U.S. patent number 3,672,174 [Application Number 05/070,048] was granted by the patent office on 1972-06-27 for method and apparatus for supporting the roofs in underground excavations.
Invention is credited to Hansjoachim Von Hippel.
United States Patent |
3,672,174 |
Von Hippel |
June 27, 1972 |
METHOD AND APPARATUS FOR SUPPORTING THE ROOFS IN UNDERGROUND
EXCAVATIONS
Abstract
A walking mine roof support wherein one or more roof engaging
caps are pivotable on the upper end of at least one extendable pit
prop which is mounted on the floor engaging base. Balancing rams
connect the rear ends of the caps with the base or such rams carry
bars which are movable against the roof behind the caps. The props
and the rams are operated by a hydraulic control system in response
to signals from pressure gauges mounted on the front and rear ends
of the caps. Such signals indicate changes in pressure which the
mine roof exerts against the respective ends of the caps.
Inventors: |
Von Hippel; Hansjoachim (7771
Oberstenweiler, DT) |
Family
ID: |
5752927 |
Appl.
No.: |
05/070,048 |
Filed: |
September 8, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Dec 4, 1969 [DT] |
|
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P 19 60 807.2 |
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Current U.S.
Class: |
405/295; 299/1.7;
91/390 |
Current CPC
Class: |
E21D
23/0017 (20130101); E21D 23/22 (20130101) |
Current International
Class: |
E21D
23/00 (20060101); E21D 23/22 (20060101); E21d
011/16 () |
Field of
Search: |
;61/45D,63 ;299/1
;73/389 ;91/390 ;248/354H,356,357 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Taylor; Dennis L.
Claims
What is claimed as new and desired to be protected by Letters
Patent is:
1. A method of preventing collapse of the roof in an underground
excavation, particularly in longwall mining, comprising the steps
of supporting from below, with a variable force, an elongated strip
of the roof in front of and substantially at right angles to the
mine face in the excavation; measuring the pressure which the
supported strip of the roof exerts in a downward direction; and
adjusting the variable force in accordance with the result of such
measurement.
2. A method as defined in claim 1, wherein said measuring step
comprises monitoring the pressure in the region of at least one end
of the strip and said adjusting step comprises automatically
adjusting the variable force in accordance with the result of
measurement at said one end of the strip.
3. A method as defined in claim 1, wherein said measuring step
comprises monitoring the pressure at least in the region of that
end of the strip which is adjacent to the mine face and said
adjusting step comprises reducing the force at the other end of the
strip when the pressure at the first mentioned end of the strip
increases.
4. A method as defined in claim 3, further comprising the step of
terminating the application of force to the other end of the strip
and increasing the force which acts against the first mentioned end
of the strip.
5. A method as defined in claim 1, wherein said adjusting step
comprises maintaining the force acting against the end of the strip
which is remote from the mine face at a constant value and
increasing the force acting against the remainder of the strip when
the result of the measurement indicates an increase in the pressure
exerted by the strip.
6. A method as defined in claim 1, wherein the variable force is
transmitted by way of a roof engaging assembly which is subject to
bending stresses and wherein said adjusting step comprises changing
the force in the region of that end of the strip which is remote
from the mine face when the pressure transmitted to the roof
engaging assembly generates a bending stress which exceeds a
predetermined value.
7. A method as defined in claim 1, further comprising the step of
supporting from below with a variable force at least one additional
strip of the roof adjacent to the first mentioned strip, measuring
the pressure which the additional strip exerts in a downward
direction, and adjusting the variable force which acts on said
first mentioned strip in accordance with the result of measurement
of the pressure transmitted by the additional strip.
8. A mobile mine roof supporting apparatus, particularly for use in
longwall mining, comprising a support arranged to rest on the floor
of an underground excavation; an elongated roof engaging assembly
having front and rear portions and arranged to engage the roof in
the excavation; at least one adjustable variable-length propping
device mounted on said support and connected with said assembly
between said rear and front portions whereby the assembly is
respectively urged against and moves away from the roof in response
to lengthening and shortening of said device; at least one
adjustable balancing device connected with and operative to apply
to the rear portion of said assembly a force in line with the load
upon said rear portion; and a control system comprising at least
one signal generating load monitoring member responsive to changes
in load upon said assembly and adjusting means for adjusting at
least one of said devices in response to signals from said
monitoring member.
9. Apparatus as defined in claim 8, wherein said balancing device
is connected with said support and is adjustable to exert a thrust
or a pull on the rear portion of said assembly.
10. Apparatus as defined in claim 9, wherein said balancing device
comprises at least one hydraulically operated ram having a first
portion coupled to the rear portion of said assembly and a second
portion coupled to said support behind said propping device, one of
said portions of said ram being movable lengthwise of the ram
relative to the other portion of said ram and said adjusting means
comprising means for moving said one portion of said ram in
response to said signals.
11. Apparatus as defined in claim 8, wherein said monitoring member
comprises a pressure gauge mounted in the front portion of said
assembly so as to be subjected to the pressure of the roof and
conduit means for transmitting signals from said gauge to said
adjusting means.
12. Apparatus as defined in claim 8, wherein said monitoring member
comprises a pressure gauge mounted on the rear portion of said
assembly so as to be subjected to the pressure of the roof and
conduit means for transmitting signals from said gauge to said
adjusting means.
13. Apparatus as defined in claim 12, wherein said one device is
said balancing device and wherein said signals from said pressure
gauge are indicative of maximum permissible bending stresses upon
said assembly.
14. Apparatus as defined in claim 8, wherein said balancing device
comprises at least one hydraulically operated cylinder and piston
unit of variable length and wherein said one device is said
balancing device.
