THE Goldschmidt thermite process has now become so firmly established in various industries, that we accept it more or less as a matter of course, and have almost ceased to be stirred by the spectacular liberation of energy which accompanies its application to various purposes of ordinary industrial use. When,. however, such a gigantic operation as the welding of a fourteen-inch shaft is in progress, even the most cold-blooded witness must wonder at the fierce intensity of the reaction and at the perfect control under which it is kept. Most violent reactions are explosive in character, owing to the disengagement of large volumes of heated gas. The thermite reaction has the great advantage that all substances taking part therein, both the initial material and the products, are solid. A rock crusher belonging to the North River Stone Company, Kingston, N. Y., was recently disabled by the fracture of the central sbaft. The construction and mode of working of this crusher can be gathered from the accompanying illustration. A vertical shaft S is suspended from, a head H, and extends axially through the crusher-chamber C, the walls of which are faced with a lining L. A similar lining L' is placed around the working face of the conical portion of the shaft. The latter, at its lower extremity, is held in an eccentric bearing E, which is rotated in the casing of the crusher by the gear G through the beveled pinion B and pulley P. The motion of the shaft is that of a conical pendulum, that is to say, its upper extremity is fixed, while the lower end travels around in a circle. There is no rotation about the axis of the shaft. The rock is fed into the crusher,chamber, and is there ground between the lining of the hopper-walls and the sleeve of the shaft, as the latter revolves in its eccentric orbit, thus periodically approaching toward and receding from a given point of the chamber wall. The ground rock issues at the side by a chute. The break occurred near th! point where the lower cylindrical portion of the shaft joins the tapering conical part. (The location of the fracture is indicated in the drawing by an arrow.) The shaft here measures 14 inches in diameter, while at its thickest part it Is 22 inches across. The total length is 18 feet, and the weight about seven tons. The accident to the shaft meant a period of idleness of at the very least six or eight weeks if a new shaft were ordered. The owners of the plant therefore turned their thoughts to the possibilities of repairing the damage by the aid of the Goldschmidt process. This plan was ultimately realized with a saving of several weeks' time and at about one-third the cost of a new shaft. The broken member was shipped to the works of the Goldschmidt Thermite Compa n y, at Jersey City, The fractured surface was pared off with the oxygen blast, taking away in all about 2% inches. The two portions of the shaft were then mounted upon a solid concrete bed, so as to secure perfect alinement, with the space of about two and one·half inches left open between the two ends that were to be welded. The first step toward effecting the weld is to prepare the mold. For this purpose a (wax pattern of the finished joint is first formed atout the ends to be joined, and the mold, of equal pr(Portions of f're clay, ground fire bricl and fire sand, is then built up around the shaft, leaving of course channels for pouring in the charge, a riser to allow for the contraction-of the cooling metal, and a blast hole, for the Introduction of a gasoline compressed-air torch, to preheat Section through rock crusher, The shaft broke at the point rark;d by an arrow. the mold and casting before welding, During the actual operation this blast hole is plugged. The mold is enclosed in sheet iron walls, and this completes the welding furnace. During the preheating, which occupied in this case about ten hours, the wax pattern of course melts away, leaving a free space for the metal of the welded joint. About the furnace is built a wooden scaffolding of trestles, which supports the hoppers containing the charge of thermite, as seen in one of our illustrations. It may seem odd that wood should be used for this structure, since it has to withstand not only the heat of the furnace during the preheating operation, but also the assault of the spattering charge and slag during the reaction. As a matter of fact wood serves its purpose quite satisfactorily, for though it has to be continually watched and kept moistened, and is pretty sure to catch fire during the reaction, it holds up very well even under these strenuous conditions, while an iron structure would be cut right through by any of the molten charge falling upon it. The charge consisted of 1,100 pounds of thermite, mixed with 25 per cent of small steel punchings, 1 per cent of chromium thermite, and 1 per cent pure carbon-free manganese. This charge of thermite, exclusive of steel punchings, is about enough to make 600 pounds of steel. The reaction temperature is about 5,400 deg. F. After adding a teaspoonful of ignition powder (barium peroxide and aluminium flake) to each hopper, the reaction is started by introducing a red hot iron bolt. A flash, a glare, a hiss and sputter, and clouds of smoke envelop all, as the elements wrestle in fierce combat for union with the coveted oxygen: the greater affinity of the aluminium quickly asserts itself, and after a forty seconds' round the iron is vanquished, thrown out of combination and enslaved in the service of man, About one minute is allowed to lapse in order to allow the slag to separate, then the tap-holes of the hoppers are pushed open, and the white-hot molten charge runs into the mold, flling the space prepared for it, and effecting the union of the adjoining ends of the broken shaft. The main part of the work is now done. It only remains to allow the iron to cool-a matter of some forty hours-and the mold can be broken away, exposing the welded joint to view. The excrescences left by the pouring holes and the riser are cut off with the oxygen blast, and the job is completed-for in this particular case there is no need of machining the welded joint. The repair of the crusher shaft was thus effected with complete success, giving one more striking example of the wonderful possibilities of the Goldschmidt thermite process. Horse-power and Man-power IN connection with steamship propulsion the average man is apt to speak very glibly of so many hundred, or thousand, horse-power. But, says the Railway ana Locomotive Engineering, it is extremely doubtful if one person in a hundred really has a due appreciation of what the phrase actually means. On this point some very interesting remarks were made at the last annual dinner of the Scottish staff of Lloyd's Register by Mr. John Heck, the Glasgow engineer surveyor to the society. Propos in; the toast of “shipbuilding and engineering,” he said that, calculating the strength of twelve men to be equal to one horsepower, it would require 840,000 men to produce as much energy as the 70,000 horse-power developed by the turbine machinery of the expres'S Cunarder “Lusitania.” Then, if the men were to work on the eight-hour day system those figures would give a total of 2,520,000, that being the number of men whose strength would be necessary to drive the vessel across the Atlantic Ocean. So it would take all the men in Scotland to supply the energy produced all the day round by the wonderful turbine machinery of this great ship.
This article was originally published with the title "Welding a Fourteen-inch Shaft by the Thermite Process" in Scientific American 105, 21, 455 (November 1911)