Mastering Metals in the Laboratory and Shop
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MHERE nas been introduced a new • vitreous-enamelling alloy steel which will take white and other colours without the prior application of a ground coat. This is because a thinner covering of enamel produces a better surface; less liable to chip, and with longer service life than the old, costlier multi-coat. Indications are that the drawing properties of the new steel equal those of the best deepdrawing sheets, including those provided for the commercial-motor industry. Another important property of the new tel is •that it does not strain age. Drawn shapes are free from strain lines, regardless of the time lapse from production to fabrication; neither special temper rolling nor roller levelling is required to prevent strain lines. The material has also better resistance to sagging.
A porous metal has been developed for filterir It has four grades of permeabili arid is made from copper tin powders of spherical form One filter will separate mixtures of petro leum and water, If wetting first occurs ' with water, water passes through and petrol remains ; if wetting first takes place with petrol, then water remains behind while the petrol passes through. These niters are being widely used as injector filters for oil engines, etc. Steel-backed babbitt bearings are another advance in powder metallurgy.
A mixture of copper and nickel pow ders is spread evenly on a strip of metal which is sintered at 1,093 degrees C.
The copper bonds the nickel to the steel, and a sandpaper-like surface 0.g5 in. to 0.3 in. thick results. Next, 0.017 in. of babbitt is flowed on to the nickel copper surface in vacuo. The bearing is then finished 0.001 in,. to 0.003 in.
above the copper-nickel layer, and a thin layer that will withstand high loads and eliminate scoring results,
New Metal-plated Plastics
Plated plastics are a recent development. They are much lighter than an all-metal part, often have improved moisture resistance, and may be protected from many solvents. The part retains its shape and its " internal " non-conducting properties, is more resistant to heat and vibration, and is stronger than an all-plastic . article, whilst not being subject to the• corrosion often experienced as a result of the electrolytic action between the layers of a metal-to-metal plating job.
The extrusion of aluminium bronze is now a significant engineering achievement, and makes availaSle to designers a new material. Ford interests have developed a new tri-alloy bearing that will give from two to three times the service life of the conventional bearings, even under the most severe conditions. 'Another advantage is claimed to be its ability to withstand abnormally heavy loading at high speed operation. The tri-alloy material comprises 35-40 per tent lea,4i-5 per cent, silver, and the balance copper, with a trace of iron.
A processfor producing bronze-faced pistons is announced. Investigations in a different direction have shown that increased corrosion resulting from the coupling of metals can be reduced by painting the cathodic metal surface. This is preferable to painting the anodic or corroding surface, which may lead to pitting.
Tungsten-carbide shapes are now being produced by a new extrusion process, which renders it possible to make numerous different forms from twist-drill sections to tubing having an outside diameter of -/J6 in., and inside diameter of l-04 in.
Low-temperature Al Welding
The welding of aluminium has 'become. increasingly important, and a new electrode for sheet and castings of this metal_ has recently been intro diced. It opens up for arc welding a new field in the salvage and reclaimingof aluminium castings. With this electrode, it becomes possible to add metal without completely preheating the casting, and particularly without danger of overheating the metal adjacent to the weld. The operation is thus extremely rapid and, consequently; economical, rendering the salvage of defective castings simple and inexpensive.
The rod is claimed to be highly successful in the addition of metal to faulty or improperly machined castings, the overlaying of surfaces improperly cast, the filling of low spots, the changing of aluminium patterns already machined, the filling of badly drilled holes, the filling and overlaying of porous castings, and the welding of castings to aluminium Sheet.
In the joining of aluminium sheet, the extremely high rate of fusion of the rod produces a smooth, strong, homogeneous fillet with great, speed, avoiding distortion. The rod itself is a-high aluminium and low silicon composition alloying itself to virtually all types ofaluminium.
A rieW method of coating steel rod . and wire with glass which eliminates
acid-cleaning operations by mechanical means has been developed. In this process, spray guns are suitably located to spray molten glass on to all surfaces of the hot rod after the finishing pass, or just as it enters the reel guide, so insulating it against fur. tiler Oxidation during cooling. Below oxidizing temperatures, the coating will separate from exposed sections, removing what oxides are formed with it The rod ii drawn to wire and transferred to the galvanizing branch, where it is passed through a container ot molten glass heated to approximately 1,100 degrees C.
On cooling to below oxidizing tern. perature, the glass coating separates, removing any oxides formed with it, effecting a perfectly clean, annealed surface. It can then be passed directly through a -flux, into the spatter bath. The method has so far been applied only to wire products and narrow widths of stainless-steel strip, but there is no reason to _believe that it cannot be used for all grades of strip, sheet and bar steel. It is claimed to result in improved quality, increased production and reduced metal loss.
Good progress has been made in closed-die forging, and parts of fairly complicated shape can now be dealt with. Small forgings of symmetrical form can be made in closed dies with
no flash at the parting line, This -is achieved by rotating the part while it is being forged, and allowing the surplus metal to extrude through an opening left in one end of the die.