15. Apparatus as defined in claim 14, wherein the cylinder of said
unit is a double-acting cylinder.
16. Apparatus as defined in claim 14, wherein said unit is a
multi-stage cylinder and piston unit.
17. Apparatus as defined in claim 8, wherein the front portion of
said assembly comprises a cover plate which yieldably engages the
roof and said monitoring member comprises a pressure gauge mounted
in said front portion below said cover plate to produce signals in
response to displacement of the cover plate by the roof.
18. Apparatus as defined in claim 8, wherein the rear portion of
said assembly has a downwardly and rearwardly inclined
roof-engaging upper side and said balancing device comprises at
least one hydraulically operated ram coupled to said rear portion
and to said support and extending substantially at right angles to
said upper side.
19. Apparatus as defined in claim 8, further comprising means for
pivotally connecting said assembly to the upper end of said
propping device.
20. Apparatus as defined in claim 8, further comprising a link
connected to said support behind said devices and to the front
portion of said assembly.
21. Apparatus as defined in claim 20, wherein said support
comprises a transversely extending rear wall having an upper
portion located substantially midway between the upper side of said
assembly and the underside of said support, and means articulately
connecting the ends of said link to said front and upper
portions.
22. Apparatus as defined in claim 20, further comprising a second
mine roof supporting apparatus having a floor-engaging support
laterally adjacent to and connected with said first mentioned
support said link being disposed in a vertical plane between said
two apparatus and being further connected to the front portion of
the roof engaging assembly of said second apparatus.
23. Apparatus as defined in claim 8, wherein said roof engaging
assembly comprises an elongated beam, means for pivotally
connecting said beam to the upper end of said propping device, and
at least one roof engaging cap reciprocably supported by said
beam.
24. Apparatus as defined in claim 23, wherein said cap is pivotable
in a vertical plane with reference to said beam.
25. Apparatus as defined in claim 23, wherein said balancing device
comprises at least one ram mounted on the rear portion of said cap
and having a portion movable upwardly against the roof.
26. Apparatus as defined in claim 25, further comprising means for
coupling said ram to said support.
27. Apparatus as defined in claim 25, wherein the portion of said
ram is shorter than said cap and is slidable along the roof.
28. Apparatus as defined in claim 25, further comprising means for
articulately connecting said portion of said ram to said cap.
29. Apparatus as defined in claim 8, wherein said roof engaging
assembly comprises an elongated beam connected to the upper end of
said propping device and a pair of interconnected elongated roof
engaging caps reciprocably by said beam.
30. Apparatus as defined in claim 29, wherein said caps have front
end portions connected to each other and wherein said monitoring
member is supported by the front end portions of said caps.
31. Apparatus as defined in claim 29, wherein said balancing device
comprises two hydraulically operated rams each connected with the
rear portion of one of said caps.
32. Apparatus as defined in claim 8, wherein said roof engaging
assembly comprises a pair of parallel elongated beams mounted on
the upper end of said propping device and an elongated roof
engaging cap disposed between and reciprocably supported by said
beams.
33. Apparatus as defined in claim 32, wherein said cap is pivotable
in a vertical plane with reference to said beams.
34. Apparatus as defined in claim 32, wherein said balancing device
comprises a hydraulically operated ram connected with the rear
portion of said cap.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for
supporting and preventing collapse of the roofs in underground
excavations. More particularly, the invention relates to
improvements in a method and apparatus for supporting the roofs in
underground excavations wherein the material is removed from the
mine face and the apparatus which supports the roof is
intermittently advanced toward the face to prevent cave-in in the
area accommodating the material removing machinery and the
conveyors for transport of removed material to the surface.
Presently known mine roof supporting apparatus for use in longwall
mining normally comprise a battery of discrete or interconnected
mine roof supports each of which has a roof engaging cap, a floor
engaging base or support and one or more pit props which are
mounted on the base and carry the cap. The props can be extended
and contracted to move the cap against or away from the roof and to
furnish the necessary resistance to collapse of the roof. If the
cap is supported by a single prop or by several transversely
aligned props, it is free to tilt with reference to the prop or
props so as to automatically find an optimum position for
engagement with the roof when the props are extended to urge the
cap against the underside of the roof.
It is a well known fact that, during mining of coal or similarly
deposited minerals by longwall mining, the roof of the excavation
tends to fracture in the general plane of the mine face. The
relatively long front portions of the caps, namely, those portions
which extend forwardly of the props, are thereby required to resist
greatly increased loads. Such loads considerably exceed those which
are resisted by the relatively short rear portions of the caps,
i.e., those portions which point toward the waste behind the mine
roof supports. Frequently, the load upon the rear positions is
insufficient to prevent the front portions from being forced down
in the area immediately in front of the mine face. This contributes
to further loosening of overlying strata and can lead to sudden
overloading of mine roof supports and to collapse of the roof
supporting structure.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method which prevents
the collapse of roofs in underground excavations and according to
which the roof engaging assembly is protected against undue bending
and/or other stresses.
Another object of the invention is to provide a method according to
which the collapse of the roof in an underground excavation is
prevented in a fully automatic way so that the number of attendants
can be reduced and that the prevention of roof collapse is not
dependent on the skill and/or conscientiousness of the
attendants.
A further object of the invention is to provide a method according
to which localized stressing of the roof engaging assembly can be
counteracted without any delay and which is particularly suited to
neutralize overstressing of the roof engaging assembly in longwall
mining wherein the roof tends to develop fissures or cracks in the
general plane of the mine face.
An additional object of the invention is to provide a mine roof
support whose roof engaging assembly is protected against undue
stresses in a novel and improved way.
