GB2245632A

GB2245632A - Mine roof support

Info

Publication number: GB2245632A
Application number: GB9014178A
Authority: GB
Inventors: Colin Gordon Michael Merriman; David Jameson
Original assignee: Gullick Dobson Ltd
Current assignee: Gullick Dobson Ltd
Priority date: 1990-06-26
Filing date: 1990-06-26
Publication date: 1992-01-08
Also published as: GB9014178D0

Abstract

A mine roof support is provided having a floor engaging base (21), a roof engaging canopy (11), hydraulic jack means (12, 13) acting therebetween and operable to urge them apart, means (25) to compare the degree of angular displacement of the canopy relative to a pre-determined datum, and means responsive to the comparison for controlling the pressure fluid supply 10 the hydraulic jack means, The invention can be used to prevent excessive tilting of the canopy 11, for example with respect to the base 10, such as might otherwise occur, if irregular roof conditions are encountered. <IMAGE>

Description

MINE ROOF SUPPORTS The invention relates to mine roof supports, such as those used in the longwall method of mining.

During underground mining operations, particularly when using the mining technique known as the longwall method of mining, the mine roof may be supported by means of roof supports of the hydraulically operable selfadvancing type. This type of supporting system comprises a row of support units placed in a side-by-side relationship along the mine workings or face, and each roof support is attached to a conveyor which is not only used to transport cut mineral from the face, but also serves to anchor the line of supports and to provide a track for the mining machine as it passes in front of the line supports and along the face, as the machine removes mineral, for example, the coal bearing strata from the surroundIng stratification.

The object of the longwall method of mining is to extract substantially totally a layer of mineral, for example coal, from between other layers of strata wit the minimum adverse subsidence effect at the earths surface.

The degree of subsidence and the period over which settlement takes place after the removal of the required mineral is governed by many factors, including the depth of the mine workings from the surface, and the nature of the strata overlying such workings.

Mine roof supports of the type described can only control the rate at which convergence between the mine roof and mine floor takes place during the extraction cycle, and after the machine, conveyor and line of supports have been advanced to a new location, the overlying strata is allowed to fall behind the supports to take up the space created by the removal of the mineral once this space has been vacated by the supports. This space is often known as the waste area.

Under good mining conditions, the mine roof remains competent and in tact, until the roof supports have been advanced, whereupon it falls or caves immediately to the rear of the support units into the waste as the roof supports are reset in their new, advanced location. The resetting of the supports to the mine roof often stresses the overlying strata and the rear edge of the roof engaging structure serves to Induce a fracture in the roof bed above the support.

If, however, the mine roof conditions are poor, t the strata above the mine roof support may disintegrate in such a manner that part of the roof bed material slips into the waste before the supports can be advanced and reset, thus leaving a space or void above one or more supports, making it virtually impossible to set those supports because of the void immediately above the supports.

Often it is the task of miners to construct a supporting timber structure above, and resting on, each such mine roof support, to allow the mining operation to continue. If such a timber construction is deemed necessary then the process of removing mineral must be temporarily delayed, and of course there are hazards encountered by the miners during the time when such structural work is carried out. The timber is usually lost during subsequent advances of the roof support, as it is allowed to fall into the waste area as the support advances, thus making the operation costly, in addition to the loss of production.

The need for the timber or other additional support is governed by the size of the cavity above the support and if the cavity can be negotiated without the need for constructing the timber frame work, or the cavity can be tolerated in the knowledge that the support will be located under a competent roof when the support is next reset, then the mining sequence can continue unhindered.

Sometimes the cavity above the support only occurs to the rear of one or a small number of adjacent supports and it then becomes possible that the front part of each relevant support to be set to the mine roof whilst the rear part of the support is not in contact with the mine roof and is hence set in air, and is non-supporting.

The sequence which is often used in the resetting of the mine roof support to the roof, particularly if the mine roof supports each have two rows of support legs ifl the form of hydraulic jacks, the rows running parallel to the mine face, is to set the front row of jacks initiall using low pump pressure to ensure contact when the roof is established, after which both rows of jacks are subjected to an increased hydraulic pressure.

