Speeding Output and Cutting Costs
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Call for High Production Has Stimulated the Practical Adoption of Metallurgical and Structural Finesse' in Everyday Works Practice
WE shall hear much more of powder metallurgy after the war. It is no possible to detail in this article the use being made of it in certain directions. One or two new developments may, however, be
briefly mentioned. The first is the manufacture of oil-pump gears, the second the Making of filters for oil' for s high-speed oil engines, whilst .a. third application is to permanent magnets, although there are limitations in this field that must be taken into account.
A new type of suspension conveyor has been developed in Germany. This is a tubular conveyor in which the moving chain passes along the inside of a split tube, whilst the arms,carrying the hook, tray or bucket pass through thceslit. The advantage of this method is that fewer brackets are required to support the tube than would he neces • . sary with an angle iron chain, less space is occupied and, in consequence, the shadow thrown on the operating area is minimized. .
Some ' improvements have been effected in machines for the electric welding of tube strip into tubes. A. process for welding tube strip has also been invented in which the work is done by a combination of electric resistance welding and hammering. The welding current is supplied by disc electrodes, and a pneumatic or electrically driven hammer operates between the electrode and the edges to be 'united. This strikes rapid blows on the weld as it is heated and fused together, which action may be carried on during the cooling circle if required,
' Shot blast units have been 'designed for cleaning the inside and outside of steel tubes from 2-14 ins, diameter in lengths of 18-50 ft. It is claimed that a 41-in, diameter tube may be cleaned at IS It, per minute on the outside and 14 ft. per minute on the inside.
A new process has been developed.for the hot-dip coating of wire and strip with metals such as zinc, babbitt metal, cadmium and tin. The procedure is to elean, flux and preheat the material by causing it to pass through a bath of Molten salt befoie the metal bath.
Graphitic Steel Facing Alloy • In Germany, an iron-base alloy has been produced designed for hard-facing. This contains carbide-forming elements and up to about 3.5 per cent. carbon. It is known as " Gridur E, ",possesses . excellent welding. Properties, and is hardenable by a. heat-treatment process up te Rockwell C65 and even higher.
An interesting range of ball bearings has been developed in the U.S.A. These are not ground, but carefully machined end smoothly finished. They are subjected to a carburizing, normalizing, hardening, and tempering treatment, and are manufactured from a steel high in carbon and containing 0.65 per cent.
chromium. The outer rings are of various forms, plain and flanged, but are not hardened. There are numerous designs and dimensions, and extensive application is possible.
A26
One of the drawbacks of magnetic chucks is that they tend to magnetize' the part held on them. This'makes it advisable to demagnetize them to 'revent their holding of the chips and metallic particles encountered, e.g., in cutting tools. A new, portable demagnetizer has beep produced which. rapidly demagnetizes all those parts and tools that have been gripped by magnetic chucks or become magnetic in any other manner. Large parts are also, dealt with by simply, passing the demagnetizer itself over the job. The instruments are usually wound for 113 volts, 50-60 cycles, hut Other voltages are obtainable. An index light reveals when the current is." on."
"Patenting" in Attempts have been made in Germany to discover . an alternative for the lead bath in the patenting of steel wire. Molten-salt baths have been experimented with, and it is claimed that a molten sodium nitrate bath with a specific gravity of 2.26 is suitable for dealing with wires of normal strengths and types, and in fact is a little superior to lead bath patenting.
The induction hardening method has been. applied to the hardening of gears and in various instances' it has been found as satisfactory to use. a 0:4 carbon steel as to use a case-hardened low alloy steel, whilst certain operations may be eliminated. For example, after the teeth of a low-alloy steel gear were roughed out, they had to be car' burized, finish cut, hardened, tempered and lapped. With induction heating, it is sufficient to rough out_and finish cut the teeth and then incluction harden.
An investigation has been carried out to find the best flux for welding highsulphur steels. The most satisfactory results are said to have been obtained with a mixture containing .5 parts manganese dioxide. 3 parts borax, 3, parts ground silica, and 1 part kaolin. ,
A new procedure has been developed for detecting cracks. This has as its principle the fluorescence of various materials when exposed to ultra-violet. light. The piece to be tested is plunged into a bath of fluorescent material maintained at. 75 degrees C. After a brief period it is taken out and washed in a solution to eliminate all the fluorescent material from the surface. If cracks occur, the fluorescent material remains wedged into them, and as soon as the , piece is subjected to the action of ultra. violet light, the cracks are diselosed vividly against a black or purple background.* Lacquers, narticulatly those with a base of synth,etic resin, should not, it is said, be applied to the surface of steel until the metal has received a preliminary phosphatizing treatment. This is the result attained by the carrying out of a series of experiments. A phosphate film between the steel surface and the lacquer prevents rusting under the film, whilst at the same time increasing the durability and adherence of the lacquer. The phosphate films should he as thin and of as fine a grain as possible, and the method of application advocated is a modified Bonderizing process, a characteristic of which is that the phosphate solution is sprayed on to the surfaces to be lacquered.
The welding of a galvanized strucfure destroys the zinc coating at and near the weld. These areas are being regalvaniztxl by the following procedure. While the joint is still hot-from the welding operation, it is cleaned with a wire brush, and the surface is rubbed with a bar of low-melting-point galvanizing compound. The molten compound is then uniformly spread over the hots surface with the same wire brush.