Still another object of the invention is to provide a mobile mine
roof support which can be combined with similar mine roof supports
to prevent collapse of a larger part of the roof in an underground
excavation and to provide the thus combined apparatus with a novel
control system which automatically responds to overstressing of any
given roof engaging assembly and can at the same time adjust the
adjoining assemblies to insure more uniform distribution of
stresses.
A concomitant object of the invention is to provide a mine roof
support with novel means for monitoring the load upon its roof
engaging assembly and with novel means for automatically responding
to signals from the monitoring means to avoid overstressing of the
roof engaging assembly and to also prevent collapse of the
roof.
An ancillary object of the invention is to provide a mine roof
support which need not be shifted toward the mine face as
frequently as presently known mine roof supports.
Another object of the invention is to provide novel means for
balancing the roof engaging assembly of a walking mine roof
support.
The method of the present invention is resorted to for preventing
collapse of the roof in an underground excavation, particularly in
longwall mining. The method comprises the steps of supporting from
below, with a variable force, an elongated strip of the roof in
front of and substantially at right angles to the mine face in the
excavation, measuring the pressure which the supported strip of the
roof exerts in a downward direction, and adjusting the variable
force in accordance with the result of such measurement. The
measuring step preferably comprises monitoring the load on the roof
engaging assembly which applies the variable force to the strip in
the region of at least one end of the strip, and the adjusting step
preferably comprises automatically adjusting the variable force as
a function of the result of measurements at the one end of the
strip. Such measurements can be carried out by resorting to
pressure gauges which can be installed in the roof engaging
assembly and transmit signals which are utilized for adjustment of
the variable force by way of a suitable control system, preferably
by way of a hydraulic control system which can regulate the fluid
pressure in one or more props or struts on which the roof engaging
assembly is mounted and which are in turn mounted on a
floor-engaging support.
In accordance with a more specific feature of the invention, the
pressure which the strip exerts is measured at least in the region
of that end of the strip which is adjacent to the mine face, and
the adjusting step comprises reducing the force at the other end of
the strip when the pressure at the first mentioned end of the strip
(close to the mine face) increases. In some instances, it might
become necessary to terminate the application of the force at the
other end of the strip and to increase the force which acts against
the end of strip which is adjacent to the mine face. This can be
achieved by connecting the rear portion of the roof engaging
assembly with one or more double-acting balancing rams which can
apply a thrust or a pull whereby a thrust increases the force which
is applied to the other end of the strip whereas a pull causes the
front portion of the assembly to exert a greater force against the
strip in the region of the mine face. This is due to the fact that
the roof engaging assembly is pivotally mounted on one or more
props or struts and acts not unlike a two-armed lever whose front
arm bears against the roof with a force which increases if the rear
arm is caused to actually move downwardly or is merely subjected to
the action of a downwardly oriented force.
In accordance with another more specific feature of the invention,
the adjusting step comprises maintaining constant the force which
acts against the end of the strip that is remote from the mine face
and increasing the force which acts against the remainder of the
strip when the result of the measurement indicates a rise in
pressure which is exerted by the strip. This merely involves
preferably automatic adjustment of the prop or props whereby the
force which is transmitted by the balancing ram or rams remains
unchanged.
The roof engaging assembly is subject to bending stresses which
should not exceed a predetermined value. The adjusting step may
comprise changing the force in the region of that end of the strip
which is remote from the mine face when the pressure transmitted to
the roof engaging assembly generates a bending stress which exceeds
the permissible value.
The method may further comprise the steps of supporting from below
with a variable force one or more additional strips which are
adjacent to each other and to the first mentioned strip, measuring
the pressure which the additional strip or strips exert in a
downward direction, and adjusting the variable force which acts on
one or more strips when the pressure exerted by a neighboring strip
varies. This renders it possible to further reduce the likelihood
of collapse in that the measurement brings about adjustment of the
force which acts against the most affected strip as well as against
one or more adjacent strips.
The novel features which are considered as characteristic of the
invention are set forth in particular in the appended claims. The
improved mine roof support itself, however, both as to its
construction and its mode of operation, together with additional
features and advantages thereof, will be best understood upon
perusal of the following detailed description of certain specific
embodiments with reference to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side elevational view of a mine roof support which
embodies one form of the invention and is located in an underground
excavation in front of the mine face;
FIG. 2 is an end elevational view as seen from the right-hand side
of FIG. 1 and illustrates three groups of pairwise arranged mine
roof supports each of which is constructed in a manner as shown in
FIG. 1;
FIG. 3 is a plan view of the structure shown in FIG. 2;
FIG. 4 illustrates the hydraulic control system of the mine roof
support shown in FIG. 1;
FIG. 5 is a schematic side elevational view of a modified mine roof
support;
FIG. 6 is a plan view of the mine roof support shown in FIG. 5;
FIG. 7 is a fragmentary side elevational view of a third mine roof
support; and
FIG. 8 is a plan view of the third mine roof support.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a so-called walking
mobile mine roof support which comprises a roof-engaging assembly
having a cap or roofbar 1, a floor-engaging base member or support
2, and a propping device here shown as consisting of a single
adjustable hydraulic pit prop or strut 3 which carries the cap 1
and is of variable length. The upper end portion of the prop 3
engages an intermediate portion of the cap 1. The rear portion 4 of
the cap 1 (behind the prop 3) is connected to the rear portion of
the support 2 by an adjustable balancing device here shown as
consisting of a single ram 5 which preferably constitutes a
hydraulically operated prop or strut of variable length and is
designed to exert on the rear portion 4 a thrust or a pull,
depending on the nature and distribution of pressures on the cap 1
and in line with the direction of such pressures. In the
illustrated embodiment, the balancing ram 5 comprises a
double-acting cylinder which is mounted on the support 2 and a
piston whose piston rod is coupled to the rear portion 4 of the cap
1. For better guidance of the piston rod, the latter can be
slidably telescoped into an upwardly projecting tubular extension
of the double-acting cylinder as shown in FIG. 1. The prop 3 may
also comprise a double-acting cylinder which is mounted on the
support 2 and a piston whose piston rod is coupled to an
intermediate portion of the cap 1. If desired, the prop 3 can
employ a single-acting cylinder which can lift the piston rod and
the cap 1 in response to admission of a pressurized hydraulic fluid
into its chamber whereby the cap can descend by gravity and/or in
response to the pressure of the mine roof when the pressure in the
chamber of the cylinder is reduced. It is also possible to replace
the single prop 3 with a group of two or more props. Embodiments
with plural props are shown in FIGS. 5 to 8.
