Schneider Process.— Armored plates are cemented on the surface in furnaces designed for that special purpose. At the Creusot works hydrocarbon gas is used, introduced through pipes. At a dark red heat the hydro-carbons separate, and the liberated carbon penetrates the surface of the steel. The furnaces are fitted with movable hearths on wheels. The plates, having been already molded to their curves by templet, are placed one above an other, with spaces between them, into which the gas is introduced. Each space is enclosed by a cast-steel frame inserted between adjacent plates and rendered gas-tight with an asbestos strand. The sides of the frame are drilled to receive the rows of gas pipes. The pipes, which are water-cooled, contain passages for the gas inlet, the water outlet and the gas es cape. The furnace is fired from each side, with blast. The deposition of the carbon goes on until, by a certain appearance of the flame given by the ignition of the escaping gas, the progress of the cementing operation is esti mated when the admission of the gas is stop ped for a while to permit of equal saturation of the opposed faces. It is then turned on again for a time and these stages are repeated until the cementation is equalized and com pleted. The temperature of the furnaces • is regulated in such a way as to effect the maxi mum of cementation without risk of melting the surfaces of the plates. The plates cool down in the furnaces to be reheated and hard ened subsequently. They are reheated in the vertical position in furnaces and for the water hardening they are suspended vertically in tanks, through which jets of water are sprinkled on the surfaces of the plates. The rates of cooling can be varied by altering the distances between the plates and walls.
Cementation Process.— It has been the practice of some manufacturers of armor plate to use a series of rolls instead of a press, but it has been proved that the forging of a plate under a hydraulic press effects a more uniform working of the metal and produces a finished plate far superior to one which has been rolled. This statement is borne out by the fact that many of the plants which had installed a costly set of rolls have had the same removed and replaced by powerful hydraulic presses. After forging, the sink-head is cut off and the plate allowed to cool a little in air before annealing. From the annealing furnace the plate is taken to be scaled by pneumatic hammers prepara tory to carbonizing. This process consists es sentially of heating the plate in the presence of dry carbon or in a gas-carbonizing furnace.
Dry-Carbon Process.— In this process a special dry-carbon furnace is employed; coal is used in the furnace as fuel and the flame passes over the plates, down in front and back under again to the smoke-stack. Usually sev eral plates are carbonized at the same time, the plates being arranged in pairs. The faces to be carbonized are placed together, separated only by a layer of finely powdered wood and animal charcoal. The edges are well sealed and the plates are placed in the furnace through the top and lowered on a bed of sand; the whole is then well covered with sand and if more than one pair are carbonized at the same time they are treated in like manner and placed on top of the first. When all are well pro tected from contact with the flame the furnace top is closed and the furnace brought up to heat. The heat is maintained at a uniform
temperature for a considerable length of time, this time depending on the amount of carbon to be absorbed by the plates and then the fur nace allowed to cool. Almost a month is em ployed in this process from the time the plate is charged until it is taken from the furnace.
Gas-Carbonizing Process.— In the em ployment of this process the plate, with the face to be carbonized exposed, is placed on a bed of sand in a furnace which is heated by some highly carbonized gas. The flues for the flame entry are built on each side of the furnace and so arranged that they can be used alternately, while a deflector causes the flame to first strike the top of the furnace and then pass downward. After the furnace has been raised to heat, coal gas or one rich in hydrocarbons, is passed along the surface of the plate and the intense heat causes this to be broken up, depositing carbon on the face of the plate. The plate is left in the furnace until the required degree of carbonization is attained. The plate is again scaled and reheated for its second or final forg ing to bring it to gauge. This forging also serves to smooth up any roughness on the sur face. After forging it is again annealed and from the anneahng furnace goes to the ma chine shop, for such machining as can be done preparatory to bending. On return from the machine shop the plate is heated preparatory to bending and this operation requires the greatest skill and experience in order to pre vent cracking to a degree which would result in the condemnation of the plate. An allow ance, too, must be made for any slight dis tortion which may occur in the next operation, that of tempering and water hardening. The plate is heated to the required temperature and then subjected to a cold water spray. The bath is of a special design and is arranged to give a pressure of about 15 pounds per square inch.
The process of manufac ture in every detail is of scientific nicety. The melted steel is drawn off into ladles, transported by electric cranes capable of lifting 120 tons and poured into massive ingot moulds, some of which weigh 60 tons without the steel. Some of the ingots weigh 50 tons and are 36 inches thick. They are reheated and rolled out in an immense mill. One of these mills at Messrs. Vickers' works has rolls 36 inches in diameter and 12 feet in length. An ingot 36 inches thick can be rolled down to six inches within half an hour. The thickness after rolling is equal, but the edges are rough and irregular. At this stage the first portion of the cementing process is performed. The plates are laid one on top of another in specially constructed furnaces. Powdered •charcoal is sprinkled between the opposed surfaces and the plates remain in the furnaces from 10 to 12 days, the temperature being regulated by pyrometers. During that period the charcoal is absorbed by the plates, increasing the quantity of carbon at and near the surfaces. This does not harden the sur face of the plate, but it prepares it for the sub sequent hardening which is done at a later stage, after the bending in the case of those plates which have to be curved, and after the planing off of the rough edges in the case of all plates. Both operations involve the use of much massive machinery and careful handling.