bluuebunny/crossref_metadata_2025 huggingface dataset:
Gear-Tooth Stresses at High Speed
Authors: Tuplin W. A.
Published: October 2007

If the maximum stress in a gear tooth is less than the fatigue limit for the material, the tooth should not fail even after indefinitely prolonged running. Fatigue data collected in the conventional way suggest that the number of stress cycles required to cause failure of a given material under any particular stress is independent of the time-rate of repetition of stress. It should therefore be permissible to stress any gear, regardless of its speed, up to the fatigue limit for its material, although this suggestion may need modification because of the difference between the impulsive nature of the application of load to a gear, and the more gradual fluctuation of stress in a fatigue-test specimen of the Wöhler type.

Where high-speed gears have failed under stresses apparently lower than the fatigue limit, it becomes necessary to consider whether the actual stress was as low as had been supposed. Errors of pitch and profile in gear teeth may cause actual stresses to be higher than nominal stresses by an amount that increases with speed in any particular installation, up to a limit that would not be exceeded even at infinite speed. The nominal permissible stress (corresponding to the mean transmitted torque) should therefore take account of probable errors in the teeth.

High tooth-loads may also be induced by running a geared system in a condition approaching that of resonance with some type of vibration. In general, this danger is more likely in high-speed installations than in others, and it is not always wise to follow the usual practice of ignoring its possibility.
The Variation of the Coefficient of Static Friction with the Rate of Application of the Tangential Force
Authors: Parker R. C. , Farnworth W. , Milne R.
Published: October 2007

The coefficient of static friction has been measured for a number of different materials under impact conditions. An analysis of the conditions of impact, derived from collision between solid bodies, and from a suitable hydraulic system, showed the latter to be the more convenient and equally effective method of applying tangential force. The method adopted consisted of feeding oil at a constant rate into an oil cylinder, the piston of which constituted the striking head. The friction members were so arranged that the struck member was in the form of a bar that was clamped between two massive plates. The normal force was applied hydraulically and the tangential force was measured by wire resistance strain-gauges.

The static friction was measured for rates of application of the axial force up to 103 tons per sec. Under dry conditions the friction increased with the rate of applied force, an effect more pronounced between a non-metal and a metal than between metals. Lubrication with oil diminished the variation of friction with rate of application of force for all combinations of materials tested. The magnitude of this effect was sufficient to explain a type of failure commonly encountered with safety clutches, and similar mechanical devices.
The Regenerative Heat Exchanger for Gas-turbine Power-plant
Authors: Cox M. , Stevens R. K. P.
Published: October 2007

The desirability of using a heat exchanger to improve the efficiency of gas-turbine plant of moderate gas temperatures and pressure-ratios has often to be considered in relation to the large space requirement and cost involved in the installation of a unit of the normal tubular type. This lecture shows that the possibilities of reducing the- bulk of the heat exchanger lie mainly in the use of passages of small diameter and length. The potentialities of the regenerative type of heat exchanger, and the requirements which have to be met if a practical unit working on this principle is to be achieved, are examined. It is thought that the most practical form of regenerator is one employing a rotating heat-exchanging element, and a stationary seal system to prevent the loss of high-pressure air; the relative merits of units of this type are discussed. The main problem to be overcome is that of developing an efficient and reliable sealing system. Work at the National Gas Turbine Establishment on a rotary-disk regenerator to study the sealing and general mechanical problems is described, together with the results of tests made on a smaller unit built to determine the heat-transfer properties of heat-exchanging elements of the flame-trap type.
Overall and Stage Characteristics of Axial-flow Compressors
Authors: Howell A. R. , Bonham R. P.
Published: October 2007

Axial compressors, particularly near design conditions are, on the whole, amenable to analytical treatment, and usually a good estimate of their performance can be made before they are run. Away from the design points, the performances are conveniently thought of in terms of the overall characteristics of pressure-rises, temperature-rises, and efficiencies plotted against mass-flows. For these performance estimations the aerodynamicists must have knowledge of the stage and overall characteristics of previous compressors and of methods of predicting such characteristics. Obtaining the overall characteristics from a stage-by-stage calculation is a lengthy process, but, fortunately, simplified methods can often be used.

