Right Materials in. the Right Places
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Substitute Alloying Elements, Boldly and Scientifically 'Used, are Taking the Place of Strategic Metals for Heavy-duty Purposes
AMONGST a number of useful developments of more recent .date may be mentioned a new method of making differential bevel -gears with: out the necessity of carrying out machining operations. This is done by forging and coining, and it is claimed that, because a much smaller blank is employed, scrap loss is reduced to 1 per cent., whilst a great dealof time and expense are eliminated as compared with previous methods.
Hitherto, a 70/30 copper-nickel alloy: in the massive form has been widely used for engine •parts called upon specially to withstand the del,eterious effect of exhaust gases. Now, the employment of steel plate clad with cupro-nickel sheet has been found more expedient. The steel base plate is covered with a slight film of a suitable flux, and a copper-foil sheet is placed on this with the flux-coated coppernickel sheet on top; lastly, cubes of steel serving to hold down the assembly are placed on top of the entire batch, which is then inserted in a brazing furnace at a temperature of 1,120 degrees C. in a reducing atmosphere.
Shot Blasting and Service Life of Springs Prolongation of the service life of springs, together with an improvement of fatigue strength, is achieved by a method of shot blasting, in which castiron shot, 0.025 to 0.023 in. dia., is flung by centrifugal force at a velocity of 200 ft, per second against the springs. The method is expensive, but it is believed that the results justify its use. The effect of the treatment is to give rise to pre-stressing at surface hardening.
Austenitic steels containing about 16 per cent, of manganese are rather new in Great Britain and U.S.A. It is stated that they possess good mechanical properties when Coldworked, whilst being easily w,elded by normal processes. Steels of this type are particularly -suitable. for applications requiring considerable resistance to corrosion, although they are inferior in this, respect to the 8/18 nickel chromes.
In the exhaust systems of internalcombustion engines, there is a tendency to replace zinc-plated -bolts by cadmium-plated bolts because of the improved resistance to corrosion at high temperatures of the cadmium plating. The zinc plating is rapidly attacked when in contact with stainleSs steel in heated exhaust systems.
Experiments in America appear to indicate that raising , the vanadium percentage in high-speed steels causes a considerable lengthening of the service life of lathe, planing and shaping tools made from these materials, when machining hard metal and for finishturning. The increase in vanadium is from 1 per cent. to. 2 per cent. The optimum of 2 per cent, must not, however, be exceeded, as this may result in tenderness in the cutting edge.
Equipment has been designed for the a30 purpose of eliminating beads or solidified drops of paint and other protective finishes from metallic parts. A screen charged to a high voltage-is employed as an electrostatic cleaner for the air in the neighbourhood of the work.
Ueneral tendencies obterved in steels for' motor-vehicle use, largely the result of war conditions. may be sumniarized as follow:—In the first place, smaller quantities of alloying elements are being used wherever possible. The deep. hardening of parts liable to encounter bending or twisting stresses is being discarded. Everything is being done in the designing stage to eliminate or minimize stress raisers. Applied compressive stresses to surfaces are being more extensively used. Annealing time is being reduced; and dry cyaniding is becoming more popular. Steel castings are employed to a greater extent than formerly, and welding is being enormously extended in its application. Materials are • being chosen more intelligently, and specifications are becoming more practical and less academic. Boron as an alloying clement is being introduced more voluminously. Lastly, it is believed that, on the cessation of. hostilities, there will be a marked reversion to non-ferrous metals, which* have been dropped on account of war conditions.
Salt Baths for Heat Treating Gears
Gear steels arc being hardened with great success in electrically heated salt baths. The furnace employed has a container Or pot measuring 40 ins, in depth, and has closely spaced electrodes immersed to within 12 ins, of the bottom. Silicon-manganese steel gears, which are liable to decarburize badly in normal circumstances, are successfully hardened by this process.
The electro-galvanizing of steel strip enables uniform films of whatever weight may be required to be deposited, whilst the coating will withstand more severe forming operations. . An interesting series of experiments on the influence of lubricating-oil viscosity on cylinder wear in buses 'has been carried out in the United States. Cast-iron cylinders and piston rings formed the subject of the tests, and the conditions, with the exception of viscosity, were controlled so as to simulate heavy-duty operation. Each oil was tested in six engines for eight hours, six oils in all being used with wide variations in viscosity. It was found.that,eylinder and ring wear progressively declined with an increase of viscosity.. .
In Germany, special methods of case-ca.rburizing and heat-treating chro • miutn, ehrornium-manganese and silicon-manganese steels have been developed. Salt-bath carburizing, together with a diffusion treatment, is employed, and by this means it becomes feasible to control the depth of case with., great precision. Air convection furnaces are used for the preheating of the parts to 260-425 degrees C., in advance of their transference to the hot salt bath. Quenching in oil, draining and rinsing follow. Tempering is carried out by an air furnace for preheating and a salt-bath furnace for the actual tempering operation.
Refrigeration treatment for highspeed steels continues to arouse the interest of experimenters, and machining tests have now been carried out on a number of steels, the heat-treatment of which included cooling to temperatures as much as 100 degrees C. below zero. It was found, that in each instance_ there was an improvement in the service life of the cutting tools employed if this sub-zero treatment be adopted.
Sub-zero Treatment of Carbon Steels
Temperatures below —73 degrees C. are necessary for .these steels, but for.. carbon and low-alloy steels it is not _necessary to go so far, temperatures of —40 to —62 degrees C. being adequate to ensure the improvement desired. It is, of course, possible to obtain in this country commercial refrigeration equipment for carrying out this treatment, which depends on the destruction of residual austenife.
