Oct., 1935.1 CURREKT TOPICS. 329

Free Cutting Aluminum Alloys for Screw Machine Work.- (Iron Age, Vol. 136, No. 4) “Free cutting” is a term coined to denote the rapid breaking up of cut scrap so that it falls away from the machined piece, leaving the metal surface clean and not cluttered for the oncoming tool. The Aluminum Co. of America has supplied data that show that this material has now been added to the list of “free cutting” metals. The problem to solve consisted of the proper alloying of aluminum, and the solution was found with the discovery that the simultaneous presence of small concentrations of a multiplicity of elements was much more efficient in producing satisfactory machineability than any one element alone. From a number of elements found to be satisfactory, lead and bismuth were chosen to supply multiplicity because it was further found that these elements had relatively small effect on the other proper- ties of the alloy. The effect of copper on machineability was also kept in mind and its concentration was placed at about the masi- mum for the satisfactory hot working of large ingots. There are now available at least two alloys in large scale production ; one with magnesium content, one without, in two tempers, so that there is a choice of four different materials. Tool wear on free cutting aluminum alloys appears to be slightly higher than on free cutting brass, but is much lower than that obtained with steel or dur- aluminum screw machine stock.

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New Automatic Adjustable Blade Turbine.-( Power Plant Engi- neering, Vol. XXXIX, No. 8.) There is now under construction by the Kanawha Valley Electric Co. at its Marmet Plant in West Virginia, a hydraulic development, involving a 7600 hp. adjustable blade turbine of new design with an experimental runner. Here- tofore this runner has been built only in model sizes for esperi- mental purposes in the laboratory of the Newport News Shipbuild- ing and Dry Dock Co. The runner vanes are pivoted on roller bearings and connected through gears and racks to a dashpot in the runner hub. Each vane is pivoted slightly above the center of pressure so that the water flow creates a hydraulic moment which tends at all times to open or increase the pitch of the vanes. This moment is opposed by a device which creates a reactive moment that tends at all times to close or decrease the pitch of the vanes. The reactive device may be pre-compressed springs or any. one of several other devices. The runner vanes therefore remain in a balanced position with changing load which in turn governs the adjustment of the wicket gates. The relation between

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the position of the vanes and the position of the wicket gates is not fixed, but varies with the head and speed. The vanes open wide when the turbine is started and this gives maximum starting torque. As the turbine approaches normal speed with no load on the unit, the vanes move to the closed position, after which they move to the position required by the load.

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Heat Transmission in Boilers.-What appears to be a very important development in heat transmission in boilers is described by P. ST. GEORGE KIRKE in the Gas Journal, Vol. 21 I, No. 3766. After considerable experimenting the author produced a new boiler tube, the object being to enable many more molecules of gas that are near the tube walls to arrive there and transmit their heat to the wall themselves. In practice this has resulted in an actual acceleration of heat transmission of ISO per cent. In other words, the heating surface required has been reduced by 60 per cent. and the heat transmission per unit of heating surface has been increased in the ratio of 2% to I. “ Sinuflo” is a registered trade mark. The tube as illustrated is bent in curves similar to a sine wave, to the degree that a brush or scraper on a shaft can easily be poked through. Due to the shape of the tube the gases are always flowing towards the tube wall, first towards one side then towards the other. A town gas fired “Sinuflo” boiler fitted with vertical tubes 2 in. O/D X 5 ft. long, submerged in water 4 ft. was independently tested by a gas company and the thermal efficiency found by deducting the known losses from IOO per cent. was 91.25 per cent. This boiler is entirely independent of chimney draught. There is a separate gas jet opposite each tube and combustion takes place in the tube, so that the bottom tube plate is not subject to any flame temperature at all, which enables them to be made for pressures as high as 750 lbs. per sq. in.

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Airplanes Solve Alaskan Mining Problems.-The opening up of new mining fields in rugged out of the way places no longer presents the old-time difficulty of the transportation of supplies and mate- rials. CLARENCE WM. POY, Manager of the Big Four Mine, Inc., Valdez, Alaska, describes airplane freighting methods in Mining and Metallurgy, Vol. 16, No. 344, which eliminated to a great extent transportation handicaps. Most of the supplies are delivered in winter on ski-equipped planes to the mine high up in the mountains. A Fairchild monoplane is used with a load capacity of about 800 Ibs.