In this lecture we have indicated some of the methods that are employed to obtain and predict the overall characteristics and their associated stage characteristics. Reference is made to test-results from various National Gas Turbine Establishment research compressors, one of which uses water instead of air as the working fluid, and also to published information on other compressors. The importance of blade and test errors on performance and analysis work is also emphasized. In our simplified method of analysis and prediction of overall characteristics we have reduced the individual overall characteristics at each speed to what are, in effect, mean stage characteristics plotted relative to their maximum-efficiency-point conditions. Then the maximum-efficiency-point conditions at the different speeds are plotted and considered separately.
Form Grinding by Mechanical and Optical Methods
Authors: Cooke E. A.
Published: October 2007

Methods of producing profile tools and gauges remained for many years particularly conservative and often expensive in the use of highly skilled toolroom labour.

Up to comparatively recent times it was not uncommon to find high-class machine tools, such as jig boring machines, applied to the task of marking out centres of radii and so on, because they embody accurate means of measurement.

The early introductions of special-purpose machines for this work were mainly continental, and the advantages normally to be expected from the use of such machines were not altogether realized as the result of designs based inherently upon the use of master copy.

Later, machines were developed intended to be independent of copy to a very large extent, and this was facilitated by a trend of component design based upon the use of geometric and definable shapes wherever possible.

The application of optics to this class of machine, mainly in the form of microscopes or projection systems, is now fairly common, and in its application to engineering the optical projector perhaps reaches its highest standard of definition and accuracy of reproduction. The incorporation of optical and electrical measuring devices has also helped greatly in providing an accurate and versatile machine tool.

The object of the paper is to reveal aspects of design more peculiar to this type of machine, particularly the association of optics and mechanical linkages, and is therefore mainly confined to the copying and generating mechanisms. It also indicates the development trend of this class of design.

Methods of forming and truing the grinding wheel are not considered.
On the Solution of Beam-on-elastic-foundation Problems by Means of a Mechanical Analogue
Authors: Wells A. A.
Published: October 2007

The equation d4 y/ dx4- f(x)y + g(x) = 0 may be solved by means of the differential analyser, but only straightforwardly when the four boundary conditions are specified at one point. When the equation is associated with beams on elastic foundations, or elastic shells, the boundary conditions are more often specified at two points, and a quicker method of solution is desirable. In the analogue, direct use is made of the beam in the form of an elastic wire, supported at intervals in cradles on which weights may be made to simulate the terms f(x)y and g(x); the wire takes up a transversely deflected form which may be measured, and boundary conditions are imposed where they are required.

A specific problem is examined and the results are shown to agree reasonably with the solution by calculation. A disadvantage when d2 y/dx2 is required is the inaccuracy inherent in differentiating by finite differences, but for engineering calculations the simplicity of the method may have its advantages.

The solution of a typical pressure-vessel problem, by means of the analogue, is described.
Some Experiments on Tapping
Authors: Johnson E.
Published: October 2007

The research was undertaken to investigate tap breakage and the production of accurate threads. Descriptions are given of the machine and the test method used. The threads tapped were inspected by taking plaster casts and profiles of the casts were projected to a × 50 magnification. These revealed serious errors in thread form, and details are given of a method devised for axial loading of the tap which resulted in the production of almost perfect threads. For precision tapping, it is recommended that the tap is held rigidly. Mention is made of the effect of swarf building up in the flutes and its influence on torque value; the effects of taper, number of flutes, and surface finish of the tap; the speed of tapping and lubrication. Taps of diameters , and -inch B.S.F. and B.S.W., having three and four flutes and a wide range of different metals, were used.
Screws and Screwing
Authors: Eatough C.
Published: October 2007

The paper describes the various commercial methods of producing screw threads by cutting, rolling, grinding, and milling. The operating principles on which the several processes depend are dealt with and their advantages and limitations are discussed.

A workshop method of determining the torque required for tapping and for threading is described, and a chart based on the results gives figures suitable for determining the power of machines to undertake the tapping or screwing of a wide range of work.

A mathematical treatment of the clearance between the flanks of a tool and a screw thread is given. This permits the investigation of clearances at any point on the tool profile or flank, and enables relief and tilt angles to be chosen to suit various conditions of lead, thread profile, and diameter for both internal and external threads. For design purposes, a simple formula is available which gives clearance angles in relation to the portions of the tools most subject to interference.
Mechanical Handling
Authors: Roebuck A. , Carnegie H. S. , Taylor E. G.
Published: October 2007

The authors of this paper were members of the team appointed by the Anglo-American Council on Productivity to study and report on materials handling in industry in the United States of America.

The purpose of the paper is to focus attention on certain aspects of the report, “Materials Handling in Industry”, which contains the findings, conclusions, and recommendations of the team, with particular reference to the application of mechanical handling inside factories. The importance and advantages of applying modern techniques in materials handling and also the need for more extensive use of known methods and equipment already available in Britain, are points particularly stressed by the authors. The opinion is expressed that better materials handling offers a greater opportunity to cut production costs and to increase productivity than any other single factor.

