New Treatments and Neglected Materials
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Aid Substitution Campaign
Pickling Inhibitors, Surfacecolouring Solutions, Fluorescent-liquid Crack Detectors, Low-temperature, Shrink-fit Baths, Are Amongst the Developments Referred to in this Review
HE Tocco process of induction hardening has been known for some time, and has proved an invaluable help in the treatment of " steels. A new application of the process is to the brazing ef carbide tips to mild-steel tool shanks. The rapid heating (20 secs.), which is localized to the brazed zone, produces firm, uniform brazing.
Spheroidizing is becoming more widely used to develop the best properties of carbon and carbon-vanadium steels with more than 0.9 per cent. carbon content. The treatment is applied in advance of hardening, and for these steels, is carried out by annealing at temperatures in the region. of 760 degrees C. To promote greater uniformity, it may be achieved by quenching in oil at a temperature of . from between 845 to 870 degrees C., or by normalizing (air cooling),
• from between 870 to 925 degrees C. After the steel has cooled, either operation is succeeded by annealing at about 760 degrees C. The holding period, for the annealing temperature, must be
. adequate, and the cooling rate low enough to produce the necessary spheroidal structure in the Pearlite con . stituent of the steel.
Scale and stain are being removed from brass by the aid of ferric sulphate. Black 'smut and red cuprous oxide scale are quickly eliminated, with less waste of metal.
Spark-testing Mo and W Steels Separation, by the spark test, of the, tungsten high-speed steels from the alternative molybdenum high-speed steels, when these two steels have become mixed, is highly successful. The tungsten steels give long, thin, dullred spark streams containing no carbon bursts. The molybdenum steels have Much shorter and more plentiful sparks, orange-red or straw-yellow in colour, with traces of red near the • • wheel. They end in clearly defined spear. points, preceded by bursts due to carbon. The state of the steel, i.e., whether it is annealed or hardened, makes some difference to these spark streams, but, in the main, they do not greatly alter. It is also possible to tell one molybdenum high-speed steel from another, if standard specimens of each type be kept at hand for comparison. Thus, 4-6 high-speed steel does not yield such a plentiful supply of sparks as the 6-6, or higher, molybdenum types. The latter also show a more marked carbon burst, and a longer spear point at the extremity of each spark. The presence of cobalt in the steel lessens the length of 'the stream, but increases the number and obviousness of the carbon bursts. A straightmolybdenum high-speed steel has 'a short, intense spark stream, readily distinguishable from the streams of the other steels.
There has been great developthent in the use of carbide tools for machining. The plain, sintered tungsten-carbide tools are being confined, mainly, to the machining of those metals that produce well broken-up chips, -such as cast iron and certain alloys of copper. Ferrous metals, yielding curly chips, are being preferably machined with combined carbides, such as mixtures of tungsten, titanium and tantalum carbides. With a low percentage of binder (3 to 5 per cent. Co) maximum hardness is secured with reduced shock resistance. With 15 per cent, or more of binder, strength and impact resistance are considerably increased, but hardness and wear resistance are lessened. It is not feasible to obtain both maximum strength and maximum hardness in the one tool.
It is claimed that heavy steel blocks are being cut eight times faster, by an entirely new machine-gas-cutting technique. A special plant is used hav. ing an oscillating oxy-acetylene torch designed to cut kerfs up to l ins. wide. This allows the oxygen stream to retain its cut when impurities are encountered. Blocks 32 ins, thick have Veen successfully cut at a forward speed of about 1 in, per mm.
Fusion Temperature Indicator
A new product, for rapid temperature measurement, comprises a substance daubed on a working surface the temperature of which it is desired' to know. The product is made in a wide range of predetermined melting points between 50 and 870 degrees C. So soon as the temperature stated on the container is reached, the smear, which dries almost as quickly as applied, swiftly liquefies. On cooling, it solidifies, leaving a glossy, or vitrous mark entirely finlike its original appearance.
A new steel-surface conditioner comprises a free-running powder, which is added to hydrochloric and sulphuric acid pickling baths. Used in small quantities, it produces bright, smut-free surfaces on iron and steel, and lessens acid consumption and metal loss.