A new steel known as " Armasteel " has been developed in the U.S.A. and is being applied to drop-forged steel parts such as crankshafts, camshafts,. rocker arms, gears, etc., Of automobiles. It is also being used successfully for pistons, of oil engines so as to save 'aluminium... It is made from a whitecast iron of special composition, melted in a cupola and refined and superheated in an electric arc furnace.
Heat treatment is one of the most important operations. The steel is saideto haye a uniform structure giving increased mechanical strength and shock-resistance, a wide range of mechanical properties, good response to local hardening, high hardenability and excellent wear-resisting qualities. It has, in addition, gbod machinability, a mirror finish beiug possible, with low finishing costs, has high rigidity with maximum deflection and highfatigue resistance. It ie, in effect, a graphitic steel.
Deep-casing—a •
New Technique -A new operation termed deep-case
carburizing has been developed. It is based upon an immersed-electrode salt-bath furnace, which is said to produce cases up to / in.. deep as compared with previous restrictions of 005 fn. The process .can be applied to gears, splines, cams, transmission and . other parts calling, for heavily carburized cases for strength and wearresistance.
A new process has been introduced for the blackening of Copper ernd copper alloys. It is a simple, direct, lowAernperature process involving immersion in a solution of blackening salts operated near the boiling point (100 degree.s C.)-. and is completed in' 2-10 mins., according to the alloy being dealt with. The coating is .
essentfally cupric oxide, and as it is integral with the base metal it cannot chip or flake.. It is hard enough to be buffed and 'does not need lacquering to prevent wear. • Weld spatter is being cut out by inean of a new product. This pro
duct. is brushed, sprayed or wiped
along the edges of the Metal surfaces to be united by the welding operation. Then molten metal droplets fall off instead of adhering to the areas close to the weld seam.„ Later grinding or scratchings are not called for, andsthe
seam has greater srhoothnessand is stronger because impurities are
eliminated from ;the' weld. The material is an excellent conductor of electricity and assists in holding the arc.
Gearboxes are being internally protected against rust and corrosion by painting their interiors with a special type of chlorinated rubber dissoli-ed in an ,organic solvent and containing a large percentage of powdered zinc.
A new design in oxy-acetylene machine cutting tips is cIaineed to raise the cutting speed of any ordinary machine torch . by 20-30 . per cent, without any increase in the consump tion of oxygen. The tip has a nozzle with a diverging exit portion, ejecting a narrow, high-Ifelocity stream of oxygen, virtually free from exit turboknee. This This burns a narrower path through the metal and cuts to cane limits.
Heanium,': an. extremely hard, abrasionare_sisting ceramic material, is now being employed instead of metal tot the inserts and liners of abrasive blast /nozzles. The sand blasting of
metals is a case in point Operating results ,show that in this way the cost of compressed air is minimized because the nozzle wears so slowly and
uniformly. As the original hole imaintained after several hundred hours
of service, the shape of the blast stream is kept and the work is cleaned more swiftly and evenly.
Another interesting development is a rapid temperature signal mark. Sticks of a special material are drawn
over a heated sutface. These leave behind a chalk-like mark .which melts , sharply as soon as the surface cif the metal attains the temperature stamped on the stick.. Melting point ranges from 50-870 degrees C. can be covered
in convenient intervals. This. is. a handy way of indicating required tem peratures on places difficult of access, e.g.,. vertical, sloping and overhead surfaces, where the ordinary seager cone. for example, or a fusible pellet, would not rest.
Simplifying Tool Tipping ' To enable tipped tools to withstand the severe service nriposed upon them. great care is essential to ensure an efficient brazed joint, One of, the difficulties is the difference between the :thermal coefficients of the tip and the tool shank. Contraction on cooling proceeds at different rates in the two metals and may crack the hard metal tip. This problem has been overcome by inserting between tip and seat a thin strip of special steel having a very lowcoefficient of expansion, which neutralizes the strains set up by cooling, contraction in the tip.
Another. cause of weak joints is thefailure of the brazing material to flowfreely and evenly between the joint surfaces. This is now being overcome by a patent corrugated strip of steel, which is cut and bent to the shape of the seatrng in the tool shanks, and' inserted between the tip and the seat
in advance of brazing. The seat is machined to a smoothfinish, and the tip faces in contact with it are ground with a suitable grinding wheel. Tip, corrugated strip and seat are then cleaned with carbon tetrachloride and a small amount of super-cleaner is placed on the seat to prevent oxidation. The shank is preheated at about 800 degrees C. and when cherry red is taken out awl the seat bruabed clean.
A -suitable brazing metal is then placed on the seat in sufficient quantity to form a good coating and powder flux is appliedover it. The shank is next heated up to 1,000-1,050 degrees C. and taken out when the brazing. material has melted. Excess brazing material is shaken off, a suitable, piece of the corrugated strip, correctly formed, is placed on the seat "and the tungsten carbide tip on top. More brazing compound is placed over the' joint at the rear of the seat and covered with powdered flux.
. The tool is then heated in the furnace until the brazing material melts and .runs freely round the joint. The tool is taken out and. the tip pressed firmly into position. Cooling is done by placing he tool in •charcoal powder or grinding wheel dust. Water must not be used.
A new method of ,hard-facing tools has been evolved. This comprises forming a paste of _particles of hardfacing material, such as tungsten carbide, by mixing with them a small quantity ()tan alloy of iron and copper in powdered -form and a flux such as sodium silicate. This paste is then applied to the to surface and the tools are submitted to a temperature materially lower than the melting point of the hard material used, but above the fusing point of copper.