280 Chap. 6. Rotary Seals 1. Conservation of mass ( i f cross section is considered to be always c ircu la r ): o 2 ttW tt( W ’ ) ^ (OD - W)TT = (G - W ’ ) tt Relationships: therefore W^(OD ) - = (W ')^G (W )^ (O D ) = (W ')^G + - (W )^ 2. Since OD and G differ much more than W and W’ and since is very close to (W ’)^ , we can ignore the last two cubed terms. They are of the order 0.0003, compared to OD and G, which are of an order greater than 0.210. For example, if we inserted typical values: W^(OD) = (W’ )^G + - (W ’ )^ (0.070 )^(2.372) (0.075 )^(2.196) + (0.070)^ - (0.075)^ 0.0049(2.372) =» 0.0056(2.196) + 0.00034 - 0.00042 0.0116 «> 0.0123 - 0.00008 The last term of the equation is small compared to the other terms and therefore can be ignored, giving W ^O D ) = (W ')^G This states the square of 0 -r in g width times the diameter is a constant W^ (D ) = K Take the derivative 2W dW (D ) + w 2 d (D ) = 0 therefore 2W dW = -W 2 d (D )/D ^ dW _ - d ( D ) W D
Reduction of 0~Rlng and Increase In Cross Section 281 Free Diameter FREE O-RING - H K-Compression Diameter S! K - Compression Diameter STRETCHED O-RING 20 10 E ;z: OBSERVED DATA-AFTER REMOVAL OF PLASTICIZER •OBSERVED DATA-NEW AND DRY ---------------CALCULATED DATA A N 6227 SERIES 0-R IN 6S OF 70 ( SHORE A) DUROMETER OTHER DUROMETERS HAVE D IFFER EN T CURVES 5 10 I5 20 % OF DIAMETRAL STRETCH (l.0.)(a) ASSY. 25 F ig u r e 36. Loss in compression diameter due to stretch. In the stretched condition, an 0 -r in g cross section is no longer circular. It is often necessary to compensate for the loss in squeeze resulting from the reduced compression diameter. Dimensional changes in the free diameter do not affect the seal. (From 0-R ing Handbook» Parker Seal Co. , Lexington, Ky., October 1967) 3. Therefore (with cross sections always circular) % increase in W dW/W _ 1 % decrease in D - d ( D ) /D
282 Chap. 6. Rotary Seals 4. Because the 0 -r in g cross section does not remain circular when the 0 -r in g is pressed into the smaller groove, the minimum width will be less than that calculated through Step 3. Thus, the actual W’ can be estimated to be about 2.5 percent less using a logical analogy from Fig. 36. Therefore, the actual data would probably fall between the calculated and estimated curves shown below .
References 1. 0-R ing Design and Selection Handbook, No. 110-A, Stillman Seal Division, Sargent Industries, Carlsbad , C a lif., 1976. 2. 0-R ing Handbook OR5700, Parker Seal Company, Lexington, Ky. , January 1977. 3. Parker 0-R ing Handbook, Parker Seal Company, Culver City, C a lif., 1968. 4. Seal Compound Manual, Parker Seal Company, Culver City, C a lif., 1964, pp. 1-2. 5. Richard S. Fein, Boundary Lubrication, Lubrication (Texaco, In c .) 57(1):3-12 (1971). 6. O -ring insertion tool developed by L. J. Martini, Naval Ocean Systems Center, Patent Application. 283
