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
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