Burnt Metal

If iron or steel is heated to bright white, it will crystallize when cooled. This will make it brittle, and makes the wrongly called burnt iron. To prevent this brittleness the metal must be worked or hammered when cooling. Steel especially is easily burnt because its carbon is apt to crystallize with the iron to form brittle alloys, above bright red heat.

Chamfer

To bevel the edge of a sheet or bar of iron so that it will be the proper shape for welding.

Cold-Short

When a metal is brittle below incandescence. Generally caused by an impurity, as 1 per cent, of phosphorus in iron. Pure zinc is cold-short at about 260 deg. Cent.; aluminum above 600 deg. Cent. The latter may be said to be hot-short, but not red-short.

Critical Temperature

Used to designate the temperature at which the metal itself or any important constituent begins to crystallize. The more sharply defined are the critical temperatures, the less weldable is the metal, as high-carbon steel.

Ferrite

The mineralogical name for pure iron, to distinguish from martensite, cementite, etc., which are terms for the iron-carbon series.

Flux

Any substance, compound, or mixture used to clean the surface of the substances to be welded or soldered. The flux must be chemically or physically active toward the surface impurities, but not toward the substances to be joined. Sand is a flux for iron, as it forms a fusible silicate with the iron scale, but has no affinity for the iron. Zinc chlorid is a flux for lead, zinc, copper, etc., to be soldered, as it dissolves the surface oxids, leaving a clean surface.

High-Carbon Steel

A general term for a hard, brittle steel. The carbon content is about o. 50 per cent, or more.

Oxidizing Flame

A flame is commonly caused by the chemical union of oxygen with another substance. If the flame has more oxygen supplied it than is needed for perfect combustion, the free oxygen in excess makes it an oxidizing flame - one that rusts or burns the metal. A flame may be oxidizing in one place and reducing in another.

Red-Short

When a metal becomes brittle at a red heat, it is said to be red-short. Generally caused by an impurity, as 1 per cent, of sulphur in iron, or a minute quantity of bismuth in lead or gold.

Reducing Flame

A flame in which the fuel is in excess of the oxygen necessary for perfect combustion. The tendency of such a flame is to draw some oxygen from the burned parts of the metal. At all events it prevents burning within its radius.

Spelter

Now used in commerce as the name for pure zinc. Spelter is also the name for half-and-half brass used for brazing. The best way to use this term is not to use it at all.

Swage

A shaping tool, used in finishing a weld.

Upset

To enlarge the metal pieces at the place where they are to be welded. The enlargement at the welded joint is called the upset.