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METALLURGICAL RESEARCH

13th December 1946
Page 49
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Page 49, 13th December 1946 — METALLURGICAL RESEARCH
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Shows Marked Virility MUCH of the secret information concerning metallurgical and other developments introduced during the war is row being released.

A machinable heat-resistant cast iron of "grey 'type containing 0.05-0.5 per cent, of boron is an innovation from the United ,States, and ,follortts the work being done -in this country on boron as a steel alloy. Theart of blackening stainless-steel parts and products has been discovered, and includes treating the stainless-steel articles by immersion in a molten salt bath consisting essentially of sodium dichromate and potassium dichromate, while maintaining the bath at a temperature within the range of 400-500 degrees C.

Permanent magnets are widely employed in electric clocks, speedometers, magnetos, and so on, and this makes more interesting the development Of a range of new permanent-magnet alloys of a novel type. One of these is an alloy steel consisting of 1 per cent, to about 8 per cent. chromium, about 0.11.25 per cent. carbon, and beryllium from About 0.03-0.7 per cent., the balance being iron.

This alloy has a BH value of about 600,000, a coercive force above 60, and a Rockwell hardness value greater than that of a magnet made from a similar alloy steel without beryllium.

Another magnet alloy is of the aluminium nickel iron base type, and contains an amount of sulphur effective to improve the grinding and sawing characteristics of the alloy as compared with the same alloy containing only a trace of sulphur.

In alloy steels, mention must be made of a low-alloy steel adapted for use as a high-tensile steel, and for case carburizing purposes, whilst having improved heat-treating properties in the higher carbon ranges. It contains about 0.7 per cent. carbon, 0.7-1.0 per cent. manganese, 0.5-0.9 per cent. silicon, 0.5-0.75 per cent, chromium. and 0.1 per cent, vanadium, the remainder being iron.

There is also an alloy steel containing 0.08-1.5 per cent. carbon, 0.5-4.5 per cent. silicon, 1-8 per cent. copper, and 0.1-0.5 per cent. beryllium, This has a low melting point and high physical properties in the as-cast or hot-worked condition,

An interesting and useful new tool is

the metal-bonded diamond hand file. which has a concentration of 100. It retains the flat surface, and can outlast five ordinary resinoid-bonded hones., Because of its small size, it can reach difficult spots on the job, is useful for dressing short angles on abrasive wheels, filing down high spots on dies, honing tools, etc. One minute of resharpening is all that is necessary, with the kind of dresser stick• used on metal-bonded diamond wheels.

Bearings are being made by compression of powdered iron. They have the unusual feature of keeping themselves oiled throughout their working life. As the bearing maintains its porosity after compression, the cavities become impregnated with oil when the original gas in the pores has been removed. When the bearings are installed, the heat of friction causes them to release the oil during operation. When work has stopped and the bearings become cool, they' again absorb the oil.

Imperfect aluminium castings are being repaired by means of the atomichydrogen arc-welding process,-thus saving valuable time and materials. At one establishment, the rejection rate of these repaired castings was less than 1 per cent. Careful welding, using metal which is similar to the base metal, is carried out on the castings. Even the X-ray cannot detect the weld after the grinding process.

Worn metal faces, edges and other surfaces are' being restored to a condition said to be just as good as new when overlaid with a special new alloy. Applied by means of the electric arc or oxy-acetylene .torch, this metal flows smoothly and needs no bonding fluxes. It provides an excellent way of reclaiming tappets, wrist pins, rocker arms and other parts of vehicles, and tools.

A study has been made of a number of metals to find one to use as a bond between. aluminium and steel, so as to produce a joint with high thermal conductivity. The conclusion reached was that plating a layer of silver of the correct thickness on the steel was the best means for obtaining a good bond when afterwards welding aluminium sheet to the steel. The actual seam-welding of aluminium fins to steel cylinder barrels has been carried out by this method.

Another investigation was into the question whether exhaust manifolds of stainless steel picked up carbon from the hot exhaust gases. In the manifolds examined there was an increase in the carbon of 0.023-0.06 per cent., which contributed to the formation of a hc.avy .netwofk of carbides; The corrosion resistance was not materially reduced by the increase in carbon.

The effects of cold-straightening. 3 degrees of shot peening and recarburization, on the fatigue strength of lowalloy chromium-nickel-steel axle shafts for commercial vehicles, have been studied. The endurance limit of unstraightened axles was found to be about 25 per cent, higher than that of straightened ones. The endurance limit of shot-peened straightened axles was about three times that of straightened axles not shot-peened. If carburized shafts were accidentally decarburized during heat treatment, their fatigue resistance was lowered.

A photo-elastic investigation has been made into the stress concentrations produced around open transverse holes in circular shafts subjected to pure bending, the axis of the hole and the bending couples being in one plane with the axis of the shaft. This problem is of practical interest, because open holes in shafts often form psrt of the lubricating system of an engine.

The latest development in powder metallurgy is a technique that consists of heating a porous part, made of iron or steel powder in contact with a copper alloy, to a temperature above the melting point of the alloy. The molten alloy then fills up all the voids in the compact, and, on cooling, all the particles are welded together.

Materials with tensile strengths between 27 and 45 tons per sq. in. have been obtained by this process. Cheap raw materials and low compacting pressures make it economical. Parts made in this way can be readily brazed without a flux, and the surfaces obtained are sufficiently smooth and dense to permit electroplating without infiltration of the plating solution.

