Proceedings of the Institution of Mechanical Engineers

During the past ten years extensive developments have been made in engineering workshop practice and carbide tools have been increasingly employed to expedite production. Under certain conditions these tools can be operated at speeds considerably in excess of those possible with the most modern high-speed steel tools. Sufficient experience is available to show that for the satisfactory working of carbide tools it is necessary to ensure uniform cutting speeds, rigidity of the work and machine, together with freedom from chatter or vibration. High speeds and fine feeds lend themselves to the establishment of these conditions. But the economic range of utility of these tools has been somewhat limited and ill-defined, and the Cutting Tools Research Committee was of the opinion that more complete information should be made available for members. A Carbide Tools Subcommittee was, therefore, appointed, the immediate object of which was to inquire into the present state of development in the manufacture and use of carbide tools.

To this end information has been sought of manufacturers and many users of carbide tools and a summary made of the published literature on the subject. The information gleaned from these various sources has been embodied in the present report. The subject matter has been classified for convenience under the following heads: (1) the manufacture and physical properties of the cemented carbides; (2) preliminary tests of tips; (3) the shank and method of securing the tip; (4) grinding and preparation of the cutting edge; (5) tool angles; (6) tip and shank size and shape; (7) the disposition of the tool relative to the work; (8) the cutting fluid; (9) chip disposal; (10) cutting tests to determine the relations between speeds, feeds, and depths of cut; (11) some speeds, feeds, and cuts recommended by makers and users and cutting data; and (12) general information.

The Subcommittee was not satisfied that the report reveals the latest practice with carbide tools and recommended that an independent experimental investigation be instituted. The Research Advisory Committee approved of the recommendation of the Carbide Tools Subcommittee and recommended that the report, in its present form, be presented at a General Meeting of the Institution in the hope that further information could be elicited in the discussion, and opinion obtained as to the desirability of embarking on an experimental inquiry and the possibility of obtaining means to prosecute the research.

The paper deals with some of the problems that arise in the transmission of power by fluid couplings working on the Föttinger principle in connexion with internal combustion engines and electric motors driving a variety of loads. The influence of the core guide ring on the torque and speed characteristics in fluid couplings of the variable-filling type is considered, and an indication is given of the changes in thrust as the filling of the working circuit is varied. Considerable progress has been made towards the simplification of auxiliary means for controlling the quantity in the working circuit. Particulars are given of several methods of dealing with the residual or drag torque in fluid couplings of the constantly filled type, for use with change gear drives. Slip curves relating to backward curved impeller vanes illustrate the variations between theory and practice in this case. Methods of mounting couplings on engine crankshafts and arranging outboard or driven shaft bearings are illustrated, and a variety of applications of fluid couplings are considered from the aspects of heat generation and dissipation.

The internal forces in the ring valve type of fluid coupling may be utilized to close the valve automatically in order to disconnect the drive in case of overload.

The subject is very complex and a great deal of research has been devoted to it on account of its great economic importance. The magnitude of the problems involved is shown by reviewing underground conditions on the Witwatersrand goldfields. Consideration of the limiting air conditions underground enables a specified mine-cooling problem to be enunciated.

The final section of the paper reviews the various methods that have been tried for cooling the air in deep mines; some have been wholly or partially given up and some have survived. In particular, the possibilities of meeting requirements on a large scale have been analysed. Reference is made to cooling schemes which have been inaugurated on the Witwatersrand goldfields during the past two or three years. An analysis sets forth the relative merits of water, brine, and air as media for cooling deep mines, and a comparison of cooling plant performances and costs is made on the basis of: (1) vapour refrigerating plants on the surface and underground, using air and water respectively as cooling media, and (2) compressed air refrigeration.

As an introduction to the visit of the members of the Institution to the Cardiff Works of Messrs. Guest Keen Baldwins, Ltd., the paper has been written to describe the blooming mill, and to indicate some of the reasons governing the adoption of this particular layout. It refers to some of the troubles experienced in operation and how they were overcome.

Rapid output of blooms is the result of several factors, ample heating furnaces close to the mill, good roller gear and manipulators, rapid reversal and screw-down gear, good shears, and the general robust construction of the mill —all of which are dealt with in detail in the paper.

The aim of the paper is to obtain as accurate a solution as possible to problems arising in the transmission of superheated steam over long distances for (a) industrial heating and (b) power generation. After a general survey, with a description of two typical installations, the problem is discussed under headings (a) and (b), and the usual practice in fixing steam velocities is given. The present state of knowledge of radiation losses is reviewed; first, the standard English practice of using a coefficient based on the pipe surface and varying with the thickness of the insulating material; and second, the method, used mainly in America, which involves conductivity coefficients. The effect of air currents on heat loss is investigated and a new equation is deduced for the equivalent velocity past the pipe, due to natural convection.

Standard formulæ for the coefficient of friction and the viscosity of steam are discussed; for the former a new formula of the rectangular hyperbola type is derived from Carnegie's results and corrected for roughness. Steam viscosity is considered in the light of Speyerer's and Sigwart's investigations; curves of Sigwart's results are plotted on a convenient base of logarithms of pressures.

Conditions during flow in a horizontal straight pipe with perfect insulation are considered and new equations, simplifying the problem, are derived from the fundamental equations.

The author treats from a new viewpoint the problem of power transmission by steam over long distances, based on the loss of available Rankine heat drop. Numerical examples are worked out, as also is the effect of air currents on the coefficient of heat loss. Finally the limiting factors, including the effect of radiation losses, in the long-distance transmission of steam are analysed and their practical importance is discussed.

The author draws attention to the difficulties facing the engineer to whom spring design is merely incidental. These difficulties are mainly due to the complicated formulæ concerned, to lack of information regarding the materials, and to incorrect appreciation of the real functions of the spring. Standard formulæ require corrections for the effect of curvature; without these adjustments very dangerous results can be obtained. Corrections due to Wahl and Woods are incorporated in the formulæ, and finally two nomograms, for stress and deflexion calculations respectively, are produced to enable these involved formulæ to be handled easily and rapidly.

Consideration is given to physical properties, and it is pointed out that except for special conditions of service, the torsional elastic limit of the material is the most important physical property of the material in most helical tension and compression springs. Data are given for this property for patented carbon spring steel and for chromium-vanadium spring steel. Tolerances and limiting conditions are considered, and an arbitrary figure of 70 per cent of the torsional elastic limit is adopted as the maximum safe stress. Curves of load-carrying capacity are given for all standard gauges from 0·020 to 0·50 inch diameter-Special service conditions are finally considered, and suggestions made for dealing with them. In an Appendix are given various examples illustrating the use of the curves and nomograms, and the derivation of some special formulæ.