Proceedings of the Institution of Mechanical Engineers

The lecturer discusses considerations affecting harbour salvage, the growth and the existing plant of the port salvage organization at Liverpool and the reasons why such an organization is required. Emergency operations are briefly discussed. The removal of wrecks by lifting or dispersal is considered and the operation of lifting vessels with the aid of wires and external buoyancy provided by camels is described in detail, two recent operations being given as examples. In January 1953 the Empress of Canada, a passenger liner of 20,021 gross tons, sank on her side in Gladstone Dock, Liverpool, as a result of a fire. The events leading to the loss and the operations of uprighting and refloating are described with details of methods and materials used and the difficulties encountered.

In this paper is described an experimental investigation of properties and some developments in the utilization of hydrodynamic-type gas-lubricated bearings, of both journal and thrust types, as distinct from hydrostatic bearings. Two specific developments are described, the one a pump for circulating carbon dioxide gas at 100 lb. per sq. in. gauge and 150 deg. C. through a loop in a nuclear reactor, the other a gas-bearing motor driving a pump for molten radioactive bismuth, the whole within a hermetically-sealed container. The simple machining requirements and special design principles are described. The performance of gas bearings may be predicted from normal liquid bearing theory if the loading is so small that the pressure rise within the bearing is a small fraction (for example, 10 percent) of the ambient pressure. For higher pressure ratios compressibility effects must be taken into account. The experimental results and techniques used are reported, those for plain journal bearings embracing a wide range of working conditions and absolute size including compressible flow operation. An explanation of the physical reasons for the change in performance in compressible flow bearings is given. The dynamic instability sometimes encountered in journal bearings and methods of avoiding it is also discussed.

This paper summarizes published information concerning the aerodynamic performance of exhaust diffusers and propelling nozzles for turbine aero-engines, and extends and supplements this with additional data obtained from tests made at the National Gas Turbine Establishment (N.G.T.E.).

The factors influencing the exhaust system design are reviewed and the effects of the type of engine installation and the use of reheat are discussed. The influence of ducting losses on the thrust are then considered in terms of their effect on the performance of a typical turbo-jet engine.

The paper continues with a review of some previous work on turbine exhaust diffusers, which was concerned with the effects of the diffuser area ratio and wall shape and with the effect of inlet swirl. This has since been extended by experimental examination of the influence of the bullet support struts on the performance of an engine, and the results of these tests are given.

Little published information is available concerning the performance of propelling nozzles over the range of pressure ratio relevant to the turbo-jet engine. The results of tests up to a pressure ratio of 9 on a series of convergent-divergent nozzles are given and the effects of design pressure ratio and divergence angle are illustrated.

A one-dimensional theoretical treatment is used to show the relationship between the non-dimensional and specific thrusts and the applied pressure ratio. The test results are then analysed in terms of these thrust parameters and their related coefficients.

The paper concludes with reference, in general terms, to some of the more important mechanical engineering considerations which arise in the design of exhaust-duct installations in jet-propelled aircraft.

To meet a programme of research into the behaviour of underwater weapons, major research facilities including a rotating-beam channel and a 30-inch water tunnel have been designed and constructed by the Ministry of Works in collaboration with the Royal Naval Scientific Service.

The rotating-beam channel provides for towing submerged bodies in a circular path of 45-55 feet radius at speeds up to 150 ft. per sec. Models up to 20 feet long can be accommodated. The water is maintained at optical clarity by continuous filtration and chemical dosing.

The water tunnel has a slotted wall working section 30 inches in diameter and 15 feet long, providing for experiments on models up to 10 inches in diameter at water velocities up to 60 ft. per sec., static pressure can be varied from 0·1 to 3 atm. Ancillary plant maintains the water to within a specified temperature range and air content.

Both plants are provided with high-accuracy speed control by means of a Ward Leonard system equipped with electronic speed-holding servo.