It may be envisaged that, dependent upon the size and location of the cavity immediately above the roof support and the rows of mine jacks, the roof engaging structure, under the influence of the higher setting pressure, may tilt downwardly from the rear towards the front of the support, the leading edge of the cavity or void acting as a fulcrum.

A common feature of a conventional mine roof support is to provide a cantilever roof engaging member extending towards the mine face from the forward row of the mine jacks up to the mine conveyor on which the mining machine travels. Although the cantilever member is so arranged that it normally avoids the cutting part of the machine, it is however positioned above the body of the machine, i.e. above that part of the mining machine whlch is located immediately above the mining conveyor.

The tilting of the roof engaging structure in the manner described above can be substantial and can result in the forward part of the cantilever member becoming an obstruction to the passage of the mining machine, or to the miners operating the machine.

To avoid or reduce this problem, we have developed a mine roof support having means to limit the angular displacement of the roof engaging structure of a hydraulically operable mine roof support by controllIng the flow of pressurised fluid to the supporting means in response to the degree of angular displacement Accordingly, the invention provides a mine roof support having a floor engaging base, a roof engaging canopy, hydraulic jack means acting therebetween and operable to urge them apart, means to compare the degree of angular displacement of the canopy relative to a predetermined datum, and means responsive to the comparison for controlling the pressure fluid supply to the hydraulic jack means.

The pre-determined datum may comprise the plane of the floor engaging base.

There may be means to detect angular misalignment between the base and the canopy.

There may be one jack means positioned between the rear and the front of the support.

Alternatively, there may be a plurality of jack means lyIng between the front and the rear of the support.

The or each jack means may comprise a pair of hydraulic jacks arranged side by side Where there are two rows of jacks, the angular displacement or tilt may be quantified by measuring the different extension between the front and rear rows of mice jacks. However such a method cannot be used if there is only one row of jacks, and so it is preferred that the detection means comprises a gravity responsive device.

The gravity responsive device may be provided with adjustment means to compensate for the effect which is produced when the mine roof supports are working on a gradient.

The adjustment means may comprise a signal generating means arranged for attachment to the roof engaging canopy using a slot and bolt mounting means.

The control of the pressure fluid supply to the hydraulic jack means may have varying degrees of sophistication. For example, the control may be such that when the canopy attains an unacceptable degree of displacement relative to the datum, the supply of fluid to the hydraulic jacks means which is causing the displacement will be reduced until the degree of angular displacement is correspondingly reduced, indeed the supply of pressure fluid may be terminated altogether, for example if no further realignment is possible.

Where there is a plurality of jack means lying between the front and rear of the support, the detection of mis-alignment may cause the flow of fluid pressure to the rear jack means to be controlled.

The flow of fluid pressure to the hydraulic jacks means may be controlled by electrically operable valve means. The means to detect the angular mis-alignment may be provided with a degree of free travel before a signal is transmitted to control means, thus per:ritting a limited degree of angular displacement prior to any remedial action being initiated.

There may be signal generating means which is provided with a damper or compensation means such that a positive non-fluctuating signal is produced.

The control signals may be electrical.

Where a gravitational responsive device is used, may comprise a pendulum connected to the roof supporting canopy.

Alternatively, the gravitational responsive device may comprise a switching device such as a mercury level switch.

Although a gravitational responsive device is of more general application, the invention does include an embodiment in which the angular displacement is monitored by the comparison of the extensions of a plurality of extensible means, which are connected between the canopy and the base and are spaced apart in the for and aft direction of the support.

During the advance stage of a mine roof support, it is commonplace to have to advance the mine roof support over obstructions in the floor. There may for example be steps in the floor caused by different passes of the mining machine, or there may be loose material on the floor. To ease the advance of the support over such a surface the base members of mine roof supports may be equipped with base lifting devices which are operable to lift the front end of the base so that as the support advances, only the rear part of the base is in contact with the floor. Normally, this is carried out prior to the setting of the support, with the hydraulic jack means unpressurised, and so any angular mis-alignment caused by base lifting will not initiate the correct effect of the invention.

