Proceedings of the Institution of Mechanical Engineers

Earlier theories of tube sinking through conical dies have been considered and the factors important in the calculation of stresses and strains have been determined. Using these theories drawing stresses have been calculated for a particular stress-strain curve by assuming an exponential strain hardening characteristic. These drawing stresses are essentially ‘lower bounds’ but comparative ‘upper bounds’ have been obtained using velocity field techniques; Coulomb friction has been included. Thickness strains for a smooth die and a non-strain hardening material have been computed. Experimental data has been obtained using conical dies under normal industrial conditions and comparisons made with theory. In addition, the problems encountered in the inlet and exit of the die are discussed.

It is suggested that drawing stresses and thickness strains determined for conical dies can be applied to other die profiles when the die inlet semi-angle does not exceed 15°.

A survey is given of progress in the development of self-lubricating materials for load-carrying components (bearings and gears) or for transfer lubrication (rolling element bearing retainers). Various methods for producing composites of inorganic solid lubricants, metals, polymers, carbons and ceramics are briefly described, and some suggestions for further work are included.

The frequency-dependent effects of mechanical vibration on human comfort and working efficiency are now clearly recognized, as are the effects of airborne noise on hearing. But vibration and intense noise at very low frequencies can also provoke disturbing non-auditory symptoms which are as yet ill understood.

Moreover, the establishment of frequency-and time-dependence of these effects calls for further research.

The author reviews current problems in this field and mentions the work of the International Organization for Standardization aimed at defining limits of acceptable human exposure to vibration and intense noise.

Lateral Helmholtz resonators are ineffective for fast flow because of the turbulence caused by the movement of the gas mass from the resonator neck into the main pipe flow. The absorption of this turbulence at its source is an effective method for keeping the resonator silencing ability at a high level. Experimental results on an acoustic filter formed by resonators for flow velocities up to 80 m/s, so treated, are compared with the theory. There is evidence of lateral resonance of the gas column in the exhaust pipe at high flow velocities, detected as an intense noise of a discrete frequency (1000 Hz). The excitation of this resonance was found to be due to the pseudo-acoustic wave caused by the neck jets in the resonator. The influence of the flow upon the natural frequency of the resonator is also discussed. The Reynolds number of the flow seems to play an essential role on this point.

One of the factors that has to be considered when planning the installation of a turbocharger or gas turbine is the amount of noise that is likely to be radiated from the intake. Frequently such plant employs axial flow compressors, either single-or multi-stage. The object of this paper is to describe how noise is generated in that type of compressor.

This paper reviews the experience in London Transport of fatigue cracking in railway axles, and presents the results of laboratory fatigue tests on full-scale axle specimens under simulated rotating bending. The investigation was undertaken with the aim of entirely eliminating fatigue cracking and fretting under the press fits of wheel-axle sets. Whilst cold rolling of wheel seats, which is standard L.T. practice, strongly inhibits the propagation of such fatigue cracks, it does not prevent their initiation. The introduction of a stress-relieving groove, such that the edge of the press fit overhangs the groove, leads to a marked reduction in fretting and increase in life of test specimens, and the results of a limited service test suggest that the presence of such a groove reduces the stresses under the wheel hubs to a level at which cracking is eliminated. Since the presence of a press fit near to a groove increases the stress level at the root of the groove it is desirable to cold-roll the grooves, and a suitable rolling technique employing three rollers of slightly different profile radii has been developed.

Major items of C.E.G.B. power plant are now being designed to operate at high steam temperatures and hydraulic pressures. In consequence, the risk of fires due to leaking petroleum lubricants is increasing. Suitable fire-resistant (f.r.) fluids are therefore desirable. Some of these have, however, given rise to difficulties in service due to changes in their physical and chemical properties.

The physical properties of non-aqueous synthetic f.r. fluids (i.e. phosphate esters and chlorinated diphenyls) have been surveyed, and their chemical stability and anti-corrosion properties determined.

Whilst the physical properties of the phosphate esters are better than those of the chlorinated diphenyls the chemical stability and corrosion properties are much worse.

A brief review of previous work on the mechanics of vibratory conveying is presented followed by a new theoretical analysis of vibratory feeding on a track which vibrates with simple harmonic motion and where a phase difference may exist between the parallel and normal components of the track motion.

For a wide range of practical conditions, the theoretical predictions are found to agree closely with the results of experimental tests. These show that certain fundamental limitations exist in the performance of conventional feeder drives where the two components of track motion are in-phase.