This paper describes some experiments with disk machines in which the electrical resistance between the disks was measured at various stages of running. It also describes some experiments with mild steel disks run at such loads that considerable plastic deformation occurred.

The resistance measurements illustrate the process of ‘running-in’ and show that a state of almost complete hydrodynamic lubrication is eventually reached. It has also been found that the surface temperatures of the disks have a very considerable influence upon the hydrodynamic film.

The flow of material in the plastically deformed disks is described and its bearing upon the mutual accommodation of engaging tooth surfaces and their subsequent pitting is discussed. An explanation of the greater propensity to pit of surfaces with the lower peripheral speeds may be provided by one unexpected feature of the flow. It was also found that even at the high loads, which produce gross plastic distortion, the mild steel disks did not scuff, and this is attributed to the persistence of hydrodynamic lubrication even under such extreme conditions.

A very brief review is made of the American system of education and training of mechanical engineers and some of its salient features at the present time are contrasted with the British system. Points of particular interest are the emphasis being placed on the scientific foundations of the subject with a corresponding lack of emphasis on present practice by the colleges, an attempt to produce a more cultured graduate, and a rapid growth of postgraduate education. Points of particular contrast are the small number of engineers who ever undergo apprentice training, and the system of recognition by State boards rather than by the Engineering Institutions.

A short illustration is given of the cost of a university education to the student.

Systems of education in certain European countries are surveyed in detail in relation to the special circumstances of each country. Reference is also made to the numbers of those trained in allied branches of science. In addition to this provision, it was found that in these countries technical schools and colleges exist which cater for ‘technicians’ and in which considerable numbers of students attend full-time courses and reach standards roughly comparable to Higher National Certificate (H.N.C.)

Among other matters, the survey reveals that, in spite of the fact that Great Britain is the most industrialized country of those considered, in the relative numbers of engineers educated to degree level it shares with Austria and Belgium the lowest positions. The lack of qualified engineers to fill posts abroad is mentioned, a lack which, in the long-term, must lead to loss of trade. On the other hand, Britain's position with respect to higher degrees is relatively better.

Notwithstanding Britain's need for engineers, there are vacancies in some of her universities. The ‘bottle-neck’ in the supply is in the restricted numbers studying science in the sixth forms of schools; to make use of the increasing provision now being made for high-level engineering studies, these are the numbers most in need of attention.

Blade vibration, with the possibility of a failure, is one of the major factors controlling the reliability of axial-flow compressors. Self-excited vibration occurring at part load, when some blade rows are stalled, often causes most trouble. In this paper an investigation which has been undertaken into this phenomenon is described. The main objective has been to determine the major factors governing the vibration, and to establish, if possible, some design rules which would reduce the chances of a failure to an acceptable minimum.

The self-excited vibration of blades in cascade has been studied, and a simple theoretical correlation attempted. This has been supplemented by single-stage work and by multistage full-scale tests. Both flutter and stall cell excitation have been encountered, and are described. A semi-empirical design rule is suggested, and its interpretation in terms of the normal blade design parameters is included.

The objectives of this work were to examine the tube expanding process in relation to as many variables as possible and to determine whether there would be any significant ‘size effect’. For these investigations an apparatus has been constructed which enables detailed observations to be made of the behaviour of a specimen tube-plate joint during expanding.

A typical record is given showing how the strains and mandrel torque develop during expanding. No appreciable size effect was found on the three geometrically similar systems tested. It is shown that the residual strains are much greater on the back than on the front of the plate, leading to lack of parallelism in the joint face, and that the plastic-elastic interface can extend much farther into the plate than was previously thought possible.

Comparison is made between these experimental results and the predictions of a theory proposed by the authors, and it is concluded that higher seat pressures could be obtained if axial extrusion of the tube could be restricted. This finding was confirmed by axially compressing short lengths of tube into a plate, the axial compression causing the tubes to bulge and expand themselves into the plate seat.