The mine face in an underground excavation wherein the mine roof
support of the present invention can be put to use is shown at 50.
The mine roof support can be used with a battery of similar or
identical mine roof supports which can be assembled and grouped
side-by-side in a manner as shown in FIGS. 2 and 3. When the
material along the mine face 50 is removed by the customary
machinery which forms no part of the present invention, some or all
of the mine roof supports are advanced toward the mine face, either
singly or in groups of two or more, and the removal of material
from the mine face begins anew. The thus removed material is
transported from the excavation by a system of conveyors one of
which runs along the mine floor in front of the mine face 50 and is
shown in FIG. 1, as at 150. The conveyor 150 can be coupled to the
mine roof supports so that it is automatically advanced when the
mine roof supports are caused to walk in a direction to the fight,
as viewed in FIG. 1. The means for advancing the mine roof supports
toward the mine face is of known design and, therefore, is not
shown in the drawing. Such advancing means normally comprises
hydraulically operated cylinder and piston assemblies.
In the illustrated mine roof support, the length of the front
portion of the cap 1 (in front of the prop 3) exceeds the length of
the rear portion 4. The upper side 6 of the rear portion 4 slopes
downwardly and rearwardly. An intermediate portion of the cap 1
contains a block or headpiece 7 which is articulately connected
with the piston rod of the prop 3 by a joint here shown as
including a transverse pivot pin 8. The cap 1 rests on the piston
rod of the prop 3 not unlike a balance beam or weighbeam. However,
it is equally within the purview of the invention to provide the
block 7 with a concave socket for a spherical head of the piston
rod. It is preferred to design the cap 1 in such a way that its
maximum width is in the region of the pivot pin 8. Also, the
portion of maximum height of the cap 1 is preferably in the region
of the block 7 and pivot pin 8.
The support 2 is provided with side walls 9 and a rear wall 10
which acts as a shield to retain loose rock 11 of waste material
against penetration into the space between the side walls 9. The
rear wall 10 preferably extends upwardly to or beyond the level of
the upper end of the cylinder of the prop 3. The upper edge portion
of the rear wall 10 carries a hinge 12 for the lower rear end of a
radius rod or link 13 the front end of which is coupled to the cap
1 in front of the pivot pin 8, preferably by means of a further
pivot pin 14. The link 13 slopes downwardly and rearwardly from the
pivot pin 14 toward the hinge 12. The purpose of the link 13 is to
stabilize the position of the cap 1 but it does not interfere with
necessary pivotal movements of the cap with reference to the prop 3
and balancing ram 5 or with expansion and contraction of the part 3
and/or 5. The rear end portion 15 of the link 13 is wider than the
remaining major part of the link. A hydraulic adjusting unit or
control unit 25 is mounted on the forward part of the support 2 in
front of the prop 3 and is connected with various other components
of the hydraulic control system by pipes and conduits which in part
extend in or along the link 13. FIG. 1 shows conduits 24 and 32
which respectively connect the adjusting unit 25 with signal
generating pressure gauges or load monitoring members 22 and 31.
The link 13 shields the adjacent or surrounded portions of the
conduits 24 and 32.
FIGS. 2 and 3 show that two or more adjoining mine roof supports
can be assembled to form a group constituting a twin or multiplex
mine roof support. The means for coupling the adjoining mine roof
supports may comprise bolts or analogous fasteners which rigidly
connect the side walls 9 on the supports of neighboring mine roof
supports. Each group of, for example, two mine roof supports may
share a common link 13 which is then located in the central
vertical plane extending between two interconnected mine roof
supports. The pintle of the hinge 12 and the pivot pin 14 for such
common link 13 may extend through all of the interconnected caps 1
to enhance the rigidity of the apparatus, especially as concerns
the resistance to lateral distortion.
Referring again to FIG. 1, the balancing ram 5 has a rounded lower
end portion which is received in a bearing 16 of the support 2. A
pivot pin 17 connects the ram 5 to the support. The upper end of
the ram is articulately connected to the rearmost part of the rear
portion 4 of the cap 1 by a pivot pin 18. The support 2 is further
provided with a concave socket or shoe 19 for the spherical lower
end portion of the prop 3. The socket 19 is located between the
adjusting unit 25 and the bearing 16.
The aforementioned pressure gauge or monitoring member 22 is
mounted in the foremost part 20 of the cap 1 below an elastically
deformable cover plate 23 consisting of steel or the like. The
cover plate 23 abuts against the underside of the mine roof 21 and
the purpose of the pressure gauge 22 is to monitor the pressure
which the mine roof 21 exerts against the cover plate 23 in the
region of the front portion 20 of the cap 1. The pressure gauge 22
produces signals which are utilized for automatic adjustment of the
prop 3 and/or balance ram 5 as a function of the pressure against
the cover plate 23 close to the mine face 50. As best shown in FIG.