From further theoretical and experimental work, it is shown that under conditions where the appropriate phase difference exists between the two components of track motion, many practical advantages over conventional vibratory feeding are obtained. With a new design of vibratory bowl feeder drive based on the results of the work, significantly higher conveying velocities may be obtained under stable feeding conditions and, further, these high conveying velocities are virtually independent of the coefficient of friction between the component and the track.

The results of the present work apply equally to the design of spiral elevators and in-line vibratory feeders.

The theory of rolling is modified to allow calculation of a hydrodynamic film thickness and viscous friction coefficient using Reynolds equation for the lubricant. Calculations are made for the case where the fluid film covers the arc of contact. The film thickness is assumed uniform and is determined by the principle of minimum rate of entropy production. It is shown that the apparent coefficient of friction varies significantly over the arc of contact. At small reductions the roll load tends to decrease with speed of rolling, while at high reductions the load tends to increase. The point of maximum roll pressure does not coincide with the neutral plane; and under certain rolling conditions there may be no maximum in the pressure over the arc of contact.

The existence of cavitation in hydraulic equipment leads to inefficient operation, mechanical damage, and vibration. The performance of valves in fluid power control systems is affected by cavitation. The spool valve finds numerous applications in this field and it is essential that these effects be thoroughly understood. In this paper a study is made of the occurrence of cavitation and its effect on the discharge characteristics of spool valves.

It is shown that over a range of flow conditions cavitation has a profound effect on the flow coefficient.

This paper describes the results of cold backward extrusion tests on aluminium and copper specimens, using test rigs in which impact velocities up to 300 ft/s could be obtained. The maximum energy available was 10 000 ft lbf, but for the work described here, 6000 ft lbf were adequate for the extrusion of billets of 1-in diameter, 1.5-in long. Comparison was made with extrusion at very low speed, and the effect of impact velocity on extrusion pressure and mean work of deformation assessed.

For aluminium, reductions of area of between 44 and 86 per cent were examined. Surprisingly little variation in deformation energy over the speed range was noted, but the optimum impact speed appeared to be in the region of 50-80 ft/s.

In the case of copper, where impact speeds up to 240 ft/s were investigated, the optimum impact velocity was about 60 ft/s.

A limited series of tests in combined forward and backward extrusion was also carried out in both materials. It was found that both reduction in area and impact velocity had a marked effect on the relative proportions of metal extruded in the two directions.

Mention is also made of metallurgical examination into the effect of high-speed working on the properties of extruded metals.

This paper describes the results of forward and backward extrusion tests on steel and titanium specimens at very high impact speeds, using reductions in area of 44 to 86 per cent. The specimens were in all cases of 1-in diameter, 1.5 in long. For the cold forward extrusion of steel, impact speeds over the range 68-310 ft/s were used. Comparison of mean extrusion and work of deformation at these high speeds was made with the values arising at very low speed. Extrusion pressures were minimal in the impact velocity range 40-80 ft/s.

Tests using steel billets preheated to temperatures between 300 and 600°C showed no great advantage in preheating above 400°C. This degree of preheating showed considerable advantages over the cold process, in that extrusion pressures were much reduced, product quality was improved, and higher extrusion ratios could be obtained. Limited backward extrusion tests at 66 ft/s proved the feasibility of the process.

Gold forward extrusion of titanium at 65 and 167 ft/s was successful only at the relatively low reductions in area of 44 and 61 per cent. At higher degrees of deformation, the extruded product broke into small pieces.

An unusual and often severe type of journal and thrust bearing failure has been encountered in both marine and land-based turbine installations. These failures have occurred with steel rotors running against high-tin babbitt metal. From the outward appearance of damage, these failures have been called ‘machining’ or ‘wire-wool’ failures.

The potential magnitude and known consequences of this type of failure on large machinery units has led to the undertaking of an extensive research programme. The objective of the programme is to determine the causes, mechanisms, and means of eliminating or reducing the risk of such failures. This paper discusses the results obtained from a bench-scale apparatus, run under defined conditions, in which service-type failures can be reproduced. Main emphasis in this paper is on the influence of steel rotor metals on failure susceptibility. Also treated is the influence on failure susceptibility of chlorine-containing, load-carrying additives in the oil environment. The failure mechanism strongly implies that rotor steels can be developed which are less susceptible to this type of failure.