In this paper a technique is described which is intended to assist in the preliminary stages of developing a high-intensity combustion chamber for an aircraft gas-turbine or ram-jet. Since the chief unknowns are aerodynamic rather than chemical, an air-flow model is made; the chemical reaction is then simulated by electric heaters distributed through the chamber. External controls regulate the heat input in accordance with the local temperature and the properties of the fuel which is to be simulated.

The apparatus used is a prototype intended to demonstrate the principle rather than to make predictions, but good agreement is found between predicted blow-out velocities of baffle-stabilized flames and experiments on these flames reported by other workers.

Tests are also reported on two-dimensional combustion chamber designs for burning pre-mixed fuel and air, the efficiency, space utilization, and pressure-drop performance being compared. It is shown by an example that separate injection of fuel to the combustion chamber greatly reduces the blow-out velocity and space utilization, but increases the combustion efficiency and the range of fuel-air ratios over which a flame can be maintained.

The analogue does not simulate atomization, heat loss, carbon formation, or gas-dynamic instability.

The mechanism of oil loss past pistons was investigated in a laboratory test rig in which a piston was both reciprocated and subjected to gas pressures. The investigation brought to light the following facts and it is believed that this is the first time that they have been demonstrated:

(1)

Oil control is a two-way and not a one-way problem. The only reason why the rate of oil consumption is reasonably small in most engines is that, although a large amount of oil flows towards the combustion chamber past the rings during part of the engine cycle, nearly all of it returns to the sump during the remainder of the cycle.

This paper describes an experimental study of the lubrication between a one-ring piston assembly and a cylinder. Instantaneous friction forces of the piston assembly were recorded by means of a special apparatus with a stationary piston and a reciprocating liner. Tests were carried out to determine the effects of viscosity, speed, and pressure on the friction, from which the oil film thickness under the ring was calculated. A suggested lubrication theory of piston rings is given, based on a balance of forces acting radially on the ring, leading to a theoretical formula for calculating the ring film thickness, which is in reasonably good agreement with the experimental results. Suggestions are made for the design of rings to give improved friction and heat transfer and to reduce cylinder wear, especially in the initial running-in period.

The historical background of electro-erosion technique is briefly outlined and the difference between spark and arc*** discharges is defined. The underlying principle of the relaxation-type spark circuit as employed in industrial machines is explained, and development trends are discussed. The various factors bearing upon the efficiency of spark-erosion operations are enumerated. The mechanical features of a typical spark-erosion machine are described, and the range of machining operations for which spark cutting machines can be designed, is outlined. Typical samples of work produced on a commercial unit are described and illustrated, and the properties of spark-machined surfaces are discussed.

Much theoretical and experimental work has been published on the flexure of pipe bends. Examination of the results to date show considerable differences between certain measured results and the predicted behaviour.

The theoretical works relate mainly to long radius bends and all make many simplifying assumptions.

This paper presents a more detailed theoretical study, for bending in the plane of the pipe bend. Examination of both typical and extreme cases and a comparison with the experimental evidence shows which of the various theoretical simplifications can be accepted for a given pipe bend.

It is concluded that although complete stress distributions calculated by previous theories may be seriously in error over particular ranges of the variables, the peak stresses and flexibilities are, by a combination of circumstances, unlikely to be more than 5-10 per cent in error if certain factors introduced in the more recent of these theories are used.

Manufacturing and other variations between nominally similar pipe bends, however, seem to preclude the possibility of predicting the behaviour of a particular bend to closer than ±20 per cent.

In the design of pipelines for high-temperature service, allowance has to be made for the thermal expansion of the heated pipe. One particular aspect of this problem is the use of bellows expansion joints which, particularly on board ship, can transmit the pipe movements through bulkheads whilst providing a watertight flexible anchorage.

An approximate theory has been developed for the compression of a bellows, the convolutions of which have a cross-section formed by circular arcs subtending any semi-angle α. Numerical results have been calculated for the two cases α = π/2 and α = 3π/4.

