Reactivity and wear Chemical activity of metals in their elemental state, ie their reaction potential, influences the adhesion, friction and adhesive wear of these metals when in contact with themselves or with other materials. While this basic concept is fundamentally very useful, most practical bearings, and other systems involving wear, contain alloys. An investigation has therefore been conducted at the NASA Lewis Research Center to determine how fifteen alloying elements affect the friction and adhesive transfer of copper-based alloys in contact with a bearing steel. Simple binary alloys were selected for study in order to isolate the influence of a single alloying element on friction and adhesive transfer behaviour.
Radio telescope bearings The world's largest radio telescope for mm wavelengths has been in operation at Rao in Sweden since 1976. Aspects of its design and operation were described in an article by Hansson and Ragneback in the latest issue of Ball Bearing Journal. Radio waves impinging on the 20 m diameter parabolic reflector are directed by a secondary reflector to the receiver. To operate efficiently down to wavelengths of 2mm, the shape of the paraboloid should be accurate to within -+ 0.2mm. The reflector is protected from distortion due to atmospheric conditions by a 30m diameter sphere-shaped radome but it was not possible to provide a supporting structure for the antenna, at a reasonable cost, which would be sufficiently stiff to keep deformations within acceptable limits when the elevation of the antenna changes. The solution to this problem was to adjust the position of the secondary reflector, as the main reflector deforms to correspond to the focus. This is performed by 5 motor-driven SV series roller screws with a 12mm diameter and a l m m lead. These screws have been manufactured with an accumulated lead error of the thread of less than 7/~m over 25mm. More information in Ball Beating Journal, 198 (1979) pp 12-15, published by SKF
A composition of 1 at % was chosen to determine the effect of small concentrations of an alloying element on the friction and transfer properties of the host metal. Riders of the copper-based binary alloys were made to slide in a vacuum against a steel disc surface under a load of 100 g and at a sliding velocity of 1 mm/s. Transfer of the copper alloy to the bearing-steel surface was monitored by Auger spectroscopy. Residual surface oxides were present on the steel disc and no attempt was made to remove these oxides before the tests. The alloying elements were: magnesium, aluminium, silicon, manganese, gallium, zinc, tin, indium, nickel, germanium, antimony, palladium, platinum, silver and gold.
relation between the free energy of formation of the oxide of the alloying element and the adhesive transfer of the alloy to the bearingsteel surface. The more stable the oxide, the greater is the adhesive transfer. There is also a direct relation between the reaction potential of tile alloying element and the adhesive transfer of the alloy. The more reactive the metal, the greater is the adhesive transfer or wear.
Results show that there is a direct
Further information is contained in a 19-page report 'Role of alloying elements in adhesive transfer and friction of copper-base alloys' by D.H. Buckley, reference N78-26198, available as microfiche £1.19 (inc vat) or reproduced paper-copy £1.50 from TechAlert*
Fluid Power and Sealing
In the December 1978 issue of Tfibology International, we published reprints on the 5th International Fluid Power Symposium and the 8th International Conference on Fluid Sealing, both held at the University of Durham in September 1978. Proceedings of both meetings have recently been published.
Use of epicyclic gearing has grown considerably in recent years. According to APE-Allen "the advantages of epicyclic design together with its proven performance have resulted in its adoption for many applications for the transmission of a very wide range of powers and speed ratios".
Fluid power contains 30 papers and costs £23.00 (UK only) or US $52.00 (p&p extra) for the set of two volumes. Fluid Sealing contains 29 papers and the set of two volumes costs £22.00 (UK only) or US $50.00 (p&p extra). In both cases a second volume to be published shortly will include indexes, discussion records and delegates lists. Contact Publications Sales, BHRA Fluid Engineering, Cranfield, Bedford MK43 0AJ, UK
APE-Allen have recently published a booklet on 'Epicyclic gearing ['or industrial and marine applications'. The 20 page booklet covers general applications, basic types, design features, lubrication and specification. This is followed by detail on specific marine and industrial applications and some comments on manufacturing. APE-Allen Gears Ltd., Atlas Works, Pershore, Worcestershire WRI 0 2BZ, UK
Condition monitoring It has been suggested that price trends for petroleum products will result in the use of increasingly poor oil qualities for marine main propulsion machinery and thus "therisks of wear, scuffing and fouling of the combustion chambers in marine diesel engines will increase substantially." One way of avoiding potential problems is the rational application of condition monitoring.
Two articles in the latest issue of ASEA Journal describe the CyldetCM electronic system for condition monitoring of marine diesel engines. The modular system can monitor combustion pressure, wear, piston ring condition, and bulk and surface cylinder liner temperature. More information in ASEA Journal, 51, 6, published by ASEA AB, S-72183 Vasteras, Sweden
TRIBOLOGY international June 1979