CARBON FIREBRICK FOR FURNACES.
For the preparation of these brick, coke is ground and sifted and intimately mixed with about twenty per cent. of tar, the mixing being under certain conditions effected in a somewhat warm state. The extraordinarily plastic mass is then stamped in thin layers into sheet-iron boxes, which can be closed with hinge-joints, care being had in filling in new mass to always scratch up the surface. The brick cannot be taken from the mould, but remain in it for drying, which requires about four teen days. The manufacture scarcely differs from that of ordi nary fire-brick. In burning the brick the air has, however, to be entirely excluded ; even the interspaces in the muffles are filled up with coke dust. By heating, the brick become first soft and try to expand,"which, however, is prevented by the coke dust.
The manufacturers usually use for the purpose muffles of crude clay which burn to chamotte. It is unnecessary to re mark that everything must be thoroughly luted to prevent the access of air. By burning the tar carbonizes and forms a solid mass with the particles of coke. Hence the manufacture of these brick, whether large or small, presents no especial diffi culties.
As long as the Enskirchen steam brickyard at Mechernich had the monopoly of the manufacture of these brick in Ger many, the forms prescribed there had, of course, to be accepted.
However, this is now changed, and well-shaped brick 20 to 32 inches long, 20 inches thick, and inches wide are now manufactured.
The price of these brick is at present twice that of ordinary refractory brick for furnaces. They are, however, specifically much lighter, the weight per one cubic yard being about 2640 pounds, whilst at least 4400 pounds must be calculated for fire brick.
Carbon brick were at first only used for hearth blocks and the hearth up to the tuyeres, but at present the boshes are also built of these brick, Which must be considered an advance of great importance since the danger of the charge remaining sus pended can thereby be avoided.
Great practical difficulties were encountered in placing the brick in position. After being rubbed smoothly upon each other, they had to be warmed and the tar, which served as mortar, applied warm. The workmen suffered much from the tar vapors, ulcers and boils being formed on the hands and eyes. This mode of setting the brick is now, however, done away with, a mortar four parts coke powder and one part fine red clay being at present used.