Metal Science Makes More
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Progress
AMONG the newest•developments of interest in metallurgy and allied research, a gas-fired furnace has been introduced for the heat-treatment of goods-vehicle rear-axle housings, it is designed to heat the housings to 900 degrees C. in 48 minutes, and to maintain them at that temperature for an hour. Each housing is on a separate tray, and •a clock controls the pusher mechapism, so that the Cycle of operations is automatic.
Brittle fracture of case-hardened lowalloy steels, and particularly of chromium vanadium steel, has been investigated. A form of impact test was devised and the number of blowg required to cause fracture was made the criterion of the toughness. Casehardening in solid, liquid, and gaseous media was tried.
Cyanide Hardening
Hardening in a molten cyanide bath always gave the lowest impact strength. The best results were obtained on the chromium valadium steel by carburizing at 900 degrees C. in either a solid or a gaseous medium, cooling slowly, reheating in a controlled aunosphere, quenching in oil, 1.nd tempering for an hour at about 340 degrees C.
A. flame-hardening machine has been invented to deal with gears, wheels, and small circular parts, in which the article to be hardened is spun while being heated by radially positioned oxy-acetylene burners. The application of induction heat treatment to internal surfaces of commercial and other automobile vehicle parts has been the subject of experiments. The technique is being applied to static and progressive cylinder heat-treating machines.
The results of sawing, turning, drilling and tapping tests on various, types of stainless steel have been outlined. It has been demonstrated that when free-cutting elements have been added to the steel, its machinability is greatly -improved, and is practically, equal to that of normalized medium carbon steel. The broken chips produced with small drills and taps readily clear the flutes in these tools, Chromium Impregnation
The free-cutting stainless steels also have a much lower tendency to seize when in moving contact with metals. Methods of impregnating the surface of steel with chromium to a depth of 0.1 mm. have been developed, This surface layer attains a corrosion resistance equal to that of a 30 per cent. chromium'ateel.
A process of applying an extremely thin coating to steel, zinc,. and other metals has been introduced.'it. comprises a phosphate coating sprayed on at room temperature. Acting as a rust preventive, it is plastic enough to permit bending or stamping without cracking.
The encasing of metallic parts in skin of plastic material, as a protection against corrosion—a method developed during the war and now available for peace-time use—consists of applying a coating by hot dipping. This coating is transparent, waterproof, and resists corrosion and abrasion. The protection can be applied in two to five seconds, lasts an indefinite period, and is completely, easily, and rapidly removed when the part is needed for use.
Infra-red ray heating equipment is now in full commercial use at the works of a goods-vehicle builder in the United States. The equipment consists of two tunnel-shaped ovens with sides and a roof made up of banks of infra-red lamps. One tunnel is employed for drying the priming coat, and the other for baking the finishing coat at temperatures of 130 and 105 degrees C. respectively. • Alloys and processes have been introduced by a British concern for making wearand heat-resisting liners for cylinders. 'In particular, there are two new cast irons, one of which contains 2.5-3.5 per cent. of silicon, 0.6-1.5 per cent,. of chroinium, and up to 0.5 per cent. of molybdenum The other contains 2 per cent. silicon, 1 per cent. of manganese, 13-15 per cent. of nickel, 5-7 per cent. of copper, and 1.5-4 per cent, of chromium. This is an austenitic type of cast iron.
Tank Lining'
In Germany, during the war, methods were developed of applying synthetic coatings on the insides of tanks used for string petrol. For small tanks, baked phenol-formaldehyde resin coatings were employed, whereas for larger tanks a plasticized nitro-Cellulose air-dried lac' quer was applied. This lacquer was. . however, modified by the addition of soluble urea-formaldehyde resin, which was cured by the addition of phosphoric acid to effect good adhesion and to make the film insoluble in petrol.
A new alloy known as Eatonite has been introduced for facing engine valves and maintaining a high hardness at redheat. It contains chromium, nickel. ,tungsten, and cobalt.
A new stainless heat-treatable steel was manufactured in America during the war. In the annealed condition it has a hardness of C.22 to 28 Rockwell, and a tensile strength of about 54-67 tons per sq. in. By proper heat treatment, these figures -can be raised to C.39 (to 47, and 87 to 100 tons respectively).
Graphitic carburizin g steels are another new development. They contain from 0.1 to 0.3 ner cent. carbon, 0.25 to 0.75 per cent. molybdenum, 1 to 1.25 per cent, silicon, and 0.3 to 0.8 per cent. manganese. Cups and cones for bearings are being made from these steels. The parts are pack-hardened for 24 hours at 930 degrees C., diffusion heated at this temperature, oil-quenched, reheated to 830 degrees C., oil-quenched. then tempered at 180 degrees C. The case-hardness produced is 59-60.5 Rockwell C. Service life tests indicate that bearings made from these steels are equal to those made from a normal bearing steel.