Experiments have been carried out on six bellows, four corrugated-pipe type α = π/2, one S-type α = 3π/4, and one flat-plate type which was not analysed theoretically. Deflexion and resistance strain-gauge readings were taken on each bellows, and reasonable agreement was found between the theoretical and experimental results for the five bellows in which these could be compared.

It has been found that for certain design conditions optimum relationships exist between bore, wall thickness, and radius of convolution for the maximum flexibility. Stress intensification and flexibility factors have been calculated to cover a range of bellows proportions.

The paper describes experimental work that has been carried out over a number of years to find an efficient rocket-nozzle shape that could be manufactured simply. Experiments have been conducted with nozzles generally of 1/2-inch diameter throat discharging air to atmosphere from reservoir pressures in the region of 900 lb. per sq. in. and the thrust reaction and discharge rate have been measured. The air flow within the nozzle and the issuing jet have been examined photographically. The apparatus used and the experimental techniques are fully described.

The investigation has determined the best design for simple nozzles of conical divergence and found these to have a thrust efficiency of some 96 per cent. Suitable entry radius and divergence angle are recommended and the effect of machining errors, of obstructions in and near the nozzle and of operating at incorrect pressure ratios have all been considered experimentally.

In the course of this study, a number of unusual designs has been considered. These include annular nozzles, a variable thrust-nozzle, and a nozzle designed to be mounted at the front of a rocket. These unconventional nozzles all have some special feature which makes them particularly suitable for certain requirements.

The paper gives data on all the nozzle-design details investigated and an attempt has been made to relate the observed thrust-losses in conical nozzles to a simple theory. Throughout the research and in presenting the results, the requirements and interests of the rocket-motor designer have been kept in view.

The measurement of residual stresses with particular reference to alloy steel forgings by a trepanning method and by Sachs method is discussed. The precautions necessary are investigated experimentally. The possibility of plastic yielding during the machining operations in the Sachs method is demonstrated and the effect of this on the residual stress distribution in water-quenched mild-steel cylinders is investigated.

The determination of residual stresses in an induction-hardened roll is given as an example of the use of some of the refinements described.

The paper describes an investigation to establish the mechanism by which sealing is achieved in the conventional synthetic rubber oil seal when used on a rotating shaft.

After demonstrating that the contact between the seal and the shaft cannot be dry contact—that there is in fact what appears to be a coherent film of oil between the sealing lip and the rotating shaft—further experiments are described to find out why the oil in the film does not flow out past the seal.

The conclusion is reached that there is a meniscus at the oil/air interface and that retention of the oil in the oil film is effected by the surface tension of the oil.

The main object has been to facilitate economic design of pipework for compressible flow; it being recollected that the cost of pipework in a given installation may not infrequently exceed the cost of compressor plant. It is found that the conclusion reached by Keenan and Neumann, namely, that compressible, subsonic flow in ‘smooth’ pipes is independent of Mach number and depends upon Reynolds number exactly as for incompressible flow, may be extended to commercial pipes of appreciable wall-surface roughness. While non-adiabatic flow is also examined, attention is mainly given to adiabatic flow; and various devices, tabular, graphical, and nomographical, are proposed to assist rapid estimation of such quantities as flow rate, pressure drop, maximum power transmitting capacity, etc.

Encouraging correlation is found to exist between directly measured wall-surface roughness, as represented by the British Standard centre-line average index, and roughness as expressed hydrodynamically by the equation of Colebrook and White. This points to the practicability of predicting the flow characteristics of large pipes, for which flow tests may be difficult until in situ, by surface measurement alone.

The frozen stress photo-elastic technique is used to study the stresses in four different shapes of full drumheads and in five drumheads with circular or elliptical manholes. Circumferential and meridional stresses on inside and outside surfaces are presented, and some of these are compared with stresses calculated from different thin shell theories. These theories were modified to be more realistic for thick shells by considering the pressure to act on the inside instead of the middle surface of the shell. The wall thickness of every drum was one-tenth of the mean diameter of the drum.

