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Written instructions on the technique of welding and cutting are necessarily incomplete. The beginner will profit by personal instruction, practice, and friendly criticism in acquiring the ability to make strong, sound welds at reasonable speed. Although cutting is more quickly learned than welding, the cutting operator also needs to follow approved practice in setting up, lighting, and shutting down. He should train to conserve oxygen, which means holding the torch steadily, moving it uniformly forward and using the smallest tips and lowest oxygen pressures consistent with the thicknesses cut. Here also some personal instruction, as well as practice, is necessary to acquire skill.
All common commercial metals are readily fused with the oxyacetylene flame, and practically all can be welded. The list includes wrought iron, steel, steel castings, alloy steels, grey and white cast iron, aluminium, copper, brass, bronze, nickel, monel, the principal commercial alloys, the precious and the semi-precious metals. Welding dissimilar metals to each other, such as steel and cast iron, steel and copper, is also practicable.
The filling material or ,welding rod as a rule should be of nearly the same chemical composition and physical characteristics as the base metal. Low-carbon steel is generally welded with low-carbon rods, cast iron with cast-iron rods, copper with copper rods, and so on. When welding dissimilar metals the welding rod as a rule is of the metal having the lower melting-point. Thus copper rods are used when welding steel and copper.
The pressures of the gases in the cylinders are too high to be used directly for welding, and are reduced, as they flow through the pressure regulators, to the working pressure required in the torch. The pressures for welding range from 1 pound to 20 pounds per square inch for the oxygen, and from 1 pound to 12 pounds for the acetylene, depending on the tip size, torch type, and thickness of the metal.
The oxyacetylene hand-welding torch is a tool for mixing oxygen and acetylene in nearly equal volumes and burning the mixture at the end of a tip, the object being the fusing of metals for welding.
Oxygen and acetylene pressure regulators
The function of the pressure regulator is to reduce the pressure of the gas flowing from the cylinder to the required working pressure in the torch, and to regulate the flow volume. Airco-Davis-Bournonville oxygen welding regulators have a 3000-pound high-pressure gauge and a 50-pound working-pressure gauge. The high-pressure 3000-pound gauge indicates the pressure in the oxygen cylinder. The working pressure, adjusted by turning the regulator adjusting screw in the front of the case, is indicated on the working-pressure gauge, graduated to 50 pounds. A safety disk is provided to relieve over-pressure beneath the diaphragm.
Should the safety disk be blown by a leaky seat or over-pressure due to any cause, the defect should be rectified, and the safety replaced only by a standard disk. The inlet connecting the regulator to the oxygen cylinder contains a special filter to prevent ingress of scale and other foreign substances injurious to the working parts.
The valve seating on the inlet nozzle is readily accessible for replacement. Removal of a screw cap in the back of the case uncovers the stirrup cap, equalizing pin and seat holder.
The Airco-Davis-Bournonville acetylene pressure regulator is of the same design as the oxygen regulator, differing only in the graduations of the gauges and certain details. The high-pressure gauge, indicating the pressure in the acetylene cylinder, is graduated to 400 pounds, and the working-pressure gauge to 30 pounds. The acetylene regulator is provided with a safety disk to relieve overpressure beneath the diaphragm.
Worn valve seats are readily replaced by removing the screw cap in the back, taking out the stirrup cap screw and the equalizing pin. The new seat is dropped into place and the equalizing pin placed behind it, taking care that it is properly positioned. The stirrup cap is replaced and the screw plug, with a copper gasket under the shoulder, is screwed tightly in place.
Airco standard oxygen cylinders contain 220 cubic feet of free oxygen when under initial pressure of 2000 pounds per square inch at 70° F. The small Airco oxygen cylinder contains 110 cubic feet of free oxygen.
Airco oxygen cylinders are made of drawn steel without seams and are tested by hydraulic pressure to 3360 pounds per square inch when manufactured, and periodically thereafter. Each cylinder is stamped with a number for identification, and is equipped with a high-pressure valve and valve protector cap. A frangible disk and fusible plug assembly in the cylinder valve is designed to relieve the cylinder of its contents in case it is subjected to over-heating or excessive pressure from any cause.
