ness, Inches Seconds Minutes Per Lineal Inch, Per Lineal Foot, Width lof Cut. Cut Cut Lineal Lineal Inches per per Inch Foot Thick Time Gas Consumption in Cubic Feet ness, Seconds Minutes Per Lineal Inch, Per Lineal Foot. Cost of Gases, Oxygen at 22 cents. Hydrogen at 14 cent Per Lineal Per Lineal Operation of Cutting Torch. When starting a cut, the steel is first heated by the welding flame; then the jet of pure oxygen is turned on. The flame should be directed a little inward, so that the under part of the cut is somewhat in advance of the upper surface of the metal. This permits the oxide of iron produced by the jet to readily fall out of the way. If the flame were inclined in the opposite direction or in such a way that the cut at the top were in advance, the oxide of iron would accumulate in the lower part of the kerf and prevent the oxygen from attacking the metal. The torch should be held steadily and with the cone of the heating flame just touching the metal. When accurate cutting is necessary, some method of mechanically guiding the torch should be employed. Thickness of Metal that can be Cut. The maximum thickness of metal that can be cut by these high-temperature flames depends largely upon the gases used and the pressure of the oxygen; the thicker the material the higher the pressure required. When using the oxy-acetylene flame, it might be practicable to cut iron or steel up to 7 or 8 inches in thickness, whereas with the oxy-hydrogen flame the thickness could probably be increased to 20 or 24 inches. The oxy-hydrogen flame will cut thicker material principally because it is longer than the oxy-acetylene flame and can penetrate to the full depth of the cut, thus keeping all the oxide in a molten condition so that it can easily be acted upon by the oxygen cutting jet. A mechanically-guided torch will cut thick material more satisfactorily than a hand-guided torch, because the flame is directed straight into the cut and does not wabble, as it tends to do when the torch is held by hand. With any flame, the cut is less accurate and the kerf wider, as the thickness of the metal increases. When cutting light material, the kerf might not be over 16 inch wide, whereas, for heavy stock it might be 4 or % inch wide. Application of Cutting and Welding Torches. A few of the purposes for which cutting and welding torches are commonly used are as follows: For cutting steel wreckage, steel piling, steel beams in structural work, risers from steel castings, openings through steel plates, etc.; for welding seams, reclaiming cracked castings, filling blowholes in castings, adding metal to worn surfaces to secure the original thickness, welding piping without removal, filling holes that have been incorrectly located, replacing broken gear teeth by welding in new material, sealing riveted seams to secure tight joints without calking, etc. High-and Low-pressure Torches.-The difference between high- and lowpressure oxy-acetylene welding and cutting torches, according to the generally accepted meaning of these terms, is in the pressure of the acetylene gas. The oxygen, in each case, is under a pressure of one or two atmospheres. With a highpressure torch, the acetylene gas has a working pressure of one pound or more (depending upon the nature of the work); in the low-pressure type, the acetylene gas only has a pressure of a few ounces. The operation of the low-pressure torch is on the principle of an injector, in that the jet of oxygen draws the acetylene into the mixing chamber which is in the torch tip. The proportion of oxygen to acetylene varies somewhat with different torches; it usually ranges between 1.14 to 1 and 1.7 to 1, more oxygen being consumed than acetylene. Welding with Thermit Thermit Process. This process of welding metals is effected by pouring superheated thermit steel around the parts to be united. Thermit is a mixture of finely divided aluminum and iron oxide. This mixture is placed in a crucible and the steel is produced by igniting the thermit in one spot by means of a special powder, which generates the intense heat necessary to start the chemical re action. When the reaction is once started, it continues throughout the entire mass, the oxygen of the iron being taken up by the aluminum (which has a strong affinity for it), producing aluminum oxide (or slag) and superheated thermit steel. Ordinarily the reaction requires from 35 seconds to one minute, depending upon the amount of thermit used. As soon as it ceases, the steel sinks to the bottom of the crucible and is tapped into a mold surrounding the parts to be welded. As the temperature of the steel is about 5400 degrees F., it fuses and amalgamates with the broken sections, thus forming a homogeneous weld. It is necessary to pre-heat the sections to be welded before pouring, to prevent chilling the steel. The principal steps of the welding operation are, to clean the sections to be welded, remove enough metal at the fracture to provide for a free flow of thermit steel, align the broken members and surround them with a mold to retain the steel, pre-heat