The paper enlarges on some of the conclusions listed in the report, such as those relating to applications of methods and newer techniques, periodic reviews, layout and design, team work, and use of small power tools.
On the Calculation of Forces in Power-Shovels
Authors: Jenike A. W.
Published: October 2007

A power-shovel is essentially a revolving crane mounted on a self-propelled carriage and equipped with a digging device. The paper describes the process of calculation of forces for the stage of digging, that is, for the time when the dipper is in contact with the excavated face, and the influence of forces arising during slewing on the boom and the handle.

It is shown that the maximum values of the main forces acting in the shovel are governed by the maximum values of the bail-pull and of the braking torque of the crowd-motion. In view of the fact that the handle and boom form a toggle arrangement, the induced forces will reach destructive values unless the governing forces are controlled.

Equations relating the forces are established and, as an example, a cu. yd. power-shovel, weighing 17·3 tons is analysed. The main forces are evaluated and presented graphically for the area of action of the dipper after which the critical loading conditions are specified.
The Training of Craftsmen
Authors: Loxham John
Published: October 2007

The author outlines a plan to secure for each engineering apprentice the best possible development of his natural aptitudes and abilities as a potential craftsman, technician, or fully trained technologist. This plan calls for the close co-operation of all the agencies concerned with education and with the organization of labour, including the responsible ministries, universities and technical colleges, professional institutions, local education authorities, and, perhaps most of all, the employer.

Emphasis is given to the best possible provision of facilities, both in works and in colleges, for those who show capacity for training as highly skilled craftsmen. The importance of the contribution of such men to the national economy is examined, and regret expressed at the relatively inadequate provision made, both in works and in colleges, for the training of those whose primary interests are in actual manufacture.

The bearing of recent changes in legislation affecting the structure of secondary education, and the availability of technical courses in their relationship to the age, quality, and outlook of recruits entering the engineering industry, is discussed in some detail. The possibility of setting up new national awards in craftsmanship, with the co-operation of all the agencies concerned, is foreshadowed.
Steam Piping for High Pressures and High Temperatures
Authors: Bailey R. W.
Published: October 2007

Consideration of the following matters is made important by recent progress to high operating steam pressures and temperatures: the changing and more favourable distribution of stress in a pipe, the accompanying creep, and their application to the rational and economical design of steam piping; the determination of permissible working stress; differences in American and British procedures and consequent differences in stress magnitudes; the influence of operating fluctuations of pressure and temperature and the choice of a design temperature at rated pressure to provide for them; tentative considerations of behaviour of ferritic and austenitic steels; the action of creep at operating pressure and temperature in reducing and removing the initial thermal expansion loading of a pipe-line, and in imposing it fully when cold.

In these connexions some consideration should be paid to bolted, or otherwise removable, joints at terminal or other special positions; the problem of making a joint between ferritic and austenitic steel piping and components; the factors of materials and corrosion; promised adequacy of existing ferritic steels for present requirements, and application of the principles operative at very high temperatures to piping for less advanced conditions, and economy arising therefrom.
Creep under Complex Stress Systems at Elevated Temperatures
Authors: Johnson A. E.
Published: October 2007

During the last few years a programme of creep tests under general stress systems at elevated temperatures has been carried out at the National Physical Laboratory (N.P.L.), using four metallic alloys (a cast 0.17 per cent carbon steel, an aluminium alloy—RR. 59, a magnesium alloy containing 2 per cent aluminium, and a nickel-chromium alloy—Nimonic 75) chosen as representative of basic groups of materials used in practice, and tested at temperatures lying within their normal working range.

In this paper an effort is made at a general comparison of the complex stress creep characteristics of the materials, and such generalizations as appeared possible.

Appendices are provided, dealing respectively with: experimental data for one of the materials (data for the others having been published elsewhere); the effect of hydrostatic stress on complex stress creep, and specific examples of application of the data.
Problems in Design and Research on Condensers of Vapours and Vapour Mixtures
Authors: Colburn Allan P.
Published: October 2007

The theoretical background is outlined for condensation of pure and mixed vapours in conditions of a film-type condensate. The effect of vapour velocity is important for both pure vapours and those mixed with non-condensable gases. On the basis of the fundamental mechanism of condensation involved, approximation procedures are developed which are particularly useful for designers who wish to have quick methods for use in estimating and rough checking.