4, the pressure gauge 22 comprises a cylinder 22a whose chamber
below a reciprocable piston 22b is filled with hydraulic fluid and
wherein the piston 22b is biased upwardly by a spring 22c. A motion
transmitting plunger 22d is connected with the piston 22b and bears
against the underside of the cover plate 23. The aforementioned
conduit 24 connects the chamber of the cylinder 22a with the
adjusting unit 25. The latter contains all the necessary hydraulic
accessory equipment some of which is shown in FIG. 4 and which
includes pressure-responsive valves, relief valves, check valves,
control valves and others. The construction of many valves in the
adjusting unit 25 is known and, therefore, some such valves were
omitted for the sake of clarity and the others are merely shown by
appropriate symbols.
Conduits 26, 28 connect the adjusting unit 25 with the chambers in
the cylinder of the balance ram 5 and a further conduit 27 connects
the adjusting unit 25 with the chamber below the piston in the
cylinder of the prop 3. A supply conduit 29 connects the adjusting
unit 25 with a source 30 of pressurized hydraulic fluid. As shown
in FIG. 3, this source extends along the front portions of the
supports 2 of the battery of mine roof supports which are located
in front of the mine face 50.
The pressure gauge 31 constitutes a second signal generating
monitoring member and is mounted in the rearmost part of the rear
portion 4 of the cap 1. The construction of the pressure gauge 31
is preferably identical with that of the gauge 22 (see FIG. 4) and
its plunger 31d abuts against a resilient cover plate 33 which
overlies the rear portion 4 and bears against the adjacent loose
rock. The conduit 32 connects the adjusting unit 25 with the
chamber in the cylinder 31a of the pressure gauge 31. The cover
plates 23 and 33 are mounted in such a way that they can flex
downwardly when the pressure against their upper sides increases
whereby the cover plates respectively depress the plungers 22d, 31d
to generate pressure pulses or signals which are transmitted to the
adjusting unit 25.
The hydraulic control system of the mine roof support shown in FIG.
1 includes the aforementioned adjusting unit 25, the pressure
gauges 22, 31, the conduits 24, 26, 27, 28, 29, 32, and the source
30 of pressurized hydraulic fluid. This control system serves to
automatically adjust the prop 3 and/or the balancing ram 5 in
response to changes in pressure upon the cover plates 23, 33. As
shown in FIG. 4, the conduit 24 connects the chamber in the
cylinder 22a of the pressure gauge 22 with a valve 34 which
controls the flow of hydraulic fluid into the conduit 27 and hence
into the chamber of the prop 3. The valve 34 is connected with the
aforementioned supply conduit 29 and with a second supply conduit
35 which can admit highly pressurized hydraulic fluid. Such
pressurization of hydraulic fluid for admission into the supply
conduit 35 can take place in a suitable pressure accumulator or the
like, not shown. When the supply conduit 35 is permitted to
communicate with the conduit 27 (by way of the valve 34), the
chamber of the cylinder in the prop 3 receives fluid at a high
pressure so that the prop 3 can withstand substantial pressures
which are applied against the upper side of the cap 1. The supply
conduit 29 conveys hydraulic fluid at normal system pressure; this
conduit contains a check valve 29a and a shutoff valve 29b.
The conduit 24 is further connected to a valve group 36 which
includes a pressure reducing valve 46, a pilot piston 37 and a flow
interrupting or stop valve 38. The purpose of the valve group 36 is
to regulate the flow of hydraulic fluid to and from the chambers of
the cylinder in the balancing ram 5. When the pressure of fluid in
the conduit 24 rises, i.e., when the cover plate 23 moves the
plunger 22d of the pressure gauge 22 downwardly, as viewed in FIG.
4, the fluid moves the pilot piston 37 upwardly against the
opposition of a helical spring 37a whereby the piston 37 first
completes an idle stroke x before it can engage and open the stop
valve 38. As the pilot piston 37 moves upwardly to stress the
spring 37a, it relieves a second spring 41 which biases the valve
member of the pressure reducing valve 46 to closed position in
which the valve member engages a seat in the body of the valve 46.
The piston 37 completes the idle stroke x when the valve 46 permits
the pressure in the chambers of the cylinder in the ram 5 to drop
to zero. When the stop valve 38 opens, it permits hydraulic fluid
to flow from the supply conduit 29 to a conduit 39 which is
connected to an inlet of a control valve or stop valve 40. If the
valve 40 opens, the fluid can flow from the conduit 39 into the
conduit 28 and hence into the upper chamber of the cylinder in the
ram 5. This causes the piston rod of the ram 5 to descend or at
least to exert a pull on the rear portion 4 of the cap 1.
The control valve 40 is connected with a second control valve 42 by
means of a conduit 43 which is further connected to the conduit 32
for the cylinder chamber of the pressure gauge 31. A third control
valve 44 is also connected with the conduit 43 and with a return
conduit 45 which can discharge fluid into an exhaust pipe 47 in
response to opening of the pressure reducing valve 46. The valve 40
functions as a stop valve for the conduit 39. A conduit 48 connects
the control valve 42 with the conduit 26 and hence with the lower
chamber in the cylinder of the balancing ram 5. This lower chamber
can receive hydraulic fluid from the supply conduit 29 by way of an
adjustable shutoff valve 29c before the automatic control of the
operation begins. Thus, the operator can decide to extend the ram 5
in response to partial or complete opening of the shutoff valve
29c. It is clear that the cylinders of the prop 3 and ram 5 are
provided with customary pressure relief valves and exhaust valves
for evacuation of spent fluid. Such valves are not shown for the
sake of clarity. Furthermore, even though FIG. 4 shows pilot
pistons of equal size, it is evident that the diameters of such
pistons can vary within a wide range. Also, the springs shown in
FIG. 4 are preferably adjustable so that the control system can be
programmed to effect opening and/or closing of its valves in a
desired sequence.
