Cladding of bearing metal and process for production thereof

Details Cladding of bearing metal and process for production thereof Cladding of bearing metal and process for production thereof

1988-04-22

1990-02-13

Rutledge, L. Dewayne

Stock material or miscellaneous articles

All metal or with adjacent metals

Having composition, density, or hardness gradient

428653, 428674, B32B 900

Patent

active

049006398

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a cladding of bearing metal applied to a supporting member, directly or over an intermediate layer, and comprising a dispersion alloy of at least two metallic constituents in a mixture leading to miscibility gaps, such as aluminum-lead, aluminum-tin, copper-lead dispersion alloys and the like, and to a process for production thereof. Claddings of bearing metal are employed as functional surface layers in many different fields of application.
The most familiar cladding methods today for producing semifabricated stock, journal bearings or bearing elements clad with bearing metal consisting of dispersion alloys are casting methods (e.g. centrifugal or stationary casting) and coating methods (flame or arc or plasma discharge, cathode disintegration and vapor deposition). Various processes owe their original development to the fact that journal bearings or bearing elements with working surfaces of dispersion alloys must be produced in widely varying shapes and sizes. Bushings over 1200 mm in inside diameter or friction members in the form of balls or sockets cannot be clad by centrifugal casting methods.
Stationary casting is preferred for this purpose. The necessary thickness of the layer of bearing metal likewise substantially influences the choice of a cladding process. Thin films of bearing metal, only about 20 microns in thickness, may be applied for example by cathode disintegration directly to a bearing surface suitably prepared for the purpose. For thicker layers, this process is too cost-intensive.
The main reason for the use of different methods of application lies in the specific layer texture of dispersion alloys. In the solid state, they are not alloyed but form a mechanical mixture of pure substances in various crystallite sizes. The intimate structure of the layers of bearing metal is altogether decisive for the endurance, corrosion resistance and critical lubricating condition of the bearing. This applies especially to the layer structure in the miscibility gap of e.g. monotectic alloys. In practice, many alloys that may be used in journal bearing technology are affected with the disadvantage of miscibility gaps. Hence it becomes necessary to circumvent the physical constraint by special methods of manufacture, to arrange compromises. By interposing (e.g. dispersion hardening) additional alloy components, it is possible to compensate the disadvantage of lower stability of layer due for example to lacking Pb content in an AlPb bearing metal layer and thereby enhance the endurance of the bearing layer.
To illustrate the problematics of producing layers of bearing metal, the stationary casting method for lead-bronze bearings will be taken as an example. The support member prepared for casting must be mounted, screwed down and sealed up on a foundry platform. With temperature control, the support member is preheated to the casting temperature, about 1700.degree. C. Immediately after pouring in the CuPb bearing metal, controlled withdrawal of heat is effected by cooling with water to avoid a directed solidification of the melt and shrink the metal onto the support member. By pumping, froth and inclusions of air can be moved to the surface. As the metal level sinks by shrinkage, the pour is topped off. The cooling process is especially critical for monotectic alloys, since the textural configuration of the layer determines endurance. Long cooling times are unavoidable because of the thickness of the cast layer. They interfere with bonding to the support member and prevent a homogeneous structure. Forced formation of copper crystals involves the hazard of vertical transcrystallization from the bottom up to the surface of the layer. Such "stalk" crystals tend to conduct superficial fatigue cracks up to the surface of the substrate and thus severely curtail the life of the bearing. Coarser, lineal segregations of Pb, jeopardizing the internal structural stability of the bearing, can be avoided practically only by abrupt quenching, which especially in the case of very large suppor

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