709-90 AMS 7276 AMS 7259
- 23. B-type Fluorocarbon (FKM) -15 F to + 400 F Recommended For Petroleum oils Silicone Fluids Acids (Black ONLY) Aromatic solvents Halogenated hydrocarbons Air Not Recommended For Ketones Steam and Hot Water Amines Low Temperature Automotive Brake Fluid Aircraft Brake Fluid V0834-70 V0494-70 Called “Acid Resistant” in Compound Offering Manual.
- 24. F-type Fluorocarbon (FKM) -15 F to + 400 F Recommended For Petroleum oils Silicone Fluids Acids (Black ONLY) Halogenated hydrocarbons Aromatic Solvents Alcohols Not Recommended For Ketones Steam and Hot Water Amines Low Temperature Automotive Brake Fluid Aircraft Brake Fluid V0965-80 VG162-70 (19727) Low swell in alcohols, but gives up a lot of compression set vs A-type.
- 25. High Fluorine FKM -15 F to + 400 F Recommended For Petroleum oils Alcohols Silicone Fluids Acids (Black ONLY) Aromatic solvents Halogenated hydrocarbons Air Not Recommended For Ketones Steam and Hot Water Amines Low Temperature Automotive Brake Fluid Aircraft Brake Fluid V1262-65 V1263-75 V1264-90 Combines low swell of F-type with comp set of A-type.
- 26. GLT Fluorocarbon (FKM) -40 F to + 400 F Recommended For HTS Turbine oils Petroleum oils Silicone Fluids Aromatic solvents Halogenated hydrocarbons Air Not Recommended For Ketones Steam and Hot Water Automotive Brake Fluid Aircraft Brake Fluid VM835-75 AMS-R-83485
- 27. Low Temp Fluorocarbon (FKM) -50 F to + 400 F Recommended For Petroleum oils Silicone Fluids Acids (Black ONLY) Aromatic solvents Halogenated hydrocarbons Air Not Recommended For Ketones Steam and Hot Water Amines Automotive Brake Fluid Aircraft Brake Fluid V1289-75 AMS spec in draft
- 28. GFLT Fluorocarbon (FKM) -35 F to + 400 F Recommended For Petroleum oils Alcohols Silicone Fluids Acids (Black ONLY) Aromatic solvents Halogenated hydrocarbons Air Not Recommended For Ketones Steam and Hot Water Amines Automotive Brake Fluid Aircraft Brake Fluid V1163-75 VB184-75 (19487) Combines low swell of F-type with low temp of GLT-type. Worst comp set of all FKMs.
- 29. ETP Fluorocarbon (FKM) -15 F to + 400 F Recommended For Practically everything Not Recommended For Refrigerant gases Low cost applications Low temperatures V1260-75 Polymer trade name is Viton Extreme – similar performance to Hifluor, but usually a lot less expensive.
- 30. Parofluor ULTRA(FFKM) +5 F to + 600 F Recommended For Engine exhaust Semicon Chip fab operations Jet engine oil (Practically everything) Not Recommended For Refrigerant gases Low cost applications Low temperatures FF200-75 FF350-75 AMS 7257
- 31. Hifluor (FKM) -15F to + 400 F Recommended For Practically everything Not Recommended For Refrigerant gases Low cost applications Low temperatures V3819-75 V8534-90 Same chemical properties as Parofluor but about 20% less expensive.