A method is given for calculating the incompressible flow of a perfect fluid through multiple cascades of blades with one or more cascades moving relative to the frame of reference. Finite differences are used and the stream function evaluated by relaxation. From this velocities and pressures are calculated throughout the field for a sequence of relative blade positions allowing the spatial and time variations to be obtained.

The method is applied to an i.g.v.-rotor combination with three values of axial spacing. The results show that the mechanism of blade row interaction is that the i.g.v. prevents accelerations of the fluid in the direction normal to the i.g.v. camber line which would occur if the i.g.v. were not present.

The resultant pressure differences across the i.g.v. are the primary source of alternating forces and provide sources of discrete frequency noise at typical blade row axial spacings. The present investigation is confined to the near field and estimation of noise radiation is beyond its scope; however, if the analysis is used to design blades producing the minimum fluctuating pressures, relatively low noise radiation should result.

The closed loop hydraulic servomechanism is analysed graphically. The fluid is assumed to be incompressible.

Electrical and mechanical feedbacks are considered and the effect of feedback on the system step response is demonstrated. Viscous and Coloumb friction forces and inertia and spring loads are considered. A non-linear valve area-displacement characteristic is shown to have a considerable effect on the response.

The rotors of a majority of rotating machines are supported upon bearings whose flexibility has a significant effect on the dynamics of the system. Supports incorporating hydrodynamically maintained oil films in particular, in addition to possessing different stiffness and damping in mutually perpendicular planes, exhibit non-reciprocal coupling between motions in these planes. The author develops the equations of motion for a rotor-bearing system of this type, and describes how both the response to an out-of-balance forcing and the unstable behaviour of such a system may be predicted by evaluating separately the dynamical characteristics of the rotor and the bearings. The method is applicable to systems in which the rotor is axisymmetric and has an arbitrary mass and stiffness distribution symmetrically disposed about its centre of span. Some new aspects of the resonant and unstable behaviour of rotating shafts are brought out due to the nature of the method of solution.

Theoretical predictions are compared and agree very well with the results of tests on a 1380 lb model rotor supported on two 4 in diameter cylindrical journal bearings.

The design and development of a power circulating rolling contact disc machine is described. Each disc is mechanically coupled to a separately excited d.c. electrical machine whose armatures are connected electrically. When the discs develop traction, power circulates by one machine acting as a motor and the other as a generator. In this way controlled traction with a stepless variation of sliding speed can be maintained between the rolling discs.

Dawson has shown that the pitting fatigue life of steel discs depends inversely upon the ratio of surface roughness to oil-film thickness. The disc machine has been used to measure the sliding friction between rolling discs under conditions similar to Dawson's fatigue tests. Large variations in surface roughness and film thickness resulted in relatively small changes in friction force. It is concluded that the effect of surface roughness and film thickness upon pitting life cannot be accounted for by changes in the friction force transmitted between the discs.

The insensitivity of the observed friction to variation in the surface roughness of the discs is explained in terms of the shear behaviour of the lubricant film at high contact pressures.

Measurements of frictional traction in a circular elastohydrodynamic contact have been made over a comprehensive range of conditions. The results suggest the existence of a limiting shear strength in the fluid film and this is shown to be a function of temperature and contact size. Existing theories of fluid behaviour under extreme conditions of stress are considered and some modifications are suggested.

The contribution of asperity contact to surface traction is examined.

The variation with sliding speed of the traction transmitted by E.H.L. oil films has been measured in a rolling contact disc machine, at contact pressures up to 260,000 lbf/in² and at various rolling speeds and disc temperatures. From the traction measurements at very low sliding speeds, under isothermal conditions, the variation in apparent viscosity of the oil with pressure and temperature has been found. The variation with temperature at high pressure was exponential with an index similar to that at low pressure. The variation with pressure showed a striking reduction in the rate of increase with pressure in the high pressure region (> 10⁵ lbf/in²).

At high sliding speeds the traction coefficient was found to approach a common ‘ceiling’, which was largely independent of contact pressure, rolling speed and disc temperature. The ceiling appears to be a function of sliding speed only; it falls from 0.07 at 5 in/s to 0.04 at 60 in/s.

