Two endless chains or other linkage between which carriers are mounted and
controlled, so that the carriers remain in an upright and horizontal
position throughout the complete cycle of the conveyor.
The pressure of the rocks over active mine workings. It is the roof weight
that acts on the packs and the solid coal in the working area.
See also:abutment; nether roof; underweight. Nelson
Excessive breakage of rock beyond the desired excavation limit.
See also:neat lines
See:overhand stoping
a. Designates material of any nature, consolidated or unconsolidated, that
overlies a deposit of useful materials, ores, or coal--esp. those deposits
that are mined from the surface by open cuts. Stokes
b. Loose soil, sand, gravel, etc. that lies above the bedrock. Also called
burden, capping, cover, drift, mantle, surface. See also:baring; burden;
top. Stokes
A special diamond-set bit, similar to a set casing shoe, used to drill
casing through overburden composed of sand, gravel, boulders, etc.
Long
a. A technique developed in Sweden that involves the sinking, by
percussive-rotary drilling, of a drill casing through the overburden to
where it seats in the underlying rock. A rotary percussion drill hole is
then continued to the desired depth in the rock. While the casing is being
sunk through the overburden it is coupled to the drill rod and rotates and
reciprocates with it. The rock bit on the end of the drill rod projects
about an inch beyond the end of the ring bit with which the casing is
fitted and acts as a pilot bit for the casing bit. Woodruff
b. A drilling method whereby drilling is carried out through subsoil and
boulders or underwater to and through bedrock. Eng. Min. J., 2
a. An enclosed airway that permits an air current to pass over another one
without interruption. Syn:overcrossing; overgate. CF:undercast
See also:air crossing
b. To place the overburden removed from coal in surface mines in an area
from which the coal has been mined.
c. Pushed forward, so as to overlie other rocks, such as in thrust faults.
See also:jack pit
A procedure used in certain mining activities including strip mining and
in some heavy construction work such as channel excavation. Overcasting
may be performed in a simple operation consisting of digging out the
material, lifting it from one position, moving it over, and dumping it in
the spoil position where it remains, for practical purposes, indefinitely.
The mechanics of the operation are called "simple overcasting."
Woodruff
Adding material in excess of the capacity of the equipment used for
processing.
A soil deposit that has been subjected to an effective pressure greater
than the present overburden pressure. ASCE
See:air crossing; overcast.
Relay used to trip circuit breakers when an abnormal current of two to
three times the normal flow is detected in a circuit. Relays are adaptable
to transmission lines, buses, feeder circuits, transformers, and motors.
Coal Age, 3
a. A machine cut made along the top or near the top of a coal seam;
sometimes used in thick seams or a seam with sticky coal. By releasing the
coal along the roof, its mining becomes easier. See also:overcut;
turret coal cutter. Nelson
b. The process of producing a larger size hole than the outside diameter
of a bit and/or reaming shell used, due to the eccentric rotational
movements of the bit, core barrel, or drill stem. Long
Coal-cutting machine that is an adaptation of a shortwall machine,
designed to make the cut, or kerf, at desired place in the coal seam some
distance above the floor. The main difference between an overcutting
machine and an ordinary shortwall machine is that the cutter bar in the
overcutting machine is mounted at the top of the machine instead of at the
bottom. See also:turret coal cutter
Medium of specific gravity greater than that in the separating bath;
usually produced in the medium recovery system and used to maintain the
desired specific gravity in the bath. BS, 5
The act or process of drilling a run or length of borehole greater than
the core-capacity length of the core barrel, resulting in loss of the
core. Long
The act of inducing a velocity higher than the steady state velocity in a
column of explosive material upon detonation by the use of a powerful
primer or booster; it is a temporary phenomenon and the explosive quickly
assumes its steady state velocity.
A term related to the condition of a ceramic product which has been heated
to a temperature in excess of that required to produce proper
vitrification.
Heating ceramic materials or ware above the temperature required to
produce the necessary degree of vitrification. Usually results in
bloating, deformation, or blistering of the ware.
A standpipe in which water rises and overflows at the hydraulic gradeline.
Seelye, 1