It is concluded that there is great need at present for testing theoretical and approximate methods against full-scale performance data.
The Automatic Hydraulic Ram
Authors: Krol J.
Published: October 2007

After describing the operation of a typical hydraulic ram installation, the paper reviews the fundamentals of the water hammer as a prerequisite to the proper understanding of the limitations of this hydraulic machine. The historical development is discussed in some detail with the object of ascertaining what research work remained to be done. The author presents his own theory based on the application of general laws of mechanics to the study of a specially designed experimental hydraulic ram. By means of a theory developed, which agrees satisfactorily with experiment, it is possible to forecast the behaviour of any automatic hydraulic ram, provided that the following four properties of a given installation have been determined separately by experiment: ( a) loss of head in the drive pipe; ( b) loss of head due to the impulse valve; ( c) drag coefficient of the impulse valve; and ( d) head lost during the period of retardation.
Friction Losses in Turbulent Pipe-flow
Authors: Prosser L. E. , Worster R. C. , Bonnington S. T.
Published: October 2007

Significant developments in the theory of turbulent flow in smooth and rough pipes are reviewed to establish a rational basis for the commonly accepted logarithmic laws for pipe friction. The Prandtl (1932)‡ smooth-pipe law, , where f is the friction coefficient in the formula , agrees with measured results on smooth pipes up to Reynolds numbers of at least 3 × 106. With rough pipe walls and sufficiently high Reynolds numbers, viscosity (and hence Reynolds number) ceases to have any direct effect and the friction coefficient depends on wall roughness and pipe size only. Almost all practical cases of water flow in commercial pipes lie between these two extremes of completely smooth and fully rough conditions, where the friction coefficient varies with both Reynolds number and roughness.

Exponential flow formulae of the Manning type— V = *** Am1xiy—can be rearranged into a more rational form f = B( Re) p( k/d) q*** relating f to Reynolds number and relative roughness for a given class of pipe carrying a fluid of given viscosity. A detailed study is made of published test data on wrought-iron and steel pipes which generally operate in the transition zone, and an exponential formula is derived which agrees with these results. This is found to be similar to that given by Blair for this class of pipe.

The relative merits of these exponential formulae, and of the Colebrook-White transition function, are discussed and it is concluded that, for most practical cases of water flow in pipes, the simple formulae are no less reliable.
Load Distribution in Riveted and Spot-welded Joints
Authors: Williams D.
Published: October 2007

It is known that a spot weld is a much more rigid connexion between two sheets than a rivet, and that this is likely to have some bearing on the relative strengths of the two types of joint. A recent test has emphasized this point. A spot-welded box, identical with a riveted box except that spot welds replaced rivets, failed at about two-thirds of tie failing load of the riveted box in spite of the fact that the shear strength of an individual spot weld was nearly twice that of a rivet, as determined by tests.

In this paper the problem is examined theoretically on the basis of experimentally obtained stress-strain curves for riveted and spot-welded joints in shear. The theoretical treatment takes account of the plastic, as well as the elastic, part of the stress-strain curves, and examples are given of the relative behaviour of the two types of joint in certain simple structural elements.

A multi-row lap joint is the first example chosen, and the second is a stringer reinforced panel in which there is appreciable shear-lag. In each example the riveted specimen gives the higher failing load (assuming the fastenings fail and not the connected members), although the experimental failing load of the individual rivet is less than half that of the spot weld. For lower loads, curves are shown which indicate the radical change that takes place in the distribution of shear among the rivets and welds, as more and more of them are loaded beyond their yield points. While such changes are of only incidental interest so far as the ultimate failing load of the structure is concerned, they are of paramount interest when assessing the life of the structure under repeated loading at loads that may be small compared with the ultimate load, for the distribution of shear among the fastenings is then clearly an important consideration.

The shear-lag case is of interest as showing how the difference between rivet and weld shear flexibility tends to be masked by that of the sheet panel connecting the booms and stringers. It is therefore a useful example for emphasizing that the character of the structure must be taken into account, as well as the individual properties of the fastenings, when comparing the likely behaviour of rivets and welds.
Cup-drawing from a Flat Blank: Part I. Experimental Investigation
Authors: Chung S. Y. , Swift H. W.
Published: October 2007

Part I gives an account of an experimental investigation of the forces, work and strains involved, and the conditions for successful drawing of a cylindrical shell from a flat circular blank. It is claimed that the results are sufficiently accurate to provide a basis of reference for theoretical treatments of cup-drawing, as well as an empirical basis of comparison between different drawing conditions.

