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Newest Metallurgical Advances

6th February 1942
Page 24
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Page 24, 6th February 1942 — Newest Metallurgical Advances
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Aid Tool-foom and Heat-treatment Shop

SOME interesting new developments in metals and machines for industrial use should, with a view to their adaptation, be examined with care by the commercial-motor industry, even where they have not been speci fically designed for this sphere. For example, a new type of tube-fonrning machine has been invented, and comprises three heads mounted on a long horizontal bed. One head rotates the tube, the second holds two forming wheels that bear on the exterior of the tube at cilarnetrically opposite points, and the third is hydraulically controlled for increasing or decreasing wall thickness. This machine will form a tube 20,1 t. in length by 8 ins, in diameter, which can, if desired,be reduced to 2 ins, in diameter with ti..e svall increased in thickness from No. 8 gauge to 5-16 in. Several changes in diameter and vall thickness can be Marie along the lingth..of the same tube within the limits of cold work of the material.

Activated-gas Carburizing

A new gas-carburizing process known as the " hypercarb " has been evolved. In this, the -hydrocarbon gases are specially treated before they come into contact with the steel, The object of the treatment 'is, in the first plae*e, to activate the atmosphere, and secondly, to eliminate excess carbon that would otherwise be deposited on the steel. Town's gas or natural gas is preheated to about 925 degrees C. by passing it over a series of radiant tubes and allowing it to rise into the heat-treatment chamber, through which it travels in the opposite direction to that of the .charge.

Attempts have been made in the past to caseharden stainless steel containing about 15 per cent, chromium, but have not been successful. A method of achieving the desired result has now, however, been invented, and comprises holding for-6 hrs, at a temperature of 920,-950 degrees C. in freshly prepared charcoal activated by heating to 800-900 degrees C. with the exclusion of air. After being casehardened, the steel is quenched in oil from about 1,020 degrees C. with or without an intermediate anneal. A surface hardness of Rockwell C 57-59, is procurable by this method, and no lowering of corrosion -resistance occurs.

. An easy and commercial means for testing the machinability of cast iron comes from America. The rnachinability 'index is founded on the time, in inches per minute, taken to drill a isin. diameter hole, conditions being carefully standardized. The conditions found suitable are 490 r.p.m. drill speed, 60 lb. pressure on drill point; 118 degrees point angle; the drills are ground on a new machine with the same setting by the same operator the time taken to drill a hole -Ain. in depth is ascertained with a stop watch. An addition to the group of highnickel alloys has been announced, and the new metal combines four outstanding charactet'istics. It has high . strength,_ can be fabricated in automatic screw machinery, resists corrosion, and can be heat-treated after fabrication to provide an extra measure Of strength and hardness. It is being produced in rod and wire form: It has free-machining characteristics and is non-magnetic.

• Hand fuel pumps have in the past had their thrust. discs made of bronze". This metal is now in some types of . pumps being replaced by a high-nickel copper alloy. A method of producing a porous bearing metal •by powder metallurgy from powder produced by grinding cast iron borings and turnings has-been developed in Soviet Russia.

New High-strength

Bronze

Modification of commonly used bronze mixtures by adding small percentages of nickel has been general practice when it has been desired to increase mechanical properties, and pressure tightness. A new commercial alloy of this type is that containing 88 per cent. copper, 5-per cent. tin, 2 per cent. zinc. Even in the as-cast condition, this alloy possesses high mechanical properties. They cost much the same as ordinary copper-tin-zinc bronze, but have better properties. When an inexpensive heat-treatment is applied, mechanical properties resemble those of many costlier materials. Properties can be modified by slight changes in composition and heattreatment. Ageing at 290 degrees C. provides high strength and ductility. As cast, the new alloy has a tensile strength of over 20 tons/eq, in. as compared with 30-40 tons/sq. in. when heat treated. Brinell hardness is 86 as cast, and 140-200 heat treated. Elongation is 42 per cent. on 2 ins., as cast, and 25 per cent, heat-treated.

Of particular interest to the comrnere cial motor industry is the production of a new type of precision bearing, which not only offers specific engine economies, hut also permits an increase in safe power for a given engine size, or conversely, makes feasible a decrease of engine size for a given power rating.