- 32. Aflas (TFE/P) +15 F to + 450 F Recommended For Petroleum oils Alcohols Silicone Fluids Bases Amines Air Steam / Hot water Not Recommended For Low Temperature Gasoline V1006-75 AMS 7
- 33. Silicone (VMQ, PVMQ) -175 F to + 500 F Recommended For Dry Heat Temperature Extremes Environmental Seals Air Not Recommended For Ketones Dynamic Applications Long-Term Gas and Vacuum Sealing Petroleum oils Automotive Brake Fluid S0469-40 S0604-70 S0595-50 S1224-70 S0899-50 S0383-70 S0613-60 S0355-75 S0455-70 S0614-80 AMS 3301 AMS 3302 AMS 3303 AMS 3304 AMS 3305 AMS 3337 AMS 3345 AMS 3357 AMS 7267 A-A-59588 MIL-G-21569
- 34. Fluorosilicone (FVMQ) -100 F to + 350 F Recommended For Petroleum oils Gasoline Dry Heat Temperature Extremes Environmental Seals Air Not Recommended For Ketones Dynamic Applications Long-Term Gas and Vacuum Sealing Automotive Brake Fluid LM158-60 LM159-70 L1077-75 LM160-80 L1186-80 AMS-R-25988 AMS 3325 AMS 7xxx for 70 duro in draft AMS 7xxx for other duros planned for next 2 years
- 35. Rubber Testing Most Testing is Performed on Slabs and Buttons Provides uniform standard for testing Eliminates effects due to geometry Can test some o-rings & molded shapes Results will not be the same as from platens Testing of asymmetrical geometries can result in significant variation in results.
- 36. Top and bottom temperature capabilities usually expressed in degrees Fahrenheit and/or degrees Celsius. Overspecifying a temperature range to include a “safety factor” often results in needing a specialty material and paying too much. Temperature Range
- 37. Low temperature testing How is a low temperature limit determined? Brittleness (ASTM D2137) Impact resistance Resilience (ASTM D1329) TR-10 Glass transition point (Tg) DSC Application experience Customer feedback O-rings may seal below their “official” limit
- 38. High temperature testing How is a high temperature limit determined? Heat Age testing (ASTM D1418) Hardening Change in tensile properties Ultimate tensile strength Ultimate elongation Modulus (tensile strength at 100% elongation) Compression Set (ASTM D1418) Deformation due to compression over time Compressive Stress Relaxation Compressive load retention over time
- 39. Gland design What makes a reliable O-ring design? Squeeze Seal deforms significantly (~25%) Rubber does not compress or lose volume Stretch Gland fill Volume-to-void ratio Surface finish Balance of machining costs with application & testing needs Installation Protect seal from sharp edges Provide lead-in chamfers
- 40. Compression expressed as a percentage of the free-state cross-sectional thickness of the O-ring. (O-Ring C/S) - Gland Depth (O-Ring C/S) Face Seal: 20-30% Static Male/Female: 18-25% Reciprocating: 10-20% Rotary: 0-10% Squeeze
- 41. Squeeze and Service Life
- 42. Squeeze and Service Life
- 43. Squeeze and Service Life
- 44. O-Ring volume as a percentage of Gland volume. (O-Ring Volume) (Gland Volume) About 25% void space or 75% nominal fill Need space in groove to allow for volume swell, thermal expansion, and increasing width due to squeeze Narrower groove for sealing vacuum or gas O-Ring can get squeezed out into clearance gap or get squeezed in two directions if fill approaches 100%. Greater than 100% is impossible – rubber materials are not compressible. Results in pinching, tearing, or incomplete assembly. Gland Fill
- 45. Excessive Gland Fill Seal cannot change volume and prevents further compression. Seal suffers long-term damage.