An important new development is the building up of .worn tools by atomic hydrogen welding, and, for the first time, it has been found possible to treat tools of high-speed steel in this way; hitherto, the atomic hydrogen process has not been suitable for this material, because, in the process, carbon was extracted from' the deposit, 'with the result that much of the cutting power of the steel was lost. The new technique, for which a patent has 'been applied, and which is the invention of a British steel concern, enables the carbon content to be closely controlled in high-speed steel deposits. Worn tools, particularly those which have to be kept closely to dimensions, such as slotting tools, can now he efficiently and cheaply built up to their original size and form, and will give extremely good service. .Deposits can be. made on mild-steel shanks or .bodies, and 'on solid Or high-speed steel.
A process 'of chromium-plating cylinder liners comprises electrolytic etching in Chromic-acid solution, followed by' immersion in a bath containing triva lent and hexavaIent chromium, The, Cylinders so plated are claimed to give a. considerably increased service life. Current consumption is approximately 15 arnp.-hr; per sq. in. of surface for a 0.015-in. deposit. After plating, the liners arc treated anodically in the etching bath to eliminate a certain amount of chromium, in order to leave a porous surface capable of retaining lubricating oil.
Induction heating is being applied to thin-case carburizing. Frequencies in the 1-20 megacycle per second range are used for depths of case ranging from 0..005 to 0.03 in.
A qaick process introduced for cleaning steel is to wash it with a mild alkaline_ solution pumped through nozzles. A watei-rinse follows, and before the parts have been given time to dry they are wiped, with a cloth impregnated with a proprietary cleaner containing chromic and phosphoric acids, . When the parts are, dry, a good surface remains for the application of a priming coat.
.131ack matt surfaces are being pro' duced on steel by first cleaning the surfaces concerned, then immersing the parts for approximately 10 minutes in a solution of sodium hydroxide, with small additions of potassium nitrate and sodium nitrate. The bath is main-Lair:rod at 145-150 degrees C.
Multi-colour Electro-deposits Valuable tests have been carried out on the production of multi-coloured electroplates, the co-deposition of nickel and copper, and the deposition of chromium with either copper, nickel,
Dr iron, A brilliant Multi-dolOured plate was secured by means of a solution of 20 g. per, litre of .ammonitina malybdate with 1 g. per litre of sodium cyanide. The process is termed rainbow plating because the colours are zoned.
A most interesting development in testing equipment is the Cyclograph, an apparatus for carrying out nondestructive investigations on ferrous and non-ferrous metals The specimen to be tested is held in a case which is actually a tuned pick-up coil. Variations or alterations in the characteris tics of the steel set up variations in core-loss, and these change the pattern of the oscillograra displayed on a
screen. It is possible to adapt the machine to the automatic' sorting of large numbers of parts at speeds as high as five pieces per second.
The oscillograph is, however, not a robust instrument, and it is, therefore, not highly suitable for the workshop sorting of bars of different steels. A more simple apparatus has now been evolved for this purpose, and comprises an amplifier with a cathode-ray tuning indicator. The magnetic differences between a standard specimen and the sample, which should preferably be of identical cross-section, are measured under the influence of equal alternating magnetic fields. The equipment is readily portable, low in cost, and easily manufactured.
New Low-alloy
Heat-resisting Steel
An emergency heat-resisting steel, designed for war. conditions and the conservation of alloys, contains 0.30.35 per cent. carbon, 2 per cent. silicon, 10 to 12 'per cent. chromium, 4 to 10 per cent, nickel, and 2 to 12 per cent. manganese. The nickel and manganese supplement each other.
A method of electric welding has been cleVised in which the end of the electrode is constantly. submerged in a layer of granulated, .semi-refractory material. A part of this material-melts, and the melted portion, which is expended or used, acts as a conductive and resistant medium for transmitting current from welding rod to work, and helps the unmelted portion mechanically to exclude the air. The unmelted, unused portion can be picked up and
used later. .
A new contour control embodies the principle of the precision air-measuring gauge to secure high accuracy in the automate operation of machine tools.
It employs a pneumatic system to scan a thin-metal template and controls hydraulic cylinders which accurately locate the cutting tool or the work in relation to thetool. On turning, boring and facing from templates, accuracy of repetition is within 0.0002 in. and surface smoothness is limited only by factors other than the control. When both tool and template have been correctly ground and hardened, the control has operated an engine lathe to produce a surface smoothness of 61e micro in.
New Molybdenum Magnet Alloy A new magnet material capajale of being employed for magneto magnets is termed Comol, and contains approximately 12 per cent. cobalt, 17 per cent. molybdenum, with the remainder iron_ It has a coercive force of :aPproximately 245, as compared with 210 for 36 per cent. cobalt magnet steel, is readily cast, and, if suitably heattreated, can be 'machined_ -. Residual induction of 10,300 gauss is obtained. which is superior to that of either 36 per cent, cobalt steel or Alnico' IL It is believed to be manufactured by the Westinghouse Co. ' ' Natural gas and oxygen have been
used in America for the metal'spraying of .zinc or-copper on light steel, with a resulting economy of 15 per cent, in. fuel cost and a 'higher spraying speed. Carbo-nitriding, a ease carburizing process in which both carbon and nitrogen' are imparted to ferrous products by a gaseous atmosphere, is another new development. A higher carbon content isnormally obtained by this method than is obtained from a cyanide bath, and, because of this, it becomes possible to oil-quench itraight carbon steels to full file hardness. Case depths up to 0.015 in. can be economically produced without any objectionable brittleness.