ROOF SUPPORT UNIT FOR A MINING MACHINE

Technical Field

The present invention refers to a roof support unit for a mining machine and to a mining machine, in particular a longwall mining system, which is equipped with such a roof support unit.

Longwall mining systems are used for underground coal mining. Such systems are configured to mine coal by undercutting soil layers along a broad coal face. For doing so, coal along the coal face is removed in layers upon successively advancing the longwall mining system under ground, while the roof and the overlaying layer collapse into a void generated behind the advancing longwall mining system during operation.

In order to hold off the collapsing material and thus for maintaining a safe working space along and in front of the coal face, such longwall mining systems typically comprise a plurality of powered roof support units placed in a long line side-by-side in front of the coal face. The roof support units, also referred to as shield units, are configured to selectively support and hold the roof overlaying the longwall mining system. Further, the roof support units are usually connected to an armoured face conveyer via an advance mechanism, in particular in the form of hydraulically driven linear actuators, also referred to as relay bars.

The armoured face conveyor extends along the coal face and carries a shearer unit having rotatably actuated cutting drums for cutting coal from the coal face. The shearer unit is translationally supported on the armoured face conveyor so as to drive the cutting drums back and forth along the coal face, thereby removing and disintegrating coal from the coal face which is loaded on the armoured face conveyor. The armoured face conveyer then conveys the removed coal to a side of the longwall mining system where it is further loaded onto a network of conveyor belts for transport to the surface.

In the following, the operation of such a longwall mining system is specified. At first, the longwall mining system is positioned in front of the coal face for enabling removal of coal from the coal face by means of the shearer unit. For doing so, the shearer unit is actuated and translationally moved along the whole width of the armoured face conveyor so as to remove and ablate a complete layer of coal from the coal face. During cutting operation of the shearer unit, the powered roof support units are operated in an engaged state, in which they support or reinforce the roof above the longwall mining system. For doing so, a support canopy of the roof support units is in a raised state in which it is pressed against the roof of a mine gallery.

Then, after removal of a coal layer, the armoured face conveyor together with the shearer unit is moved towards the coal face so as to bring the cutting drums of the shearer unit into engagement with the coal face again. This may be performed by means of the powered roof support units and the advance mechanism. More specifically, in the engaged state of the roof support units, the linear actuators of the advance mechanism are actuated so as to protrude and thereby push the armoured face conveyer towards the coal face.

Thereafter, the roof support units are individually and successively moved to approach the armoured face conveyer. For doing so, the individual roof support units are actuated so as to retract, i.e. to lower, their support canopy. Accordingly, the support canopy no longer exerts a supporting force against the roof. In this lowered state of the support canopy, the roof support unit is then pulled towards the displaced armoured face conveyor by a retracting actuation of advance mechanism. In this way, individual roof supports are moved to follow up the armoured face conveyor. This may be performed successively for each roof support unit.

As a result, by repeatedly and successively pushing the armoured face conveyer and thereafter pulling the roof support units to follow up the movement of the armoured face conveyer, the longwall mining system is enabled to advance in a feed direction.

For raising and lowering the support canopy, known roof support units are equipped with hydraulically or electro-hydraulically driven actuators, also referred to as prop means or leg cylinders. It has been found that, during operation of such a mining machine, in particular upon lowering the support canopy, components of the roof support units may be subjected to vibrations or sudden movements, e.g. due to the inherit energy stored in the leg cylinders. For example, upon lowering the support canopy, a hydraulic system for actuating the prop means may be subjected to transient pressure pulses in the return hydraulic system where the leg cylinder fluid is expelled to which may lead to excessive component vibrations, e.g., of hydraulic hoses, but also to system contamination due to possible delamination of internal hose rubbers from high transient fluid velocities and wave dynamics. This particularly applies to recent developments, according to which roof support units used in mining machines are getting bigger along with the forces and stored energy acting upon its components during operation.

Summary Of The Invention

Starting from the prior art, it is an objective to provide an improved roof support unit of a mining machine which in particular ensures high operational reliability. Further, it is an objective to provide a longwall mining system which is equipped with such a support unit.

These objectives are solved by the subject matter of the independent claims. Preferred embodiments are set forth in the present specification, the Figures as well as the dependent claims.

