Page 280 - The Tribology Handbook
P. 280
Mechanical seals B24
Table 24.5 Thermal properties of seal face materials
Expansion Conductivity Dlffusiuib Specijc Maximum
Material coef%ient heat temperature
X 106/k W/mK x lo6m2/s J& K "C continuous
Stainless steel (18/8) 16 16 4 510 600
Ni-resist - 17 40 12 460 400
Alumina (99%) 8 25 7 1000 I500
Tungsten carbide (6% cobalt) 5 90 31 195 600
Silicon carbide (rezction bonded) 4 150 44 1100 1350
Silicon carbide (converted) 4 46 29 840 450
Carbon graphite
(resin impregnated) 5 18 13 750 250
(antimony impregnated) 5 22 13 750 400
PTFE + glass 100 0.3 0.2 900 200
Stellite (cobalt based) 12 25 7 430 800
~~ ~
Bronze (leaded) 17 150 48 340 300
Thermal diffu:sivity is a measure of the rate of heat diffusion through a material (for copper the value is 112).
thermal conductivity
It equals ~
specific heat X density
High diffusivily increases the performance of a mechanical seal.
Low diffusivity can lead to damaging thermal cycling behaviour.
Table 24.6 Chemical pH tolerance of materials
Tungsten carbide (cobalt binder) 7-13 Silicon carbide (sintered alpha) 1-14
Tungsten carbide (nickel binder) G13 Filled PTFE 0-14
Silicon carbide (reaction bonded) 5-12 High alumina ceramic 0-14
Tungsten carbide (nickel chrome moly bonded) 2-13
Spring arrangements Table 24.7 Spring arrangements suitable for
various sizes and speeds
The spring arrangements which can be used depend on Spring arrangement
the size, operating speed and product sealed: guidance is -
given in Table 24.7. Speed redmin Shaft dia mm Rotq Stationary
Rubber or metal bellows can be used in place ofsprings.
Single Multi Single Multi
Up to 3000 Up to 100 Yes Yes Yes Yes
Up to 3000 Over 100 No Yes Yes Yes
Up to 4500 Up to 75 Yes Yes Yes Yes
Over 4500 Up to 100 No No Yes Yes
Over 4500 Over 100 No No No Yes
B24.4