Welding

The great obstacle heretofore experienced in welding copper has been that the oxide formed is not fusible. If any fusible compound of this oxide could be found, it would render such a weld possible. We find in mineralogy two copper salts of phosphoric acid, viz. - libethenite and pseudo-malachite-each of which melts readily before the blowpipe. It was therefore natural to suppose that a salt which contained free phosphoric acid, or which would yield the same at a red heat, would make the weld easy by removing the oxide as a fusible slag. The first trial was made with microcosmic salt (soda and ammonia phosphates), and succeeded perfectly. As this salt was dear, it was found advisable to use a mixture of 1 part soda phosphate and 2 boracic acid, which answered the same purpose as the original compound, with the exception that the slag formed was not quite so fusible as before. This welding powder should be strewn on the surface of the copper at a red heat; the pieces should then be heated up to a full cherry-red or yellow heat, and brought immediately under the hammer, when they may be as readily welded as iron itself.

For instance, it is possible to weld together a small rod of copper which has been broken; the ends should be levelled, laid on one another, seized by a pair of tongs, and placed together with the latter in the fire and heated; the welding powder should then be strewn on the ends, which, after a further heating, may be welded so soundly as to bend and stretch as if they had never been broken. Rust states that, as long ago as 1854, he welded strips of copper-plate together, and drew them into a rod; he also made a chain, the links of which had been formed of pretty thick wire and welded. It is necessary to carefully observe two things in the course of the operation: (I) The greatest care must be taken that no charcoal or other solid carbon comes into contact with the points to be welded, as otherwise copper phosphide would be formed, which would cover the surface of the copper, and effectually prevent a weld. In this case, it is only by careful treatment in an oxidizing fire, and plentiful application of the welding powder, that the copper can again be welded.

It is, therefore, advisable to heat the copper in flame, as, for instance, a gas flame. (2) As copper is a much softer metal than iron, it is much softer at the required heat than the latter at its welding heat, and the parts welded cannot offer any great resistance to the blows of the hammer. They must, therefore, be so shaped as to be enabled to resist such blows as well as may be, and it is also well to use a wooden hammer, which does not exercise so great a force on account of its lightness. (Eng, Mech.)

Alloys

See pp. 11-21, 29-31, 34-5, 40-2. _____