Accordingly, a roof support unit for a mining machine, particularly for a longwall mining system, is provided. The roof support unit comprises a support canopy which is supported on a base via at least one damper unit and at least one actuator, for example in the form of a prop means or leg cylinder, configured to move the support canopy relative to the base. Furthermore, a longwall mining system is provided which is equipped with at least one such roof support unit.

Since the longwall mining system is equipped with the roof support unit as described above, technical features described herein in connection with the roof support unit may thus relate and be likewise applied to the longwall mining system, and vice versa.

The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which:

Figure 1 schematically shows a roof support unit of a longwall mining system;

Figure 2 schematically shows an enlarged longitudinal section of a damper unit used in the roof support unit depicted in Fig. 1;

Figure 3 schematically shows an enlarged longitudinal section of the dumping unit according to another embodiment; and

Figure 4 shows a diagram illustrating operating parameters in conventional roof support units.

Detailed Description Of Preferred Embodiments

In the following, the invention will be explained in more detail with reference to the accompanying Figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

Fig. 1 schematically shows a roof support unit of a longwall mining system. Although the roof support unit is described in the following in connection with its use in the longwall mining system, the suggested roof support unit is not limited to this application and may be used in any suitable mining machine which makes use of roof supports or support canopies. The longwall mining system equipped with at least one roof support unit as depicted in Fig. 1 may comprise a material removing unit configured to be placed in front of a coal face to be processed by the longwall mining system. Specifically, the material removing unit may comprise an armoured face conveyor provided in the form of a long line configured for being placed along the whole width of the coal face. The material removing unit may further comprise a shearer unit which is translationally supported on the armoured face conveyor. The shearer unit may comprise a carriage or main body engaged with a rail system of the armoured face conveyor by means of a tractive motive unit configured to drive the shearer unit along the rail system. By this configuration, the shearer unit is configured to move along the armoured face conveyor and thus along the coal face. The armoured face conveyor is configured to receive coal removed from the coal face during cutting operation of the shearer unit and to convey the removed coal to a side of the longwall mining system where it may be loaded onto a network of conveyor belts for transport to the surface.

The longwall mining system preferably comprises a plurality of roof support units 10 which are placed in a long line side-by-side behind and along the armoured face conveyer. In this context, the term “behind” refers to a movement or feed direction of the longwall mining system. Each roof support unit 10 is connected to the armoured face conveyer via an actuatable linear relay bar 12, also referred to as advance mechanism, via which each roof support unit 10 is translationally moveable relative to the armoured face conveyer, thereby enabling movement of the longwall mining system as described above.

The basic structure and function of such a longwall mining system are well known to a person skilled in the art and are thus not further specified. Rather, characteristics of the roof support unit 10 which are interlinked with the present invention are addressed in the following. Specifically, the characteristics of the present invention are exemplarily described hereinafter based on one roof support unit 10 of the longwall mining system which, accordingly, may also apply to the other roof support units of the longwall mining system. The roof support unit 10 comprises a support canopy 14, also referred to as shield or roof shield, which is supported on a base 16 of the roof support unit 10, also referred to as floor sill, via at least one damper unit 18 and at least one actuator 20. The damper unit 18 and the actuator 20 are connected in line, i.e. in series, between the support canopy 14 and the base 16. Preferably, the roof support unit 10 comprises more than one damper unit 18 and more than one actuator 20, for example two damper units 18 and two actuators 20 provided at opposite sides of the support canopy 14 and the base 16.

The roof support unit 10 further comprises a rear shield 22 which is pivotably connected at opposite ends to the support canopy 14 and the base 16. Specifically, the rear shield 22 is pivotally connected to a rear end of the support canopy 14 by means of a pivot joint (not shown). Further, a lower region of the rear shield 22 is connected to the base 16 by means of a lemniscate linkage constituted by at least one pair of connecting rods 24, each of which is pivotably connected at opposite ends to the rear shield 22, i.e. its lower region, and the base 16 via pivot joints 26.