Using the measurements of apparent viscosity obtained at low rolling speed, it has been shown conclusively that the limitation (or ceiling) in traction at intermediate sliding speeds cannot be explained by Crook's theory of a reduction in Newtonian viscosity by frictional heating. Alternative explanations based upon plastic shear of the lubricant when a critical shear stress is reached are much more consistent with the observations. But further work is necessary to elucidate fully the behaviour of E.H.L. films in sliding.

The authors are concerned with the proper provisioning of turbochargers and fuel-injection equipment for diesel engines, particularly in the automotive class. Medium-speed engines are run at high mean effective pressures and there is a tendency towards similar outputs in automotive engines. Because of transmission demands these outputs will be required over a wide speed range and the relation of engine air and fuel requirements is examined.

The simple turbocharger is not ideally suited to wide range matching and the extent of the compromise inherent in fixed geometry compressors and turbines is discussed.

In order to survey engine, turbocharger, and fuel-system interactions tests are reported where turbocharger limitations are avoided by the use of two units in series. Engine operating limits were selected on the basis of safe engine factors and the output assessed with respect to the principal variables of turbocharger pressure ratio and engine compression ratio. The resulting compromise between high cylinder pressures and smoke control tended towards a traction-type torque curve with a higher-than-conventional fall-off in torque with speed.

A suggestion was verified that smoke occurred at higher air/fuel ratios as the charge density increased. Nevertheless accepted methods of heat-release prediction from rate of injection characteristics were not affected by variation in charge density.

Natural-gas-fuelled total-energy systems for supplying the utility demands of residential and commercial buildings typically require 500 s.h.p. for the machinery drives. Although gas turbines are competitive prime movers in this size range, difficulties arise from the need to compress the natural gas fuel to the pressure of the turbine combustion chamber.

In this study the use of non-condensing single-and two-stage steam-jet ejectors was analysed for gas compression to a pressure of 150 lb/in². Steam-supply conditions from 5000 to 1000 lb/in² and 800 to 1200°F were considered; methane was supplied at 15 lb/in² and 60°F.

The specific steam consumption (lb steam per lb gas) of a two-stage ejector was found to be much better than that of a single-stage ejector. The minimum specific steam consumption (6 lb steam per lb gas) occurred at the extreme steam conditions considered in the study.

The steam-methane mixture this produced was not flammable when mixed in any proportion with air. Of several methods considered to reduce the steam content of the mixture delivered by the ejector, only one, post-ejector cooling and condensate removal, was suitable for analysis. Cooling-water flow rates in excess of 14 lb water per lb gas were necessary to produce potentially flammable mixtures.

Estimates were made of the major effects on turbine engine performance arising from the use of a steam ejector for gas compression. A comparison was drawn for two idealized cycles and for two others in which realistic values of component efficiencies were included. In each series the gas was compressed by conventional means in one cycle and by means of a steam-jet ejector in the other.

The steam injected with the methane in the turbine combustion chamber caused an appreciable decrease in the cycle temperatures and significant improvement in both the turbine output and thermal efficiency. When the additional heat input necessary to generate the steam for the ejector was included, the overall thermal efficiency of the steam-ejector cycle was less than that of the conventional cycle.

This paper looks into the types of flatness errors produced in typical machining operations. The effect of these flatness errors on the pressure/deflection curves of the surfaces is reported. An empirical relation, based on the experimental results, between surface deflection and mean interface pressure is suggested. The effect of bonding joints is shown to eliminate plastic deformation of the surfaces and produces a joint having linear characteristics.

The gas-cooled power reactors operated by the C.E.G.B. are refuelled on-load. Thus there are a number of devices which operate in the coolant, and solid lubricants offer an attractive solution to the lubrication problems encountered. These problems are discussed, and the characteristics of suitable lubricants are elucidated. The main requirement is that of long lifetime at constant (but not necessarily extremely low) friction.

Present solutions to some of the problems are described, and their limitations are pointed out. A brief review of some possible solid lubricants is given, with an indication of the temperature ranges within which they are usable.

Results of friction and endurance tests on sprayed films of unbonded molybdenum disulphide, tungsten disulphide and graphite are presented for tests at 200 and 400°C. At 400°C tungsten disulphide was the most promising lubricant, whereas molybdenum disulphide was best at 200°C. In general, lifetimes of sprayed films showed a wide scatter.

Preliminary experiments on some hot-pressed composite materials containing a metallic (nickel) matrix and a lubricant powder (tungsten diselenide or calcium fluoride) are described. None of the formulations tested was fully satisfactory at 100°C or 400°C when both wear rate and friction were considered. However, all proved superior to plain nickel when rubbed against stainless steel.

