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Metallurgy Laboratory The following major investigations have been made during the year:— (a) Manufacture of Screw-ring Gauges.—ln the manufacture of hardened screw rings two interdependent problems are encountered, the prevention of distortion in heat treatment and the final lapping to correct form. In an effort to hold pitch and diameter of rings to 1/10,000 in. in hardening, all types of commercial tool steels were investigated, and overseas rings were examined to determine materials and technique used. A satisfactory combination of hardening and lapping with, materials available has now been evolved. _ (b) Determination of Magnetic Change Points of Steel. —An investigation was undertaken to determine the applicability of the magnetic test as a means of determining correct hardening temperatures. This simple test is widely used in industry, but gives satisfactory results with only a limited class of steels. All commonly-used tool steels were accordingly investigated, and the relation between the magnetic change points and upper and lower critical points determined. These results will shortly be circularized to tool-rooms. (c) Linear Changes in Refractories at High Temperature.- —Apparatus has been constructed for the determination of linear expansion of refractories up to I,ooo° C. A series of eight types of refractory brick has been investigated for a cement company, and results compare very favourably with published figures. The work will be extended to cover all types of locally-available bricks as time permits. t (d) Thermal Insulation Values of Refractories at High Temperature. -Equipment for the determination of thermal insulation of refractories up to I,loo° C., designed along the lines of the A.S.T.M. apparatus, will be completed shortly. Bricks used in the construction of rotary kilns will be first investigated, and subsequently all other available. (e) Optimum Annealing-conditions for Steel used in drawing Bomb Casings. In an effort to improve tool life and quality of finished product, an investigation into the correct interstage annealing procedure for mortar-bomb drawn casings has been carried out. Machinability, physical properties, life of dies, and difficulty of final pickling all have to be considered together in this problem. (/) Optimum Annealing-conditions for Fuze Brass. —The change over from Australian forgings to English forgings in the manufacture of fuze bodies has given rise to a serious machining problem. Laboratory work directed at overcoming this difficulty has been completed, and large-scale tests are now being carried out. (g) Casting of Alnico Magnets.—The difficult problem of remelting and treating Almco magnet alloy has been overcome by a very rapid melting technique employing an indiiect arc furnace. The laboratory is now in a position to supply limited quantities of castings up to 101b. in weight. . , . . (h) Determination of Stresses in Welded Girders. — lhe adoption of welded joints for the main girders of the new Whirokino Bridge has given rise to the question ol best welding procedure to minimize residual stresses. A very sensitive strain-gauge has been constructed for the investigation, and two full-scale test welds are now being prepared. (i) Uniform Hard Chrome-plating of Steel Balls. —The application ol barrel plating methods to hard chrome-plating has been successfully undertaken, and spherical drifts for use on mortar-bomb tail units are now being processed. (j) Electroplating of Bearing Surfaces with Lead. —At the request 01. the Air Depaitment, a small pilot plant was instituted for the lead-plating of radial engine master-rod bearings. After the technique had been established, Air Force personnel were instructed and details of full-scale equipment supplied to the Department. The process is now being worked very satisfactorily. ■ . (k) Investigation of the Cause of Failure of Rocker-boxes on Aircraft Lngines. A detailed investigation of the failure of rocker-boxes on certain aircraft-engines has been completed This entailed metallographic examination combined with destructive tests on cylinder heads and an investigation of the actual running conditions of the engine. (I) Manufacture of Suitable Alloys for Fusible Links to prevent the Overheating of Salt Bath Furnaces.—'The whole question of fusible alloys for furnace protection at various temperatures has been investigated. Several different type,s have been supplied and are operating satisfactorily. For operating-conditions in which fusible links are unsuitable .a differential expansion-type relay has been designed and is now being constructed. The above investigational work is additional to the routine testing and examination ox metals, the calibration and inspection of works' pyrometers for outside industry, the determination of heat treatment procedures for outside industry, the X-ray examination ot castings, and the hard chrome-plating of dies, tools, and gauges. Over one hundred separate items of work have been dealt with under these various headings In addition, this laboratory has exercised technical control over all heat treatment of steel tools and gauges carried out in the Dominion Physical Laboratory furnace-room for the Laboratory s tool-room and for industry. Design Section and Instrument Workshop (including Glass-blowing, Glass-grinding, and Electrical-instruments Workshop) The design, manufacture, and repair of instruments and equipment has been done on a large scale this year. In round figures, over 250 items of construction, 500 items ot repair, 1 500 items of glass construction, and 150 items- of electrical-instrument repair and construction have been despatched. This work has been confined as far as possible to that requiring specialist attention such as the combined laboratory and workshop iaeilities and the scientific and technical staff of the Dominion Physical Laboratory are now capable of. The work has all been directly or indirectly related to the war effort. The United States Marine Corps made full use of the facilities available for the overhaul ol: optical and other equipment requiring laboratory supervision. _ An appreciation of the variety and type of work accomplished can be gained from-the following list of special apparatus which has passed through the hands ot the Dominion Physical Laboratory this year: Gun telescopes, range-finders, binoculars, theodolites, surtacealuminized mirrors, casettes, aerial and other cameras, microscopes, projectors, bomb-sights, gun-sigHts lenses, photometers, chronometers, stop-watches, barometers, barographs, aneroids,

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