However, mine roof supports can be used in a socalled contact advance system. With such a system, the roof engaging canopy is designed to remain in contact with the mine roof throughout the advance. With such a system, uncalled for corrective action could be initiated by default if base lifting was also used. To compensate for this and avoid the possibility of re-alignment being carried out unnecessarily, the gravitational responsive device may be arranged to have considerable free movement, so that a particularly severe movement of the gravitational responsive device is required before any corrective action is taken with respect to the supply of pressurised fluid to the hydraulic jack means.

By way of example, a specific embodiment of the invention will now be described, with reference to the accompanying drawings, in which Figure 1 is a side view of an embodiment of mine roof support according to the invention, with the roof engaging canopy correctly aligned with the floor engaging base; Figure 2 shows the roof support of Figure 1 with the roof engaging canopy mis-aligned; Figure 3 is an end view of a gravitational responsive device of the support; and Figure 4 is a front view of the gravitational responsive device of Figure 3 with the protected cover removed.

Figures 1 and 2 show a mine roof support indicated generally at 10, having a roof engaging canopy 11 and a floor engaging base 21. There are two sets of hydraulic jack means for urging the base and canopy apart. A first set comprises a rear pair of jacks 12 and the second set comprises a front pair of jacks 13. It is not essential to have two jacks 12 and two jacks 13. There may be a single jack or more than two jacks. The canopy 11 and base 21 are also interconnected at the rear end of the support by a shield 14 attached to the canopy and the four element lemniscate linkage 15, 15a. A substantially horizontal hydraulic jack 16, used for advancing the support, is housed in and attached to the base 21 and the jack 16 can be attached in use at the front end of the support to a mine conveyor (not shown) by a clevis 17.

The base 21 comprises two parallel pontoon like members connected at their forward ends by a bridge member 23, but other configurations of base are possible. The rear of the base structure pontoons may be connected by a shield plate (not shown) which connects either the upper or lower pair of elements 15a, 15. Alternatively a four element linkage connected together by the shield 14 may be used in such a way that the shield 14 resists any forces tending to displace vertically one base pontoon relative to the other. The travelling way for use by miners, along the mine face, is defined by a passage identified as W and bounded by a canopy 11, base 21, and the rear and forward jacks 12 and 13.

The functions of the support in this embodiment are controlled by a conveniently located valve 24 which is attached to the roof engaging structure.

In accordance with the present invention, the mine roof support has a gravitational responsive device 25 which is also mounted on the roof engaging structure 11.

The gravitational responsive device will now be described in more detail, with reference to Figures 3 and 4.

The device 25 has a housing 26 having a base plate 27 and a cover plate 28 secured in position in a flame proof manner by four screws 29. The base plate has a mounting hole 30 at its upper end, and a mounting slot 31 at its lower end. Inside the housing 26, as can be seen from Figure 4, there is a pendulum 32 pivotally mounted on a bracket 33 and retained by a plate and screw device 34.

At a mid point along the pendulum arm 35 there is attached the piston rod 36 of a damper 37 which has an adjusting screw 38.

Also mounted in the housing 26 is a micro switch 39 arranged to engage with the pendulum 32 if excessive tilt of the roof engaging structure 11 is sensed by the device 25. The micro switch 29 is connected electrically to an electrical socket 40 for subsequent connection to electrical valve means for controlling pressure fluid to the rear jacks 12.

It can be seen from Figure 4 that in this embodiment the switching angle is 100 and it is only when there is an angular displacement of the pendulum of 100 from the vertical that contact will be made with the micro switch 39.

The switching angle can however be adjusted by presetting the angle of the housing 26 with respect to the vertical. This can be done by pivoting the housing about its upper mounting hole 30 and then clamping the housing in the desired attitude by means of a clamping screw located in the slot 31.