The roof support unit 10 is intended and configured to be arranged between a roof and the sole of a mining gallery. Accordingly, during operation, the base 16 is configured to be positioned on the sole of the mining gallery, while the support canopy 14 is configured to be selectively pressed against the roof of the mining gallery upon actuation of the actuator 20. For doing so, the actuator 20 is configured to move the support canopy 14 relative to the base 16. In other words, the actuator 20 is configured to raise and lower the support canopy 14 relative to the base 16. As such, the actuator 20 is configured to selectively and variably exert a support force acting upon the support canopy 14 to change the position of the canopy 14 relative to the base 16 or to maintain the position of the canopy 14 against the roof of the mining gallery.

In the shown configuration, the actuator 20 is a hydraulic linear actuator, i.e. which is hydraulically or electro-hydraulically actuated. Specifically, the actuator 20 is a multi-stage hydraulic cylinder, also referred to as telescopic hydraulic cylinder, which is powered or actuated by a hydraulic system. That is, the actuator 20 is operated by pressurized hydraulic fluid, in particular a water/oil emulsion mixture, which is selectively supplied by a pressure source (not shown), such as a pump, into at least one cylinder or barrel 27 of the actuator 20 and selectively discharged therefrom via a discharge valve mounted to the actuator 20 (not shown), also referred to as a "Leg Pilot Operated Check Valve" (Leg POCV) so as to move the piston tube 28a (first stage) and piston rod 28b (second stage) within the cylinder barrel 27 back and forth. In this way, the piston tube and rod 28a/28b of the actuator 20 can be extended or retracted in order to move the support canopy 14 relative to the base 16. For supplying and discharging the hydraulic fluid to and from the actuator 20, the hydraulic system comprises hydraulic hoses (not shown) which fluidcommuni catively connect the actuator 20 to the pressure source and a fluid reservoir (not shown), respectively. These hydraulic hoses are, at least party, installed in or at the roof support unit 10.

As set forth above, the support canopy 14 is supported on the base 16 via the damper unit 18 and at least one actuator 20. That is, a supporting force for supporting the support canopy 14, in particular for changing or maintaining a position of the support canopy 14 relative to the base 16, is transferred between the support canopy 14 and the base 16, at least partly, via the damper unit 18 and the actuator 20. In other words, both the damper unit 18 and the actuator 20 are configured to transmit a support force between the support canopy 14 and the base 16 for maintaining or changing of position of the support canopy 14 relative to the base 16 during operation. As such, the damper unit 18 is configured to structurally support the support canopy 14 on the base 16. That is, the support canopy 14 is structurally connected to the base 16 via the damper unit 18 and the actuator 20.

In the context of the present disclosure, the term "damper unit" refers to a device which is configured to convert motion energy of components structurally connected thereto and/or to store energy, in particular as potential energy, and thus may also be referred to as "energy absorbing device" or "energy compensating device" or "energy transfer device". In the shown configuration, the damper unit 18 is configured to allow movement via internal compression and decompression, in particular to a certain extent, of the actuator 20, in particular of its piston tube and rod 28a, 28b, relative to the support canopy 14 and the base 16. Further, the damper unit 18 is configured to dampen the movement of the actuator 20, in particular of its piston tube and rod 28a, 28b, relative to the support canopy 14 and the base 16. That is, the damper unit 18 is configured to convert motion energy of the actuator 20, in particular its piston tube and rod 28a, 28b, into heat and/or into potential energy, i.e. stresses within the damper unit 18. In this way, the damper unit 18 may reduce and absorb some of the stored energy when the actuator 20 experiences sudden activation, in particular induced by actuation of the hydraulic system, such as upon opening the control valve in order to decompress and lower the actuator 20 connected to the support canopy 14. Specifically, the damper unit 18 is configured to dampen and/or absorb and/or transfer part of the stored fluid potential energy, in particular of the two compressed fluid volumes that reside in the actuator 20, relative to the support canopy 14 and the base 16 in a direction parallel to a retracting or extending movement of the actuator 20.

As can be gathered from Fig. 1, the damper unit 18 is mounted to an end section of the actuator 20, in particular to piston rod 28b. Thus, the damper unit 18 and the actuator 20 are mounted, i.e. arranged, in line, i.e. in series, in particular as regards the direction of the support force transmitted between the support canopy 14 and the base 16 via the damping unit 18 and the actuator 20. As such, the damper unit 18 is interposed, i.e. structurally interposed, between the support canopy 14 and the actuator 20, in particular via the piston rod 28b. In other words, the actuator 20, in particular via the piston rod 28b, is structurally connected, in particular directly connected, to the support canopy 14 via the damper unit 18.