Index Angle, slant, 249-251 Annulus, oil, 249-261 Asperities, 116, 246, 247 Backup rings, 51 Bal-Seal, 4 Bearing, 258, 270 Blowout, 51 (see also Extru sion) Bosses, 95-97 Buna-N , 20, 259 Buna-S , 22 Butadiene, 22, 55-62 Butyl, 22, 43-46, 55-62 Chloroprene, 22 Chlorosulfonated polyethylene, 23, 55-62 Chrome, 257 Compound, 18-26 capability, 19 chemistry, 20-26 compatibility, 43-46 properties, 18, 19 Compression modulus, 51 peripheral, 233, 256, 261- 276 Contamination, 108 Corrosion, 52, 108 [Corrosion ] products, 247 Cylinder, rod, 109-125 Design, consideration, 39-64 Distributors, 30-38 Durometer, 47, 51, 232 Elasticity, modulus of, 51, 232 Epichlorogydrin, 25, 55-62 Ethylene propylene, 23, 43-46, 55-62 Expansion, thermal, 49, 234 Extrusion, 4, 41, 42, 49 Face seal, 68, 101-107 Failure extrusion, 4, 41, 42, 49 spiral, 4, 109 Finish, surface, 95, 257 Fittings, 95, 96, 98-100 Fluid adsorption, 234 compatibility, 43-46 Fluorocarbon, 23, 43-46, 55-62 Fluorosilicone, 24, 43-46, 55-62 Force compressive, 240-244 radial, 240-244 restoring, 110-115, 132-231 285
286 Index Friction, 116-131, 233, 249- 251 dynamic, 116-125, 249 hysteresis, 119-131 static, 116-126 Geometry (see Seal) Gland (see also Seal) application, 40, 248 assembly, 40, 260 corrosion of, 52 depth of, 234-240 design, 39-64 face, 68, 101-107 floating, 110, 257 fretting of, 52 pitting of, 52 radial, 68 Gow-Joule e ffect, 232-249, 255 Graphite-impregnated, 256 Groove slanted, 249-256 width, 68-85, 234-239 Heat (see also Temperature) shaft - generated , 240, 244, 246-251 sink, 246 Housing assembly, 260-261 groove, 264-270 seal, 54-64, 234-240, 248- 258, 260-263 Hysteresis (see Friction) Isoprene, 24, 55-62 Load (see also Force) compression, 86, 103-107 restoring, 110-115, 132- 231 side. 111 Lubrication, 110, 233, 246- 256 Machine, tooling, 18, 256 Manufacturers, 30-38 Material housing, 258 performance, 54-64, 248-258 seal, 20-30, 47 shaft, 258 Modulus of elasticity, 51, 232 Natural rubber, 24, 55-62 Neoprene, 22, 43-46, 55-62, 259 Nitrile, 20, 43-46, 55-62, 259 Oil, 260 (see also Lubrication) annulus, 249-261 hydraulic, 116 0 -R ing (see also Seal) installation, 245, 248 snake, 233, 245 Performance, material, 54-64, 248-258 Peripheral compression (see Compression) Piston, eccentricity of, 110, 132-231 Polyacrylate, 24, 43-46, 55-62 Polysulfide, 25, 43-46, 55-62 Polyurethane, 25, 43-46, 55-62, 259 Porting, 40 Pressure, differential, 240-244 Propylene, 23 Radiation, 52 Rod, cylinder, 40, 109-125 Rubber (see also specific compounds) epichlorogydrin, 25 isoprene, 24 natural, 24 polysulfide, 25, 55-62 silicone, 25, 43-46, 55-62 SBR, 22 Seal application, 5-7, 248 assembly, 260
Index 287 [Seal] clearance, 41, 234 compression, 41, 51, 233, 256, 261-276 configuration, 3-7 cross section, 3-7, 40-48, 69-85, 261, 262 extrusion, 4, 41, 42, 49 face, 68, 101-107 geometry, 3-7 hardness, 47, 51, 232 housing, 54-64, 234-240, 248-258, 260-263 life, 248-256 (see also Failure ) material, 20-30, 47 performance, 54-64, 248-256 pressure on, 50, 51, 116, 232-246 reciprocating, 41, 108-131 rotary, 232-260 shrinkage, 51 size, 7-14, 47, 264-270 snaking, 234, 245 squeeze, 82, 91, 116, 240 static, 41, 91-107 stretch, 47-49, 86, 92-95 swell, 51 Shaft bearing, 258 [Shaft] chromed, 257 diameter, 68-85, 264-270 finish, 257 speed, 232, 262 stainless, 257 Shock, 108 Silicone, 25, 43-46, 55-62 Specification, 26-29 comparison, 67-90 industrial, 67, 73-85 military, 9-14, 67-72 Stiffness (see Modulus of elasticity) Stress compression, 240-244 resultant, 240-244 tensile, 232, 233, 240 Temperature capabilities, 21-26 cryogen ic, 26 testing, 26 variation in, 49 Tool, insertion, 245, 246 Tooling, cost, 256 Torque, running, 249-255 Valving, 40 Wear, 255 Wearlife, 250