A symmetry axis requiring two repetitions to complete 360 degrees and
return to identity. Syn:diad
Contains two horizontal rolls, one above the other. In some two-high mills
the direction of rolling can be reversed, and these are known as reversing
mills; i.e., when a piece has passed through the rolls, the rolls are
stopped and then rotated in the opposite direction, thus imposing another
pass on the steel, the operation being repeated until the desired
reduction is attained. Between passes, adjustment is made to the height of
the top roll, and/or the piece is moved sideways by means of manipulators,
to be in line with other grooves in the rolls. Osborne
A rigid frame hinged at both supports. It may have an arched or
rectangular form. Hammond
The provision of two intake airways, generally side by side, to a
ventilating area of a mine. Nelson
A chuck equipped with two movable clamping or holding devices by means of
which the motion of the chuck is imparted to the drill rods. Long
A sling having two chains or ropes which hang from a thimble.
See also:single sling
two-liquid differential manometer
Consists of two concentric glass tubes, each expanded into a large bulb at
the upper end. The lower end of the outer tube is sealed, and the inner
tube reaches nearly to the bottom of the outer tube. Two liquids are used,
and the movement of the interface between the two liquids down the central
tube is used as an index against which the change in pressure is measured.
See also:manometer
A granite containing both dark mica (biotite) and light mica (muscovite).
This rock was called true granite by Rosenbusch and binary granite by
Keyes. CF:aplogranite
A single strand of rope or cable doubled back around a sheave so that two
parts of it pull a load together. Nichols, 2
A set of timbers consisting of a cap and a single post. If the ground is
loose and must be supported over the side or back, lagging, commonly of
2-in (5.1-cm) boards, is used. These boards extend from the center line of
the post or cap to the middle of the next post or cap. If they are placed
touching each other, such an arrangement is called tight lagging; if a few
inches apart (which depends on the nature of the ground to be held back),
it is called open lagging. See also:timber set
A troughing idler in which the troughing roll shafts are in a vertical
plane separate from but parallel to a vertical plane through the shaft of
the center roll or rolls. NEMA, 1
A method of cleaning raw coal in which the material from 8 to 1/16 in (203
to 1.6 mm) in size is treated in heavy-medium washers, and the fines below
1/16 in are treated by froth flotation. Nelson
A differential having a high-flow gearshift between the drive shaft and
the ring gear. Nichols, 1
Air compression carried out in two stages as is usual for pressures
exceeding 60 psi (414 kPa) or for outputs greater than 100 hp (74.6 kW).
See also:intercooler
Deep-shaft hoisting with two winders, one at the surface and the other at
middepth in the shaft. The surface engine winds minerals from the middepth
pocket, and the other winds from the pit bottom to the middepth point. The
arrangement is often adopted in turned vertical shafts.
See also:tandem hoisting
In flotation, a system in which the manipulated variable alternates
between two predetermined values. Fuerstenau
A working cycle of a piston in an internal combustion engine consisting of
two strokes, in which the piston during the first stroke compresses the
fuel mixture on one side while receiving the expansive thrust of
previously compressed gases on the other side, and during the second draws
in a fresh charge on one side while expelling burnt gases on the other.
Webster 3rd
A hydraulic cylinder in which fluid can be supplied to either end, so the
piston can be moved by power in two directions. Syn:double-acting ram
Nichols, 2
An isometric mineral, Na6 Mg2 (CO3 )4 (SO (sub
4) ) , having iron replacing magnesium toward ferrotychite; isomorphous
with northupite, Na6 Mg2 (CO3 )4 Cl2 ,
with which it occurs; forms small white octahedra; at Borax Lake, San
Bernadino County, CA.
Systematic exploration by a mine rescue team of all intersecting and
adjacent passageways so that the team is never forward (toward the working
face) of an accessible, unexplored area. MSHA, 4
See:sieve