The effect of large elastic strains was studied by means of two identical models tested at different pressures. Calculations showed that the stresses were slightly decreased when Poisson's ratio was changed from 1/2 to 1/4. The effect of a reduction of the wall thickness of hemispherical heads was calculated and was found to be in good agreement with experimental results. The stress distribution in the walls of the shells was also determined for some critical sections.

The paper stresses the importance of water in the life of the community, the various factors governing the location and size of pumping stations, the magnitude and diversity of demand and the topography of the area of supply, all of which have a bearing on the type of machinery and the system of control to be employed. Trends from the past are traced from the slow-speed and mainly steam-driven plant of the nineteenth century, to modern high-speed installations, including progress in the design of pumps of improved efficiency and high-tension motors for surface duties and for submersible application. Reference is also made to new problems which have arisen, such as surge control, the limitations of the A.C. electric motor as a driving agent, and the increasing use of automatic and remote controls. The paper concludes with a few thoughts on the future.

This paper is concerned with the vibration of disks particularly the form known as the ‘stationary wave’ which can develop in a rotating disk by the application of a stationary axial force at the periphery. The forms of vibration involving n nodal diameters are considered, and phenomena associated with linear and non-linear free and forced vibration are discussed in detail. Thereafter, attention is focused on the behaviour of real disks which, owing to inevitable imperfection, possess two independent modes of vibration, and thus two natural frequencies, for each value of n. It is shown that the stationary wave is greatly influenced by the degree of imperfection present. Experimental studies with stationary and rotating disks are presented covering forced vibration in the linear and nonlinear zones. The results show that a non-linear stationary wave may exist in a rotating disk over a wide speed range depending on the magnitude of the applied force. As speed increases this wave finally collapses and in doing so becomes a travelling wave which accelerates slowly in the direction of disk rotation as its amplitude subsides. Experiments conducted with large artificial imperfection show that the stationary wave may be transformed into two modes of vibration which are fixed in position in the disk. These modes resonate separately at their respective frequencies and apparently suffer a high degree of aerodynamic damping due to rotation. The magnitude of disk vibration is thus greatly reduced by the introduction of imperfection. Short mathematical appendices are included which contain the main theoretical results.

Previous investigations of the vibrations of circular disks confined themselves to small amplitudes when it can be assumed that the strain energy of the disk is due to pure bending only. At large amplitudes this assumption ceases to be valid and the stretching of the middle surface has to be taken into consideration. As a result, the equations of motion become non-linear.

The investigation is concerned with the vibration of ‘real’ disks, that is, disks which contain small imperfections. It is shown that, in general, the imperfections eliminate the indeterminancy of the angular position of the radial nodal lines which is characteristic of perfect disks. For those modes which contain at least one radial nodal diameter, there are two fixed nodal configurations which possess slightly different natural frequencies. At small amplitudes these nodal configurations are normal modes of vibration which vibrate independently of each other. At large amplitudes, when the equations of motion become non-linear, these configurations become coupled. The coupling is unsymmetrical in the sense that the configuration with the higher natural frequency can vibrate on its own at all amplitudes. On the other hand, above a certain amplitude, the configuration with the smaller natural frequency cannot vibrate on its own since it also excites, by parametric excitation, the other configuration. Under such conditions the phase difference between the two configurations is fixed to 90 deg. and as a result the motion of the disk corresponds to a beating travelling wave.

The main functions of heavy-duty lubricating-oil additives are to control engine fouling, bearing corrosion, and wear of liners and piston rings. Alkalinity is desirable for the control of wear and is one of the major requirements for the avoidance of piston fouling when conventional organo-metallic additives are used. In a well-balanced oil, sufficient dispersive power and oxidation stability may be incorporated to ensure adequate piston cleanliness and freedom from bearing corrosion provided that the alkalinity level is satisfactory.

