War's Demands Stimulate Metal Practice
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FEW processes have attracted so much interest in the past few
years as flame hardening, in which steel parts are hardened by the passage across their surfaces of an oxy-acetylene flame. The latest development in this direction is the automatic flame " thrower " for the hardening of automobile crankshafts. It is claimed that this device gives extremely hard surfaces to the crankshafts and therefore produces lengthy bearing life combined with exceptionally low consumption of lubricant.
The crankshaft is mounted between centres and, when it starts to revolve, the oxyacetylene jets situated in ' couplet at each of the bearing surfaces come into action automatically. The flames impinge upon the part for a full 60 secs., and are then once more extinguished, again automatically.
The heated surfaces are now, at once, quenched by means of a water spray whilst the crankshaft is still rotating at about 200 r.p.m. The process occupies a bare 3 mins., and the result is bearing surfaces file-hard but not brittle.
Impregnated Wheels
For grinding metallic tools a new type of metal-bonded wheel has been produced, consisting of diamond powder embedded in a rim of solid metal, a special alloy that grips the diamond grains firmly yet allows just sufficient wear to maintain the sharpness--of the wheel. The metallic rim is -firmly locked to a moulded plastic 'centre or Core.
Thin cut-off wheels are composed wholl,y of metal; but have the diamonds embedded only in the outer edge, usually to a depth of 114in, or * in. The great advantages of these new wheels are said to be long wheel life-and low grinding cost, whilst they are virtually fool-proof and give a superior finish to the cutting edges of
such items as cutting tools chip "breakers and the like.
A new tool teel. produced in :the United States, is the medium-carbon 'manganese-molybdenum steel for dies, punches, cutting tools and chisels, and for a wide range of purposes demanding extreme toughness in thin sections, such as step-down dies and scraper knives. A I-in. section in the hardened and tempered state shows a 'Rockwell hardness of 58 C. and will take an appreciable permanent set without cracking..
A new type of apparatus for detecting surface or hidden flaws has been invented. It is intended to locate flaws in non-magnetic parts • such as sheets, castings, and other fabricated units in aluminium, copper, duralumin and austenitic stainless steel. Its principle is the induction of a predetermined type of eddy current in a perfect test specimen of the material to be examined by the employment of alternating magnetic fields. Sensitive pick-up coils, correctly arranged in relation to the eddy currents, measure, in any similar part being tested, only the departures of the eddy current pattern from the pattern in the perfect sample.
Another new cutting alloy is announced, of the cobalt-chromium tungsten type. It is particularly recommended for all machining operations on cast iron, semi-steel, 'steel, er other matetia.ls. Higher .cutting speeds and feeds are said to be feasible with this new material as compared with previous qualities of similar alloys..
Transmission gears are called upon to resist wear. shock and high tooth , pressures, which make good elastic properties in bending and compression necessary. Spline shafts, in particular, are subject to sliding metal-to-metal wear, and compressive stresses an the spline sides and to high torsional stresses. Nickel steels are being increasingly employed to give these requilements, particularly for countershaft gears and shafts, for which 5 per cent. nickel steel is being used.
For other gears, where stresses are rather low, nickel-molybdenum steel is being used in America because it has so low a distortion during heat treatment. Main shafts in both forward and rear sections are being made of nickel-chromium-molybdenum steel of high torsional strength.
As a substitute for nickel plating, a bright, heavy copper plating process has been developed, the basic ingre dients of which are copper sulphate, diethylene triamine and ammonium sulphate. The current efficiency at both anode and cathode is Virtually 100 per cent. The throwing power compares with that of a cyanide copper bath and is claimed to be much superior to that of an acid copper solution. Average current density is approximately 40 amps./sq. ft, for maximum brightn,ess. Operating temperature is about 60 degrees C.
Electrolytic Polishing An electrolytic process for polishing 18/8 stainless steel is of interest. A glycerine/phosphoric acid mixture is employed as the electrolyte, the best result being obtained with 42 per cent. of phosphoric acid, 47 per cent, of glycerine and 11 per cent, of water by weight, held at 100 degrees C. or higher, with a current density at the anode of at least 0.1 amp isq: in.
An easy way of determining the quantity of oxygen in a heat-treating furnace atmosphere when this is between 1 and 5 per cent. has been put
forward. A -small wood block, not
more than in. square, is placed on the hearth, the door is shut, and the way it burns watched. If the wood smokes and chars without perceptible flame, then reveals" intermittent flashes of pale blue flame, 14-2-i per cent, of oxygen is present. When the flame is 50 per cent, blue and 50 per cent. yellow, the oxygen is between 2i-4 per cent. At approximately 5 per cent, of oxygen, or above, the wood bums steadily with a yellow flame, and the residual charcoalwill glow all over.
Engine cylinders for nitrogen hardening. are being completely degreased, tinned, rinsed, dried, painted and baked in the rough machined state, then coatings being removed from the bore before nitrid ing. The cylinder barrels are hung from special carriers attached to pulleys on an overhead conveyor system. The barrels pass through the tinning plant at the rate of approximately 30 per hour, and through the paint tanks and baking ovens at the rate of 25 per hour.
Induction Testing
Another electrical method of detecting flaws in metal calls for description, and is applied principally to tubes. A discontinuity in the tube wall, when the tube is passed through energizing coils carrying an a.c. current, sets up changes in the value of the current induced in the tube wall. Electronic apparatus indicates and records these changes. Automatic switches stop the tube from passing through as soon as an irregularity is detected. Short cracks and pinholes call for a modified apparatus. Testing machines have been designed for testing tubes up to 5 ins. diameter ; with smaller diameters, tubing can be tested at about 50 ft./min.
