When any industry or art stands practically still for a few thousand years and then suddenly begins developing at an enormous rate, it is always sure to attract attention and receive a large amount of study. This results in still more rapid development.

The art of welding had been limited almost entirely to joining a few of the metals by hammering them together, either hot or cold, from the beginning of history until within the present genera- tion. Then the idea of rising high temperatures for fusing metals together presented itself and the art began to progress.

Combinations of gases, electric arcs, and the heat of resistance have all been used as the means for heating the metals at the point to be welded, and practically every known metal and alloy has been successfully welded. During the Great War development was accelerated and operations performed that had been considered commercially impractical before.

The development of gas welding for all sorts of repair and production work caused the arc-welding systems to improve, and this in turn made development of gas-welding systems necessary in self defense. The result has been a greater advance in the past five years than had been made in the previous twenty-five years. Each system has its limitations, but both are good.

The application of all welding processes to railroad equipment, ship building, sheet metal work, and on castings of all kinds has revolutionized many lines of manufacture, and the development of automatic machines for welding the seams of tubing, tanks, and other sheet metal articles is worthy of special note.

Considerations of safety and reliability lead to careful tests, and the study of processes and the effect of various combinations of metals and their action at high temperatures has almost entirely eliminated the element of chance from modern welding operations - even the personal equation of the operator has been reduced.

In this volume will be found a complete exposition of the practical side of welding by all processes, with descriptions of the more important apparatus, and no engineer or mechanic can lay claim to being up to date in his business unless he has a fair working knowledge of this subject. The demand for men with such knowledge is steady and the work is both interesting and profitable.

It is recommended that the student supplement his study of this book by visits to shops having welding apparatus of the various kinds described, thus seeing for himself just how effective the processes are.

Classification. There are numerous processes for welding metals, and these may be divided into four main classes - electric welding, gas, or hot-flame, welding, chemical welding, and smith welding, or forging. There are several allied operations for joining metals, namely, soldering, brazing, and riveting.

In order that the student may know something about all methods of welding, and about joining metals by the several processes, short descriptions of the more important ones are given, so comparisons may be made between the various processes and their applications. More complete data may be found in other books issued by this institution, and should be referred to by students desiring to go more completely into any phase of the subject. The following information will also be of value in determining which of the several processes would be suitable for any special work the student may have in hand to be done.

Electric Welding. Electric welding has recently been developed commercially to such an extent that it is rapidly coming to the front as the most important of all the welding processes. Six different systems have been developed for using electrically generated heat for welding purposes. These are the Benardos, Slavianoff, Percussive, Thomson, Zerener, and LaGrange-Hoho systems. The first four are of chief importance.

The Benardos system employs a piece of carbon or graphite as one electrode of the arc; the arc is drawn between the carbon and the work (which. is the other electrode), and the heat of the arc melts the filling material required for joining the pieces.

The Slavianoff system consists in drawing an arc between the work and an electrode, but in this case a piece of the filling material is used as one of the electrodes, which melts directly into place on the job. This is the most important of the electric- welding processes, although but recently developed to a commercially practicable point. It is applicable to practically every class of welding and for nearly all metals.

In the Zerener system two pieces of carbon are employed. The arc, or flame, is deflected toward the work by means of a magnetic field and the filling material is thus melted.

The Percussive system was developed as the result of experiments in welding aluminum wire. The apparatus consists of a moving holder for the wires, which are connected across the supply circuit with a condenser in parallel and so arranged that a rush of current takes place across the point of contact or joint when the wires are forcibly brought together. This process is now in use for welding the many kinds of metals used in the manufacture of small parts.

The Thomson system requires the use of alternating current, whereas the other systems generally use direct current for welding. In its latter-day modifications it consists in bringing together the two pieces to be welded, in a special machine, passing an alternating current through the point of contact until the parts are heated sufficiently to be soft, and then squeezing them together until they unite. The heating is due to the resistance of the joint to the electric current.

The La Grange-Hoho system also is based on resistance. The pieces of metal to be welded are placed in a bath of electrolyte, which conducts the current from a positive electrode. The actual weld is made by hammering, the same as in smith-welding, after the metal is hot and soft. This is not at present a very important process commercially. In the three other processes the electric arc furnishes the heat, and additional material is used to join the pieces.

Gas Welding. Gas welding, or hot-flame welding, is at present next in importance to smith welding. It is applicable to many kinds of work which cannot be done by forging. The three most important processes commercially are known as the oxy-acetylene, oxy-hydrogen, and blau-gas. All these processes consist in using oxygen and another gas to give a flame of sufficiently high heating capacity to melt the material to be welded. The gas used with oxygen is indicated by the name of the process.

Chemical, or Thermit, Welding. Chemical welding is practiced today almost exclusively by the process known as thermit welding. Aluminum in fine grains or filings is mixed with some metallic oxide, usually of iron. On being heated by a priming the aluminum combines so rapidly with oxygen of the oxide as to generate intense heat, which sets free the iron from its oxide. The fluid thus produced forms what is known as a cast-weld which is very strong and is much used in welding large articles.

Smith Welding. Smith welding, or forging, is the process of shaping or joining metals by hammering or pressing the pieces together. It may be done either with or without heat. It is the most common of all the welding processes, and depends upon the skill of the operator more than the other processes of welding; hence it is gradually being superseded by them.

Brazing and Soldering. Brazing and soldering are processes which approach welding so closely in some of their applications that they are worthy of serious consideration as a part of that subject.

Brazing consists in joining pieces of metal by fusing them with an intermediate material called "spelter," the surfaces of the joint having been previously prepared with a suitable flux. When brass is brazed, the process really becomes welding, since brass is the principal constituent of spelter. The heat is produced by a gas flame and the work is done at a comparatively high temperature.

Soldering, or "metallic gluing" as it has been called, is done with a soft alloy, which is melted and used somewhat as glue in the space between the parts to be joined. Soldering can be done with a gas flame or a heated soldering copper and at comparatively low temperatures. Soldering "is a comparatively old process, is cheap, easily learned, and in wide use, but it should not be used for any joint requiring much strength.

Riveting. In joining metal plates and sheets small malleable pins or bolts are passed through the parts to be joined and then flattened into a head at each end to make them tight and secure. This process is also old and will be described in detail later in order to bring out the comparison between this and the newer methods of joining materials.

Miscellaneous Processes. Several other processes of joining metals have been invented, among them the "Ferrofix" for brazing and Laffitte for welding. Neither of these last is in very wide use.


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