The valve protector cap must always accompany the cylinder, and be screwed in place when shipped, to protect the valve from damage. This is a highly important requirement in the interest of safety, and should be scrupulously observed by all concerned in any way with the handling and transport of oxygen or other gases under pressure. They should also observe the rules prescribed for handling oxygen cylinders, and especially avoid rough handling and use of oil, grease, or other readily oxidizing substances on the connections. Care should be taken to avoid exposure to furnace heat, fires, and sparks from torches.
Airco acetylene cylinders for industrial use are known as Nos. 4 and 5. The No. 4 cylinder contains approximately 125 cubic feet of free acetylene under initial pressure of 250 pounds per square inch, at 70° F. The No. 5 Airco acetylene cylinder contains approximately 270 cubic feet of free acetylene.
Acetylene cylinders are closely packed with an absorbent filler. The packing is saturated with acetone, and the compressed acetylene is dissolved in the acetone. The design and construction are such as to preclude the possibility of voids and collection of appreciable volume of undissolved acetylene under high pressure.
Airco acetylene cylinders are fitted with high-pressure valve, the cylinder is stamped with an identification number, and this number should be reported to the shipper in all cases where a cylinder is damaged or found to be in a leaky condition.
The key or wrench controlling the acetylene cylinder valve should be left on the valve stem when operating. Each operator should have his own acetylene cylinder key or apparatus wrench with square opening for the acetylene valve. The valve should be opened one full turn when discharging gas.
Acetylene cylinders require special care as regards handling, exposure to heat, flying sparks, and position when in use. They should be handled carefully and never be bumped or dropped from trucks. They should be stored upright in a cool place under cover away from furnaces, steam pipes, or other sources of heat.
It is not good practice to bring an acetylene cylinder into the shop during cold weather and start drawing off gas before it warms up. Cylinders needed for the day's work should be stored in a moderately warm room the night before in order to get the best results.
Cylinder caps must be replaced when the cylinders are discharged. Always close the valves of empty acetylene cylinders. This is a highly important requirement to prevent discharge of free acetylene and acetone during shipment.
A highly useful if not indispensable accessory for welding and cutting is the spark lighter. It provides convenient and instant means for lighting the torch. Use of matches for lighting the torch should be generally avoided. The puff of flame produced by the ignition of acetylene flowing from the tip is likely to burn the hand if not protected by gloves. An Airco round file spark lighter furnishes a convenient, safe and effective means of torch ignition under every condition of use, and should be a part of every operator's outfit.
Goggles fitted with coloured lenses that exclude harmful heat and the ultra-violet and infra-red rays should be worn by operators when using welding and cutting torches. The coloured lenses should be chosen to fit users individually, being neither too dark for efficient work nor so clear as to afford inadequate eye protection. The cups should fit the eye sockets closely to exclude flying sparks and globules of hot metal. Operators should not interchange goggles, because of individual fitting and for sanitary reasons.
The use of inferior or unsuitable welding rods has caused much trouble and loss. It slows up welding and is likely to produce weak and brittle welds. Commercial wire, such as used for fences and other common purposes, is unfit for welding. It is generally high in impurities—sulphur, phosphorous, and absorbed gases. Even though commercial wire might be found by analysis to contain quantities of carbon, sulphur, and phosphorous substantially in agreement with the American Welding Society specifications, it still may not be, and probably is not, of good weldability.
A test for weldability of rods is easily made with the oxyacetylene torch. The rod sample is laid horizontally and partly fused. Its behaviour under the flame and appearance after fusion determines its weldability.
The test should be made with a No. 1 tip and a strictly neutral flame. Fusion should penetrate to about one-half the diameter of the rod.
A rod of good weldability will have a surface after this test is made somewhat like that of narrow ripple weld. The metal will have been displaced into smooth blended drops, one merging into another, and none extending much beyond the original rod diameter. There will be a little sparking during fusion, and no pinholes in fused metal after cooling.