The work was carried out in an experimental crank-press of 50 tons nominal capacity, and was based on a cup diameter of 4 inches. Blank thicknesses from 0·025 to 0·060 inch were used, and although most of the work was carried out on a low-carbon rimming steel, comparative tests were made with aluminium, brass, and copper, of different tempers.

The conditions examined included methods of blank-holding, drawing ratio, punch and die profile radii, punch-die clearance, and blank thickness.

Although this part has no theoretical pretensions, it includes a descriptive account of stresses and strains in the deep-drawing process, based on plastic theory.
Cavitation Mechanics and its Relation to the Design of Hydraulic Equipment
Authors: Knapp Robert T.
Published: October 2007

The objective of this lecture is to outline the various characteristics of the cavitation phenomenon and to point out in general how this knowledge may be used to alleviate and, in some cases, to eliminate the losses due to damage of materials and decrease in performance of hydraulic equipment. It is shown that difficulty with cavitation is encountered over the entire field of hydrodynamics but that, although the manifestations may appear to differ widely, they can usually be understood on the basis of present concepts of the mechanics of cavitation. It is found that such understanding usually brings with it suggestions of methods for lessening or eliminating the difficulty.
Considerations on Bogie Design, with Particular Reference to Electric Railways
Authors: Graff-Baker W. S.
Published: October 2007

An examination is made of the dynamic characteristics of wheel sets and bogies, and of the various forces which act upon a bogie under service conditions. The fundamentals of bogie design are considered, and particular mention is made of recent developments in methods of body suspension. Problems of frame construction, braking, and power transmission are also considered. The paper concludes with a survey of the development of bogie design on the railways of London Transport Executive and elsewhere, and a restatement of the basic problems in the relation of bogie to track.
The Marine Gas-turbine from the Viewpoint of an Aeronautical Engineer
Authors: Fletcher A. Holmes
Published: October 2007

In view of the intensive development of gas turbines for aeronautical purposes, the author advocates the adoption of aero-design techniques for the production of gas turbines for marine and stationary purposes. A review is made of the more obvious features of various typical aircraft turbines, and the conclusions are drawn that multiple combustion systems and single- or two-stage turbines should be employed with a considerable reduction in the mass of metal in the assembly as compared with extant stationary designs, in order to reduce transient temperature stressing.

A description is given of an experimental heat exchanger embodying the principles of light scantlings, symmetry of design, and purity of suspension.

A brief excursion into the performance calculations for a marine turbine leads to a recommendation to use a compound cycle of 8/1 overall compression ratio, with centrifugal compressors for robustness, and with a high combustion-temperature involving the use of air-cooled blading. A life of 10,000 hours appears to be within reach, which figure is considered to be adequate for merchant ship service. A compact arrangement is suggested for a turbine of this type giving 4,000 s.h.p. at an overall thermal efficiency of 30 per cent. The manoeuvring and reversing problems are to be overcome by the fitting of a variable-pitch propeller, but development work on this device is required to reduce its alleged tendency to greater losses as compared with the fixed-pitch type.
Mechanical Engineering around Bristol
Authors: Cooper A. B.
Published: October 2007

A general outline of the mechanical engineering activities of Bristol and the surrounding areas is used to illustrate the achievements resulting from local enterprise and development. Details of industrial techniques are not described.

The production of aircraft engines of world renown and the work of paper conversion, for which Bristol is one of the most important centres in Britain, are given major emphasis and reference is made to the manufacture of mechanical handling equipment, and brewing and paint-making machinery.
Explosions in Enclosed Crankcases of Reciprocating Engines: Their Cause, Effect, and Possible Remedy
Authors: Lamb John
Published: October 2007

In this paper is treated the important problem of crankcase explosion prevention in practice. After dealing with the cause of such explosions the author concludes that, whilst much can be done to minimize explosions, to prevent them altogether is not practicable. The merits of ventilation of crankcases are discussed and ways are suggested to prevent bearings running hot, while means to detect a temperature rise in inaccessible bearings and pistons are described.

Tests carried out with the object of preventing injury to personnel and damage to property in the event of an explosion are described. A relief valve which opens and closes instantly is described and illustrated. The danger of burning gases issuing from relief valves is discussed, and the experiments are described which resulted in the evolution of a simple but effective flame trap.

