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Spotlight on Special Steels

27th July 1945, Page 29
27th July 1945
Page 29
Page 29, 27th July 1945 — Spotlight on Special Steels
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The Development of a Special Vitreous enamelling Sheet Needing No Groundcoat is Symptomatic of the Urge to Economize in Time and Material

I T is stated in certain reports that German authorities claim to have pushed forward their efforts to eliminate the unnecessary use of special alloy steels to such gnod purpose that plain carbon steels were, to a great extent, replacing them with advantage.

A process of finishing and polishing metallic surfaces is known as liquid honing or vapour-blasting. It is the direction of a stream of fine abrasive material mixed with a chemical emul; sicn at high pressure against the metallic surface. The mixture can be discharged from an ordinary sand-bleat nozzle by compressed air at a speed of 3,200 ft. per sec.

Improving the' pliability of hot-dip zinc coatings on steel sheet and wire is 'being achieved on sheets by roughening the surface mechanically or chemically before coating, using either emery or sand, or pickling for a short period in nitric acid. Wire ma? also be provided witl. a pliable coating if all pickling salts be eliminated by sandblasting in advance of the coating oparation.

The application of lead coatings on steel has found a considerable field of use in recent years. Pure lead may be used, but, as a rule,the load is alloyed with small quantities of tin, antimony, zinc or silver. A coating thicicness of 0.0005 in. minimum gives adequate corrosion resistance, because of the selfsealing•properties of lead. A new leadplating process is based on commercially produced ,sulphamic acid, an aqueous solution of lead sulphamate being provided for the plating process. Extensive research has been carried out on the best methods of painting steel, and it has been conclusively established that a system comprising phosphate-treated galvanized steel, zinc-chromate priming, and aluminium top-coat paint; combines to a high degree the fundamental needs for withstanding corrosive atmospheres.

A statistical analysis was made in Germany of the causes of failure of gudgeon pins. The two principal causes were found to be ° .slaa inclusions in the steel and defective heat treatment. Sand-blasting or grinding the inner surface of a pin improves its fatigue strength.

Improving Grey Iron with Va,

Grey cast iron is being alloyed with vanadium, which is claimed to improve the properties of the material in the heat-treated Condition, particularly the resistance to Wear, deformation, hotcracking and warping at high temperatures. Density is also increased.

Methods of alloying Steel with nitrogen have been investigated. Heattreated, cold-rolled steel containing 17 to 19 per cent. chromium, 5 per cent. nickel and 0.15 to 0.2 per cent, of nitrogen is equal to 18-8 stainless steel in mechanical properties and resistance to corrosion.

Castings "that have tca' be hardened throughout With the-least ribssiblel diStortionalter being Machined arc now Made from an air-hardening steel. can

taming 0.55 per cent. carbon, 0.7 per cent. manganese; 0.75 per cent. ehro•mints, 1.5 per cent: nickel and 0.5 per cent. molybdenum, with approximately 0.4 per cent., silicon.

Steel parts for ,motor vehicles are being made by centrifugal casting. Close dimensions are obtained in one suah process by applying air under pressure through. the top of a riser while solidification takes place.

Magnetic methods of testina° ballbearing steels have been developed, and are based on measurements of the induced current when the part is placed in a magnetic field. , Several instruments for detecting differences in the hardness of ball races have been developed.

Eliminating Need tor GroundeOat A steel containing a percentage' of titanium haS been produced which ia capable of taking a single coat of vitreous enamel in light colours, and which will be free from black specks, pits, or blisters, thus doing away with the need for two coats. The steel has good drawing properties.

A continuous heat-treatment plant for the improvement of leaf springs of varibus lengths has been invented. Both the hardening and tempering furnaces has a chain-like conveyor running through them, its speed being adjustable so that the heating time may be regulated. The copper-brazing of steel assemblies with definite clearances and in such a way that the components stay in the required location until the joint has been made is being carried out by means of pure copper, in the form of wire, foil, or powder made up as a' paste, which is placed in a. position from which, when molten, it will readily flow into the spaces to be filled. The assembly is heated and maintained for a period of 5 to 10 minutes at approxiinately 1,120 degrees C. in a reducing atmosphere. It is then cooled, normally in the same atmosphere, by being passed through a tunnel furnace with a cooling zone.

Electrostatic methods of spraying small parts with paint and of removing excess paint after dipping and in advance of stoving 'have been introduced. To apply the paint, it is necessary to hang the part between vertical electrodes charged at 100,000 volts. Both paint and time are economized, and ;the coating is of great uniformity.

• A new brake-shoe tool is American in origin and has been designed: mainly,: fOr uset on the brakes of General MotbralOrriesa. Normally; it ia'said to take one man half a day or longer to

reface a set of brakes; this tool saves approximately one to one and a half hours on this work.

To America credit must also be given for the invention of a simple, compact and efficient machine for cutting or peelina° the outer rubber treads and beads from the inner fabrics of motorvehicle tyres or casings. The two operations maybe carried out either at the same time, or separately and independently.

'A new internally heated electric saltbath furnace has been specially constructed and designed for heat treating vertically long tools, such as broaches liable to warp or distort if treated when in the horizontal position; '

Cast irons are being greatly improved in mechanical properties by " inoculation," in which a small percentage of an inoculant such as ferrosilicon or silicon-zirconium is /dded as to lessen the tendency to chill, thus yielding the best possible, tensile Strength, transverse strength, higher abrasive value, superior heat resistance, less linear change, and less deflection under load.

A new precipitation-hardening alloy. claimed to have exceptional uuiformity in response to heat treatment contains • approximately 60 per cent. copper, 20 Per cent, nickel, and 20 per cent. manganese.

Recent developments in, materials of industrial importance include a lowexpansion aluminium alloy; aluminium plating; ,the refrigeration of heattreated aluminium alloys; porous clam-. mium plating; tinless solders; silver bearing and other babbitt metals and laminated metals. A hot-press method of making large carbide parts incorporates in a single operation the three separate processes of pressing, pre. sintering and sintering.

Improvementslo Tin-plating Baths

Potassium stannate solutions appear to offer a solution to one of the 'greatest drawbacks to alkaline tin plating, viz., the innately slow plating speed obtainable with the sodium stannate bath. They will do all the sodium' stannate bath can do, more quickly and with a lower power, consumption. These solutions also have greater freedom from sludge formation, higher conductivity and more favourable solubility relations.

Research into the fatigue life of heattreated gears has revealed that their resistance to fatigue fracture can be improved by increasing the chamfer at the shoulder of the teeth; modifying the thickness of the rim; removing grooves caused, by grinding and polishing in the tooth gullet; and removing the marks of the final polishing running at right angles ..to the teeth.

Small high-speed-steel cutting tools are 'being cast to shape by the lost wax

refractory mould process. This is a process by :which. castings, in a wide range of alloys can be produced, of such dimensop*r. accuracy and extel leru.:e.of as cast surface finish that little machining is needed.

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