The important factors in the method of application of solid lubricants are not understood. It is clear that much more basic research is needed, and the directions this might take are discussed.

The terminology of that branch of science concerned with temperature has always been in a most unsatisfactory state. Concepts which are essentially different in kind, such as those of thermodynamic temperature and scales of temperature, are still universally described in identical terms, and completely different quantities continue to share the same symbol. This unscientific state of affairs should not be allowed to persist. The rational treatment of the subject set out in this paper endeavours to remove these existing confusions and ambiguities.

This paper presents some theoretical and experimental studies of the phenomenon known as bulge formation, during drawing with light reductions under conditions of plane strain. Experimental observations of the initiation of bulging agree approximately with values predicted by earlier theories. The development of the bulge as drawing proceeds has not hitherto been studied. A simple analysis is presented which predicts the growth and equilibrium height of the bulge and the influence of friction. This is substantiated by measurements with cold-worked aluminium.

The paper deals with tabular methods for calculating the least squares line and the least squares plane with respect to which errors in straightness and flatness may be defined.

This paper describes an analytical examination of chip formation in the hobbing of spur gears. The process is analysed by considering relative rather than absolute motion, and is reduced to a two-dimensional problem. The mathematics were carried out on a digital computer.

The analysis shows the number of hob teeth engaged in forming a gear tooth space, the shapes of the chips and the volume of metal removed. The analysis is applied to a given hob and gear and the results indicate that: the flanks of the hob teeth remove a greater volume of metal than the tips, but the tips accomplish their metal removal in fewer cuts and are therefore loaded more severely; the volumes of metal removed by, and hence the wear on, the two flanks of a hob tooth are unequal; the machining forces exert a fluctuating and reversing torque on the worktable.

Research on turbo-machinery carried out at Liverpool University in the period 1958-66 is reviewed. The work described includes:

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The accurate determination of two-dimensional incompressible flow in cascades; and an assessment of the effects of contraction of the mainstream.

The present state of knowledge on the hydraulic lock phenomena of oil hydraulic control system components is reviewed briefly. A general one-dimensional solution of the Reynolds equation which governs hydraulic lock is presented. The solution embraces the particular solutions of past workers, and allows ready solution for piston-cylinder configurations for which a one-dimensional solution is adequate.

A general method for making full solutions of the Reynolds equation is presented, requiring the use of a digital computer for particular solutions. Pressure distribution, the lateral force on the piston which produces hydraulic lock, and the location of the lateral force can be obtained. The commonly occurring case of a single-land piston lying tilted in its bore is examined in detail.

The limit of accuracy of a one-dimensional solution is clearly shown by illustrating the discrepancies between the one-dimensional and two-dimensional solutions for several configurations.

Experiments are described in which the break-out force associated with hydraulic lock on single-land pistons is measured. The test pistons used were of 0.5-in diameter × 1 in long, with diametral clearances in their bores in the range 2-20 × 10^-4 in. The pistons were subjected to axial pressure drops in the range 0-5000 lbf/in². The finish of the pistons and bores was closely controlled as regards surface finish, roundness and parallelism. It was found in all cases that a relatively small inherent lateral force acted on the pistons. The lateral force-pressure profile was found to increase linearly with clearance. Beyond a particular pressure for each clearance used, the lateral force necessary to generate hydraulic lock disappeared.

Leakage flow rates were measured and used to help assess the attitude of a test piston in its bore.

An hypothesis is given which explains the presence of hydraulic lock with single-land piston configurations. The hypothesis relates the hydraulic couple due to small residual tilts of pistons in their bores, and the mechanical friction in the reaction bearing required to support the piston against axial pressure forces. Experiments designed to test the hypothesis give positive support to it.

Published work on pin-loaded lugs is reviewed, particular attention being given to photoelastically determined stress distributions and to results of fatigue tests for the purpose of identifying those factors that affect fatigue strength.

Fatigue tests have been conducted on lugs of width 1 in made from alloy steel FV 520B and loaded by means of a -in diameter pin. A systematic investigation was made of pin fit for both clearance and interference and the effect of various treatments was investigated; these included cadmium plating the lug bore and pin, applying the ‘Sulfinuz’ process to the lug and overstraining the lug bore. Two conditions of mean stress were investigated, namely, pulsating or repeated tension and 15 tonf/in² mean tension.

