MITIS METAL.
The introduction of wrought-iron castings by the ‘Mitis process,’ to which attention has lately been directed, forms a new and an important departure in the employment of this class of iron. Up to the present time, wrought-iron has been worked into the requisite forms by means of hammering; whilst a system of stamping in moulds was deemed a considerable advance in economical working. It is now, however, proposed to treat wrought-iron in the same manner as cast-iron—namely, by melting and pouring it into moulds made in sand, and corresponding in shape with the object desired. By such a process a considerable saving in the cost of production is obtained. Annealing is found to be unnecessary.
The difficulty which has hitherto barred the adoption of this method has been the high temperature to which it has been necessary to heat the iron before it became sufficiently fluid to flow into the moulds. Wrought-iron fuses at about four thousand degrees Fahrenheit, but a considerably higher temperature had to be obtained before the metal passed out of the viscid state; and on reaching this increased heat, it was found to absorb gases which caused cavities and flaws in the castings, rendering them worthless, and what are technically known in the foundry as ‘wasters.’ To obviate this difficulty, Peter Ostberg, a Swedish engineer, has taken advantage of the fact that the melting-point in alloys is considerably below that of their components; and by combining with the iron a small percentage of aluminium, he has succeeded in lowering the temperature of fusion of the mixture to such an extent that excellent castings can be obtained, the temperature reached not being high enough to cause the absorption of gases. The castings are clean and sharp in form, and remarkably strong and fine in texture, being in some cases, it is said, half as tough again as the metal from which they were made. The great reduction in price cannot fail to procure for the new process an opening commensurate with its intrinsic merits.
In the United States and Sweden, Mitis Metal has already established itself as an article of commerce at once reliable and economical; and there can be little doubt that the engineers of this country will avail themselves of this new form of iron, placed at their disposal by an invention which promises to rival in importance any introduced into this branch of industry for many years past.