It is not essential for a gravitatIonal responsive device to be used, particularly when there are two ros of jacks 12 and 13. In an alternative embodiment, the inclination of the canopy 11 can be measured at the front and rear ends of the roof engaging structure, for example by devices similar to those described in our earlier U.K.

Patent specification number 1002844 although the signals from those devices would be used in a different manner.

For example the two signals, front and rear, would be compared and only when the rear extension signal exceeded the front extension signal by a predetermined value would pressure fluid to the rear jacks be cut off.

In both embodiments, the object is to prevent the canopy 11 from tilting by an undesirable extent, when the conditions described in the introduction of the specification are encountered. Thus information relating to the attitude of the canopy 11 is used to control the supply of pressurised fluid to the jacks 12 and 13 in the most desirable manner. Electrical control signals and electrically controlled valves may be used.

In general, the supply of pressurised fluid to the rear legs 12 will be reduced, or even cut off altogether, until such time as the canopy 11 returns to an unacceptable angle.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A mine roof support having a floor engaging base, a roof engaging canopy, hydraulic jack means acting therebetween and operable to urge them apart. Means to compare the degree of angular displacement of the canopy relative to a predetermined datum, and means responsive to the comparison for controlling the pressure fluid supply to the hydraulic jack means.

2. A mine roof support as claimed in Claim 1, in which the predetermined datum comprises the plane of the floor engaging base.

3. A mine roof support as claimed in Claim 1 or Claim 2, in which there is detection means to detect angular misalignment between the base and the canopy.

4. A mine roof support as claimed in Claim 3, in which there is detection means mounted on the canopy.

5. A mine roof support as claimed in any one of the preceding Claims in which there is one jack means positioned between the rear and the front of the support.

6. A mine roof support as claimed in any one of Claims 1 to 4, in which there is a plurality of jack means positioned between the front and the rear of the support.

7. A mine roof support as claimed in Claim 5 or Claim 6, in which the, or each, jack means comprises a pair of hydraulic jacks arranged side by side.

8. A mine roof support as claimed in Claim 6, in which the angular displacement is qualified by measuring the different extension between the front and rear jack means.

9. A mine roof support as claimed in any one of Claims 1 to 8, in which the angular displacement is qualified using a gravity responsive device.

10. A mine roof support as claimed in Claim 9, in which the gravity responsive device comprises a pendulum.

11. A mine roof support as claimed in Claim 9 or Claim 10, in which the gravity responsive device is provided with adjustment means to compensate for the effect which is produced when the mine roof support is working on a gradient.

12. A mine roof support as claimed in Claim 11, in which the adjustment means comprises a signal generating means arranged for attachment to the support using a slot and bolt mounting means.

13. A mine roof support as claimed in any one of the preceding Claims, in which the control is such that when the canopy attains an unacceptable degree of displacement relative to the datum, the supply of fluid to the hydraulic jack means which is causing the displacement will be reduced until the degree of angular displacement is correspondingly reduced.

14. A mine roof support as claimed in any one of Claims 1 to 13, in which the control may cause termination of the supply of fluid to the hydraulic jack means which is causing the displacement.

15. A mine roof support as claimed in Claim 13 or Claim 14, in which the hydraulic jack means causing the displacement comprise rear jack means.

16. A mine roof support as claimed in any one of the preceding Claims, in which flow of fluid to the hydraulic jack means is controlled by valve means.

17. A mine roof support as claimed in any one of the preceding Claims in which the means to compare the degree of angular displacement as provided with a degree of free travel before a signal is transmitted to the control means, thus permitting a degree of angular displacement prior to any remedial action being initiated.

18. A mine roof support as claimed in any one of the preceding Claims, having signal generating means provided with a damper or compensation means such that a positive non-fluctuating signal is provided.

19. A mine roof support as claimed in any one of the preceding Claims, in which electrical control signals are used.

20. A mine roof support as claimed in Claim 19, utilising a pendulum, in which the pendulum is arranged to come into contact with and activate a micro-switch.

21. A mine roof support constructed and arranged substantially as herein described with reference to the accompanying drawings.