Process for spraying the bits and/or the facing with pressurized liquid as well as apparatus for performing this process
The invention refers to a process for spraying the bits and/or the mine face with pressurized liquid, in particular water, by using a partial cut cutting machine as well as to an apparatus for supplying a pressurized liquid, in particular cooling water, to exit openings of a rotatable cutting head, in which apparatus the liquid is fed via an axial bore within a part non-rotatably connected to the cutting arm into the interior of the cutting head and via radial channels to the exit openings located at the periphery of the cutting head. For reducing the water consumption, there was developed a number of proposals by which it is intended to cool the bit and the mine face only if a substantial heating effect occurs on account of the cutting work. It is, for example, known to make the supply of water dependent on the load on the bits, which, however requires expensive constructions, because a separate valve must be associated with each individual bit. In connection with cutting rolls it is further already known to provide a sector control such that pressurized water arrives at the exit openings only within that range of central angles of the roll which is facing the mine face. 
     The invention now aims at providing a process of the initially mentioned type in which beside a marked reduction of the water consumption it becomes possible to work in mines without the danger of surpassing the ignition temperatures of explosive gases. For solving this task, the process according to the invention essentially consists in that the water is intermittently sprayed within an area of center angle of the cutting head facing the mine face. By intermittently delivering the pressurized liquid or, respectively, water there results a substantial reduction of the water consumption, thereby simultaneously obtaining the advantage that the rock to be excavated is repeatedly quenched, heated and quenched again. Such a thermal load of the rock facilitates crushing of the material, and the cutting expenditure and therewith, the energy consumption can be reduced. There results simultaneously a reduction of the maximum cutting temperature so that explosion hazard is minimized. The time span between the individual spraying steps or, respectively, ejection steps must be selected sufficiently small for reliably preventing ignition of explosive gases, noting that the time interval between the injection steps must be shorter than the ignition delay time of the gases in consideration, for example methane. In case of methane and in case of temperatures of 650° C. at the mine face there result, for example, ignition delay time intervals of approximately 10 s and these ignition delay time intervals become rapidly shorter with increasing temperature. At temperatures of approximately 1000°  C., the ignition delay time intervals to be expected amount to approximately 1 s, for example. For this reason, the process is preferably performed with an ejection frequency between 10 and 20 Hz thus obtaining an optimum security against any ignition of explosive gases. With consideration of the usual rotating speeds of cutting heads there results an injection time interval of approximately 0.1 s, the ejection time being in an advantageous manner selected of approximately the same magnitude as the time interval between immediately subsequent ejection steps. 
     The process according to the invention can be performed in a particularly simple manner with an apparatus of the initially mentioned type which is, according to the invention, designed such that a plurality of radial perforations adjoins the axial bore, said radial perforations coinciding during rotation of the rotatable cutting head with one or more radial channels of the cutting head and said radial perforations extending over part of the circumference of the component part comprising the axial bore. In addition to the sector control, in which supply of water into the radial channels of the rotatable cutting head is effected within a predetermined area of center angle of the rotational axis or, respectively, the head, there is obtained in a particularly simple manner a subdivision of the spraying operation into individual spraying intervals. 
     In an advantageous manner, the radial perforations are arranged within a center angle of less than 180°, in particular 120° to 150°, so that the water consumption is limited to that partial area of one rotation of the cutting tool or, respectively, cutting head within which the bits can contact the mine face. 
     The radial perforations are preferably provided within a bushing being non-rotatably coupled to the cutting arm. Such a bushing coupled to the cutting arm or, respectively, to the head carrier rigidly connected with the cutting arm can in a simple manner be used in cutting machines comprising two cutting heads being rotatably supported on a cutting arm in an approximately normal relation, noting that the identical bushing can be inserted at both sides of the cutting arm in a position turned for 180° respectively, so that the area of center angle within which spraying of water is made possible, is always facing the mine face. For obtaining ejection time intervals and non-operative intervals of approximately equal magnitude between the individual ejection steps, the central distance of the radial perforations at the periphery of the bushing is approximately equal three times the free diameter of the perforations. The radial perforations can in a simple manner be formed of radial bores, and preferably 6 to 10 radial bores are arranged within the center angle extending over less than 180°, so that with consideration of usual rotating speeds of cutting heads within the range of 1 to 4 s -1  ignition phenomena can reliably be avoided. 
     In the following, the invention is further illustrated with reference to an example of embodiment shown in the drawing. 
    
    
     In the drawing, 
     FIG. 1 shows a cross section through a cutting head of the prior art, 
     FIG. 2 shows a cross section through the water supply means according to the invention analogous to the section of FIG. 1 and 
     FIG. 3 shows a section along line III--III of FIG. 2 in an enlarged scale. 
    
    
     The cutting head 1 shown in FIG. 1 is composed of mutually welded discs 2 rotatably supported on a cutting arm not shown. The last stage of the reduction gearing is indicated by dashed lines and designated by 3. The cutting head is supported by anti-friction bearings 5 in a carrier 4 connected with the cutting arm. 
     The water supplied first flows through channels 6 provided within the carrier 4 and enters a distributing chamber 7 from where the water flows through a correspondingly sealed supply conduit 8 and radial conduits 9 into the distributing cavities 10 extending in axial direction of the cutting head. The front plate 11 of the cutting head 1 is connected with the base member of the cutting head by means of screws. From the distributing cavities 10, the water flows via substantially radial bores 12 to the exit nozzles which may be housed in the bit holder. 
     In the embodiment according to FIG. 2, the axial supply conduit 8 opens into a bushing 14 non-rotatably coupled to the carrier 13. For facilitating positioning of the bushing 14 in correct position, the axial supply conduit 8 passes over into the bushing 14 via a sealing intermediate piece 15, the sealings being designated by 16. The bushing is non-rotatably connected with the carrier 13 by means of a claw clutch 17 and has radial bores 18. The front part 19 of the cutting head rotates on the bushing 14 and the cutting head can be connected with the drive means for the cutting head in an analogous manner as is the case with the embodiment according to FIG. 1. The bushing 14 is held in position by the front plate 20 being connected with the front part 19 by means of screws 21. The front part 19 includes the rotating and essentially radially directed bores 22 which are connected with the exit openings of the cutting head via a sealing sleeve 23 and the radial channels 24. The front part 19 rotating on the bushing 14 is sealed relative to the bushing 14 by means of sealings 25 and 26, the sealing 26 being held in position by means of a retainer ring 27 supported on the bushing 14. The retainer ring 27 is fixed to the rotating front part 19 by means of the screw 28. The further components of the cutting head being, for example, composed of individual discs can, for example, be connected with the rotating front part 19 by means of the screw 29, noting that the cutting head is supported, for example, on the carrier in the manner shown in FIG. 1, the carrier being stationary relative to the cutting arm. 
     As can be seen from FIG. 3, the radial bores 18 of the bushing 14 extend over a range of center angle of approximately 120°, this range of center angle of 120° facing the mine face.