Metallurgical Terms
R
Ra
Chemical symbol for radium.
Rabble
An iron rod used for stirring the molten bath in steel making.
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 or 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. Often added to steel in the form of
Mischmetal.
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.
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 the slag and certain additions.
(c) Grain refinement.
Refractories
Heat-resisting materials, usually consisting of metallic oxides, used for
furnace linings. The principal acid refractory is silica; basic refractories are
magnesite and dololnite. Chromite (often in association with magnesite) and
fireclay are also widely used.
Regenerative Furnace
This consists of two pairs of chambers (regenerators), one for gas and one
for air in each pair, each filled with a checkerwork of refractory bricks. The
function of the checkerwork is to absorb heat from the hot waste gases as they
pass through on their way from the furnace to the chimney. When the checkerwork
of one pair of chambers is hot, the flow of the heated gases is reversed, to
pass through the other pair of cool chambers, whilst the hot checkerwork gives
up its heat to the incoming air and producer gas on their way to the furnace.
Regenerators
(See Regenerative Furnace).
Residual Stress
The stress which exists in an elastic solid body in the absence of, or in
addition to, the stresses caused by an external load. Such residual stress may
be brought about by
(1) Deformation, caused by cold-working, as in drawing or stamping;
(2) Change in the specific volume due to thermal expansion, a phase change, or
magnetostriction, or
(3) By the joining together of structural parts by force, e.g.. Welding.
Resilience
A general term for the power of an elastically strained body to spring back
on removal of the load. Strictly it is the potential energy stored up by an
elastically strained body and given out when the load is removed. It is
expressed in energy units. The proof resilience is the greatest amount of energy
that can be stored up by a body strained only elastically.
Resistance Welding
(See Welding).
Restrainer
(See Pickling)
Revcrberatory Furnnce
A furnace in which the ore or metal is exposed to the action of flame
deflected or reverberated, from a sloping roof above the hearth. The fuel is
burned on a separate hearth out of contact with the charge.
Rh
Chemical symbol for rhodium.
Rimming Steel Ingots
A type of ingot characterized by an outer envelope or rim of solid and
comparatively pure steel, with the interior or core of a less solid and less
pure character. Such ingots are made from steel in which the deoxidation, either
in the ladle or in the mould, has been intentionally limited, with the result
that a free ebullition of gas progressively takes place during the freezing of
the ingot. The steel freezes progressively from the mould wall, whilst the
interior remains liquid and in a state of violent ebullition. The centre may
solidify naturally, but is usually chilled by a cooler plate. Such steel usually
contains less than 0•15% of carbon, and less than 0•50% of manganese, with only
traces of silicon.
Riser
An opening in the top of a mould. It acts as a reservoir of molten metal
which prevents the formation of cavities in the casting as it contracts on
solidification. Secondly, it allows gases to escape as the molten metal rises in
the mould and thirdly, it indicates to the moulder when the mould is full. On
removal of the mould, the riser forms a projection on the casting from which it
is finally cut away.
Rising Steel Ingots
(Blown Ingots) (Unskilled Steel) Steel in which there is an evolution of gas
during solidification thus causing the metal to rise in the mould. This may be
because the heat has not been sufficiently deoxidized or killed. If so, this
evolution of gas can be prevented by the addition of a small amount of aluminium
or other suitable deoxidant, but hydrogen in excess can have a somewhat similar
effect and
deoxidation will then have no effect.
Roaks
(See Rokes)
Rockwell Hardness Tester
Rockwell hardness numbers are based on the additional depth to which an indenter
is driven into a metal by heavy load beyond the depth to which the same indenter
has been driven by a light load, the conditions under which this happens being
arbitrary but definite. For the inspection of hard steel parts the
sphere-conical diamond Brale penetrator is used with a major load of 150 kg. The
number indicated on the black scale of the dial is observed and is prefixed by
the letter C, as C-62. For testing softer metal, the penetrator employed may be
a 1/16in diameter steel ball with the other standard load, 100 kg. The readings
are then taken from the red calibration on the dial and the prefix is the letter
B, as B-68. Tests can also be made with other load penetrator combinations, for
example, a 60 kg. major load with a Brale penetrator is used for the "A" scale.
Rokes
(Roaks) Defects on the exterior of bars. They consist of fissures which have
become elongated in the direction of working, but have been only partially
closed up during rolling, their surfaces being separated by a thin film of
scale. They originate from blow-holes, formed immediately below the surface of
the ingot, which have been broken down during forging or rolling and become
oxidized or decarburized. The term should be restricted to isolated deep seams.
(Cf. Seams)
Roll Cogging
The rolling down of ingots in a cogging mill.
Rolling
(a) The process of shaping steel by passing it between two rolls revolving
at the same peripheral speed and in opposite directions.
(b) The preparation of a cylindrical forging by rounding stock between swaging
tools prior to the drop forging operation.
(c) An operation similar to tumbling, in that the metal parts and abrasives are
loaded in a barrel or similar mechanism, but differing in that the work and
abrasives are rolled in such a way that the load rolls over and over upon itself
in a continuous flowing motion in relation to the rotating barrel. Such rolling
removes flash, rough spots and scale, and cuts down a metal surface to an even
and uniform condition.
Rotary Furnace
A furnace having a hearth, circular in plan view, which is slowly rotated,
the walls and roof being stationary. The work pieces are charged through a door
on to the hearth and are carried round for one revolution during which they pass
various burners adjusted to complete the required temperature cycle.
Roughing
(See Cogging).
Ru
Chemical symbol for ruthenium.
Runner
A channel through which molten metal or slag is passed from one receptacle
to another. In a casting mould, that portion of the gate assembly which connects
the down-gate or sprue with the casting. The term is also applied to the metal
which has frozen in such a channel.
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