A low-temperature, black bath for steel, comes from the United States, It is a fused, chemical salt that, when mixed with, water and raised to a tern perature of 150 degrees C., boils vigorously, so that all steel parts, excepting those made of stainless steel, immersed in it at this temperature, are rapidly coloured a rich blue-black by chemical reaction. The finish is permanent, and will not fade, peel, flake, or wear off by rubbing, whilst it forms an excellent bond for paint, enamel and lacquer. It is being employed to penetrate motor and other bearings to prevent scuffing. Tyre chains, hand tools, springs, etc., are also being treated with it. Compounds of this type arc numerous ; they consist frequently of phosphoric acid with additions' of zinc.
Fluorescence under U.V. brings a new, high visibility, to flaw indications in magnetic metals. A great gain in cbntrast is obtained as compared with
inspection under visible light. The new method produces fluorescent patterns . against an evenly lighted background. Smaller indications are more readily seen. Speed of inspection is heightened by the glow of quenching cracks, forging laps, non-metallic inclusions, bursts, etc. • N.F. Metals and Fluorescence
Fluorescent indications on nonmagnetic parts are now being achieved by another remarkable development, known as the Zyglo, method. Application of a highly fluorescent penetrating liquid to the test surface brings out, after removal of excess liquid, vivid, glowing indications of discontinuities under black light. The entire field of non-ferrous materials is thus opened up • to inspection. The location of flaws in aluminium, bronze, magnesium, and anstenitic steels is thus now possible. Glo-crackis a similar system developed in this country.
The tin shortage is causing manufacturers of commercial vehicles to swing over from tin bronze to alternative bronzes, for heavy-duty drives. Some have used chilled • nickel-phosphor bronze with approximately 11 per cent. of tin. Others have substituted silicon. or silicon -and manganese, for the tin in the same alloy. Another favours aluminium bronze for bearings or worm gears, because it can be made with secondary aluminium. It is stronger than the nickel-tin gear alloy, forms a hard skin under sliding surface loads, and is sufficiently tough. The composition favoured is 89 per cent. copper, 10 per cent. aluminium, 1.0 per cent. iron, or, alternatively, 86 per cent. copper, 10.5 per cent. aluminium, and 3.5 per cent. iron.
Highly stressed alloy-keel parts are being given a high surface-hardness without excess carbides and correspondingly low fatigue resistance, by carburizing to the proper depth, producing a surface carbon of approximately 1.2 per cent„ copper plating the piece for surface protection, and then heating it a little above the critical
point, that is, long enough to diffuse the carbon inwardly and to convert the surface structure to approximately 0.65 per cent. carbon. After oil quenching, the parts are refrigerated in dry ice and alcohol, and the fully -transformed structure is then tempered. This is an interestIng development of the diffusion-technique long applied for coating steel with aluminium and other metals.
A better way of brazing carbide and all other types of cutting tips and cutting blades to tool shanks, adapted to both large and small-scale production, has been developed for employment with furnace, torch, or spot-iveiding methods. A special fluxed spelter is brushed on to the surfaces that make contact The work is then assembled to fit tightly, and brazed. The finished braze is said to resemble a gold-plated joint. There is no waste of joining material, and virtually no cleaning is afterwards necessary.
Sprayed-on Plastic Protective Film. A protective coating for metal has been devised, which is completely trans, parent, so that visual examination of coated parts, such as flat sheets, irregular shapes, bearings, dies, etc., may be made. One gallon, when sprayed to the thickness of one mil, will cover about 250 sq. ft. of surface, with a drying
• time of from 6 to 8 mins. at 93 degrees C. The coating can afterwards be Peeled or blown off by means of an air jet, and reduced to liquid form for farther use.
A new cobalt-chromium-tungsten cutting alloy has been developed to increase machining speed in production shops. Heavy, coarse feed, roughing cuts may be taken on steel, and metal removed at a correspondingly high rate. Tool life, however, remains long and economical, because the new alloy' is well balanced in red hardness, durability of the cutting edge, and tough-ness.
