Modern Armor 803 7 fig2 It was found that laminated and sandwiched armor gave very much less resisting power than solid rolled plates of the same thickness. Wrought iron armor is made under the hammer or under the rolls, in the ordinary manner of making plates, and has been exhaustively studied and experimented with - more so than any other form of armor.

Chilled cast iron armor is manufactured by Gruson, in Germany, and is used in sea coast defense forts of Europe.

In 1867 several compound plates were made by Chas. Cammell & Co., of Sheffield, England, and were tested at Shoeburyness, in England, and at Tegel, in Russia. These plates were made by welding slabs of steel to iron; but the difficulties were so great that the idea was abandoned for the time.

Modern Armor 803 7 fig3Modern Armor 803 7 fig4

Compound armor, as now manufactured, is of two types: Wilson's patent, a backing of rolled iron, faced with Bessemer steel; Ellis' patent, a backing of rolled iron, faced with a plate of hard rolled steel, cemented with a layer of Bessemer steel. Both these kinds are manufactured in England and France in sizes up to fifty tons weight. The Wilson process is used at the works of Messrs. Cammell & Co., of Sheffield, England, and the Ellis process at the Atlas Works of Sir John Brown & Co., of the same place. These are the two leading manufacturers of compound plate.

The method employed by Wilson in making compound plate is to first make a good wrought iron plate. To the surface of this and along each side of the length of the plate are fixed two small channel irons, as shown in Fig. 5. Modern Armor 803 7 fig5 The plate is then raised to a welding heat in a gas furnace, and transferred to an iron flask or mould. Wedges are driven in between the back of the plate and the side of the mould, thus forcing the channel irons up snug against the opposite side of the mould. Moulding sand is then packed around the back and sides of the plate (see Fig. 6). Modern Armor 803 7 fig6 The mould is lowered in a vertical position into a pit. Molten steel, manufactured by either the Siemens-Martin or Bessemer process, is then poured in through a trough that forms several streams, and forms the hard face of the plate. The molten steel as it runs down cleans the face of the wrought iron plate, scoring it in places, and, being of much higher temperature, the excessive heat carbonates the iron to a depth of one-eighth to three-sixteenths of an inch, forming a zone of mild steel between the hard steel and soft iron. The mould is placed in a vertical position to insure closeness of structure and the forcing of gases out of the steel. After solidifying, the whole plate is pressed, and passed through the rolls to obtain thorough welding. It is then bent, planed, fitted, tempered, and annealed to remove internal strains.

In 1887, Wilson took out a patent for improvements in his process of making compound plates. In this method of manufacture he takes a wrought iron, fibrous plate, fifteen inches thick, built up from a number of thin plates. While hot from the forging press, he places this plate in an iron mould (see Fig. 7) Modern Armor 803 7 fig7 about 28 inches deep, and upon it runs "ingot iron" or very mild steel to a depth of thirteen inches. In this form of mould the plate rests on brickwork, and is held in place by two grooved side clamps or strips which are caused to grip the plate by means of screws which extend through the sides of the mould. After solidifying, the plate, which is twenty-eight inches thick, is reheated and rolled down to eighteen inches. This is the iron backing of the finished plate, and it is again put in the iron mould and heated, when a layer of hard steel is run on the exposed surface of the original wrought iron plate to a depth of eight inches. This makes a plate about twenty-eight inches thick. It is taken from the mould, reheated, rolled, hammered or pressed down to twenty inches. After cooling, it is bent, planed, and fitted as desired, then tempered and annealed to relieve internal strains.

The method employed by Ellis in making compound plates is to take two separate plates, one of good wrought iron and one of hard forged steel, placing the forged steel plate on the wrought iron plate, keeping them separate by a wedge frame or berm of steel around three sides, and placing small blocks of steel at various points near the middle of the plates (see Fig. 8). Modern Armor 803 7 fig8 These blocks are called distance blocks. After covering all the exposed steel surfaces with ganister, the plates are put in a gas furnace and heated to a welding heat. They are then lowered into a vertical iron pit with the open side uppermost. The plates are held in position by hydraulic rams, which also prevent bulging. Molten steel of medium softness is then poured into the space between the plates, by means of a distributing trough having holes in the bottom, and after this has solidified, the whole plate is placed under the hydraulic press and reduced about twenty per cent. in thickness. The plate is then passed through the rolls, bent, planed, fitted, tempered, and annealed to reduce internal strains.

In heating the compound plates for rolling, the plate is placed in the furnace with the steel face down, so that the iron part gets well heated and the steel does not become too hot. Great care must be taken not to overheat the plate, and in working, many passes are given the plate with small closings of the rolls. The steel part of a compound plate is usually about one third of the full thickness of the plate.