A rod of poor weldability will spark excessively during fusion, and the fused metal will spread irregularly, giving evidence of gas inclusions. The fused surface after cooling will be rough and irregular with some pinholes; the metal may have a spongy or "bread crust" characteristic in spots.
Ordinary commercial wire costs perhaps only one-third the price charged for welding rods. This differential is sometimes made a reason for the practice of false economy. The saving in the cost of rod is swallowed up in the loss of production and increased gas consumption, to say nothing of the inferior quality of the welds made.
The highest grade cast-iron welding rods should be used in welding grey iron castings. Ordinary foundry irons are unfit for this purpose. Their use is very likely to result in hard, brittle welds, weak and unmachinable. A good cast-iron welding rod is high in silicon and low in sulphur and phosphorous. With such cast-iron welding rods, a suitable flux, and proper preheat, the experienced welder should have no difficulty in making soft, machinable welds on iron castings.
The same advice applies to welding rods and fluxes for the non-ferrous metals and their alloys, such as copper, brass, bronze, and aluminum.
When new apparatus is set up for the first time it is advisable to test for leaks in the hose and all connections. Leaky apparatus must not be tolerated. Leaks mean wasted gas and danger of fire. The beginning operator is advised to make this test to acquaint himself with the method and to determine for himself that he has made the proper connections and screw them up to the required tightness. Never test for leaks with a flame.
The approved method of testing for leaks is to apply soapsuds to all connections with a small brush. The presence of a leak will be disclosed by bubbles forming. The remedy is to apply more pressure with the wrench, or if already tightened to a reasonable degree, to shut off the gas pressure and open the connection to see what the difficulty is. A slight scratch or bruise or foreign substance may be found. Rub the bruised surface with fine emery cloth, or if caused by foreign substance, remove it and reconnect. Turn on the gas pressure and test again.
Inferior and old hose often is porous, and leaks may be found in the hose itself. The remedy for this condition is to cut out the porous section, and join the pieces with a hose connector, or better still replace the hose with hose of reliable make.
To avoid backfires and flashbacks two conditions of lighting and adjusting the torch should be considered : (A) Starting up a torch on new cylinders ; (B) Relighting the torch after having been in use.
A. Starting up on new cylinders
B. Starting up after shutting down
Carefully observe the following after shutting off the torch without having closed the cylinder valves. The regulators have been previously adjusted.
These directions must be faithfully followed in principle because they embody the basic essentials for safe, efficient operation and sound welding.
The next step is learning to hold the torch and rod while making a weld, that is, the art of manipulation.
By torch manipulation we mean holding the torch at the correct height and angle, directing the flame so as to fuse the base metal evenly, and moving the flame back and forth across the joint along an approximately zigzag path. The combination of correct flame approach to the work and manipulation across the joint may be learned by preliminary practice welding without rod. This practice welding can be done on steel plates about 6 inches long, 1 1/4 inches wide, and 1/16 inch thick, using a No. 2 tip.
The operator should be dressed for welding, and should wear goggles and gloves. Although it is true that light welding can be done without goggles or gloves, it is, nevertheless, necessary to wear them because it is part of the beginner's job to become accustomed to looking at the weld through coloured lenses, and to hold the torch and welding rod with gloved hands.
Practice welding is done on a welding table or stand. In the absence of a regular welding table one can be improvised with a work-bench, kitchen table, or box set so that the top is about 30 inches from the floor. Any wooden top must be protected from fire. Cover it with heavy sheet asbestos or with building brick laid flat and sprinkled over with dry sand to fill between. Provide two firebricks for the welding supports and a pair of steel pliers to handle hot metal.
Set the welding outfit alongside the table, at the right, turn on the gases, and adjust the working pressures for a No. 2 welding tip-2 pounds of oxygen working pressure and 2 pounds acetylene.
After having made a number of fairly satisfactory welded specimens, try building up the groove with welding rod to reinforce the weld. Use 1/16-inch welding rod.