A new drill-jig reduces tool costs and
increases output. It comprises two metal castings linked together. Both are furnished with jnild-steel plates, one of which may be fitted with pins to locate the part to be drilled, and the other may be given guide bushes to conform to the drilling operations required. The distance between the upper and lower plates is adjustable, and work up to 11 ins, thickness may be-undertaken. The capacity of the jig Is for conaponents up to st ins. square.
Boron-bearing Alloys Progress
Two boron-containing alloys have been produced for the imparting of deep hardenability to steels, and for the conservation of other elements less available to-day. It is necessary to introduce only minute amounts of boron into fine-grained forging steels to obtain surprisingly intense hardenability, as well as high strength, after hardening and tempering at low temperatures, e,g., 230 or 315 degrees C. The alloys have the following composi: Hon: 16 to 18 per cent. titanium, 13 to 15 per cent. aluminium, 22 to 24 per cent. manganese, 20 to 25 per cent. silicon, less than 1 per cent. carbon, 1.5 to 2.0 per cent, boron; 16 to 17
per cent, titanium, 2.5 to 3.0 per cent. silicon, 6.5 to 7.5 per Gent. carbon, 1 to 1.25 per cent. boron. The first alloy is the more complex, whilst the second is higher in carbon, but less complex. -• A new soft solder, of American origin, contains 87.5 per cent. lead, 0.5 per cent. arsenic, and 12 per cent. antimony. This is not only lower in cost than any other tinless solder commercially employed, but also has greater solderability on steel and tinplate. A slight variation in soldering technique is required. 'The melting point being higher, the soldering iron or flame must be hotter if the same speed, as with the 50-50 solder, is to be attained. If using a soldering iron, the tool may be tinned with this alloy by using zinc chloride rather than a sal ammoniac block. More success is probable if the iron be tinned with a small quantity Of solder comprised of 30 per Cent, tin and 70 per cent, lead, afterwards applying the tinless solder. Frequent tinning is essential. A speed of 24 ft. per mM should be well within the operatives' capaoities.. Sweating this solder into jeints is not likely . to prove a success. Much work on arsenicbearing solders has been carried out in the U.S.S.R.
Metal chilling, briefly referred to earlier in this article as refrigeration, is one of the latest and most interesting processes, and many metal problems are finding their solution through its means. For example, the shrinking of metal at —73 to —84 degrees C.. has made it feasible to assemble bearings and similar parts, requiring a press fit, merely by slipping them into position. Thus, waste caused by "pounding bearings into place is eliminated, and time caused by delay in replacement saved. Another application is the chilling of
aluminium-alloy rivets to retard ageing. The rivets can be kept soft enough for driving for a period of over two weeks. In chilling austenitic steelS, Care should be taken to avoid reversion of the structure to a marten sitic form.
Again, the testing of metals at simi• lar sub-zero temperatures his made it possible to study the reactions of instruments to low-temperature service conditions. Lubricants can also be tested for, conditions of extreme cold, tests being usually conducted over a 6 to 8hour freezing period. Then there is the treating of metal at these low temperatures, which will produce combinations of hardness, strength, and ductility, not obtainable by ordinary hardening or tempering. For the treatment of high-speed steel, temperaturea colder than —101 degrees C. are not effective, whilst temperatures above —73 degrees C. are also ineffective. Modern equipment is capable of maintaining —84 degrees C., making it ideal for the proper treatment of high-speed steel.
New Cutting Fluid Developed
A new, highwquality coolant has been introduced for severe cutting operations on tough steels. It increases cutting speed because of greater metaladsorbing oiliness at the cutting edge of the tool, and is able to dissipate frictional heat with rapidity. Th clear, transparent straw colour, enables the operator to watch his work without . difficulty.
A series of siiver-bearing welding electrodes has been developed to solve the problem of salvaging tools and dies. A new and 'excellent edge can be bebuilt on the worn tool shank. After the weld deposit is made,, the tool is reground and goes back into use.