War Gives Pioneer Techniques Their Opportunity
Page 31
Page 32
If you've noticed an error in this article please click here to report it so we can fix it.
Alloy Sleds by Powder Metallurgy, Antimony as a Major Alloying Constituent in Bronzes, and Argon Shielded -arc Welding are Pointers to a New Era of Development Ushered t'n by the Crisis FROM the United States comes a new magnet material for indicating ' instruments such , as
• speedometers. It is tough, free from brittleness, and contains 30-52 per cent. iron, 36-62 per cent. cobalt, and 6-16 per cent. vanadium.
The United States has also produced a new steel for castings designed to withstand impact. This contains aim per cent. (max.) carbon, 0.2-0.5 per cent. silicon, 0.5-0.8 per cent. manganese, 3.5-4.0 per cent. nickel. The material has an average tensile. strength of 25 tons per sq. in., with a yield point of 18 tons per sq. in., 30 per cent. elongation in 2 ins., and reduction of
area, 60 per cent. Charpy impact strength is 40 ft.lb. at normal temperature and 20 ft.lb. at 115 -degrees C. Slightly higher tensile strength, at the expense of a little impact resistance, is obtainable by the introduction, if desired, of vanadium, molybdenum, or 7.hromium. .
NI/Cr Steel by Powder Metallurgy Nickel-chromium steel has, experimentally, been manufactured from a powder, a development that may have enormous importance in the future. The steel is one of the 0.35-0.45 per cent. carbon, 1.5-2.0 per cent. nickel, 0.5-0.8 per cent, chromium type. Tests demonstrated that strict control of ' heating and pressing conditions made it possible to obtain a steel the properties of which equalled those of a similar steel made from the ingot.
Whilst it is not claimed that largescale production of nickel-chromium steel by this process is as yet feasible, it is argued that there may be an immediate application for it in the making of parts of intricate form, needing only superficial grinding after hardening. Some work has already been done in this country on the powder .metallurgy
of the 8/18 Ni/Cr steels. . • Silver solders containing lithium have been developed, the lithium cOntent being 0.12 and 0.26 per cent. The full composition of these two solders is: (a) 65.40 per cent. silver, 19.5 per cent. copper, 15.01 per cent. zinc, 0.12 per cent. lithium; (b) 65.34 per Cent. silver, 19.66 per cent. copper, 14.73 per cent. zinc, 0.26 per cent. lithium.
Tests reveal that these solders flow more readily than those of normal type, whilst joints made with them have ahigher shear strength. The 0.12 per cent. lithium solder appears to produce the more satisfactory results. Tinning is easier and quicker, particularly on monel metal and stainless steel. A silver solder, containing 60 per cent. silver, 20 per cent. copper, 15 per cent. zinc, 4.9 per cent, nickel, and '0.1 per cent. lithium, has also been found valuable as a -high-strength, high-fluidity brazing medium. .
With' the advent of the "molybdenum high-speed. tool steels, there is a con tinual risk of mixing these up with bars of tungsten high-speed steel. .A means for sorting them out, where doubt exists, has been developed. This is a modification of the quantitative colori-, metric test, which is widely employed as a method of ascertaining the molybdenum content of steel, being founded on the orange-coloured compound formed from the quinquevalent molybdenum ion by the reaction' with sodium thiocyanate after reduction with stannous chloride. The test is claimed to be suitable for steels containing percentages of over 0.2 per cent. molyb; denum.
A new heat-treating process known as " martempering '.' has been developed. This is a means for quenching steel, whereby the hard martensitic structure is formed with a minimum of hardening strains. It comprises (a) an intensive quenching for a brief period, followed by (b) treatment in a liquid bath (a salt bath, as a rule) for a period long enough to equalize the temperature throughout. The steel is then allowed to cool in air through the temperature range in which martensite forms. After this, tempering in the normal manner follows. The salt-bath temperature ranges from 205-315 degrees C.
The principal advantage of the process is that it allows use to be made of the high hardness obtained by increase ing the carbon percentage of low-alloy steels, as it eliminates the cracking and warping that take place. when steels of this type are vigorously quenched.
