Page 150 - The Tribology Handbook

A27 Bearing surface treatments and coatings

Table 27.7 The need for surface treatments and coatings

Type of application Example Function of coating OT treatment
General use on many components Allows components to be designed with a
more optimum balance between the
bulk and surface properties of the
material
Lubricated plain bearing systems using Crankshafts in heavy duty engines Allows the shaft surface hardness to be
high strength harder bearing materials increased to about five times the
hardness of the bearing material,
which is required for good
compatibility

Lubricated components with small areas Spur gears, cams and followers Allows operation with low
of contact with hard surfaces on both elastohydrodynamic film thickness
components in order to carry the with a reduced risk of scuffing and
contact pressures wear
Components operating at high loads and Bearings in mechanical linkages and Aids oil retention on the surfaces and
low speed or oscillating motion, and roller chains, etc. reduces the risk of seizure and wear
with only occasional lubrication
Surfaces which have intermittent rubbing Cylinder liners in I.C. engines and Aids oil retention on the surfaces and
contact with a reciprocating actuators reduces the risk of scuffing
component

Surfaces of components that are subject Connecting rod big end housing bores in Provides a surface layer that can allow
to fretting movements in contact with high speed engines small rubbing movements without the
others build up of surface damage
Components in contact with moving Rotors and casings of pumps and fans Gives abrasive wear resistance to selected
fluids containing abrasive material areas of the surfaces of larger
components
Components handling abrasive solid Earth-moving machines. Coal and ore Provides a hard abrasion resistant
materials mills surface on a tough base material
Cutting tools Drills and milling cutters Provides a hard surface layer resistant to
adhesion and abrasion and by
providing a hard outer skin helps to
retain sharpness

High temperature components with Furnace conveyors. Boiler or reactor Provides a surface resistant to adhesion
relative movements internals and wear in the absence of
conventional lubricants

A27.1