- 46. Groove diameter as a percentage of O-ring free-state ID. (Groove Diameter) - (O-Ring ID) (O-Ring ID) General rule is 0-5% Excessive stretch can overstress material Thins cross section and reduces squeeze The % cross section reduction due to stretch is equal to about half of the % ID stretch Possible breakage during installation O-rings can be stretched diametrically to about half of the elongation percentage shown on a test report. Stretch
- 47. O-Rings O-Rings are easy to design! It’s the O-Ring groove that needs special attention. Static Face Seal Dovetail Seal Radial (Male / Female) Seal Crush Seal Tube Fitting Seal Dynamic Radial (Male / Female) Seal Rotary Seal (Female only)
- 48. Face Seals No stretch 20 – 32% squeeze Up to 95% fill
- 49. Dovetail / Half Dovetail No stretch Predesigned Hold O-Ring in Groove Expensive to machine
- 50. Male / Female Static Seals Up to 5% stretch 20 - 30% squeeze 70 - 90% fill
- 51. Male / Female Dynamic Seals Up to 5% stretch 10 - 20% squeeze 70 to 90% fill
- 52. Crush Seals No stretch Squeeze N/A 90 - 95% fill Legs = 1.321 x CS of O-Ring
- 53. Tube Fitting Seals Predesigned 3-xxx O-Rings
- 54. Rotary Seals No stretch! 0 to 11% squeeze 90% gland fill Low fluid pressure 800 psi max Low speed (1500 fpm max) FPM = RPM x shaft dia (inches) x 0.26
- 55. O-Ring Failure Diagnosis and Correction
- 56. O-Rings can Fail in many ways ( Often an O-Ring fails from a combination of problems) Extrusion and/or nibbling Compression Set Exceeding seal temperature limits Spiral Failure Explosive Decompression Abrasion Cuts From Installation and/or Sharp Edges Chemical Attack
- 57. Compression Set Looks like the seal has been flattened or deformed. Usually symmetrical. Happens whenever rubber is compressed -- is accelerated by too much or too little squeeze, high temperatures, and incompatible fluids. Can be lessened by using a more compression set resistant compound, adjusting the squeeze (if incorrect), lowering the temperature.
- 58. Abrasion Looks like the seal is sanded off or flattened. Asymmetrical. Happens whenever a rough surface or fine particles rub the seal. Lubricating the ring better, smoothing out the surfaces, and cleaning out the seal area will reduce seal abrasion.
- 59. Low Temperature Failure Seal leaks at low temperatures only. As seal materials cool to within 15 o F of their minimum operating temperature, they lose resilience. Any movement may allow leakage of low viscosity liquids and gases. Low temperature changes are not permanent and do not damage the seal. Use a seal material with improved low temperature performance.
- 60. High Temperature Failure Rubber “melts” or becomes brittle. Every rubber polymer has a temperature above which it begins to break down. Thermal degradation is permanent and irreversible. Use a seal material with improved high temperature performance or cool the seal gland area.
- 61. Extrusion and Nibbling Looks like one side of the seal is chewed off. Is caused by high pressure “pushing” the O-Ring into a gap between the metal surfaces. Is prevented by using a more extrusion-resistant compound, adding a back-up ring, lowering the pressure, or reducing the size of the low pressure clearance gap.
- 62. Spiral Failure Looks like a split wrapping around the ring. Happens when the seal on a piston or rod “grips” instead of slides in one spot (common with long, slow strokes). Can happen on static seals with pressure cycling. Can be prevented by using a smoother surface, lubricating uniformly, using a stiffer rubber compound, or using an engineered seal.
- 63. Explosive Decompression Looks like blisters and splits on the surface of the seal. Happens when gas pressure drops suddenly. Can be avoided by dropping the pressure slowly, or use a more explosive decompression resistant material (like V1248-95).
- 64. Cuts and Physical Damage Looks like the seal has been cut by a knife. Happens when the corners of the groove aren’t rounded off, when the ring gets pinched, or when it passes over sharp metal edges. Fix it by “breaking” the corners of the groove, chamfering the parts to eliminate pinching, and covering sharp edges when the ring is installed.
- 65. Chemical Attack The seal swells a lot, shrinks, loses physical properties, or gets brittle. The seal and the fluid don’t work together Excessive swell, brittleness, and dramatic loss in physical properties: find a compatible base polymer. Shrinkage: the fluid is probably extracting something from the rubber -- change compounds (changing the base polymer usually isn’t required.)
- 66. Nitrile rubber forms lots of tiny, little cracks along the OD or ID -- especially where it’s stretched. Nitrile is not compatible with ozone or UV light. There is ozone in the air around us, and this can be enough to destroy an O-Ring. If the seal must be exposed to the environment, keep it lubed with a petroleum- or silicone- based fluid or use an ozone-resistant seal material. Cracks in Nitrile Rubber