Method And Apparatus For Supporting The Roofs In Underground Excavations

Von Hippel June 27, 1

Patent Grant 3672174

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] P 19 60 807.2
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
1796667 March 1931 Rundqvist
2923557 February 1960 Schilling et al.
3145964 August 1964 Groetschel
3427762 February 1969 Mills
3437377 April 1969 Lautsch
3447328 June 1969 Schuermann
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.

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