Strength comparisons are based on the fatigue strength at 10⁸ cycles, for the appropriate mean stress, of untreated lugs with exact-fit pins, these showing the lowest strength of all the lugs tested. It was found that clearance-fit pins and interference-fit pins were beneficial and with the larger values of clearance and interference tested the fatigue strength was almost doubled. Cadmium plating was ineffective while both Sulfinuz treated lugs and lugs with overstrained bores gave strength ratios of at least 1.6. An increase in mean stress from pulsating tension to 15 tonf/in² mean tension, significantly reduced fatigue strength in most cases.

On the basis of the present experimental results, the design method proposed for lugs with interference-fit pins in Royal Aeronautical Society Data Sheet A.05.02, amended by Engineering Sciences Data No. 67012, may sometimes prove to be unsafe and caution is warranted in interpreting the safe loads predicted.

This paper describes an analogue computer simulation of an on-off pneumatic servomechanism comprising a polarized relay with dead zone and hysteresis, power relays, and an on-off four-way spool valve supplying air to a cylinder driving an inertia load acted upon by viscous damping and Coulomb friction. The effect of varying the amount of friction and of position, velocity, and acceleration feedback is studied.

The effect of the addition of stabilizing tanks is also considered.

Conventional isolation systems are not, even when a large amount of damping is present, capable of attenuating the amplitudes of transmitted vibration at frequencies below resonance. Thus, the low natural frequency of the isolation system is essential for effective isolation of vibration. However, this requirement increases the transmissibility of the isolation system at very low frequencies due to changes in the mass of the supported body or in the exciting forces. In many instances this cannot be tolerated. In this paper it is shown that when active isolators with nozzle-flapper valve and pneumatic springs are used, not only the transmissibility at very low frequencies is reduced to 10 per cent but also the absolute displacement transmissibility is kept below 30 per cent throughout the frequency range, even at resonance.

Nozzles in cylindrical vessels have been of special interest to designers for some time and have offered a field of activity for many research workers. This paper presents some static and fatigue tests on five designs of full size pressure vessel nozzles manufactured in two materials. Supporting and other published work is reviewed showing that on the basis of the same maximum stress mild steel vessels give the same fatigue life as low alloy vessels. When compared on the basis of current codes it is shown that mild steel vessels may have five to ten times the fatigue life of low alloy vessels unless special precautions are taken.

The methods used by the Ministry of Technology to stimulate technological innovation in industry are described, primarily concerning the activities of the Engineering Group of the Ministry. The phases of surveying the scene, the diagnostic steps and the actions that are taken to bring about improvements are followed through. The paper presents a picture of the powers, objectives and machinery of the Ministry of Technology and examples are given of the measures that are used, their application to specific industries, and the attention given to creating an advancing technological base.

The fatigue properties of three aluminium alloys, DTD683, L65, and AA2024, were determined in reversed bending, with a mean stress of 10 ton/in², both with and without fretting.

Stresses are quoted as σ _m ± σ _a ; i.e. a mean tensile stress of σ _m with an alternating stress varying from + σ _a (tension) to -σ _a (compression). In bending tests only one face of the specimen has a tensile mean stress (σ _m ), the opposite face having a compressive mean stress (-σ _m ). However, failure always starts from the face having a tensile mean stress and endurance limits are quoted accordingly. The strength reduction due to fretting was greatest for the high strength Al-Zn-Mg alloy, DTD683, which had an endurance limit of 10 ± 10.3 ton/in² without fretting but only 10 ± 1.6 ton/in² under standard fretting conditions, i.e., 1/4 in span fretting pads loaded to 2.5 ton/in² contact pressure. The strength reduction due to fretting was similar over a range of fretting amplitudes and contact pressures.

Fretting will not occur if metallic contact between the mating faces is prevented and tests show that this can be achieved by interposing substances such as graphite, MoS₂ or p.t.f.e., in a suitable grease or resinous bonding material, between the mating faces. However, under fatigue loading, greases and resins tended to squeeze out from the contacting faces or break up under the high contact pressures so that they were only effective for a short time. It has been shown that more permanent protection against fretting can be obtained by metal spraying the surface of the specimen, thus preventing direct contact with the fretting pad. Shot peening also produced a significant improvement in fatigue strength under the standard fretting conditions; apparently the sub-surface compressive stresses prevented propagation of the cracks initiated by fretting.