According to an alternative embodiment, the damper unit 18 may be mounted to an end section of the cylinder barrel 27 of the actuator 20. According to this configuration, the damper unit 18 may be interposed, i.e. structurally interposed, between the actuator and the base of the roof support unit. Fig 2. shows an enlarge sectional view of the damper unit 18 which, for the sake of better visualization, is depicted isolated from other components of the roof support unit 10. The damper unit 18 comprises a retainer cap 30 at its end section via which the damper unit 18 is pivotally connected to the support canopy 14 by means of a further pivot joint 32. To the retainer cap 30, a socket 34, also referred to as guide socket or guide tube or guide barrel, is connected. The socket 34 is configured to receive an end section of the piston rod 28b to connect the damper unit 18 to the actuator 20. Specifically, the socket 34 is configured to translationally support the end section of the actuator 20 via the piston rod 28b in the damper unit 18. By this configuration, the damper unit 18 allows relative translational movement between the piston rod 28b and the socket 34 to a certain extent. Further, the socket 34 is configured to lock pivot movement of the piston rod 28b relative to the damper unit 18, in particular around a pivot axis being perpendicular to a longitudinal axis of the piston rod 28b, i.e. perpendicular to the retracting or extending movement direction of the piston tube and rod 28a/28b. For doing so, the socket 34 is provided with a guide gland 36 arranged opposite to the retainer cap 30. The guide gland 36 is provided with an inner guiding surface which is designed correspondingly to and configured to engage with an outer surface of the end section of the piston rod 28b.

The damper unit 18 further comprises a compression element 38. The damper unit 18 is configured such that, upon translational movement of the piston rod 28b relative to the damper unit 18, the compression element 38 is compressed, thereby converting motion energy of the piston rod 28b into potential energy stored in the compression element 38 and/or into heat. In the mounted state of the damper unit 18 in which the damper unit 18 is mounted to the actuator 20, a plunger element 40 is interposed between the end section of the piston rod 28b and the compression element 38, as can be gathered from Fig. 1. Specifically, the plunger element 40 constitutes a support and distributes or transfers the force between the compression element 38 and the piston rod 28b. According to one configuration, the plunger element 40 may be provided in the form of a compression plunger, for example, made of a compressible material and may constitute a further compression element.

In the configuration depicted in Fig. 2, the compression element 38 is a solid compression element. Specifically, the compression element 38 is provided in the form of a spring, in particular in the form of a plurality of stacked plate springs.

Fig. 3 depicts another configuration of the damper unit 18 which, compared to the configuration depicted in Fig. 2, includes a compression element 38 which constitutes a liquid component, in particular a compression fluid, provided in a fluid chamber 42 of the socket 34 which is delimited by the socket 34 and the plunger element 40. In this configuration, the socket 34 is provided with a control port 44 for supplying or discharging or decompressing the compression fluid to or from the fluid chamber 42.

In the following, possible technical effects of providing the damper unit 18 in the roof support unit 10 are described with reference to Fig. 4.

As to substance, Fig. 4 depicts a diagram schematically illustrating different operating parameter over time of a conventional roof support unit, i.e. a prior art roof support unit, in which, compared to the suggested roof support unit depicted in Fig. 1, the actuator is directly connected to the support canopy 14. In other words, in this conventional configuration, the damper unit 18 and thus the effects interlinked therewith are not present.

Turning to Fig. 4, the ordinate of the diagram depicts a pressure within the fluid chamber stored in the actuator barrel 27 and the abscissa of the diagram depicts the time, wherein the time to refers to a point in time in which a control valve or Leg POCV for decompressing or discharging hydraulic fluid from a cylinder of an actuator of the conventional roof support unit is opened to decompress the fluid chamber and lower the corresponding support canopy. For illustrating the effects of opening such a control valve or Leg POCV, two different curves are depicted in the diagram, each of which is associated to one operating parameter of the conventional roof support unit. Specifically, a first curve 46 depicted by a solid line in Fig. 4 represents a pressure prevailing in the cylinder of the actuator over time, i.e. after opening the control valve or Leg POCV. A second curve 48 depicted by a dashed line in Fig. 4represents the force imbalance in the discharge/return hosing of the hydraulic system of the known roof support unit through the decompression cycle of the actuator via operation of the control valve or Leg POCV.