Relevant particulars are given of a Diesel engine in which two crankcase explosions took place, one before and one after a relief valve was fitted. The gas pressure in the crankcase when damage resulted is estimated and views are expressed regarding the relation of crankcase cubic contents to the area of relief devices.
The Recovery of Diamonds by Modern Mechanical Methods
Authors: Bone J.
Published: October 2007

The exceptional hardness of the diamond and its resistance to abrasion are becoming more widely appreciated throughout the industrial world and resulting in its increasing use in the manufacture of drills, drill crowns, crowning wheels, hardness indenters, lathe tools, nozzles, saws, wheel dressers, wire-drawing dies, and many other products.

The industrial diamond as distinct from the gem diamond is, broadly speaking, one that—on account of imperfections such as inclusions, spots, cracks, cuts, inferior crystal form, or dark colour—cannot be economically cut and utilized as a gem stone. The unit of weight for industrial diamonds, like that for the gem stone, is the metric carat; which is equivalent to 0.2 gramme. Approximately tons of diamonds a year, an amount corresponding to about 80 per cent by weight of the world's present annual output, is used in industry.

The increasing demand for industrial diamonds was responsible for the reopening of the mine in the Transvaal in which the modern mechanical plant described in this paper was installed.
The Flexural Vibrations of Thin Cylinders
Authors: Arnold R. N. , Warburton G. B.
Published: October 2007

The flexural vibrations of the walls of thin cylinders are considered. In this type of vibration many forms of nodal pattern may exist owing to the combination of circumferential and axial nodes. Theoretical expressions are developed for the natural frequencies of cylinders with freely-supported and fixed ends and a comparison is made with the frequencies obtained experimentally.

In practice, the ends of cylinders are subjected to a certain degree of fixing by end-plates, flanges, etc., and the natural frequencies thus lie between the corresponding values for freely-supported and fixed ends. To make possible the estimation of such frequencies, a method is devised in which an equivalent wavelength factor is used. This factor represents the wavelength of the freely-supported cylinder that would have the same frequency as the cylinder under consideration when vibrating in the same mode. The results of experimental investigations with various end thicknesses and flange dimensions are recorded, and from these the equivalent factors are derived.

Sets of curves calculated for cylinders with freely-supported ends and covering a range of cylinder thicknesses are given. From these it is possible to obtain close approximation to the frequencies of cylinders under other end conditions by the use of an appropriate factor. An example is given of frequency calculations for a large air-receiver for which two frequencies were identified by experiment.
How American Industry is Attacking the Problem of Materials Handling
Authors: Bright James R.
Published: October 2007

Materials handling is one of the fundamental activities of mankind, and the common denominator of all industry, yet it has been relatively neglected by engineers and managers generally. In the United States realization is growing that materials handling accounts for the largest single activity cost in much of manufacturing and distribution. Although many individuals are fully conscious of this, companies differ widely in this recognition and in the way they are trying to improve their materials handling activities.

The aims of this lecture are to clarify the major objectives of a materials handling programme; to show how progressive companies are organizing for materials handling; to describe the scope of the good materials handling programme; the type of individuals to be placed in charge; the authority and responsibilities to be delegated to them, and the ways in which these activities co-ordinate with, and contribute to, other aspects of the plant.

Techniques of analysing materials handling problems and the characteristics of basic materials handling devices are presented briefly.

Some fifteen significant trends in American materials handling practice will be discussed and briefly illustrated by case examples.
Mechanical Engineering Features of Nantgarw Colliery
Authors: Dash T. G. , Pettit J.
Published: October 2007

Nantgarw colliery is the subject of a major reconstruction scheme, the details of which are of interest to mechanical engineers. Many of the major features including the shafts, winding engines, air compressors, mine-car handling equipment, and stowage material preparation plant are outlined in this paper. Because of the necessity to wind from more than one level in the pit, the shafts have equipment which is a departure from the conventional types in use in Britain.

The method of mining to be used is known as the “Horizon” system, well favoured on the Continent for steeply inclined seams. The chief feature of the system is that horizontal roadways are driven to the seams at convenient vertical distances apart.

The use of compressed-air power is mentioned, together with reasons for the choice of the air- compressors installed. The system of transporting coal and materials within the colliery is dealt with at some length, because of its originality and its improvement over the systems in being at the older collieries.