The operation of the hydraulic control system for the mine roof
support of FIG. 1 is as follows:
If a fissure 49 (shown in FIG. 1) develops in the mine roof 21
close to or in the general plane of the mine face 50, this results
in the exertion of a greater pressure on the cover plate 23 for the
front portion of the cap 1 because the mine roof 21 ceases to
adhere to the material above the mine face. The pressure gauge 22
responds to such increase in pressure (i.e., to downward movement
of the cover plate 23) and the pressure in the conduit 24 (FIG. 4)
rises. Such rise in pressure constitutes a signal which is
transmitted to the valve 34 and valve group 36. If the valve 34 is
first to respond to such signal, it connects the supply conduit 35
for highly pressurized hydraulic fluid with the conduit 27 which
admits fluid into the chamber of the cylinder in the prop 3. The
chamber in this cylinder can receive fluid at such a pressure that
the prop 3 can withstand maximum permissible stresses on the cap 1,
i.e., stresses which are below those causing the aforementioned
pressure relief valves for the prop 3 to open. At the same time, or
with an appropriate delay, the pilot piston 37 responds to
increasing pressure in the conduit 24 and begins to rise to relieve
the spring 41 and to reduce the pressure in the cylinder chambers
of the balancing ram 5. When the pilot piston 37 completes the idle
stroke x, it opens the stop valve 38 so that the latter connects
the supply conduit 29 with the conduit 39. The valve 40 permits the
fluid to flow from the conduit 39 into the conduit 28 and thence
into the upper chamber of the cylinder of the ram 5. The latter
exerts on the rear portion 4 of the cap 1 a pull whereby the cover
plate 23 exerts a correspondingly increasing force against the
underside of the mine roof 21. The pressure of fluid in the upper
chamber in the cylinder of the ram 5 can be intensified or reduced
by resorting to conventional pressure regulating means, not
shown.
The purpose of the control valves 40, 42 and 44 is as follows:
These valves cooperate with the pressure gauge 31 on the rear
portion 4 of the cap 1. If the pressure exerted by the mine roof 21
on the cover plate 33 for the rear portion 4 rises beyond a certain
value, the pressure in the chamber of the cylinder 31a increases
and the conduit 32 transmits a pressure pulse to the conduit 43.
The control valve 40 is first to close in response to such pulse
whereby its pilot piston permits the fluid to flow from the conduit
28 into a relief conduit 28a containing a check valve 28b. This
terminates the pull on the rear portion 4 by way of the ram 5.
The control valve 44 is next to close and it thereby shuts off the
return conduit 45. The control valve 42 thereupon opens and admits
hydraulic fluid from the supply conduit 29 through the conduits 48
and 26 into the lower chamber of the cylinder in the ram 5. The ram
5 applies a thrust to the rear portion 4 of the cap 1 and thus
resists the temporary overload to prevent destruction of the
cap.
If the loose rock above the cover plate 33 slides away or if a
cavity 151 (indicated in FIG. 1 by phantom lines) develops above
the rear portion 4 for any other reason, the pressure gauge 31
responds and initiates appropriate adjustments of the control
valves 40,42 and 44. The aforedescribed controlling action repeats
itself and the upper chamber in the cylinder of the ram 5 is
connected with the source of pressurized hydraulic fluid so as to
apply a pull to the rear portion 4 of the cap 1.
When two or more mine roof supports are mounted side-by-side as
shown in FIGS. 2 and 3, it is often desirable to interconnect the
pressure gauges 22, 31 and/or the adjusting units 25 of adjoining
mine roof supports by resorting to suitable connecting conduits so
that signals produced by any one of the pressure gauges are
transmitted to the adjusting units of the adjoining mine roof
supports. This enables the group of interconnected mine roof
supports to more effectively resist pressures which arise when a
fissure develops in the mine roof 21. For example, if a fissure
develops in a portion of the mine roof 21 above a single mine roof
support, the pressure of fluid in the neighboring mine roof
supports can be raised to enable such neighboring mine roof
supports to assist the most affected apparatus in bearing the
increased load. Also, such raising of fluid pressure in neighboring
apparatus can be effected as a purely precautionary measure.
An important advantage of the improved mine roof support is that
the roof engaging assembly (including the cap 1, its block 7 and
the cover plates 23, 33) is less likely to yield to unbalanced
pressure of the mine roof 21. The roof engaging assembly is mounted
on the prop 3 not unlike a weighbeam or balance beam so that it can
pivot about the axis of the pin 8. Its angle of tilt can be
positively controlled by the balancing ram 5 which can make
allowance for differential loads acting on the cap 1. For example,
when the front portion (cover plate 23) experiences a rising load
by that portion of the mine roof 21 which is adjacent to the mine
face 50, a downwardly directed force can be applied to the rear
portion 4 by means of the balancing ram 5 to thereby impart to the
front portion of the cap an upward thrust and to thus prevent
continued loosening and breakup of the strata of rock above the
cover plate 23. This insures that the rock cannot penetrate into
the space 152 (FIG. 1) between the prop 3 and the mine face 50;
such space is needed for the material removing machinery and the
conveyor 150.
As explained above, the optimum position of inclination of the cap
1 can even be maintained if a cavity (151) develops in the roof 21
above the rear portion 4 and its cover plate 33. The balancing ram
5 then again applies a downwardly oriented force (pull) upon the
rear portion 4 to insure that the front portion and its cover plate
23 can resist the load in the region of the mine face 50.