New Battery
A battery said to have oversize electrical capacity has been introduced. It has a capacity for three times as much Water as is contained in the conventidnal unit, whilst the resultant milder average strength of the acid is favourable for
longer life. Fibreglas insulation prevents loss of valuable power-producing active material from the plates,' it is claimed.
A series of filters of novel design has been introduced. They are suitable for handling virtually any type of liquid, including fuels and oils used in engine systems. They are based on the use of an edge-wound metallic element, which presents a rigid, surface to the incoming liquid.
The filtering surface is formed by wire coiled on a metal frame. This wire has a tapered cross-section, with a flat outer edge, and is provided at intervals with projections of uniform height, supporting the outer 'edge of the wire parallel with the frame on which it is wound. The height. of these projections determines the degree of filtration. Brass, stainless steel, and monel metal are used as the standard wire materials.
Valuable Alloy
A new corrosion-resistant and nonmagnetic alloy has high tensile and fatigue strength, together with a wide hardness range. Moreover, it can be counted on for uniform properties and performance. It is available in bar form, in forgings, or fully machined to specification. It is the first in a series of hardenable copper-nickel-manganese alloys, containing 40-75 per cent. copper. with the balance substantially equal parts of manganese and nickel. A major improvement in the quality of high-speed steels is being achieved by a more even distribution of free carbides throughout the steel, and elimination of their segregation in the centre: The steel produced by this process is said to be superior to, and more uniform than, the existing steels. It shows uniformly superior results under heat treatment; longer tool life; a longer run between grinds; a minimum of distor tion and cracking; and an all-round consistent tool• performance.
Dry cyaniding is a new approach to the problem of providing a skin on lowcarbon case-carburizing steel without embrittlement or excessive distortion. Distortion is eliminated, and a tougher core, as well as a better and more uniform case-depth, results from this method.
Case depths up to 0.025 in. (of true carbon combined with nitrogen), with a hardness in excess of Rockwell C.60, are readily obtainable. Depth control is unusually accurate. Where ordinary cyanide hardening is not quite good enough, ibis new method is said to afford a safe answer.
Precision Castings
_ Precision castings, developed during the war for use in certain war equipment, and now available for commercial applications, are cast of chromium, cobalt, and tungsten alloys, with hardnesses varying from Rockwell C.38 to C.58, as cast. Commercial tolerances run to plus or minus 0.005 in. On certain small applications these can be held to plus or minus 0.002 in. The net weight per casting varies from I oz. to 3 lb.
These castings have an extremely high resistance to heat, corrosion, abrasion, or a combination of these factors. They eliminate I eat treatment, reduce later machining and grinding to a minimum, and, in some applications, obviate these operations entirely.
A new alloy of the phosphor-bronze family has low melting and casting temperature, high density, good machinability, corrosion resistance, and can be welded. Bearing properties are favourable, and the cost of the alloy is low, on account of the absence ofstin, a shorter melting time, a more simple moulding technique, and the absence of heat treatment.
Removing Scale
An unusual cleaning machine facilitates the manufacture of rear-axle housings from stamped and welded tube. Loose scale formed on the interior of the housing near the welds is removed by steel brush and cleaning solution mounted on a conveyor belt, with a second automatic stop for drying with hot air.
A post-war technique that is helping to speed up the production of commercial vehicles is the installation of mechanical refrigeration equipment directly on the engine assembly line. It is used for chilling steel valve inserts to shrink them before they are inserted in the engine cylinder blocks, so that when the inserts warm to room temperature they expand in the seats and cannot become loose. Chilling at a temperature of 84 degrees C. below zero shrinks the inserts 0.002 in., and makes possible installation at a rate of 360 per hour without interruption of the assembly line.
An oil-sludge solvent for use in -fuel lines, storage tanks, and similar equipment is announced. When used in oil fuel, even in the minute ratio of one part to 8,000, ths product is said to reduce the time lost in manual and mechanical sludge removal by maintaining carbon clusters in constant suspension, and assures a steady, free flow of oil, which burns efficiently without any residue.
Gas carburizing is one of the most recent and improved techniques for parts of commercial-vehicle engines. Compared with box carburizing, it has the advantage that boxes, dirty potting shops and compound-reconditioning plants are eliminated. A far shorter carburizing cycle can be used to provide a case of specific depth; so much so, in fact, that sometimes the briefer heating period enables a core-refining treatment to be dispensed with.
The carburized work is clean, and, when desired, can be readily quenched direct from the carburizing, or at any other, temperature. Great economic advantages arise from the fact that at each carburizing cycle only the actual work, plus light jigs or baskets, have to be heated, instead of the boxes and compound, which often weigh more than the work itself. One small furnace will suffice for an amount of work that, if box carburized, would need a large furnace and extensive shop space for potting and compound conditioning.