It. is designed -to withstand the extreme operating conditions of high compression ratios; greatly inceeased power output, higher crankshaft speeds arid piston pressures, and resistance to oil corrosion. The bearing comprises a thin layer of high-lead babbitt metal bonded to a steel back by means of an interposed layer Of sin tered. nickel and

• copper powder in the approximate percentages of 40 and 60 respectively. In this process a porous matrix is formed by sintering a mixture of nickel and copper powders in a • Controlled atmosphere. . • ' The calculated life of the new bearings is said to be' Morelhan 200 per cent, greater than that of most conventional bearings in automobile use at the present time. • Alloy Die-Steel for

• Cold .Stamping A new chromium .vanadiumemolyb-' delimit die steel has been developed to meet the demand for a steel for dies used in producing cold-formed or gtamped parts cheaper than those at present used and with. properties suitable for accurate' work over short rubs.

The new steel is claimed to enable a 40 per cent. saving to be made on the cost of short-run-dies,, and has given stich excellent results in service that• it is being applied to a wide range of parts as well as dies. A characteristic. heat treatment for the material is to pack harden and air quench. from 980 degrees C., then temper at 2O5 degrees C. for 3 hrs. This produces a final hardness of 61 Rockwell C, with

negligible hardening' distortion. .

new high-speed tool steel has been invented and is said to be capable of standing up to the heaviest cut, and giving the finest of finishing cuts. The steel has a vanadium content of 2.5 per cent. combined with 0.6-0.8 per cent. molybdenum. The special feature of the new tool steel is the high carbon, content which gives a hardness of 65-68 Rockwell after standard heattreatment. No toughness is sacrificed to obtain this hardness, and the mechanical properties are still equal to those of a standard 18 per cent.

tungsten, high-speed steel. „ Good shock-resisting properties render it suitable for intermittent cutting, whilst good hot hardness enables it to take heavy cuts. The approximate composition is 18 per cent. tungsten, 4 per cent. chromium, 2.5 per cent. vanadium, 0.6-0.8 per cent, molybdenum, and I per .cent. carbon.

Monel metal tubing for engine radiators is another interesting develop ment. This tubing is of double-ply construction, but the seams and plies are eliminated by the working and heating, and the small sizes are.

virtually seamless. The base tube is reduced by anumber of extremely heavy passes to 0.28 by 0.006 in., leaving the tube very hard and stiff. Cut to short lengths, with ends expanded into hexagons, they are nested and joined together by dipping into a shallow bath of silver solder.

An accurate hardness tester for aluminium alloys and softer metals, plastics and hard rubbers, is capable of being carried in the pocket. A slight pressure against the surface for test provides immediate direct reading on a plainly visible dial. The indentor can be employed in any position, vertically, horizontally, and inverted, sa that the hardness of vital parts can be checked immediately after fabrication and installation. Costly and dangerous mistakes can be prevented by detecting the accidental employment of materials identical except for hardness.

Novel Safe-ending Process A simple, rapid, and cheap method of safe-ending all forms of hammerdriven hand tools, such as chisels, wedges, cutting-off tools, and the like, has been developed. The striking end

• of the tool that has " mushroomed '1 is ground down to sound metal, where necessary, and a stnall shoulder is ground all the way around the cut end. A reinforced band of bronze is then deposited on this shoulder, with he aid of the oxy-acetylene flame, and the sttikingend of the tool ground square.

A new practice in the heat-treatment of steel wire has been workell out. An electric current is applied directly to the moving strand of wire or strip and the material is raised to the correct temperature by -means of its own electrical resistance.

There has been devised -a handoperated torch for arc welding. It has two arms carrying two carbon electrodes, the tips of which are kept close enough together to ensure maintenance of a continuous arc. The weld metal is added from a welding rod, as in

oxy-acetylene welding. No gas pressure behind the flame forces the molten metal away from the point of impact. The method is advised for welding cast iron and non-ferrous metals, and for brazing, but is .not recommended for welding steel.

Cast-iron • Tool Shanks

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