A nickel-aluminium-titanium ferrous alloy has been developed for permanent magnets, and is being used for the magnets of a magnetic filter designed to .remove iron particles from engine lubricating systems, thus decreasing wear and tear.
From the Soviet Union Comes a new method of automatic welding with a " lying " electrode. An eccentrically coated electrode has been ileveloped, the thin side of the coating being placed downwards in contact with the metal to be welded, whilst the upper, thicker-. side of the coating, which takes longer to fuse, forms a protective hood over the arc. The special coating is free from erganic material, and comprises 37.7 per cent, of titanium dioxide, 28.G per cent. of maganer oxide, 20.4 per cent, of ferro-manganese, and 13.3 per cent, of feldspar, made up with 26.5-28.5 per cent. of water-glass. A steady arc is obtained with this coating and the finished welds have a high ductility.
A smooth lustrous surface on steel and stainless steel is now being obtained by polishing with muslin wheels about 14 ins, diameter, to which is applied a loose abrasive mixed with oil or water.
The protective value of paints for both plain and galvanized steel is greatly improved by a hat-dip phosphate sOlution treatmeht. A phosphate " cold wash and a phosphate-chromate wash have also been found effective for plain steel. This device appears to be periodically rediscovered every 15 years !
Springs are being made more efficient by the invention of a. magnetic method of checking their heat-treatment. This, again, comes from Russia. The apparatus is hased-on a magnetic-induction principle, in which the magnetic permeabilities of the specimen and of a standard at definite field strengths are compared by the differential method and provide a means for checking the suitability of the structure after heattreatment. The apparatus differentiates between correctly and incorrectly heattreated spring wire.
As a substitute for bronze, a lowalloy anti-friction cast iron has been produced. There are two compositions. One contains total carbon 323.6 per cent, 2.2-2.4 silicon per cent., 0.6-0.9 manganese per cent., 0.3-0.4 per cent, nickel, 0.2-0.3 per cent.
copper, and 0.2-0.35 per cent. .
minium. The second has the same.
composition with the exception that clapper and aluminium are omitted. The friction coefficient of both irons is, it is claimed, roughly the same as that of bronze, Tensile strengths of about 34.41 tons/sq. in. are being obtained in a new range of heat-treatable nickel-tin bronzes which give indications of being able to fulfil a wide range of purposes. This new bronze contains SS per cent. copper, 5 per cent. nickel. 5 per cent, tin, and 2 per cent, zinc. It costs somewhere abouethe same as ordinary copper-tin-zinc bronze, but has superior properties, even in the as-cast condition.
After a relatively inexpensive heattreatment, the mechanical properties approximate to those of costlier alloys. When cast in small sections it can be substantially hardened without solution treatment by simply ageing at 290 degrees for five hours, and this treatment will raise the proportional limit by 60 per cent., the yield point by 75 per cent., the tensile strength by 30 per cent., and the Brinell hardness by 40 per cent., whilst the alloy will still retain adequate ductility. Gears, holding-down nuts, hinges, locks, and other parts where a superior bronze of strength is required are said to be potential applications' of the new material.
Gas-carburizing Furnace
Cams, ball-bearing races, gears and pinions are being case-hardened in a ,type of furnace in which heat is derived from lour rows of ribbon-typo heating elements, made of n. heat-resistant 80/20 nickel chromium alloy, strung along the inside of the brick furnace wall. The parts are separated from the gases of the furnace by a retort shell of nickel-chromium-iron alloy. A high-pressure fan situated at the retort base ensures. thorough circulation of the carburizing gas. The temperature in these furnaces is usually held at approximately 925 degrees C. All the furnace parts exposed. to heat, are made Of high nickel-chromium iron alloys. The new furnace differs from others in that the parts to be carburized are 'placed in the heat-treating chamber in an open' container, thus enabling the gas to reach their entire surface area. No solid carburizing compound is used.
High-speed tools of low-alloy content and long and efficient cutting_ life are claimed to he ensured by making them from a new, alloy steel containing 0.2-1.2 per cent, carbon; 2.0-6.5 per, cent. tungsten, 2.0-7.0 per cent. molybdenum, 2.0-6.0 per cent. chromium, 0:5-3.0 per cent. vanadium. Tungsten and molybdenum constitute approximately 7-12 per cent.. of the alloy. .
A steel with good depth-hardening characteristics contains 0.05-1.2 per cent. carbon, 0.95-1.6 per cent: manganese, 0.6-1.5 per cent. silicon, 0.050.15 Per cent. molybdenum. This steel. is specially designed for parts to be case-hardened,-e.g., ring gears.
'A new range of collapsible taps enables bottom-hole tapping to be carried out with' standard chasers. The taps are made in one piece with a solid end. No end plate or cap is needed, and regular chasers extend beyond the tap , body for close to bottom tapping. Collapsing is positive and invariably at. the same point, effected by an adjustable hardened steel plate.,
,Chasers in this new tool are set in at an angle, and can be readily removed 'by simply taking out one screw. Means are provided for adjustment to cut large or small threads. The stationary type has a handle and rotary sleeve for resetting. Types can.be converted by removing the handle and. replacing the sleeve. There are 12 sizes from 4-1to 3-1 insdiameter, each size covering a threading range.