by means of a gasoline torch to prevent chilling the steel, ignite the thermit and tap the molten steel into the mold. This process is especially applicable to the welding of large sections. It has been extensively used for welding locomotive frames, broken motor casings, rudder- and stern-posts of ships, crankshafts, spokes of driving wheels, connecting rods, and heavy repair work in general. One of the great advantages of the thermit process is that broken parts can usually be welded in place. For example, locomotive frames are welded by simply removing parts that would interfere with the application of a suitable mold. Thermit is also used for pipe welding, rail welding, and in foundry practice, to prevent the "piping" of ingots Preparation of Part to be Welded. The first step in the operation of thermit welding is to clean the fractured parts and cut away enough metal to insure an unobstructed flow of the molten thermit. The oxy-acetylene or oxy-hydrogen cutting torch is very efficient for this operation. The amount that should be cut away depends upon the size of the work. Assuming that a locomotive frame is to be welded, the space should be about 4 inch wide for a small frame, and 1 inch wide for a large frame. The frame sections are then jacked apart about 1⁄4 inch to allow for contraction of the weld when cooling; trammel marks are scribed on each side of the fracture to show the normal length. If the weld is to be made on one member of a double-bar frame, the other parallel member should be heated with a torch to equalize the expansion in both sections and prevent unequal strains. Mold for Thermit Welding. The mold surrounding the fractured part should be so arranged that the molten thermit will run through a gate to the lowest D part of the mold and rise through and around the parts to be welded into a large riser. The accompanying illustration shows a mold applied to a locomotive frame that is broken between the pedestals at A. The thermit steel is poured through gate B, and rises into space C after passing around and between the ends of frame F. The mold must allow for a reinforcing band or collar of thermit steel to be cast around the ends to be welded. Space G, for forming this collar, and the opening between the frame ends, must be filled before ramming up the mold. Yellow wax is ordinarily used for this purpose. The shape of this band or collar should be as indicated by the view of the completed weld at D. The thickest part is directly over the fracture and the band overlaps the edges of the fracture at least one inch. -A For a frame of average size, the collars are made about 4 inches wide and 1 inch thick at the center, the thickness being increased for comparatively large sections. An opening is also made at E for pre-heating the ends to be welded. Patterns for the riser, pouring and heating gates can be made of wood. The riser C should be quite large because the steel that first enters the mold is chilled somewhat by coming into contact with the metal, even when pre-heated. This chilling effect is overcome by using enough thermit steel to force the chilled portion up into the riser and replacing it by metal which has practically the full temperature received during reaction. The mold must be made of a refractory material, owing to the intense heat. The best material is made of one part firesand, one part fireclay and one part ground firebrick, thoroughly mixed while dry and moistened just enough to pack well. If these ingredients cannot be obtained, one part fireclay and one part clean, dry sand may be used. When the mold and box are filled and tamped, the wooden runner and riser patterns are withdrawn. The mold is then ready for the pre-heating and drying operation which causes the wax matrix to melt and run out. Thermit Required for Welding. The quantity of thermit required for making a weld can be determined from the cubic contents of the weld. Calculate the cubic contents of the weld and its reinforcement in cubic inches; double this amount to allow for filling the gate and riser, and multiply by 0.56 to get the number of pounds of thermit required. When wax is used for filling, the weight of the thermit can be determined as follows: Weigh the wax supply before and after filling the fracture. The difference in weight (in pounds), or the quantity used, multiplied by 32 will give the weight of thermit in pounds. Thermit Additions. When a quantity of more than 10 pounds of thermit is to be used, add 10 per cent of steel punchings (not over 1⁄2 inch in diameter) or steel scrap, free from grease, into the thermit powder. If the thermit exceeds 50 pounds, 15 per cent of small mild steel rivets may be mixed with it. One per cent (by weight) of pure manganese and 1 per cent of nickel-thermit should be added to increase the strength of the thermit steel. Pre-heating-Making a Weld. The ends to be welded should be red hot at the moment the thermit steel is tapped into the mold. This pre-heating is done, preferably, by a gasoline, compressed-air torch, and, as previously mentioned, it melts the wax