The welding rod is bent, letting 4 or 5 inches stand out at right angles to that held in the beginner's left hand. The job now is to fuse the weld along the groove, and to melt the welding rod into the puddle to fill and build up a slight reinforcement.
The operator should manipulate the torch as before, moving it in a zigzag path and traversing toward the left with the puddle so as to fuse it into the groove in the right amount at the right time.
Manipulation of the rod consists of holding the end over the joint close to the flame and moving it so that it is momentarily immersed in the puddle ahead of the flame. The heat of the puddle and flame melts off a drop of metal which blends into the weld. The beginner as a rule will have difficulty in dipping the rod and lifting it at the right moment. If done too soon it will stick because the puddle is not hot enough to fuse the rod, and if done too late the puddle becomes so hot that it drops through.
If repeated effort is rewarded with little success, special practice on this phase of manipulation may be necessary.
Grey cast-iron used for making cylinder castings is welded with cast-iron welding rods or "sticks," using a flux. Cast iron melts at a lower temperature than steel—from 1850 to 2250° F., whereas steel melts at 2200 to 2800° F., depending on the carbon content. High-carbon steel melts at the lower temperatures and low-carbon steel at the higher ranges.
The melting-points of cast-iron are below the fusion temperatures of the iron oxides, and it is necessary to use flux to dissolve them in making cast-iron welds.
Flux is generally applied by sticking the hot welding rod into a can of flux powder. The quantity adhering is sufficient as a rule. When welding heavy castings, however, the weld puddle may be dusted with flux from time to time in order to supply the required quantity.
Practice welding on cast-iron should be done to acquire knowledge of its peculiarities and the necessary torch and rod manipulation. The welding rods as a rule are used straight which is not quite as convenient for manipulation as the bent rod on steel.
Expansion and contraction
Care must be taken to provide for expansion when welding a grey iron casting and likewise the contraction must be controlled in cooling to prevent cracks in the weld or adjacent to it. These are best taken care of by preheating the casting to a low red heat, using city gas, oil burners, or charcoal. A crude furnace of firebricks may be built around the part, and the top covered with sheet asbestos except where the weld is to be made. The heat is brought up slowly and as uniformly as possible. When the weld is completed and still in the furnace it is covered with asbestos and allowed to cool slowly. Heavy casting may require 24 to 48 hours to cool, depending on the size, shape, and weight.
Welds made with approved cast-iron rods and flux in the manner described should be soft and machinable when cold.
Bronze welding cast-iron
Many cast-iron repair welding jobs can be done to advantage with bronze welding rods. The preheat required is less, and the welding rod temperature is from 1625 to 1650° F. Many jobs can be done with very little or no preheating. Flux is used when making bronze welds. The strength of good bronze welds is equal to or greater than the base cast iron.
Malleable iron castings
Malleable iron castings are produced from white iron castings heat-treated in specially designed furnaces while packed in boxes with hematite ore. The resulting product is soft and bendable, but it is not weldable with iron or steel rods. It should be bronze welded when making repairs.
The white iron castings can be welded, however, with white iron rods, and defective castings can thus be salvaged in the course of making malleable castings.
Welding non-ferrous metals and alloys
Welding of copper, aluminium, bronze, brass, monel, nickel, and various alloys is accomplished with the oxyacetylene torch in production and repairs. These metals and alloys as a rule are very easily oxidized and a strictly neutral or slightly carburising flame is used ; also appropriate welding rods and fluxes. Expansion and contraction are greater than with steel, and special fixtures often are used to hold sheets and other shapes. Heat conductivity is higher, and larger tips are required for the same thickness than on steel. Copper, for example, requires tips from one to two sizes larger than for steel of the same gauge.
Welding rods as a rule are of the same metal as the metal welded. Pure copper rods are used on copper, aluminium wire on aluminium sheets, aluminium alloy cast rods on aluminium castings, bronze on bronze, nickel rods on nickel, and so on.