In the context of the present invention, it has been found that, upon opening the control valve or Leg POCV in the known roof support units, i.e. during a decompression phase of the cylinder, the pressure prevailing in the cylinder, as can be gathered from Fig. 4, at first is subject to a sudden rise before decreasing. This sudden rise can be recognized by a peak 50 in the first curve 46 and induces a pressure pulse which propagates and is transferred into the hydraulic discharge or return system. One effect of this transient pressure pulse is reflected in the second curve 48 showing that the pressure in the discharge/return hosing is subjected to a particular sharp growth which merges into an oscillating course of the pressure, thereby inducing movement and vibrations and fast shunting action of the discharge/return hosing.

By being provided with the damper unit 18, the suggested roof support unit 10 may effectively counteract or moderate the above described pressure pulse by absorbing/dampening some of the stored fluid energy transferred into the hydraulic discharge/return system from within the actuator during fluid decompression and the effects associated therewith. Specifically, upon opening the control valve or Leg POCV, a sudden rise in the pressure prevailing in the cylinder 27 may be prevented by the damper unit 18 which absorbs a part of the released energy inducing the rise in the pressure and resulting induced force imbalance in the discharge/return hosing, i.e. by converting it into potential energy and/or heat as described above. The damping unit 18 allows the piston rod 28b of the actuator to be suddenly extracted, thereby compressing the compression element 38 and thus counteracting the sudden rise in pressure in the cylinder 27. By this configuration, the pressure peak 50 and pressure decay trend 46 depicted in Fig. 4 may be substantially lowered or altered, thereby preventing the hydraulic system from being subjected to excessive pressure pulses induced upon rapid opening of the control valve or Leg POCV.

It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention. This is in particular the case with respect to the following optional features which may be combined with some or all embodiments, items and/or features mentioned before in any technically feasible combination.

A roof support unit of a mining machine, particularly of a longwall mining system may be provided. The roof support unit comprises a support canopy which is supported on a base via at least one damper unit and at least one actuator configured to move the support canopy relative to the base. The damper unit and the actuator are connected in line between the support canopy and the base. Specifically, the actuator may be configured to raise or lower the support canopy relative to the base.

The actuator may be a hydraulic actuator. Alternatively or additionally, the actuator may be a linear actuator, in particular a multi stage hydraulic cylinder, also referred to as telescopic hydraulic cylinder.

In a further development, the damper unit may be configured to transmit a support force between the support canopy and the base for maintaining or changing a position of the support canopy relative to the base during operation.

Alternatively or additionally, the support canopy may be structurally connected to the base via the damper unit. Further, the damper unit may be configured to allow movement of the actuator relative to the support canopy and/or the base. Alternatively or additionally, the damper unit may be configured to dampen movement of the actuator relative to the support canopy and/or the base. Specifically, the damper unit may be configured to dampen movement of the actuator relative to the support canopy and/or the base in a retracting or extending movement direction of the actuator. In the roof support unit, the damper unit may be mounted to an end section of the actuator. Further, the damper unit may be interposed between the support canopy and the actuator or between the base and the actuator.

In addition, the damper unit may comprise a compression element. The damper unit, in particular the compression element may be configured to convert motion energy of the actuator into potential energy or heat, in particular by means of the compression element. The compression element may comprise or be a solid compression element, in particular formed by at least one spring or spring plate. Alternatively, the compression element may comprise or be a compression fluid. Alternatively, the compression element may comprise a solid compression element and a compression fluid.

Furthermore, a longwall mining system may be provided comprising at least one roof support unit as described above.

Industrial

With reference to the Figures and their accompanying description, a roof support unit for a mining machine and a mining machine equipped with such a roof support unit are suggested. The suggested roof support unit comprise a damper unit. The suggested roof support unit may replace conventional roof support units and may serve as a replacement or retrofit part. Further, the damper unit of the suggested roof support unit may be a retrofit part which can be implemented into conventional roof support units to form the suggested roof support unit.