Technical Data

Metallurgical Terms

Ra.

Chemical symbol for radium.

Rabble.

An iron rod used for stirring a molten bath.

Radiography.

A non-destructive method for internal examination of a metallic body by exposure to a beam of X-ray or gamma radiation. Differences in thickness, density or absorption caused by internal defects or inclusions are apparent in the shadow image, either on a fluorescent screen on a photographic film placed behind the object.

Rare Earth Metals.

A group of elements having very similar properties to one another and derived from the so-called rare earths.

Rb.

Chemical symbol for rubidium.

Re.

Chemical symbol for rhenium.

Recalescence.

(See Critical Points).

Recuperator.

Equipment for recovering heat from hot spent gases and using it for preheating incoming fuel or air. It is a continuous operation, in which the incoming gases pass through pipes surrounded by a chamber through which the outgoing gases pass. (See Regenerative Furnace).

Red Shortness.

Brittleness in a metal when red hot, causing it to crack under the hammer or during rolling. It may be caused by a high sulphur content among other things.

Reduction of Area.

(a) The percentage decrease in the cross-sectional area of a tensile test piece caused by the waisting or necking of the specimen. It is expressed as a percentage of the original area of the test piece and is a measure of ductility.

(b) The percentage decrease in cross-sectional area of bar or wire after rolling or drawing.

Refining.

(a) The term, as applied to metals in general, refers to operations performed after the crude metals have been extracted from their ores, in order to obtain them in a condition of higher purity.

(b) The removal of impurities and metallic oxides from the molten bath by the reaction of slag and certain additions.

(c) Grain refinement.