A fairly full description has been given of the shale preparation plant for stowage material for underground use. This is the first plant of such a size to be designed in Britain, and it has been developed from experience gained in smaller units built at nearby collieries.
Principles and Practice Governing Interchangeability and the Specification of Manufacturing Limits of Size, as Influenced by Statistical Considerations
Authors: Adams G. C. R.N.
Published: October 2007

This paper begins with a general summary of the problem of interpreting interchangeability and a limit of size; the general nature of a fit and of the limits of size which determine it are briefly examined. Some statistical problems of assembly and inspection and their effects on interchangeability and on the practical interpretation of a limit of size are investigated. The standard of measurement is considered in some detail as defining gauge tolerances and errors of measurement, and as giving guidance in relation to certain varying degrees of interchangeability that have been shown to exist. The effect of these arguments on the standard of limits and fits is discussed and certain practical pitfalls in the statistical arguments are briefly examined. Low degrees of interchangeability are discussed and also interchangeability in relation to complex forms, position, and angular dimension. It is shown how the various degrees of interchangeability can be indicated by means of suitable provisions in the standard of drawing practice. Finally, the general attitude of mind to design, which prompts solutions of the type suggested, is set out with special emphasis on the matters discussed.
Developments in Steel Castings in the Heavy Power Plant Industry
Authors: Buckley F.
Published: October 2007

Though the application of steel castings in the field of the prime mover is selected as a basis for treatment, the opportunity is first taken of mentioning developments inside the foundry that appertain to manufacture and inspection. The trend towards more stringent service conditions has augmented the responsibility of the foundry for the production of castings free from defects. There are indications that the designer and user of castings can with advantage pursue and develop the tendency to break down designs into relatively simple constructions that can be fabricated together at a later stage, and examples of this type of construction are given. Where this trend is impracticable, a strong case can be made for the concentration of allied types of work in relatively few foundries.

Mention is made of the trend of research as applied to steel castings, and the lasting importance of methods departments is stressed.
The Athlone Fellowship Scheme for the Practical Training in Industry of Canadian Engineering Graduates in Great Britain
Authors: Abbott W.
Published: October 2007

This scheme, now in its third year of operation, is designed to bring to Great Britain every year thirty-eight Canadian graduates in engineering for post-graduate studies.

The Fellowships have a duration of two years and are tenable in industry, in universities, or partly in each of these.

The author has been connected with the scheme from its inception; he assists in the selection of the graduates in Canada and arranges for their location and training in the United Kingdom. The paper describes in some detail the origin, purpose, and operation of the scheme and raises many issues of interest and importance.

The author also gives summaries of the reactions of Athlone Fellows who are now receiving postgraduate training in Great Britain. The purpose of the paper is twofold: to give information concerning a new and important system of Fellowships, and to evoke constructive criticism from professional engineers of its objects and operation.
The Solution of Transient Heat-flow Problems by Analogous Electrical Networks
Authors: Lawson D. I. , McGuire J. H.
Published: October 2007

The design of a machine for solving heat-conduction problems by their electrical analogy with the flow of current in series-resistance, shunt-capacity, networks, is described in this paper. Consideration is given to the representation of cooling by radiation and convection, and the detailed design of the circuits is discussed.
Formulation of “Stability Equations” and Derivation of New Constructions with Complete Systems of Design-formulae for Variable-speed Control Mechanisms
Authors: Frenkel M. S.
Published: October 2007

Requirements for stability are formulated mathematically and, through the “transformatory operations of mathematics”, yield a series of “stability equations” of ascending order which are generally applicable, for example to control mechanisms, electronics†, nuclear physics, etc. From these stability equations, the equation of the stable characteristic curve of a governor, and the differential equations of the oscillations of a governor-engine system, are derived. It emerges that the first part of the new oscillatory equation is identical with the whole of the differential equation in the literature to date (unchanged since Maxwell 1868)‡, while the important second part, which consists of terms of the same order of magnitude as the first part and which is the only one containing the equation of the stable characteristic curve, is lacking in literature.

The stability equations classify all possible constructions of variable-speed governor according to “order of stability”, which signifies important operating properties. This classification accounts for the known shortcomings of conventional types.

The stability equations, combined with the mathematical formulation of practical requirements (speed-adjustment with only one actuating motion, etc.), lead to new basic types of variable-speed governor, with complete systems of design equations. In addition to determining all unknown dimensions, this set of equations is important because it derives constructions of which the complexity increases with order of stability and, furthermore, a simple construction which provides any required high order of stability with the minimum number of adjustable components.
An Experimental Single-stage Air-cooled Turbine: Part I. Design of the Turbine and Manufacture of Some Experimental Internally Cooled Nozzles and Blades
Authors: Reeman J. , Buswell R. W. A.
Published: October 2007

To facilitate future development of the cooled gas-turbine more test information is needed on the effectiveness of cooling in an actual turbine operating at high gas-temperatures. Part I of this paper deals with some design aspects of a single-stage experimental turbine built to enable an experimental investigation to be carried out on the air cooling of nozzles and blades.