matrix used for filling the fracture to form the pattern for the reinforcing band. When the ends have been heated red, quickly remove the torch and plug the pre-heating hole E with a dry sand core, backing it up with a few shovelfuls of sand, well packed. The end of the cone-shaped crucible should be directly over the pouring gate and not more than 4 inches above it. To start the reaction, place one-half teaspoonful of ignition powder on top of the thermit and ignite with a storm match. It is important that sufficient time be allowed for the completion of the thermit reaction and for fusion of the steel punchings which have been mixed with the thermit. With charges containing from 30 to 50 pounds of thermit, the crucible should not be tapped in less than 35 seconds; with charges containing from 50 to 75 pounds, 40 seconds; 75 to 100 pounds, 50 seconds to one minute. When welding a frame broken as shown in the illustration previously referred to, the screw jack used for forcing the pedestals apart should be turned back somewhat to release the pressure gradually as the weld cools. After pouring, the mold should remain in place as long as possible (preferably 10 or 12 hours) to anneal the steel in the weld, and, in any case, it should not be disturbed for at least two hours after pouring. When welding a broken spoke in a driving wheel, or a similar part, it is necessary to pre-heat the adjacent spokes in order to prevent undue strains due to expansion and contraction. If a section of a spoke is broken out, it can be cast in, but if the space is over 6 inches long, it is better to insert a piece of steel and make a weld at each end. Owing to the high temperature (5400 degrees F.) and the violent ebullition of thermit during reaction, the crucible must be lined with a very refractory material. The crucibles used for this purpose have a sheet-iron shell and are lined with magnesia. Filling Shrinkage Holes and Surface Flaws. - The filling of surface flaws in castings and forgings usually requires from 2 to 10 pounds of thermit. To make a weld of this kind, place an open mold around the part to be filled, large enough to overlap it about 2 inch. Clean the hole thoroughly and heat to a red heat by means of a strong blow-torch. Use eighteen ounces of thermit for each cubic inch of space to be filled, but do not use less than two pounds for any one weld. Place a small amount of thermit in the crucible which, in this case, is of a small size for hand use. Ignite the thermit with ignition powder and as soon as it begins to burn, add the remainder, feeding it fast enough to keep the combustion going. When the reaction is completed, quickly pour the slag (which is about three-fourths of the total liquid) into dry sand; then pour the steel into the open mold and sprinkle loose thermit on top to prolong the reaction, as the casting, even when pre-heated, will have a chilling effect on the steel. Composition of Thermit Steel. follows: Carbon, 0.05 to 0.10 per cent; 0.09 to 0.20 per cent; sulphur, 0.03 to cent; aluminum, 0.07 to 0.18 per cent. per square inch. An average analysis of thermit steel is as manganese, 0.08 to 0.10 per cent; silicon, 0.04 per cent; phosphorus, 0.04 to 0.05 per The tensile strength is about 65,000 pounds Electric Welding There are severa. processes of electric welding, commonly known as the Zerener, the Bernardos, the Thomson, the Slavianoff, and the La Grange-Hoho. Zerener Process. By this process, which is often referred to as the "electric blowpipe" method, an electric arc is drawn between two carbon electrodes. This arc is then caused to impinge upon the metal surfaces to be welded by means of an electro-magnet. The arc is pointed to concentrate the heat, and the metal is fused around its point of contact with the arc. This method is applicable to a rather limited range of small work, such as welding small steel and brass castings, plates, tubes, tanks, etc. Bernardos Process. The characteristic principle of the Bernardos process is that an electric arc is drawn between the metal to be welded, which forms one electrode for the circuit, and a carbon electrode manipulated by the workman. By placing the carbon electrode in contact with the metal, thus closing the circuit and instantly withdrawing it again, an arc is drawn between the two terminals. Owing to the high temperature of the electric arc, the metal is fused. Experience has demonstrated that the metal to be welded should be the positive electrode, and the carbon, the negative electrode. If this order is reversed, a shorter arc is obtained, and when the flow of current is toward the metal, particles of carbon tend to enter the weld, thus making it hard and liable to crack. Thomson Process. - The Thomson or "incandescent" process consists in forcing through the parts to be welded such a large volume of current that the resistance of the work is sufficient to cause fusion and amalgamation of the metals. The parts to be welded are held between two clamping members of the welding machine, which form terminals for an electric current of low voltage and high |