If the rear portion 4 of the cap 1 is suddenly subjected to a
highly increased pressure, for example, by a mass of loosened rock
(such as the rock filling the cavity 151 shown in FIG. 1), the
balancing ram 5 is adjusted to apply to the rear portion 4 an
upwardly oriented force (thrust) to thereby resist a sufficiently
large portion of the overall pressure on the cap 1. Also, such
lengthening of the balancing beam 5 prevents the generation of
excessive bending stresses upon the rear portion 4, namely, such
bending stresses which would tend to break the cap 1 in the region
of the pivot pin 8. Though the adjustments of the balancing ram 5
could be carried out by hand, for example, by periodically checking
the pressure gauge 31 and by thereupon adjusting the pressure in
the upper or lower cylinder chamber of the ram 5 in accordance with
the readings furnished by the gauge 31, this would necessitate
practically uninterrupted supervision of pressure gauges for a
battery containing a large number of mine roof supports with
attendant expenditures for additional personnel. Moreover, the
adjustments of the balancing ram 5 would depend entirely on the
skill, conscientiousness and alertness of operators.
All such problems can be avoided by employing the aforedescribed
automatic control system which is preferably hydraulic but which
can also include at least some mechanical, pneumatic and/or
electrical and electronic components. An automatic control system
reacts more rapidly than a manually controlled system and it is
more reliable, especially if the pressures upon the cap 1 are
monitored at two or more points. As a rule, it is preferred to
employ at least one monitoring member (22) in the region of the
front portion of the cap 1; the other monitoring member (31) or
members are optional even though they are desirable, especially in
the region of the rear cover plate 33. The control system generates
countervailing forces which are applied to the cap 1 by way of the
prop 3 and/or balancing ram 5 and which can be localized in such a
way that excessive pressures on the front or rear portion of the
cap can be compensated for by applying properly oriented forces to
the same portion and/or to another portion of the cap. This insures
that the cap 1 is always held in an optimum position to resist the
loads due to the pressure which the elongated strip of the mine
roof 21 above the mine roof support applies against the cover
plates 23, 33 and/or against the median portion of the cap.
In some instances, the control system can be designed in such a way
that the changes in pressure detected by the monitoring member 22
are used only for automatic adjustment of the balancing ram 5.
However, a much greater versatility can be achieved if the control
system serves to adjust the balancing ram 5 and the prop 3,
preferably in such a way that differential pressures are applied to
the ram and to the prop when differential loads are applied to
different parts of the cap.
If the mine roof support is equipped with two monitoring members,
for example, with the pressure gauges 22, 31 which are mounted in a
manner as shown in FIG. 1, the two gauges can effect automatic
adjustments of the prop 3 and/or balancing beam 5. Such pressure
gauges, mounted at the front and rear ends of the cap 1, render it
possible to immediately detect a differential in the pressures
acting on the front and rear portions of the cap and to immediately
adjust the balancing ram 5 so that the latter exerts a thrust or a
pull.
In the control system of FIG. 4, the parts which are connected with
the rear pressure gauge 31 form a safety circuit which can bring
about at least temporary changes in pressurization or a reversal in
the direction of action of the balancing ram 5 when the admissible
bending stresses on the cap 1 are exceeded. This control circuit
can be associated with a suitable alarm (not shown) which produces
visible and/or audible signals to warn the operators of the
possible collapse of the mine roof support. In the absence of
excessive loads, the control system of FIG. 4 protects the mine
roof support against destruction by temporary overloads and enables
the apparatus to absorb the momentary overload resiliently.
It was found that the improved mine roof support reduces the
likelihood of loosening of roof strata, particularly in the region
adjacent to the mine face. The roof is gently controlled by the
caps of cooperating mine roof supports and maintains its existing
cohesion. This throws less load upon the caps and protects them
from undue stresses. Thus, the danger of roof collapse in longwall
mining is reduced and the likelihood of lengthy interruptions in
material removal is avoided.
As stated above, the balancing ram 5 preferably comprises a
double-acting hydraulic cylinder and piston unit. However, it is
equally within the purview of the invention to employ multi-stage
telescopic balancing rams or pairs of single-acting rams one of
which can pull and the other of which can push the rear portion 4
of the cap 1.
The cover plates 23, 33 protect the respective pressure gauges 22,
31. Moreover, such cover plates insure that the respective pressure
gauges can generate signals which represent the distribution of
pressures upon relatively large portions of the roof engaging
assembly. In other words, the pressure gauges need not respond to
highly localized changes in pressure which could cause faulty
adjustments of the prop 3 and/or balancing ram 5.
As shown in FIG. 1, the inclination of the balancing ram 5 in such
that its axis is substantially normal to the general plane of the
upper side 6 of the rear portion 4 (cover plate 33). A cap whose
rear portion slopes rearwardly and downwardly can act as an
effective shield or baffle which prevents penetration of loose rock
into the space around the balancing ram 5 and prop 3. Also, any
particles of loose rock are free to slide along the inclined cover
plate 33 and to accumulate on the floor behind the rear wall 10 of
the support 2. The inclined balance beam 5 insures that the thrust
or pull upon the rear portion 4 is applied in line with the
pressures acting on the cover plate 33. The parts 5 and 4 are well
in front of the region where the roof is allowed to cave in behind
the mine roof support.
The mounting of the lower end of the link 13 on the rear wall 10 of
the support 2 substantially midway between the upper side of the
cap 1 and the underside of the support 2 enhances the stability of
the mine roof support. It was found that such stability is not
affected by the fact that the ends of the balancing ram 5 and prop
3 are articulately connected to the cap 1 and support 2. Additional
stability is achieved because the upper end of the link 13 is
connected to the cap 1 forwardly of the pivot 8 for the prop 3. The
conduits which are mounted in or on the link 13 are protected at
all times, regardless of the thickness of the seam (i.e.,
irrespective of the height of the excavation).