The turbine, built for operation at high gas-temperatures, was fitted with internally air-cooled blades having a large number of small cooling passages running the whole length of the blades.

A description is given of the pressed powder technique used to introduce the small passages in blocks of heat resisting material from which the blades could be machined.

Mention is made of some of the difficulties encountered in this method of manufacture and also of the need for careful consideration of suitable methods of disposal of the cooling air when internally cooled nozzles and blades of this form are used.
A Note on the Theory of Rolling with Tensions
Authors: Bland D. R. , Sims R. B.
Published: October 2007

In this note is suggested a modification to overcome the difficulty met in the application of Bland and Ford's simplified theory of strip rolling to passes where heavy back tensions are applied.

An equation for the roll force is evolved and compared with those of Orowan and of Bland and Ford. Experimental and calculated values of roll force given show an accuracy to within 10 per cent.
An Investigation of Small Helical Torsion Springs
Authors: Berry W. R.
Published: October 2007

The object of the investigation was to provide easily handled data for the design of helical torsion springs from round patented plain carbon spring-steel wire. For this purpose, the validity of the curvature correction to the stress formula was investigated and the effects of variations in low-temperature heat treatment and wire size were explored.

It was found that the theoretically derived curvature correction for maximum stress (stress at intrados) was the dominating feature in fully heat-treated springs under all conditions, and for patented wire springs when the maximum stress was tensile. In patented wire springs, however, when the maximum stress was compressive it was found that, although with springs of small index the maximum stress was still the dominant feature, with those of large index yielding was due, not to the maximum compressive stress at the intrados, but to the smaller tensile stress at the extrados, and that a critical ratio existed where yielding occurred simultaneously at both extrados and intrados; a finding that has considerable practical value. It is suggested provisionally that the phenomenon may be due to the combined effect of the low-temperature heat treatment, which relieves textural stresses (present in the wire as the result of the drawing operation and the presence of cementite) and at the same time allows the strain-age-hardening effect to become evident.

Design charts are submitted incorporating the results of the above investigation.
The Transmission of Low-pressure Steam for Process Heating
Authors: Geneve L. F. C. A.
Published: October 2007

In this paper is shown how in the case of steam transmitted entirely for use in process heaters, it is the total heat energy that finally counts; and hence a pipe-line can be designed for a high pressure drop and a high velocity of flow, since the friction work and the kinetic energy will be reconverted into heat which is also available at the outlet of the pipe-line. The size and cost of the piping and lagging can therefore be kept low, and radiation losses will also be reduced.

In a long transmission, however, the very rapid increase of velocity towards the end of the pipe-line may cause the steam velocity to reach the “acoustic” value; and when this occurs a “choking” effect results in the discharge being lower than the expected value.

The method of design proposed is to calculate the size of pipe required so that the given length of pipe-line is an assumed fraction, say, 0.80 to 0.90 of this “choking” length. This ensures that the required discharge will be obtained with the minimum size of pipe, and with no danger of “choking”.

Simple formulae are derived with the help of the approximate Callendar expression for total heat, which is applicable with reasonable accuracy at low pressures; and a case is worked out for a combined power and process steam installation, which shows that the problem may have several solutions of equal heat utilization efficiency.
High-temperature Turbine Machinery for Marine Propulsion
Authors: Brown T. W. F.
Published: October 2007

The lecturer examines present practice in steam turbines for ship propulsion and describes some of the high-temperature marine installations in Great Britain and overseas. High-temperature land installations are considered and particular note is made of high-temperature high-pressure turbines used. Properties of materials available are given in Appendix I and are used in the main text of the lecture to determine the upper limit of temperature to be explored. Reheating by steam, gas, and liquid metal, are mentioned, and the latter is recommended. Temperatures are then examined at various pressure levels up to 1,500 deg. F. without reheat and with up to two stages of reheat. The maximum gains are assessed and the possible type of future marine propulsion-turbine is discussed. Some of the problems of uncooled gas turbines are described in particular relation to the Pametrada 3,500 s.h.p. unit. The possibility of cooled gas turbines is discussed and calculations are made as to the efficiency attainable in relation to cooling at various temperatures. The results are contrasted with those possible with high-temperature steam-turbine machinery. The cooled gas turbine would appear to have the greater potentiality for improvement. The argument is summarized by stating that the alloy materials required for high-temperature operation amount to under 2 per cent of the ‘steam up’ weight, but that the fuel used during the lifetime of the ship is 25,000 per cent of this weight.