• War Stimulates New Methods and Materials
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Boron Additions to Steel, Special Lightweight Battery Plate and Unusual Uses for Low-carbon Steel, are
Features of Interest
IN. view of the demands of war 'industry for increased production with a reduction in the number of metals employed, it Will be understood why, on the whole, the latest metallurgical developments. have tended to concentrate on the more intense and effective employment of alternative
materials. The word " alternative " is used deliberately instead of " substitute," because, often enough, the new material is an improvement upon the old, and the term " substitute." does not give the'correct impression.
It seems probable that there is a distinct future for the introduction of boron-carrying additions to low-alloy steels so as to give them increased ability to be hardened, with a noteworthy improvement in mechanical properties. It is essential, however, that. the proper percentages of boron be added, and the technique studied carefully.
The steels to which boron has been so far added include case-hardening steels up to 0.25 per cent, carbon, both plain and alloy types, and medium carbon steels ranging from 0.3-0.6 per cent. carbon. Steels heat-treated to high hardness values appear to derive molst advantage from these additions.
Centrifugal casting is coming very much to the fore in both the United States and this country, and many prominent metallurgists are paying special attention to the problems and
possibilities thereby represented. Three main types of product are centrifugally cast—true centrifugal castings, manufactured by teeming metal into a revolving metal die; semi-centrifugal, or formed castings manufactured, in dies, sand or core assembly moulds, the interior surfaces being provided by cores; pressure castings, in which centrifugal action drives liquefied metal into moulds. As feeding beads, etc., are cut out by this process, there is a considerable economy in metal, and this is. particularly interesting to, founders.
Extensions in Centrifugal-casting Technique
Both ferrous and non-ferrous materials are being centrifugally cast, and it is claimed that parts so produced are. sounder, denser and cleaner, often need no cores, and are more readily inspected. As against this, it must be pointed out that there are restrictions on the dimensions and forms suitable for casting by this method, installation and upkeep of plant are somewhat expensive, and there is some difficulty in varying the plant to suit jobbing work.
Powder metallurgy continues to gain ground at an amazing rate, but it is not possible, at the moment, to outline all the interesting and valuable developments that: are taking place. Powders extensively employed are usually produced by reducing metallic salts by means of gases, electrolytic action, or atomization. Numerous small parts to limits of 0.001 in. are being made by sintering, e.g., gears, bearings, filters, contact points, copper.. carbon brushes, anddivers brass, steel and aluminium products. Ironand aluminium-powder moulding techniques have been greatly improved, and further work is going forward.
Commercial-motor parts are being increasingly made from ferrous metal powders. Such parts a.s thrust washers. fan bearings, oil-pump gears, levers, cams, bearing retainers, etc., are examples. Moreover, it is clear that before very long a low-priced iron powder possessing, in the final form, a tensile strength of more than 20 tons per sq. in., will be available. Already an iron powder approximating to this strength is being commercially produced and sintered.
" Improved Welding Process for Carbon Steels Over, the preceding 12 months, much experimentation has been carried out in connection with 'the spot welding 'of hardenable steels containing as much as 0.48 per cent, carbon, and satisfactory results have been achieved by a post heat treatment of the welds by a second current flow following the welding impulse. Tests revealed that astonishing improvements in physical properties are feasible if the weld cycle time interval between welding and heat-treating and the length of the heat-treating cycle be correctly controlled. Shear strength and toughness are greatly increased, as also is shear impact strength.
In' 'a.c. arc Welding of thin-walled tubing, in which the current must be maintained low in order to prevvit burningof the material, the danger that the arc will be put out as the voltage wave passes through zero has been removed by the invention Of a nes,i/ stabilizer. This is built into an a.c.welding unit, and imposes a highvoltage, high-frequency current on the normal welding circuit. The oscillatory circuit is set up by a spark gap, and suitable inductance coils and condensers give ..the inductance • and capacitance for circuit 6;)nstants. This high-frequency current ensures ionization of the air in the arc. gap, as Well as unbroken passage of the welding current.
Many parts of commercial motors contain small burrs. Many also have recesses, Skits or irregular surfaces and are hard to manipulate as well as difficult to produce, if these burrs be only partly eliminated or removed in such a way that design dimensions are modified. Power brushing has been successfully used to eliminate such edges from aluminium and steel parts, castellated nuts, etc. Fast Cutting wheels employed with a cutting compound are used, the wheel being run at between 2,400-3,000 rpm. according to the type of material.
Deep slots are being successfully broached to fine limits on small parts by means of a special hydraulically operated clamp. The parts are alloysteel drive spline inserts for hydraulic disc brakes.
Blanking-die Production Speeded and Simplified
Blanking dies for aluminium-alley sheet-metal parts are being manufactured in mass by means of flat plough steel punches used in conjunction with rolled zinc-alloy dies, which are broached to the final dimensions by the punch itself.
A new invention is a unique means for sorting and testing non-destruc tively ferrous and . non ferrous materials. It will check, evaluate and sort by such factors as Machinability, toughness, internal stresses, structure, analysis, 'case depth, plating thickness,
and heat treatment. It operates by electronic means, and is founded on the principle that these various properties set up variations in the core loss of a tuned pick-up coil surrounding the test-piece. Such variations modify the form of, a readily interpreted oscillogram. The machine is Capable of dealing with large quantities and, in such circumstances, automatic sorting is carried out at speeds of the order of five pieces a second,
01 interest to the commercial-motor maker or repairer not posseseing special equipment for manufacturing blanking and forming dies is a. new process comprising the manufacture of these dies from low-carhon steel, using tool-steel inlays arc welded into position. It is said that savings up to 64 per cent. can be obtained in this way.
fle,cause'of present restrictions on the employment, of bronze-, cast-iron welding rods have once again come into employment as a means for repairing by welding iron castings. In Switzer land, . high-speed steel is being deposited on carbon steel and as a means for repairing worn milling cutter teeth by gas welding.