A method of quickly sorting steels by their magnetic properties comes from Canada. The method is founded on the employment of comparison induction coils and an oscilloscope.
Nickel-Antimony • Bronze Gears
A tin-free gear bronze has been developed,. also in Canada: This contains approximately 90.5 per cent. copper, with 7 per cent, antimony and 2.0 per cent. nickel. The alloy is claimed to be highly suitable for thin-sectioned sand-cast .bushes and gear blanks and heavier Sections niade by -the centrifugal process. The use of antimony in this way 'has been' experimented upon for some years.
A method of welding stainless steel in an inert atmosphere has been introduced. It comprises the employment of a special torch containing a carbon electrode, around which 'idyls a steady
stream of helium. The helium gas blankets the liquid weld metal, keeping -air away,-serves as a flux, and prevents oxidation. The arc in this process is produced directly between a carbon electrode and the base metal, rather than between carbon electrodes, as with atomic hydrogen welding. Purity of the helium gas is essential to secure the best results.
Stainless steel may also be successfully welded in an argon atmosphere, the use of which was first suggested in our companion journal, ` Light Metals," as a substitute for helium, of which there is insufficient in this country.
Corronizing is an interesting new process. It comprises successiveapplication of two thin electro-deposited coatings, followed by heat treatment designed to eliminate porosity and make the finished coating denser. The heat treatment also makes the coating metals alloy with their base, thus greatly improving corrosion resistance of the plating. The process is covered by British patents and is particularly valuable for copper and copper alloys, in which case the coating is of nickeltin. These coatings are readily soldered and may be applied with equal effect to ferrous bases. There are numerous coating compositions and coating-processes covered by the patents.
From researches made, it has been established that large-diameter electrie welding rod is desirable for minimizing the time needed for the deposition of a specified weight of metal. An interesting welding advance is the introduction of new, heavily coated. a.c. electrodes, suitable for high-quality welding. The new type of electrodes give 32 tons per sq.•in. strength, with 27 per cent, elongation in 2 ins.
Fuel Corrosion of Nitrided Steels Another important series of experiments has been devoted to the investigation of fuel corrosion on nitrided steels. These experiments were carried out in Germany, and, as a result, it appears to be shown that anti-knock fuel does not attack nitrided Steels to any great extent. Test pieces steeped in petrol, with an addition of leadtetra-ethylene, remained unchanged, Whilst steels that had not been nitrided were strongly attacked. It is recommended, therefore, that these nitrided steels be employed for taps, cocks. plugs, and other parts of tanks and of fuel piping. No information is given on their resistance to corrosion by acetone or alcohol-bearing mixtures.
A new British solder gun has been produced. This is fitted with a pushbutton, by means of which 50 per cent. of the resistance may be eliminated, and wattage and temperature raised by 100 per cent. Thus, soldering temperature is attained inside 90 secs. The 50-60-watt button enables the bit temperature to be sustained and, at the same time, Prevents corrosion of the copper. It is stated that this new appliance has been found extresdely economical in plants where soldering is carried out in continuous shifts.
There has always been difficulty in grinding thread-cutting tools to the desired accuracy. A new American master gauge has been developed and is said to be so acctrrate and easy to operate that thread-cutting tools may be rapidly and economically ground with complete accuracy, even by relatively unskilled labour.
The gauge is made from hardened tool steel, is simple in design, and is ground to fine limits. There are milled slots on top and bottom, giving correct grinding angles for opposing tool surfaces. The cutting tool is placed in the slot and the knurled-head thumb-screw maintains it firmly in position. • A small setscrew at the end prevents any sideways movement.
A plant has been put down in America for reconditioning used casehardening compounds automatically. The plant comprises an arrangement of conveyors, a cooler and ash remover, and a mixer for mixing in a proportion of new compound.
