G.W. Rowe

A quantitative comparison between residual stresses and fatigue properties of surface-ground bearing steel (En 31)

Abstract Experimental measurements of the residual stresses in hardened and tempered En 31 steel have been made after grinding under various conditions. Wheel speed, downfeed, wheel hardness, dressing speed and lubricant type have been studied separately. Three combinations of parameters were then selected to represent abusive, conventional and gentle grinding conditions. It is clear that high tensile residual stresses can be generated even under “conventional” conditions mainly owing to the martensitic transformation and its associated volume change. A strong dependence of the endurance limit on the maximum residual stress level is found in reverse-bend fatigue tests.

Surface roughness changes during rolling

Abstract The changes in surface topography of a rolled strip have been examined after sequential passes giving various total reductions of cross-sectional area. A relocation technique has been used to reveal details of individual surface hills and valleys, and the data have been digitised for computation of selected surface parameters. It is found that the hills are very easily flattened, but that the valleys persist much longer, even after 40% reduction when a grease lubricant is used. A thin layer of MoS 2 provides lubrication but allows a smooth shiny surface to be produced by rolling.

Running-in of plain bearings

Abstract Running-in is widely recognised to be of great importance but there appears to have been little detailed study of the process. This paper presents a basic investigation of surface topographic changes during running-in of grease-lubricated plain bearings, and an evaluation of greases with extremepressure and solid-lubricant additives. The results are obtained mainly from digitised surface profile measurements, supported by scanning electron microscopy. The characteristic pattern found is a wearing and deformation of the softer surface to produce a smooth condition. This state can be retained with a suitable lubricant containing an extreme-pressure or solid additive, but with an inert lubricant it encourages metal transfer, and there may be serious damage. The initial surface finish of the softer member is of relatively little importance, but that of the hard journal should be economically optimised.

An analysis of changes in surface topography during running-in of plain bearings

Abstract The well-established process of running-in is examined in detail using a variety of machines with different lubrication conditions. A general pattern is seen in which the bearing surface steadily becomes smoother. Galling is then likely to ensue with lubricants of insufficient reactivity but prolonged running is possible with suitable solid lubricants. Using digital computation and a precise relocation technique the sequence of topographic changes can be closely followed in terms of roughness average, bearing area and various other parameters. Both plastic deformation and abrasive wear can be detected from the results, supported by examination with a scanning electron microscope. A practical consequence of these studies is the prediction of optimum concentrations of solid lubricant additives and the selection of suitable load and speed conditions. The effects of journal roughness are also clearly demonstrated.

A simple correlation between deformation in some sliding-wear and metal-working processes

Abstract A number of examples are shown which suggest that the pattern of shear in several processes (grinding, broaching, strip-drawing, machining and sliding wear) is basically similar. The slip-line field for light strip-drawing resembles the observed deformation zone, and it is suggested that strip-drawing could serve as a large-scale model for studies of wedge or prow formation and associated wear features.

Frictional properties of metal oxides at high temperatures

Abstract The high-temperature frictional properties of oxide scales formed in air at elevated temperatures on several metallic alloys have been studied using a simple slider technique. In accordance with earlier metalworking studies, some of these oxides have been found to give low friction under certain conditions. The friction is low when the oxide is soft and ductile, and also when a normally high-friction oxide occurs as a friable layer which can shear easily during sliding. Anomalous frictional behaviour observed with some copper-zinc alloys has been explained using the results of a scanning microprobe X-ray analysis study of the scale formation on these alloys.

Lubricating properties of grinding fluids. II: Comparison of fluids in four-ball tribometer tests

Abstract The traditional four-ball tribometer tests, although disputed in principle, are used in practice as a supplementary tool for comparison and preliminary evaluation of cutting and grinding fluids. Little of the information obtained in such tests is published, and four-ball machine data, especially on water-based fluids and on grinding, are scarcely available. However, a relatively simple, reproducible, cheap and reasonably informative technique is still needed to study lubricating effects in grinding. If the possibility of using tribometer tests for this purpose has to be studied systematically, a sufficient amount of data has to be accumulated. This paper presents four-ball machine data of fluids evaluated in previous studies of the present authors by surface-grinding experiments. Two different four-ball tribometers are employed to determine respectively the extreme-pressure and antiwear properties of the grinding fluids. The four-ball tests provide useful information on the eventual mechanisms of the lubricating behaviour of the fluids, relevant to grinding. However, for correlation studies, rheological and cooling properties at least should also be considered.

Lubricant testing for grinding operations

Abstract The International Research Group on Wear has highlighted the problems of simulating real problems of tribology by laboratory tests and has emphasized the importance of considering each tribological system as a whole. The present paper is concerned with the coordination of tests of the various chemical and physical properties of grinding fluids, their physiological actions and their mechanical performance. A simplified data bank is proposed, allocating each result to one of seven categories and combining these in a computer. Various weighting factors are applied according to the practical requirements of specific grinding processes.

An on-line technique to monitor running-in of plain grease-lubricated bearings

Abstract In a well-prepared plain bearing running under the designed conditions, the two surfaces will be separated by a hydrodynamic film of lubricant. It is, however, expensive to lap or to polish the surfaces before assembly, so the bearing usually requires careful running-in to remove the surface roughness left by machining. During this period intermittent close metallic contact will occur. It is desirable to optimize the speed and load conditions so that there is as much surface interaction as possible without danger of gross damage or overheating. In the course of an investigation of suitable control processes it was found necessary to monitor the progress of running-in without removing the bearing to measure the actual surface roughness. A simple on-line method based on the electrical voltage across the thin dielectric film of lubricant was developed. This shows clearly the progress of running-in and can be used to indicate automatically the achievement of a satisfactory smoothness. The associated equipment can be produced inexpensively and can be incorporated in a microprocessor monitoring system.

Microprocessor Control of Running-in of Plain Bearings

Correct running-in procedures have a major influence on the subsequent life and performance of a plain bearing. With very large bearings, the process can be both time-consuming and expensive. It is necessary to control the running-in conditions very carefully, since too thick a lubricant film, will retard the running-in, while too little lubrication will lead to overheating and possible damage or even seizure. Since the surface topography is changing continuously during running-in, the optimum lubrication condition also changes. This paper describes a new bearing rig in which running-in parameters are monitored and fed to a microprocessor which, in turn, controls the loading and speed conditions. The objective is to obtain correct running-in, in the minimum possible time.