A series of tests was made to discover the type of steel most suitable for any application in which steel runs against steel without lubrication and without scoring while maintaining flat surfaces. A wear-testing machine was used in which a ring of the steel to be tested was rotated at a surface speed of 400 ft. per min, with a 12-lb. load.

The test was run until the first sign of scoring appeared on the ring surfaces. To run two metals together without lubrication, they should produce a fine oxide powder. The best results were obtained with a 5 per cent. chromium steel. Steels higher in chromium seized, even though an oxide Was artificially introduced.

A substance made of asbestos and other non-critical materials was made in the United States during the war for deadening motor noise and vibration. It is 50 per cent lighter than mica.

A drill chuck has been invented which is bonded with neoprene rubber on the jaws, and, anchored through holes, keeps the jaws in alignment, thus permitting one chuck to take a wider range of drills. Twelve collets, with three detachable arbors, are said to fill the needs of 300 ordinary collets.

A new coating process with cadmium or zinc requirqs ohly a two-minute to five-minute immersion. The surfaces produced prevent corrosion, and form a good base for painting.

Designed for light brazing, soldering, sheet-metal work, low-temperature welding, etc., a new gas gun ignites when the trigger is squeezed, and is extinguished when the trigger is released. A regulator is provided for controlling the temperature from 500 degrees to 1,100 degrees C.

For the cleaning of vehicle bodies, a soapless foam compound has been introduced. Any desired mixture of this compound with water and air can be _obtained by the use of a proportioning device installed in the unit, which operates with air pressure.

A new process has been introduced for obtaining molybdenum in large pieces and for moulding it to any desired shape. In addition to its ptesent uses, this form of molybdenum is expected to find extensive application in engine parts Which operate at high temperatures.

A crankcase lubricant of recent intro

duction is treated with a metal salt of an arylsulfonamide, which is dissolved in the oil to the extent of 0.1-5 per cent. of the weight of the oil. The inventors have found that the addition of these salts imparts corrosion-inhibiting and sludge-dispersing properties to the oil. Being relatively inexpensive, these additives form a valuable economic improvement in the preparation of lubricants.

A 6-in, tool marker, weighing only 10 oz., which can be used continuously on iron, steel, bronze, aluminium, lead, plastics, etc., with a standard alloy point, has just been announced. For materials of 54-64 Rockwell hardness, Scale C, a diamond point is required. The marking ;s performed by an electric hammer making 7,200 strokes per minute.

An improved grease for ball and roller bearings is stable, and will not dry out, cake or separate.

The need for economy in tin used in white metal and other bearings led, during the war, to much research into the lead bronze steel backed type. Powder metallurgy has now been used to produce high lead-copper base alloys of controlled density, bonded to steel backings. This means that the copper-lead lining can have a controlled amount of voids, and the voids can be used for impregnating the entire bearing with oil.

A metal of the platinum group is being used as a sparking-plug electrode.

A method has been developed for welding two steels of different composition. This involves passing a number of shots of current. The period of each shot is about 5 cycles,. and the interval between each shot is some 20 cycles.

This method produces a recrystallized weld—one in which actual fusion has not occurred, but =Ion of the two metals has taken . place in the plastic state. It produces a weld of high strength and ductility, and is particularly useful where the mixing of the two steels during the normal process of making a fused weld would result in a weld zone having poor Mechanical properties. This is the case, for example, when welding a stainless steel of the austenitic 18-8 chromium-nickel type to a medium carbon or low alloy, high tensile steel.

Aluminium radiators, brazed in the furnace, are among the most recent developments. Bearing metals containing small amounts of tin, nickel and copper, with the remainder commercially pure aluminium, are said to give improved service under extreme loads at high temperatures. These bearings are held to resist organic acids released by lubricating oils, and to have the ability to absorb particles of bronze and steel. Silicon is teported to improve the antifrictional and anti-scoring properties of the new material. Under boundary and thin film lubrication conditions, the bearings may accommodate much greater loads than bearings of babbitt, bronze and copper-lead.

Wear on cylinders and piston rings is being greatly reduced by chromium plating. Placed in high output engines, porous chrome piston rings increased by five times the hours between engine overhauls. Tested in all types of busengine cylinder, the plated rings maintained their peak efficiency over longer periods, effected as much as 44 per cent. improvement in m.p.g. of lubricating oil, and 2.7 per cent. in m.p.g. of fuel. The average ring wall wear was 0.00038 in. per 1,000 miles of vehicle running.

The chromium, of extremely fine porosity, first holds the lubricating oil in the ring surface. As the porosity begins to wear off, which takes but a few minutes, the tiny particles mix with the oil, acting as a gentle hone to polish the cylinder, and cause the rings to seat in almost immediately. This quick and perfect seal reduces blow-by and cuts down the break-in erosion, corrosion and high temperatures.

Tests indicate that thin glass fibre mats increase the life of acid storage batteries by as much as 50 per cent. when used to enclose the positive plates. They hold migrant granular lead particles in their facial interstices, from which they are restored on to the plate surface by charging. Otherwise, the particles would drop into the sediment chambers. These retainers are lightly impregnated with oven-cured phenolic resin. L.S.

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