Tool-reconditioning by Hard-facing A process of reconditioning worn or chipped high-speed steel tools has been devised, and is termed Suttonizing. It comprises the deposition of a film or layer of metal on the worn tool,, by means of a proprietary welding rod, and afterwards grinding to shape. The tool must be pre-heated, but need not be heat-treated after welding. The final surface has the cutting properties of high-speed steel: Colmonoy (a chromium-boride-base alloy) can be used for similar purposes, particularly for cutting tools for magnesium alloys, From America, too, comes a method of preparing steel surfaces for painting. This is termed flame-priming or flamedescaling. Heat is directed by means of a burner on to the rusted surface, It firsf dries out the physically absorbed moisture and breaks down the rust, leaving an anhydrous oxide. At the same time, the reducing_ gases in the flames reduce the oxide to ferroso-ferricoxide, or black magngtite. The fortiaation of this black powder shows that all moisture has been driven off. Steel panels dealt with in this way before being coated with different paints show a. higher corrosion resistance.
Chromizing is being increasingly employed. The process comprises passing a current of chromium-chloride gas over the steel in a retort or muffle, thus causing chromium to be diffused into. the surface of the metal. The chromium consumption amounts to 0.45-0.48 oz. per sq. ft. for the normal case thickness of 0.0004 in., and there is virtually no loss of chromium.
Solvent-free Paint Spraying The protective coating of steel is the subject of a new Swedish process in which molten resin is sprayed on to tile metal. The wax in solid, cylindrical form is placed in a gun furnished with an electric heating element, which is designed to bring it to the melting point of approximately 150 degrees C. The liquefied wax is driven by compressed air in tiny drops against the steel, previously dried and slightly preheated by an acetylene flame from the tame gun. A layer of compressed air projected through a ring-shaped nozzle stops the flame from touching the wax. No solvent is necessary. If the surface of the steel has been sandblasted, excellent corrosion reaistance is conferred by the wax film deposited. (See also British Patents 275,477 and 386,101.)
A process has been patented in Germany for making permanent magnets, such as those used in speedometers. The nickel-iron-aluminium magnets are manufactured from a crushed and finely powdered alloy, which is pressed at a temperature below the sintering point, employing a binder of synthetic resin. The magnets may be provided with small holes or with studs in them. It is stated that the magnets made in this manner may have approximately 80 per cent. of the magnetic strength of cast magnets.
An ingenious saw for cutting slab
stock into brake-facing segments and clutch facings has been developed. Flat -and curved pieces of either soft or hard material may be cut with equal facility. The blade is of alloy steel, specially tempered. An adjustable gauge arm locates the cut with accuracy and is provided with a swiftly adaptable roller guide for sawing clutch facings and a floating rocker for sawing straight widths. The saw will cut any kind of clutch or brake-lining material. The gauge may be set to cut widths up to 7 ins., or, if taken right away, any size may be cut.
A new aluminium alloy has been developed to farovide castings with lower distortion and internal stresses and without any tendency to growth. The metal contains 2 per cent. copper, 1.5 per cent. tin, 0.8 per cent. magnesium, 0.8 per cent. zinc, 0.2 per cent. titanium, and remainder aluminium. This alloy has an ultimate, tensile strength of 15 tons per sq. in., yield point of 9 tons per sq. in., increasing to 10 tons after ageing at room temperature for a few months. Normal elongation is 8 per cent., declining to 3 per cent. after ageing. Brinell hard. ness No. is 72. The alloy is resistant to corrosion, is easily machined, and is weldable without effect on physical properties.
Improved Valve Steels A considerable investigation has been made of steels designed for valve facings. The range of composition that appears to be the most suitable is a steel containing 0.42-0.52 per cent. carbon, 1.5-2.0 per cent. silicon, 3-5 per cent. manganese, 6-4.5 per cent. nickel, 17.5-18.5 per cant. chromium, 0,9-1.3 per cent. tungsten.
Bearing metals are now compelled to accept a much lower tin content. With a decrease in lining thickness, the problem of securing a strong bond between lining and cast-iron or steelbacking pieces has been great. The difficulty has been overcome in America by thorough cleaning of the backing material and tinning it with an alloy comprising a solid solution of tinantimony compound in lead capable 01 dissolving up to 7 per cent, of iron. The lining alloy may then be cast on to the tinned surface. L.S.