Metallization is playing an important part in the war effort in reclaiming worn surfaces on rotating parts, with
great savings of time and money in restoringmachines to operation. One
large important war use of metallization is the spraying of engine cylinders wit'n_alisminium, to improve their corrosion resistance,
Controlled-quench Shrinking The quenching of rings on the outside so that the bore is shrunk is a useful device now being practised. it is accomplished by placing the hot ring on a piece of paper on a wood shelf, which is lowered into the quenching medium, carefully, only sufficient to bring the liquid to the top. None is allowed to get into the .bore until adequate shrinkage has occurred.
Distortion. of long, slender tools and shafts is being eliminated by rolling them between heavy, flat plates heated to about 230 degrees C. immediately after quenching.
A three-dimensional replica for surface inspection, capable of being enlarged 100 diameters or more and of being prepared in less than a minute at a cost of 3d. per print, is provided by a new method known as Faxfilm. One side of a piece of clear plastic film is softened by the use of a small amount of solvent, so that when it is pressed
On to any surface it penetrates every unevenness, The film is then mounted on •a .2-in.-square cardboard frame which fits any standard projector-magnifying 100 diameters or more.
The cathode-ray screen has been adapted to the examination of metal parts, in determining such characteristits as depth of carburization, chemical composition, internal stresses, heat treatment or thickness of plating.
. A new aluminium alloy shows an altimate strength of a-bout 36 tons per sq. in, with an elongation of 14-IS per cent. Shot peening and burnishing methods are being commonly used to obtain lucreases in fatigue resistance ranging as high as 100 percent.
An innovation of great interest is the ihankless high-speed-steel twist drill. [-his has a continuous fluted portion produced by roll-forging and hottwisting and it is driven by a removible taper shank known as a 'drill
lriver." The price of these drills is ;aid to he 20 to 30 per cent..less than that of standard drills, The usable porion is 25-40 per cent, greater than that standarddrills. The shankless drill is also claimed to be tougher and itronger, because it is roll-forged and las a heavier web..
A manganese alloy.tvith:excep!tional Uniformity' in response•tO leaf. treatment 'has,been introdaced.t has rinanittal chemical analysis. of 60 per cent, copper, 20 per. cent: nickel, and 20 per cent, manganese. It it Soft and ductile, and can be either hot or cold formed intn intricate shapes -arid then ,lardened by a comparatively low-tem
perature ageing treatfrient. hardness af 900 Vickers can be obtained by
ageing either.dead soft or cold-worked material. The physical properties, at -this hardness, are ,90 tons per sq. in. tensile strength, 76 tons per sq. in. yield stress, and 50 tons per sq. in proportional limit. The alloy is especially useful as a spring material, It is also. corrosion resistant.
A new non-porous copper plate is being used for selective nitriding as a protective plating. Nickel and bronze plating are also being' uSed for the same purpose, Recent trends in sleeve. hearings have _been the use of very thin layers of the bearing materials, and the development of new alloys. The silver-lead-indium bearing, in which a heavy, fine-grained deposit of silver is plated on to a steel backing to ensure a good bond, is _becoming standard in certain engines. A film of lead about 0.001 in. thick is then plated on the silver, and a. small amount of' indium plated on the lead. After a diffusion treatment to alloy the indium with the lead, the bearing is ready for service, and has given highly satisfactory performance. Another development is a lead-tin alloy plated as such on either a silver er.copperlead=bearing layer. This alto makes a satisfactory bearing, Tiu-19ael searing Metal:.
Whilst siNer is the heSt. base Material Minn: a loaCbearingtroint of•view, and is nicist.successful where dust can be excluded from the engine, in commercial-motor use the incliam-lead layer may wear through, so that a copper-lead base which has much better bearing properties than silver, is being widely used. The--most recent develoup
ment has been the substitution of tin.lead for indium-lead as the actual surface of the bearing.
Rapid flame heating techniques tor brazing and hardening have made possible the economical production oh wide range of • parts requiring the application of heat in definite patterns, at fixed times and at given temperatures. A new method of cold-finished steel-bar production consists of a combination of cold finishing and thermal treatments to Obtain uniform and dependable strength and straightness.
In some-recent applications, zinc has been replaced by lead at a protective coating, and tests tend to suggest that, for certain corrosive environments, the lead coats are Superior to the zinc cbating. This,is particularly true where sulphuric and hydrochloric acid spray is concerned.
The vapour-blast liquid honing process, based on the use of particles sinaller in mesh than normal silica sand, hasi,been finding greatly increased use in the finishing of metal parts. Fine abrasives are mixed with a Chemical emulsion and discharged by compressed air against the metal surface to he polished or finished. The mixture of abrasive a,nd emulsion is discharged at the rate of 3,200 ft. per second tip Velority, or about 10-15 lb. of material
Minute.
The process has been tested and found -satisfactory on supercharger impellers, art rods, bearing races, guide vanes, connecting-rod bolts, gears, splines, etc. It has also been used for debarring, polishing and preparing parts for chromium plating and anodizing.