This paper describes a unique facility for measuring the film thickness in thrust cone bearings. Full details are given of the design approach and specified characteristics, together with the resultant configuration and its attributes. Some preliminary results are included which indicate the relative capacity of flat and crowned thrust cones and the implications for operation with misaligned rotational axes.

This paper outlines relevant aspects of the operation of thrust cones and describes salient features of an unexpected form of failure encountered in small-scale thrust cone simulation tests. Interpretation of the thrust cone simulation test results in the light of related twin-disc tests at the relevant low slide-roll ratio leads to two conclusions. Rather than scuffing, the limiting surface failure mechanism in small-scale thrust cone tests was general plastic deformation with cold pressure welding promoted by the lack of support at the cone edges and the prolate epicycloidal path followed by the contact. The limiting surface failure mechanism in full-scale thrust cone bearings, which have markedly lower curvature and higher rolling speed than used in small-scale simulation tests, was predicted to be scuffing delayed to relatively severe operating conditions by prior running-in. Further development of the insights gained from the related twin-disc work results in two recommendations. Future work should be directed to assessing the surface modification that follows transition from EHL to mixed lubrication and redefining the conditions in which transition to micro-EHL occurs in order to quantify the potential enhancement of scuffing resistance offered by controlled running-in. It should also concentrate on evaluating the combined effects of microgeometry conducive to lubricant film formation and material properties resistant to weld formation in order to obviate the difficulty of assigning a representative value to the operating friction coefficient that is common to a number of proposed failure criteria.

This paper describes mineral oil lubricated twin-disc tests with nominal point or line contact at rolling (mean surface) speeds in the range 3±23 m=s and slide±roll ratios in the range 15±80 per cent. The results identify a regime in the sliding=rolling speed domain in which failure of EN36A (750 DPN) and EN24U (350 DPN) is predominantly by scuffing preceded by running-in, which delays scuffing to relatively severe operating conditions. At speed combinations above the identified regime, the steels fail by scuffing in, or close to, mixed lubrication conditions with little or no running-in, so that the conventional failure criterion based on a film thickness to r.m.s. surface roughness value of three is appropriate. At speed combinations below the identified regime, load intensity becomes sufficient so that general plastic deformation intervenes before failure by scuffing can occur and a shakedown-based criterion becomes appropriate. Observations of contact frequency variations suggest that with steel surfaces at 650 and 750 DPN running-in is produced by rubbing of asperity tips and that with steel surfaces at 350 and 450 DPN it is produced by hydrodynamic ripple pressures. For the latter materials at low slide±roll ratios, macro-and micropitting are likely concomitants of plastic deformation.

Details the friction and wear testing facilities offered to civilian customers by the DRA and lists recent projects. Cylinder and ball on plate fuel lubricity and fire resistant hydraulic fluid tests are described with line drawings and the results obtained tabulated.

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