For the preparation of metal for cannon and armor-plates Le Creusot is thoroughly equipped. The iron is produced on the premises from the purest imported ores, and the manufacture of the steel is carried on by the most approved application of the open-hearth system with the Siemens furnace; the chemical and mechanical tests are such as to satisfy the most exacting demands of careful government officials; and the executive ability apparent in all the departments and the evident condition of discipline that pervades the whole establishment inspire confidence in the productions of the labor.
The capacity for casting steel is represented by seven open-hearth furnaces of 18 tons each, equal to 126 tons; and the process of casting large ingots is a model of order and security. Ladles capable of holding the contents of one furnace, mounted upon platform cars, are successively filled at a previously determined interval of time and run on railways to a convenient position over the mould; before the first ladle is exhausted the supply from the succeeding one has commenced to run, and so on to the completion of the casting, the supply to the mould being uninterrupted during the entire process. The precision with which the several ladles are brought into position in succession makes it entirely unnecessary to provide a common reservoir into which all the furnaces may discharge. By this process the casting of a 45 ton ingot, which was witnessed by the Board, was effected in 23 minutes.
The process of tempering the gun-tubes was also witnessed by the Board. The excavation of the pit is, as at St. Chamond, 15 meters deep, with the furnace at one end and the oil tank (100 tons) at the other. One side of the upright furnace is constructed in the form of a door, which, by a convenient arrangement for swinging, is made to turn on its hinges. Thus, when the tube is raised to the right temperature, it is seized by the traveling crane, the door of the furnace swung open, and the tube at once advanced to the tank in which it is immersed.
All tubes are immersed in oil the second time, but at a temperature much below that to which they are raised at the first immersion. This process constitutes the annealing after tempering.
The manufacture of steel-armor plates is a specialty of Le Creusot, which is engaged in an active competition with the manufacturers of compound armor. Plates up to 60 centimeters in thickness and 3 meters wide are forged here; they are tempered after forging, but what subsequent treatment they receive was not explained.
The tempering pit for the plates consists of an excavation of convenient size, in the center of which is placed a tank containing 180 tons of oil. At the four corners of the pit are furnaces in which the plates are raised to a proper temperature. When sufficiently heated, a plate is seized by a walking crane and immersed in the oil.
Hoops for cannon are manufactured here in large quantities. They are cut from solid ingots, and those for guns up to 24 centimeters are rolled like railway tires; those for larger calibers are forged on a mandrel. Jackets of large size are also manufactured; these are made from solid ingots, which, after being forged, are bored out.
At Le Creusot a remarkable test of hoops was witnessed, which exemplifies not only the excellence of the manufacture of the steel but also the exacting character of the French requirements. The hoops for naval guns are made with the interior surface slightly conical. When forged, turned, and brought under a hammer, a standard mandrel of steel, conically shaped to suit the form of the cone in the hoop, but of a slightly increased diameter, is introduced, the smaller end of the mandrel being able to enter the larger end of the hoop. The mandrel is then forced in by the hammer until its lower edge has passed through the hoop. The blows are then made to operate on the upper edge, detaching it from the mandrel. Careful measurements are taken of the diameter of the hoop before and after this test, and it is required that the measurement subsequent to the operation shall show that the hoop has partially, but not entirely, returned to the diameter that it had before the entrance of the mandrel. This would show that there is left to the metal a small margin within its elastic limit. A system of manufacture which can comply with such a refinement of exactitude must be very precise.
Perhaps the most striking feature at Le Creusot is the forge, where is assembled an array of steam hammers not equaled in the world, viz.:
One 100 ton hammer with a fall of 5 meters.
One 40 ton hammer with a fall of 3 meters.
One 15 ton hammer with a fall of 3 meters.
Two 10 ton hammers with a fall of 2½ meters.
One 8 ton hammer with a fall of 2½ meters.