The alkalinity level falls during service, and for satisfactory performance with certain types of additive in common use it must be kept above a minimum value. For these additives equations are given which enable the variation of the alkalinity level with time in given circumstances to be predicted approximately. The most satisfactory arrangement is to use an oil containing sufficient alkalinity so that the concentration never falls below the critical value. The oil-change period is then determined by other considerations, for example, contamination with abrasives. If an oil of lower alkalinity-concentration is used, then the equations developed permit an approximate estimate of the oil-change period, determined solely from the aspect of additive effectiveness. The application of these results to engines with separate cylinder lubrication is discussed.

Thus oils, and, where appropriate, oil-change periods, may be selected on a rational basis instead of by trial and error.

In this paper an approximate method of analysis is developed to compare the performance of single-pump and split-pump schemes in the non-reheat regenerative steam cycle. The analytical result is shown to agree closely with figures obtained by detailed calculations based on the same standards of comparison of the two schemes as those used in the approximate analysis, although on an alternative basis of comparison the calculated difference between the performances of the two schemes is smaller. The study reveals, however, that on either basis of comparison the efficiency of the cycle is slightly greater for the split-pump arrangement. Detailed calculations for a typical reheat cycle show the same tendency. It is concluded that, on the score of both thermal efficiency and capital cost, the split-pump arrangement is to be preferred.

For the practical assessment of the operating behaviour of a multistand cold rolling mill, it is necessary to know how gauge, speed and interstand tensions are affected by screw and speed-setting changes.

This paper sets out the control equations governing the response of each stand to any combination of the external disturbances, that is, how the interstand thicknesses, tensions and final output change due to changes of ingoing gauge, coiler tensions, roll gap settings and roll speeds. The partial derivatives of the roll force, roll torque and forward slip, which enter as factors in the governing equations, are evaluated mathematically, and then expressed in nomographic form. Examples of the use of the nomographs are given.

Amongst the important matters investigated after the accident to a ‘Comet’ aircraft at Elba in 1954 and the recovery of the wreckage from the sea, was the severe damage which had been sustained by the turbine rotor hub-shafts.

Three of the four engines were recovered with the turbine rotor disks intact, though extensive cracking was discovered in the spigot recess radii of the hub-shaft flanges. In the case of the fourth engine, the turbine rotor disk was missing, through fracture of the hub-shaft flange.

A careful step-by-step examination of all the evidence enabled it to be stated quite definitely that the damage sustained by the engine hub-shaft assemblies was a consequence of abnormally severe gyroscopic bending moments imposed during disintegration of the aircraft.

Nevertheless, it was considered desirable to determine by practical tests the actual magnitude of the gyroscopic bending moment which the hub-shaft assembly could sustain and the manner in which fracture would occur.

The paper describes the special gyroscopic test-rig constructed for this purpose and discusses the results obtained. The results of supplementary investigations of the bending fatigue behaviour of hub-shaft assemblies and plain and notched laboratory specimens, with special reference to the high-stress low-endurance portion of the fatigue diagram, usually called the ‘high-level’ fatigue region, are also included.

The performance of a complete journal bearing is obtained for a vertical cyclic load of the form

It has already been established that the ratio of the rate of load application to that of journal rotation (ω₁/ω) is a prime factor in the bearing behaviour, and for the case where P_n = 0, values of this ratio slightly less than 0·5 were found to give rise to critical changes in the bearing performance depending on the ratio P₁/P₀.

Present test results show that the superposition of the harmonic load component P_n would, in general, bring some changes to the performance characteristics at the ω₁/ω value corresponding to this harmonic, that is, at nω₁/ω ⋍ 0·5, and some simultaneous related changes (in the opposite sense) at the ω₁/ω value corresponding to the fundamental component P₁, that is, at ω₁/ω ⋍ 0·5, the extent of these changes being a function of the amplitude ratio P_n/P₁.

