Articles

Common Secondary Seal Material

* Nitrile or Buna N (NBR)

Temperature Range: -30°C to + 105°C

Resistance to mineral based fluids is excellent, although resistance to fuels is not usually good enough. Strength, resistance, abrasion and heat resistance are reasonable.

 

* Fluorocarbon Rubber (Viton)

Temperature Range: -20°C to + 204°C

Commonly known as Viton. It is high temperature capabilities, excellent resistance to hydraulic oils, petrol and many chemicals, including weathering and ozone conditions.

 

* Ethylene Propylene Rubber (EPR or EPDM)

Temperature Range: -40°C to + 150°C

Excellent resistance to weathering and ozone, water and steam, with good performance in castor and some phosphate ester based fluids. Its low and high temperature capability is good, having excellent resistance to set with good resilience.

 

* Copolymer of tetrafluoroethylene and propylene (Aflas)

Temperature Range: -10°C to + 200°C

A unique fluoroelastomer based on a copolymer of tetrafluoroethylene (TFE) and propylene (P) was developed by Asahi Glass (Japan) and sold under the AFLAS trade name. TFE/P polymers exhibit improved chemical resistance to base and amine chemical environments compared to traditional FKM polymers.

 

* Perfluoroelastomer (Kalrez)

Temperature Range: -50° C to + 315° C

This material has outstanding chemical resistance and a temperature capability up to + 315°C (intermittent) Wherever rubber components are exposed to aggressive chemicals or high temperatures. Kalrez Perfluoroelastomer parts last longer.

 

* Polytetrafluoethylene (P.T.F.E / Teflon)

Temperature Range: -200°C to + 250°C

PTFE is an extremely inert material and is unaffected by virtually every known chemical including almost all acids, alkalis and solvents These exceptional properties make PTFE an ideal material for 'O' ring back up rings. It's cold flow characteristics under permanent strain are usually a disadvantage in PTFE 'O' rings e.g. it has little memory to return to its original form.

 

* F.E.P. Encapsulated 'O' Rings Viton or Silicone

F.E.P. Viton Temperature Range: -20°C to + 204°C; F.E.P. Silicone Temperature Range: -60°C to + 204°C. An encapsulated 'O' ring comprises an elastomer energising core, which has a seamless jacket made from Fluoropolymer. The elastomeric core may be Fluorocarbon (Viton) or Silicone. The jacket is made from Teflon F.E.P. (Fluorinated - ethylene - propylene)

Why are Encapsulated 'O' Rings needed? There are certain applications which prohibit the use of conventional rubber 'O' rings.

                                                                                                                                                                          

COMMON METAL PART  MATERIAL OF SEAL

* 316 Stainless Steel

An 18-12 Chromium-Nickel steel with approximately 2% of Molybdenum added to the straight 18-8 alloy which increases its strength at elevated temperatures and results in somewhat improved corrosion resistance. Has the highest creep strength at elevated temperatures of any conventional stainless type. Not suitable for extended service within the carbide precipitation range of 800º F to 1650º F. when corrosive conditions are severe. Recommended maximum working temperature of 1400º F. Brinell hardness is approximately 160.

* 316-L Stainless Steel

Continuous maximum temperature range of 1400º F -1500º F. Carbon content held at a maximum of .03%. Subject to a lesser degree of stress corrosion cracking and also to intergranular corrosion then Type 304. Brinell hardness is about 140.

 

* Alloy 20

45% Iron, 24% Nickel, 20% chromium, and small amounts of Molybdenum and Copper. Maximum temperature range of 1400º F -1500º F. Developed specifically for applications requiring resistance to corrosion by sulfuric acid. Brinell hardness is about 160.

 

* Hastelloy C-276

16-18% Molybdenum, 13-17.5% Chromium, 3.7-5.3% Tungsten, 4.5-7% Iron and the balance is Nickel. Maximum temperature range of 2000º F. Very good in handling corrosives. High resistance to cold nitric acid of varying concentrations as well as boiling nitric acid up to 70% concentration. Good resistance to hydrochloric acid and sulfuric acid. Excellent resistance to stress corrosion cracking. Brinell hardness is about 210.

 

* Inconel 718

Recommended working temperatures of 1700º F. and is some instances 2050º F. Is a nickel base alloy containing 50 - 55% Nickel, 17-21% Chromium and balance Iron, Excellent high temperature strength. Frequently used to overcome the problem of stress corrosion. Has excellent mechanical properties at the cryogenic temperature range. Brinell hardness is about 150.

* AM350

Alloy 350 is a chromium-nickel-molybdenum stainless steel which can be hardnened by martensitic transformation and/or precipitation hardening. It has been used for gas turbine compressor components such as blades,discs,rotors,and shafts,and similar parts where high strength was required at room and intermediate temperatures. Depending upon the heat treatment,alloy 350 may have an austenitic structure for best formability,or a martensitic structure with strengths comparable to those of martensitic steels. The alloy normally contains about 5 to 10% delta ferrite. The corrosion resistance of alloy 350 approaches that of the chromium-nickel austenitic stainless steel. It is worked from a maximum temperature of 2150 °F.

 

COMMON SEAL FACE  MATERIAL OF MECHANICAL SEAL

Property Units Carbon Graphite Carbon Antimony Tungsten Carbide Silicon Carbide R-Bonded Silicon Carbide A-Sintered
 Density  g/cm3 1.83 2.3 14.9 3.09 3.1
 Hardness (Knoop)  kg/mm3  95  95  1500  2100  2800
 Tensile Strength  Mpa (psi x 103)  48
[ 7 ]
 97
[ 14 ]
 896
[ 130 ]
 307
[ 44.5 ]
 206
[ 30 ]
 Compressive Strength  Mpa (psi x 103  234
[ 34]
 278
[ 40 ]
 4205
[ 610 ]
 2000
[ 290 ]
 3900
[ 560 ]
 Modulus of Elasticity  Gpa (psi x 106)  24
[ 3.5 ]
 26
[ 3.8 ]
607
[ 88 ]
 390
[ 56 ]
 410
[ 59 ]
 Thermal Conductivity W/m 0K (Btu/Hr-Ft- 0F)  9
[ 5 ]
 14
[ 8 ]
 83
[ 48 ]
 147
[ 85 ]
 126
[ 73 ]
 Thermal Expansion  X10 -6 mm/mm 0K
(10 -6 in/in 0F)
 4.9
{ 2.7]
 4.7
[ 2.6 ]
 4.9
[ 2.7]
 5
[ 2.8 ]
 4
[ 2.2 ]
 Max. Operating Temperature  0C
(0F)
 260
[ 500 ]
 375
[ 707 ]
 1090
[ 2000 ]
 1370
[ 2500 ]
 1650
[ 3000 ]