An apparatus has been designed for indicating quickly whether the carbon content of a large number of steel tubes is greater than a specified figure. An energized coil is inserted in a secondary 'coil with a steel tube
between them. It is then found that the coupling between the coils varies with the properties of the steel. Several hundred tubes may be tested in an hour by unskilled labour.
The interior of poppet valves in internal-combustion -engines is being finished by a revolving polishing rod to eliminate scratches, after which the polishing head is reciprocated to remove circumferential scratches left after the polisher has finished its work. In this way a valve stem having better mechanical strength is obtained: A new development is the making of small alloy steel, tool steel, and bronze castings by a method previously confined to dentists and jewellers. This is the use of a pattern of wax or a plastic capable of being melted or vaporized without leaving any remainder.It is claimed that if the right materials be used for moulding, and, the correct procedures followed, it 13 possible to cast parts to an accutacy of within less than 0.001 in. of the desired dimensions. The casting itself is produced by either centrifugal, pressure, or vacuum methods, Centrifugal casting is being employed for the casting of knuckle joints, sprockets, brake shoes, and other steel parts.
Induction Hardening of Heavy Sections An induction hardening machine has been invented for hardening the teeth of 124n.-dia. sprockets. Two sprockets are mounted horizontally one above the other, and an automatic device causes them to move forward in such a way that two teeth at a time enter the heating coils. They are then withdrawn and turned, and the next two teeth driven forward. The hardening cycle comprises 10 seconds for heating, 4 seconds for quenching and 6 seconds for movement.
A method of further eliminating corrosion in zinc-coated steel has been developed. It comprises immersing the cleaned, zinc-coated • part for a period ranging from five to twenty seconds in a solution made up of 200 g. of Sodium dichromate, and six to nine c.c. of concentrated sulphuric-acid per
litre of water: after which the part is rinsed and dried.
Another interesting feature is the increased employment of lead alloy as a substitute for zinc in coating steel. The ordinary hot-dip galvanizing plant can be employed with suitable modifications. The lead-alloy film contains 95 per cent, lead and 2.5 per cent, tin, andis both harder and stronger than pure lead. Age-hardening occurs after the expiration of a few 'days, and this makes the coating extremely abrasionresistant. Moreover, the • lead alloy seives to lubricate the metal when it is required for forming, stamping and drawing. It is a development of the well-known terne-plate technique. High manganese stainless steels are being again investigated, .and it is now apparent that these steels possess extremely good welding and fabricating properties, and are less liable to weld decay than the standard austenttic chromium-nickel steels.
This is especially so with welds. A process of cladding carbon-steel strip with a film of a zinc-copper alloy• (10-90) has been developed in the United States.I The finished material is being extensively employed as a replacement of brass for various purposes.
A new type of fluxed-wire solder, containing-flux in longitudinal grooves on the surface, instead of in the normal core, is now available, and is claimed to constitute the first basic improvement in fluxed-wire solder design Since this Material was put on the market some years ago: The advantage of the new material is that it liquefies and flows on to the work before the solder melts, thus ensuring thorough and perfect fluxing, with better and stronger soldered joints. Moreover, an uninterrupted flow of flux is guaranteed; and as the flux supply is external to the wire, it is invariably visible to the operator and may be speedily and easily checked.
Tungsten-carbide tipped scraper blades are a new advance. These are to be had in three widths to fit standard hand scrapers. All that is needed is removal of the high-speed steel blade, and insertion of the tungsten carbide-tipped blade. These blades are claimed to outlast ordinary blades by eight or ten times.
A new cutting-oil compound for use in machining high-speed tOol steels, chromium molybdenum steels, and various other alloy steels is on the market. It comprises a blend of animal oils and chemicals, and is said to give twice to six times as long a • tool life between regrinds, to ra,is6 production by from 25 to 100 per cent., to render higher cutting speeds possible, to minimize co:rerheating at the stool nose, to quieten the operation, and to produce a better surface finish. It is specially advantageous for tapping operations calling for clean threads, etc. Zinc is being increasingly used instead of cadmium for plating many parts needing protection against cor
rosive agencies. A special alkaline bath has been developed with which
an addition agent is used. This is claimed to yield satin-bright to bright cadmium deposits, the degree of sheen being governed by the working conditions. Another new finish for metals promises to be revolutionary. It'cOmprises both a new material and a new process. Essentially an alkali alumina silicate, it is spMyed or dipped„ and cured to form a hard, heat, acid and alkali resistant finish.
A Chicago manufacturer has invented a vibrating tool that gives identifications to jigs, dies and tools. ' It hammers and engraves on glass, rubber, cardboard, stone, wood, leather
• and steel'. The tool weighs no more
than 1 lb.
Saving Lead in BatteryPlates by Design
A new battery element is built up of an external lead sheet and an internal zinc sheet, both formed into Cups and interlocked along radial pleats_ The lead cover prevents the electrolyte from seeping through perforations in the zinc, and the battery operates until all
the available zinc is used up. Both layers of metal are so thin that the quantities employed are less than in normal batteries.