The phenomenon is explained in the light of the theory of vibrations, and the analysis is extended to include the case of a variable load on a uniformly rotating journal.

In this investigation of the problem of unsteady-state heat transfer to and from gas, experiments have been carried out with the flow of air through a passage of circular cross-section. Heat transfer takes place within a single vertical tube, around which is an annular guard space. Because of the magnitude of heat losses at lower values, the investigation is confined to values of Reynolds number between 1,000 and 2,500. Within this range, at moderate temperature differences, the processes of heating and cooling of gases reveal similar heat-transfer properties. When the tube wall-temperature is either constant or has a uniform temperature gradient, it is shown that the Nusselt number is in agreement with that predicted for steady-state heat transfer for the same wall-temperature distribution.

The investigation deals with single-cycle operation referred to as ‘single blow’, in which the supply is either hot or cold, and with cyclic operation as a parallel flow regenerator. Heat-transfer coefficients obtained from the cyclic operation tests are of the same order as those from the single-blow tests.

An analytical expression for the prediction of outlet temperatures, assuming a varying supply inlet-temperature and non-uniform initial wall-temperature, is presented and this is used in the calculation of the single-blow results.

An investigation has been made of the effect of heating to, and cooling from, a temperature above the critical range on the mechanical properties of an alloy steel to specification B.S. En 29.

It has been shown that, on rapid cooling from a temperature above the critical range, the steel possessed poor mechanical properties (low yield and tensile strengths) at all temperatures down to the commencement of martensite formation at about 300 deg. C. (572 deg. F.). Below this temperature, there was a sudden increase in yield and tensile strengths, accompanied by a marked decrease in ductility.

The relation between these mechanical properties and the incidence of cracking after repeated heating and rapid cooling is briefly discussed.

In an attempt to establish the conditions necessary to maintain ‘tightness’ in narrow-faced, bolted, flanged joints, experiments were carried out on standard 300 lb. per sq. in., 900 deg. F. screwed-on and welded-on flanges fitted to 2 1/2-inch bore pipes. ‘Klingerit’, rubber-bonded asbestos, gaskets of various dimensions were tested. Stresses in the bolts were measured by means of electrical resistance strain-gauges. The pressure fluid used was water.

The screwed-on flanges were later turned down to approximately half their original thickness to determine the effect of flange thickness on leakage pressure.

Photo-elastic studies were carried out to determine the distribution of axial stress in the gasket due to bolting up.

The following points were established:

(1a)

The gasket factor, m, of compressed asbestos jointing increases practically linearly with gasket thickness. This is the opposite of the trend of the values given in the A.S.M.E. Unifired Pressure Vessel Code of 1952 (A.S.M.E. 1952).

The object of this paper is to illustrate by means of a series of tests made on two steels, the essential differences between testing under constant load, constant total strain, and a commonly used ‘weighbar’ method that is intermediate between these two. It shows that the constant strain results do not entirely support the strain-hardening and time-hardening theories suggested by other authors. An empirical relationship, which gives reasonable correlation in the ranges of stress, temperature, and time examined, is given as an aid to analysing the results, but no correlation of this with a theoretical approach has been found, though it is hoped that it will contribute to the eventual solution of this problem.

Suggestions are finally made as to how relaxation data may be used for design purposes with reference particularly to the choice of an initial stress and the value of retightening.

The paper contains an analysis of the stress distribution in bolted flanged joints of pressure vessels, and presents a design procedure for such joints based on the analysis. Existing bases of design are unsatisfactory in that they are derived from treatments which assume elastic conditions to apply, and so lead to fictitiously high stresses. These stresses imply that parts of the joint assembly yield plastically. The analysis in the paper takes account of such plastic behaviour.

The design procedure includes methods for determining the critical dimensions of a joint, including the number and size of bolts. It is shown that there is an approximate limit of 25,000 on the product of design pressure (lb. per sq. in.) and inside diameter of flange (inches) within which it is possible to design flanged joints with flat gaskets.

