Process and apparatus for controlling the water supply to the cutting head of a cutting machine
It is known to cool with water the bits of a cutting head of a cutting machine. It is also possible to rinse the gap between the cutting arm and the rotating cutting head with water for removing dust entering into this gap, which, however, is not the subject of the present invention. The amount of water required for this purpose is considerable in pit mining. One has to save on water and, above all, the emerging water is disturbing at the areas of the cutting machine and of the mine face. Particularly with weak sill any accumulation of water is extremely disadvantageous and such an accumulation of water on the sill can even have as a result that the cutting machine is sinking into the sill. It has already been proposed to control supply of the water, which is effected for the purpose of cooling the bits and of cooling the mine face, such that always only those bits are supplied with water which come into engagement with the mine face. Such control is effected by means of valves and during the severe pit mining operation it frequently occurs that these valves become untight so that again the amount of emerging water can be considerable. Water is also emerging if cutting operation is interrupted for any reasons. Manual interruption of the water supply is practically not feasible and would also result in great dangers. If the operator forgets to switch on the water supply, there exists the danger of spark formation which might result in explosions of marsh gas. 
     Now, it is an object of the invention to reduce the water consumption to a minimum without risking any dangers. The control process according to the invention essentially consists in that water supply to the cutting head is only given free with the rotational movement of the cutting head being switched on and with simultaneous switching on of at least one second operating condition, such as movement of the cutting arm in left-hand direction, movement of the cutting arm in right-hand direction, upward movement of the cutting arm, downward movement of the cutting arm or advancing movement of the machine. For effecting cutting work it is an imperative premise that the cutting head is rotating. This alone does, however, not yet result in a cutting work. Cutting work is effected only if a second operating condition supervenes. Cutting work can thus only be effected if simultaneously with rotation of the cutting head a movement of the cutting arm for the individual cuts on the mine face is effected or if in case a penetration shall be deepened or enlarged a movement of the cutting arm and advancing movement of the cutting machine is effected simultaneously with rotation of the cutting head or if for producing a smaller penetration the cutting machine is advanced in addition to rotation of the cutting head. It is thus obvious that the rotation of the cutting head is a premise at any rate and that only if a second operating condition is supervening effective cutting work is done. By controlling the water supply in dependence on the rotational drive of the cutting head and on the simultaneous occurrence of a further operating condition makes thus sure that water is emerging only if effective cutting work is done, which results in reducing the water consumption to a minimum. The process can be performed such that supply of water to the cutting head is put in readiness when switching on the rotational movement of the cutting head and is given free when switching on the second operating condition. Thus it becomes possible to make release of the water supply dependent on, for example, the position of a control lever for switching-on the second operating condition. According to a preferred embodiment of the invention the process is, however, performed such, that supply of water is put in readiness when switching-on the rotational movement of the cutting head and is given free on a pressure rise in at least one of the hydraulic aggregates effecting pivotal movement of the cutting arm or advancing movement of the cutting machine. These hydraulic aggregates are the pivoting cylinders for the pivotal movements of the cutting arms and the hydraulic drive motor for advancing movement. In case of an electric drive of the chassis, a hydraulic pressure transmitter can be coupled with the abutment member. This provides the advantage that water supply is only switched on if the second operating condition is actually occurring and, furthermore, the control device is thus simplified. 
     The apparatus for performing the control process is essentially characterized by a water pump for supplying water to the cutting head, the switching-on device of which is coupled with the switching-on device for the rotational drive of the cutting head and within the pressure conduit of which an openable water shut-off valve is interpositioned, and by at least one pressure-sensitive member being subjected by the pressure within hydraulic aggregates effecting pivotal movement of the cutting arm and advancing movement of the cutting machine and directly or indirectly acting on the water shut-off valve in the sense of opening this valve. In view of the water pump being switched-on and switched-off simultaneously with the rotational drive of the cutting head, the water is under pressure before the shut-off valve. Actual release of water supply to the cutting head is, however, only effected if the pressure-sensitive member is opening this shut-off valve when switching on a second operating condition. 
