Emery and Carborundum Wheels.
Emery, carborundum and alundum wheels are developed from the grindstone of the distant past. That stone gives a straight-line finish or edge to the surfaces submitted to it; and as the work is shifted in front of the stone these surfaces may take a curved or other contour. But a grindstone, let it be as hard as can be found, is not hard enough to take and keep any other than a cylindrical form. Its successors of to-day, the carborundum wheel especially, can be of varied shapes, and transfer these to metal with celerity and economy.
Carborundum, a compound of silicon and carbon, is produced at Niagara Falls, New York, by a process devised by Mr. E. G. Acheson. In an electrical furnace are placed granulated coke, sand, a little salt, and some sawdust to keep the mixture porous and allow generated gases to escape freely. The crystals of carborundum thus produced require seven horse-power hours for each pound; in hardness they are excelled by the diamond only. United under severe hydraulic pressure by a vitrified bond they are eight times as efficient as emery in abrasion. Carborundum wheels are replacing lathes as a means of finishing axles, piston-rods and rolls; their accuracy is unsurpassed, while they demand but one third the time needed by a steel tool.
Emery wheels.
Carborundum Co., Niagara Falls, N. Y.
Carborundum wheel edges.
Form in Plastic Arts.
At the very dawn of art moist clay was molded into useful plates and bowls. This foreran not only all that the potter has since accomplished, but all that has been achieved in the foundry and the mint. In making bricks, tiles, and terra cotta, the first task is to make the clay plastic, then advantage is taken of its plasticity. In like manner we heat a metal to fluidity, and then pour it into a mold to make a fence rail, a stove plate, or a car wheel. An electric bath refines upon this process. Copper, let us say, dissolves in a tank, and concurrently its particles are deposited on a mold from which the metal can be readily stripped, avoiding the distortion inevitable when heat has come into play.
Within the past ten years concrete has grown into much importance as a building material, especially as reinforced with steel. It is a great deal easier and cheaper to pour a wall into molds than to lay courses of brick, or cut and dispose stone-work. Elsewhere in this book a few pages are given to [reinforced concrete], and its applications.