A formula is derived whereby a preliminary estimate of the flange thickness may be readily obtained. Other formulae are given which enable closer approximations to be made of the thickness required depending upon the extent of the influence of plastic strain. Examples are given to illustrate the design procedure.

In the present paper the static bending of pre-twisted cantilever blading is examined. The blading is pre-twisted linearly about the centroid of its cross-section to a maximum angle of π/2 radians and is considered to be mounted encastré at the root. The behaviour of such blading, particularly when bending under a distributed load, is of considerable practical importance.

By the application of variational calculus, static equilibrium equations are derived from expressions for the total potential energy of blades subject to either concentrated or uniformly distributed bending loads. Solution of the equilibrium equations yields expressions for the static deflexions. Over a range of pre-twist angles between 0 and π/2 radians deflexions are calculated for blades of (1) narrow rectangular cross-section when subjected to either method of loading, (2) narrow aerofoil cross-section when subjected to a uniformly distributed load.

Sets of steel cantilever blades of narrow rectangular cross-section are loaded laterally at their free ends and the deflexions determined by measurement. The experimental values of deflexion compare reasonably with the relevant calculated ones. Small discrepancies between the two sets of results are not yet fully explained and further investigation of the problem is under consideration.

For blades where the pre-twist angles do not exceed π/2 radians, the agreement obtained between the two sets of deflexions for the concentrated load system is such that the validity of the theory, when it is applied to other loading systems, can safely be assumed without further recourse to experiment.

This paper presents the results of experimental work carried out recently to determine the effects on the discharge coefficient of various degrees of pipe roughness adjacent to and at different distances from an orifice plate. Experiments were carried out for air flow in 12-, 6-, and 3-inch pipes and water flow in 3-inch pipes.

Downstream, severe incrustation has no significant effect. Upstream, the effects vary with degree of roughness, pipe diameter, m value, and Reynolds number. For an m value of 0·5 and severe conditions of roughness, the combined effects of roughness and pipe diminution produce disturbance factors of the order of 1·40, 1·17, and 1·08 respectively for 3-, 6-, and 12-inch pipes. A length of two diameters of rough pipe immediately upstream from an orifice plate gives an effect close to that which would be obtained for a very long rough pipe. It has been found possible to extrapolate the results to very large pipes.

One of the most important findings is that cleaning a rough upstream pipe adjacent to an orifice plate for a relatively short distance reduces errors which may be otherwise very considerable to within known small limits. A table detailing the extent of such cleaning for various pipe sizes, mvalues, and degrees of roughness is given.

It is recommended that, where reasonable accuracy is required in the flow measurement of dirty fluids, installations should be designed for easy periodic inspection and cleaning of the upstream pipe adjacent to the orifice plate.

A machine has been developed for the investigation of sleeve bearings operating in the transition range between full fluid and boundary lubrication. Results of some tests are given.

A series of bearings manufactured from two different materials and having various clearance and length diameter ratios has been tested on journals having various types of surface finish, using the machine and experimental technique described in Part I. The investigation was concerned mainly with the changes in performance which occur during running-in, and with the ultimate performance which is obtained, under conditions of thin film lubrication. Some tests have been made on the effect of a solid boundary lubricant (molybdenum disulphide).

A method is described in which flow nozzles were used for investigating steam-water mixtures discharging horizontally from geothermal bores. British Standard and 25-deg. approach nozzles were modified, so that the density in a small column, with the throat diameter as axis, could be estimated by measuring the absorption of beta rays, in their passage diametrically through the mixture. A single density determination is shown to be sufficient to estimate the dryness fraction. If the upstream pressure is also noted then the mass output can be calculated using an empirical equation similar in form to the single-phase mass-discharge equation derived from Bernoulli's principle. For the dryness fraction one calibration curve suffices for 25-deg. approach nozzles of various diameters. By nozzle rotation the angular distribution of the water was measured and hence its cross-sectional area.