FIGS. 5 and 6 illustrate a second mine roof support wherein the
base member or support 2a carries a propping device consisting of
two hydraulic pit props or struts 3a which are inclined toward each
other and form a composite prop for an elongated head piece or beam
7a of the roof engaging assembly. This beam is urged against the
mine roof 21 and is provided with longitudinally extending guides
or ways 51 in the form of grooves or the like. The beam 7a is
flanked by two roofbars or caps 1a which also form part of the roof
engaging assembly and have limited freedom of pivotal movement
about transverse horizontal pivot pins 8a. The pins 8a carry roller
followers which can travel along the respective guides 51 to move
the caps 1a forwardly or rearwardly, i.e., toward or away from the
mine face 50 (as indicated by the double-headed arrow shown in FIG.
5). The front end portions of the caps 1a are connected to each
other by a cover plate 23a the central portion of which overlies a
pressure gauge 22. The rear portions 4a of the caps 1a support a
balancing device having two discrete balancing rams 5a each
including a piston rod 52 which carries a short bar 53 movable
against or away from the mine roof 21. The conduits which connect
the pressure gauge 22, props 3a and rams 5a to the adjusting unit
25a are not shown in FIGS. 5 and 6. The adjusting unit 25a can
automatically adjust the props 3a and/or the balancing rams 5a
substantially in the same way described in connection with FIG. 4.
The pressure gauge 22 again responds to flexing of the resiliently
mounted cover plate 23a which overlies the interconnected front end
portions of the caps 1a. Due to the fork-like construction of the
composite cap including the caps 1a, a single pressure gauge 22
suffices to produce the necessary signals. If the pressure upon the
cover plate 23a increases, the balancing rams 5a are caused to move
their piston rods 52 upwardly and to exert the necessary
counterpressure.
As shown in FIG. 5 by broken lines, the cylinders of the balancing
rams 5a can be articulately connected to the rear wall of the
support 2a. This enables these rams to exert a thrust as well as a
pull to compensate for changes in pressure upon the front portions
of the caps 1a.
A double-acting shifting cylinder 56 is pivotably mounted in the
beam 7a and its piston rod is articulately connected to the caps 1a
so that the caps can be moved lengthwise relative to the beam. The
arrangement can be such that, when the mine roof support is to be
advanced toward the mine face 50, the caps 1a are advanced in a
first step and the beam 7a is advanced in the next step.
The mine roof support of FIGS. 5 and 6 can be grouped with similar
apparatus in such a way that the caps 1a of adjacent apparatus are
staggered in a direction at right angles to the mine face. In this
way, the caps can support a larger area of the roof 21. Moreover,
the caps 1a can be moved forwardly toward the mine face 50 while
the respective supports 2a remain at a standstill. This renders it
possible to increase the intervals between successive advances of
the supports 2a. Since the caps 1a are pivoted to the beam 7a and
to the piston rod of the shifting cylinder 56, they can assume
positions of optimum inclination with reference to the roof 21. The
balancing rams 5a (as shown by solid lines) are mounted on the rear
portions 4a of the respective caps 1a and are designed to produce a
thrust by pushing the corresponding bars 53 against the roof 21. If
they are coupled to the support 2a, the rams 5a can exert a thrust
or a pull, preferably in automatic response to signals generated by
pressure gauges (not shown) on the rear portions 4a and/or in
response to signals from the pressure gauge 22. When the bars 53
are located below a cavity, a pull produced by balancing rams 5a
connected to the support 2a enables the front portions of the caps
1a to urge the cover plate 23a against the roof 21 with a much
greater force. This does not affect the movability of caps 1a along
the beam 7a. The bars 53 slide along the roof 21 and protect the
balancing rams 5a when the mine roof support is advanced toward the
mine face 50. The bars 53 then constitute shoes which move behind
the beam 7a.
Referring finally to FIGS. 7 and 8, there is shown a mine roof
support wherein a single short bar 53b is articulately connected to
a single cap 1b by one or two transversely extending pivot pins 54
which carry roller followers 55 arranged to travel in guides or
ways 51b provided in the adjacent beams 7b. Thus, the bar 53 can be
entrained by the cap 1b when the latter is caused to advance toward
the mine face 50. The beams 7b flank the single cap 1b and their
front portions contain shifting cylinders 56b whose piston rods are
connected to the cover plate 23b which is mounted on the front end
portion of the cap 1b. The pressure gauge 22 is mounted below the
central portion of the cover plate 23a. A single balancing ram 5b
is mounted on the rear portion 4b of the cap 1b and has a piston
rod 52b which can move the bar 53b upwardly. The props are shown at
3b.
When the cap 1b is caused to move toward the mine face (either with
or relative to the beams 7b), the bar 53b shares all movements of
the cap but is pivotable about the pin 54. Thus, the bar 53b can
move in a vertical plane but always trails the cap 1b. In the
embodiment of FIGS. 7 and 8, the cylinders 56b can shift the cap 1b
with reference to the beams 7b or vice versa. A single balancing
ram 5b suffices here because the apparatus comprises a roof
engaging assembly having a single cap. It is clear that the lower
end portion of the ram 5b can be coupled to the support (not shown)
in the same way as shown in FIG. 1 or FIG. 5 (by broken lines).
Also, each of the mine roof supports shown in FIGS. 5 to 8 can
employ one or more links corresponding to the link 13 of FIG.
1.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge, readily adapt it for various applications without
omitting features which fairly constitute essential characteristics
of the generic and specific aspects of my contribution to the art
and, therefore, such adaptations should and are intended to be
comprehended within the meaning and range of equivalence of the
claims.
* * * * *