THE PHILOSOPHY OF WELDING.

Otago Witness, Issue 1230, 17 July 1875, Page 3

THE PHILOSOPHY OF WELDING.

In order to find a tru»» analogy to welding, we need go no further than the vulgar " sticking together" of two pieces of cobbler's wax, pitch, putty, or clay. These are in a viscous or semi-fluid condition, and they cohere by an action similar to the transfusion or intermingling and uniting of two liquids. Iron and pla° tinum pass through a viscon3 or pasty stage on their way from the solid to the liquid states, and the temperature at which this pasty condition occurs is the welding heat. Other metals are not weldable, because they puss too suddenly frmn the solid to the liquid condition. ' It is usual to cite only iron and platinum, or iron, platinum, and gold as weldable substances, but this, 1 think, is not correct. Lead should be included as a weldable metal. The two halves of a newly cut leaden bullet may be made to reunite by pressure, even when quite cold This is obviously due to tho softness or viscosity of this metal. The chief practical difficulty in weldin" iron arises from the fact that at the welding heat it is liable to oxidation, and the oxide of iron is not vworras like the metallic iron. To remedy this oxidation the workman uses sand, which cdmoinps with the oxide, and forms a fusible silicate. If he is a good workman he does not depend upon the solidification of this nim of silicate, as the adhesion thus obtained would be merely a soldering with brittle glass, and such work would readily separate when subject to vibratory violence. He therefore beats or squeezes the surface together with sufficient force So drive out from batween them all the liquid silicate, and thus ha secures a true animating or actual union of pure metallic surfaces.

Oast iron or steel containing more thrttt tmt per cent, of carbon cannot fre welded, •why ? I think I may venture to reply to this of t-Tepeated Question by stating that the compound; of iron with so" much carbon is much m<>re fusible thari puYe iron or than steel with less carbon' and. that it, runs- more suddenly or more directly from* the solid state into that of a liquid/ arid hence presents no 1 workable range of -wel'dable viewfljsy.-* W, Matti&t William, w Inn.