     In a preferred embodiment of the invention the arrangement is such that several control pistons are arranged within a common cylinder and a conduit is opening into the working space of each control piston, each conduit being in connection with the working space of one of the hydraulic aggregates and the control pistons being coupled one with the other by engagement in direction of the applied pressure and being loaded by a spring in opposite direction to the pressure applied and are directly or indirectly acting on the water shut-off valve against the action of the spring in the sense of opening this valve. Thus, a stack of pistons is guided within the common cylinder. Irrespective which working space is subjected by the pressurized fluid, the pistons arranged between this working space and the spring are shifted in direction to the spring and cause the shut-off valve to open. Preferably, the water shut-off valve is indirectly actuated by the control pistons through the intermediary of a hydraulic pressurized fluid. In this case the arrangement is according to the invention such, that the water shut-off valve is actuated by a hydraulic piston and the pressure-sensitive member or the control pistons are controlling the supply of pressurized fluid to the hydraulic piston. In this manner, the water supply is separated from the hydraulic control aggregate and the danger is avoided that in case of a break down failure, water is entering into this control aggregate. According to an advantageous practical embodiment of the invention, the arrangement is such that the last control piston as seen in direction to the spring is striking against a stem in its turn opening the pressurized fluid valve by striking against its closure member, for example the ball of a pressurized fluid valve controlling supply of pressurized fluid to the hydraulic piston, that the stem is sealingly guided within a guide means subdividing the space accomodating the stem into a space located adjacent the pressurized fluid valve and into a space located remote from the pressurized fluid valve, that a conduit leading to the working space of the hydraulic piston is opening into the space located adjacent the pressurized fluid valve, that a return conduit leading to a pressurized fluid tank is opening into the space located remote from the pressurized fluid valve and that the stem has an axial bore being open in direction to the space located remote from the pressurized fluid valve and opening at the front surface striking the closure member of the pressurized fluid valve and becoming closed by striking said closure member. 
    
    
     In the drawing, the invention is schematically illustrated with reference to an embodiment. FIG. 1 shows an axial section through the pressure-sensitive member and FIG. 2 shows the water shut-off valve together with the hydraulic piston in an axial section. 
    
    
     The pressure-sensitive member shown in FIG. 1 has a cylinder 1 within which are guided the control pistons 2, 3, 4, 5 and 6. The control pistons are coupled one with the other by means of bosses 7 and supported against these bosses by means of a spring 8. Connections for hydraulic conduits 15, 16, 17, 18 and 19, which are connected to the working spaces of the various hydraulic aggregates or, respectively, the pressure conduits leading thereto, are opening into the working spaces 9, 10, 11, 12 and 13 of these pistons 2 to 6. One of these conduits 15 to 19 each is, for example, opening into the working space of the hydraulic cutting cylinder which effects pivotal movement in left-hand direction, in right-hand direction, in upward direction and in downward direction. A further conduit is opening into the working space of the hydraulic drive motor or into the pressurized conduit thereof for effecting forward travel of the cutting machine. With an electric drive, the electric motor can, for example, actuate a pressurized fluid pump generating the pressure to be made effective within the respective working space. If thus one of the conduits 15 to 19 and thus one of the working spaces 9 to 13 is subjected to pressure, all control pistons 2 to 6 located at the right side of the working space 9 to 13 subjected to pressure are shifted in right-hand direction. 
     The last control piston 6 is acting on the stem 20, the front surface 21 of which is cooperating with the closure member or, respectively, the ball 22 of a hydraulic valve 23. When shifting the stem 20 in right-hand direction by means of the piston 6, the ball 22 is lifted off its seat and the pressurized fluid entering via the connection 24 can flow into the annular space 25 and from this space into a connection 26 for a conduit, This connection 26 is, via a conduit not shown, connected with a connection 27 opening into the working space 28 of a hydraulic piston 29 being guided within a cylinder 30. The hydraulic piston is via a piston rod 31 actuating the valve cone 32 of a water shut-off valve 33 and is lifting this valve cone. The water is thus allowed to flow via the valve 33 from an inlet 34 to an outlet connection 35. Upstream of the inlet connection 34 or downstream of the outlet connection 35, a shut-off valve not shown is arranged which is in open position when switching-on the rotational movement of the cutting head. If both valves are in open position, effective cutting work can be done and it is only with said both valves being in open position that supply of water to the cutting head is given free. 
     If none of the working spaces 9 to 13 is subjected to pressure, i.e. if water supply to the cutting head shall be shut-off, all of the pistons 2 to 6 are pressed by the spring 8 in left-hand direction into their starting position. For making possible return movement of the hydraulic piston 29, the pressurized fluid must be allowed to flow out of the working space 28. The stem 20 has an axial bore 36. The space accomodating the stem is subdivided into a space 25 located adjacent the pressurized fluid valve 23 and into a space 38 located remote from the pressurized fluid valve 23 by means of a fluid-tight guide means 37. The axial bore 36 of the stem 20 is in connection with the space 38 via radial bores 39. The axial bore 36 is opening at the front surface 21 of the stem 20. If the stem is with its front surface 21 pressing in upward direction of the ball 22, the mouth of the bore 36 at the front surface 21 is closed by the ball 22. Pressurized fluid can thus flow into the working space 28 exclusively via the connection 26. If the stem 36 is returning, the mouth at the front surface 21 is given free and the pressurized fluid can flow out of the working space 28 via the connections 27 and 26 and via the axial bore 36 into the space 38 and from there back to the pressurized fluid tank via a connection 40.