The model is concerned with the problem of calculating the expected number of failures from a population in which items as they fail are replaced by new ones.

Analytical methods are available for the failure of the first generation of items and also for the steady state, but many real problems require a solution for the transient state. This model calculates the expected number of failures for the transient state from failure data for the first generation, that failure data being in terms of one or more Weibull distributions. A feature of the model is its ability to handle early life, random and wear-out failures simultaneously. A computer programme for the model is given.

The paper describes features of large high pressure (H.P.) feed heaters developed and manufactured during recent years. Attention is devoted to heaters with steel tubes.

An outline of important design considerations is given, including reference to the incorporation of integral desuperheating and drain cooling sections.

This is followed by consideration of tubeplates, headers, tubes, and tube welding, from both design and constructional standpoints. Particular reference is made to quality control procedures which have been evolved for heater components and for final assembly. The Foster Wheeler process for butt welding tubes to the tube-plate is described, and details are given of the clean manufacturing conditions under which this process must be carried out in this application to ensure tube weld integrity.

In a final section dealing with current developments, details are given of a new design of heater incorporating a toroidal header. This design permits the full feed flow for a 660 MW set to be passed through a single train of H.P. heaters, without incurring the penalty of excessively large forgings or castings. This arrangement has been found to result in major cost savings compared with twin train heaters with conventional flat tubeplates.

The problem of a rolling ball subjected to combined normal load and tangential tractions has been studied for a variety of operating conditions. It is shown that for dry steady state loading the resultant slip may be explained in terms of a microslip theory based on the differential elastic straining of the ball and the track. Such results necessitate a careful experimental technique in which the surfaces must be free from contamination and loose wear debris. It is also shown that the preceding arguments are not significantly affected by dynamically varying loads or by speed variations in the range 0-150 in/min.

The slip behaviour is found to be markedly affected by the presence of a lubricant. The behaviour with load and speed now indicates a definite hydrodynamic effect, although the theoretical film thickness is considerably less than the surface roughness. These results agree well with the results of other investigations for similar conditions. Using these experimental results and theoretical considerations a tentative power law formulation for the slip under such conditions is proposed.

An experimental investigation is reported in which a stepped and shrouded thrust pad was formed from an initially plane pad face by elastic deflection caused by pressures generated hydrodynamically in the oil film. The pad shape was optimized experimentally and it produced thicker films than a comparable tilting pad bearing but with higher frictional resistance. Pressure and film thickness contours were investigated and plotted. A comparison is made with stepped pad bearing results. This paper is based on sections of a thesis presented in 1966 for the degree of Ph.D., University of London.

Simple compression tests have been made on solid and ring shaped billets at a temperature of 1120°C. The experimental variables were the impact speed of forging, which was varied from 0.07 ft/s to 40 ft/s, and the type of lubricant. The investigation was concerned with the effect of these variables on the friction conditions and the load and energy requirements.

Phase transformations in carbon and nickel steel journals have been shown to form a protective hard surface layer, preventing failure, when rubbed against a steel pin simulating swarf in a bearing. Under similar conditions transformations in a 3 per cent Cr-Mo steel did not occur allowing metal transfer, carburization, and eventual failure of the journal. Failures could be prevented by the selection of certain oils.

A numerical method for the prediction of oil-film and metal surface temperatures is given for the case of lubricated rolling contacts with sliding. Near-Hertzian conditions occurring in gears, discs and cams are considered and the temperature distributions, viscosity variations, and the heat partition values are calculated for a range of operating conditions. An asymmetry in the heat generation across the oil film is indicated and the effect of compression on the temperatures reached and the heat partition is also investigated.

The majority of today's machine tools were developed in the first half of the 19th century. They have been improved; but not radically altered. For 150 years batch manufacture of engineering components has been carried out in factories using these machine tools as originally intended. Big factories have had more machine tools and more people but always the same basic organization, or lack of it. Because the organization has not changed, increased size has destroyed communication, and is destroying skill. A different type of organization could use the same men and equipment with great benefits if it were oriented towards the current problems.

Numerical control is capable of revolutionizing batch manufacture but it has not done so, because these new machine tools have been incorporated into the old organizational structure. By lifting numerical control out of its present context and designing round it a completely new organization, order-of-magnitude improvements are possible. The first attempt to do this, and its performance, are described, together with a glimpse into the future showing the even greater improvements which will be possible when manufacture is integrated with design.