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MISCELLANEOUS REPAIR PROCESSES
Oxy-acetylene or Autogenous Welding-Torches for Welding—Sources of
Gas-Cost of Autogenous Welding-Instructions for Operating-Welding Cast Iron-Method of Preheating-Welding Aluminum-Welding Malle. able Iron-Welding Brass and Bronze-General Hints—Treatment of Steel, Annealing-Box Annealing-Hardening-Pack Hardening-Tempering—Case Hardening-Distinguishing Steel from Iron—Hardening Steel Tools—Temperatures for Tempering—Molten Metals to Produce Desired Heat-Working Iron and Steel-Annealing Chilled Cast Iron-Bending Pipe and Tubing-Filling the Tubing-Pipe Bending Fixture-Straightening Out Bent Fenders-Removing Dents in Tanks—Soldering and Brazing Processes-Fluxes for Soldering—Solders and Spelter for Different Purposes-Lead Burning-Soldering Aluminum-How to Braze Iron and Steel—Testing Lubricating Oils—Evils of Exhausting in Closed Shop Instructions for Repairing Storage Battery-Care of Grinding WheelsSpeeds for Grinding Wheels-Grading of Grinding Wheels.
MANY men are engaged in the automobile repair business who have been specialists in some particular branch of mechanical work before becoming interested in the automobile. Wood workers, blacksmiths and carriage smiths are especially noted owing to the decrease in carriage and wagon work and increase in automobile repairing. The review of various mechanical processes which follows cannot fail to be of value to all those not thoroughly familiar with all branches of mechanical work. Even the automobile mechanic will find the material useful for review.
Autogenous Welding.- Autogenous welding is the process of uniting metal surfaces by heat without the aid of solder or compression. High temperature, full control and easy application of the heat are necessary requisities. The most satisfactory method is termed the oxy-acetylene process, the flame having a temperature
of about 6300 degrees Fahrenheit. By this process iron, steel, cast iron, aluminum, brass, copper, platinum and other metals may be so perfectly united as to defy detection when the joint is smoothed. Its uses include the following: Reclaiming light and heavy castings coming from the sand with blow holes, sand holes, cold shuts and lugs off; reclaiming light or heavy cracked or broken aluminum; adding metal to parts subjected to friction; repairing large or small frame members in place, welding in new parts or filling in cracks; welding split piping or flanges on pipes; reclaiming imperfect steel castings; extending short shafting, adding small metal parts broken off or missing and renewing teeth broken from gear wheels. This process is of inestimable benefit to the automobile repairman and every first class mechanic should have experience in handling the welding torch. Its uses in the repair shop are legion.
'The operation of cutting steel or iron is by heating the metal at the first point of contact to the red with the ordinary welding flame. This flame is then continued with a jet of pure oxygen turned on, which unites with the carbon of the metal and disintegrates it with surprising rapidity. The cut is narrow and smooth. with no material damage by oxidation. It may be made in any shape, and the process will be found especially valuable in making many kinds of dies and in fitting steel plates. Steel beams in structural work, steel arches, steel boilers, steel piling, shaped deck plates for steamships and the hardest steel vaults may be cut with ease. The secret of the process lies in the high temperature of the flame, which increases the temperature of the metal so rapidly that very little heat is diffused into the body of the part, most of it therefore being available for fusion. The number of heat units actually absorbed by the metal is a very small fraction of that required to bring the same part to a brazing heat with the ordinary gas or oil blowpipe, and very little if any warping takes place.
One of the first points to be understood when considering the use of autogenous welding is that the heat actually has to come in contact with every particle of metal welded. It is impossible to weld by this method where this cannot be done. If a small boss is required on a given casting, it is useless to cut out a disc of metal the same size of the boss with the idea of welding it on. The correct way would be to add metal drop by drop, until the required size is reached. The torch is the most important factor in autogenous welding and cutting. The type generally admitted to be of the best construction consists of two small pipes or conduits terminating at one end with hose connections, the other entering a recess head that receives the torch tips. The pipe for acetylene is screwed into a cylinder about one and one-half inches in diameter, which serves for a handle, and is packed in porous material that prevents the possibility of communicating a flame beyond that point.
Torches for Welding. It is not generally known that three distinct types of torches have been invented for oxy-acetylene welding. These are termed respectively low, medium and high pressure, taking their name from the relative pressure under which the acetylene is used. The high pressure torch was never introduced into this country owing to certain disadvantages, finally causing the medium pressure torch to be brought out. The low pressure torch was invented by Edmond Fouche, and its principle is based on that of the injector, the acetylene being drawn by suction produced by the flow of oxygen, which is under pressure. The acetylene is brought to the torch under a pressure of a few ounces per square inch only. The flow of oxygen is regulated by the area of a nozzle and by its pressure so that the correct proportion of acetylene is sucked in. The mixture then passes out at the burner or tip of the torch.
The size of the orifice in this tip is of great importance, as it controls the resistance in the mixing chamber to the flow of oxygen, and therefore controls the proportion of the two gases. As is well known, the amount of fluid sucked by an injector is proportional to the square of the velocity of the propelling fluid. It is therefore essential that the flow of oxygen should not vary or the proportion of acetylene would not be constant. For the low pressure torch this proportion is 1.7 oxygen to 1.0 of acetylene by volume, at atmospheric pressure and any variation in either direction will produce either an oxidizing or carbonizing flame. The flame should, therefore, be carefully watched as the orifice in the tip may be expanded by the heat being deflected onto the torch, or it may be
contracted by particles of metal adhering to the tip, thus ci-anging the mixture. Owing to the fine adjustment of the injector parts, these torches are often made without any means of varying the size of the flame, it being necessary to disconnect the torch from the hose and substitute another one, when it is desired to do this, a number of torches being required if it is necessary to weld on all classes of work. Owing to the low pressure, the speed of the
Fig. 452.—Complete Welding Outfit Suitable for Repair Shop Use.
Note Appearance of Automatic Reducing Valve.
issuing mixture is very little above the speed of the propagation of the flame and "back fires” frequently occur, the gas has then to be turned off, lighted again and the mixture readjusted. The ordinary acetylene lighting generator supplies gas at a pressure suitable for use with this torch.
In the medium pressure torch, both the acetylene and oxygen are under an appreciable pressure, which results in a constant mixture under all conditions, the proportion being 1.00 of acetylene to 1.3 of oxygen. The mixture is regulated by holes at the inner end of the detachable tip, and is not affected by any variation at the outer orifice. The pressure of each gas is kept constant as required by adjustable reducing valves in the pipe lines. The speed of the gas is greater than in the low pressure torch and back firing is practically eliminated. If the flame goes out, it can be relighted without altering the gas adjustment.
Sources of Gas.—The source of oxygen and acetylene gas supply is a question which requires careful consideration for each individual case separately. It can either be generated at the plant, or can be shipped in steel cylinders from one of the several companies who are generating and compressing it.
The points to be considered are:
1. The transportation charges for the compressed gas and cost of the cylinders.
2. The quantity of gas used and, therefore, the number of cylinders that would be required to contain it.
3. The regularity of the consumption, depending on the regularity of the work, and also of its size.
4. The cost of generating the oxygen at the plant.
The first depends upon the locality and shipping facilities, as well as in the quantity of gas that will be used. The second also depends on the first, with the consideration that the cost of cylinders might equal or exceed the cost of the generating plant.
The third might necessitate the generation of oxygen at the plant, anyway, particularly if repairs were the principal work carried out as unless the supply of work were regular and all of small size, one could not depend on keeping a sufficient supply of oxygen on hand, and this class of work is generally required im