GB2183696A

GB2183696A - Reducing ignition risk when driving galleries in mine workings

Info

Publication number: GB2183696A
Application number: GB08628125A
Authority: GB
Inventors: Friedrich Wilhelm Paurat; Roland Paurat
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-11-27
Filing date: 1986-11-25
Publication date: 1987-06-10
Also published as: DE3541886A1; DE3541886C2; GB8628125D0

Abstract

A process for reducing the ignition risk when driving galleries in mine workings with a gallery driving machine (1) having a cutting head (5) carrying cutters, drenches the newly exposed part (9) of the working face (8) with a mist (13) sprayed from stationary nozzles (11) mounted on the machine (1) at a distance from the cutting head (5), the spray mist (13) having a drop size analysis between 1 and 100 mu m, and being supplied in a volume allowing 0.2-0.5 l/min per cutter (7) in contact with the working face (8) and the spray jets (13), emerging from the nozzles (11) are directed towards the cutting head (5). <IMAGE>

Description

SPECIFICATION Reducing ignition risk when driving galleries in mine workings The invention relates generically to a process for reducing the ignition risk when driving galleries in underground mine workings with the aid of a machine having at least one cutting head carrying cutters, in which process a mixture of water and air is sprayed from nozzles and the newly exposed part of the working face around the cutting head is drenched with the resulting mist. Cutting heads ofthe type in question, also known as hewing heads, usually have a maximum diameter between about 450 and 1600 mm and an axial length occupied by cutting tools of 500 to 1500 mm. The cutters are arrayed own a spiral/helical vane around a corresponding core.The cutting head can be mushroom-shaped and be mounted coaxially on a cutting arm which can swivel vertically and swing horizontally. In another embodiment, the cutting head is a cutting roll journalled in a boom orthogonal to the cutting arm and free to swivel vertically.

In the known process ofthis type (DE-PS 1935 886), the water and air are sprayed from nozzles which rotate with the cutting head. This is a case of single-cutterspraying, i.e., a nozzle is associated with each cutter. The spray jet from each nozzle is directed towards the cutting path, more specifically towards a pointjust behind the cutter.

The ignition offiredamp when operating a gallery driving machine of either type described is a highly complex phenomenon. Ignition can obviously only take place when an explosive mixture is present and energy corresponding at least to the ignition energy is impartedtothe explosive mixture. Eventhen,the geometrical and thermodynamic boundary conditions and the aerodynamic relationships can exert a completely decisive influence. It is therefore understandable that the ignition offiredamp has never as yet been defined precisely and with certainty. It has only been possible to setup rules derived from practical experience in the operation of gallery driving machines. According to current teaching, cooling means must be provided atthe cutter and in the cutting path immediately behind the cutter.It has been regarded as absolutely essential to bring the cooling water into the cutting path bythe shortest route possible. The volume of water and the nozzle settings are adjusted so as to extinguish sparks and cool the cutting path within a distance of about3 cm behind the cutter (cf.

"Gluckauf-Forschurgshefte", 1980, pp. 17to21).

Single-cutterspraying as called for in the known process is very complicated constructionally.

Moreover, there is an extremely high risk of blocking the nozzles, since they are located within the immediate working area ofthe cutters. High atomisation pressures are consequently often used to maintain the nozzles in good working order. The volume of water required per cutter is considerable.

The object of the invention is to provide a process whereby the ignition offiredamp can be prevented bysimple means,thereby maintaining very safe operating conditions under all conditions of use of the gallery driving machine.

According to the present invention, the mixture of water and air is sprayed from stationary nozzles mounted on the machine at a distance from the cutting head, to form a spray mist with a drop size analysis between 1 and 100 wm, and in total volume allowing 0.2 - 0.5 I/min per cutter in contact with the working face, the spray jets emerging from the nozzles being directed towards the cutting head, preferably in the direction of cutter advance.

There is no single-cutter spraying in the process of the invention, and the sprayjets are no longer directed towards the cutting paths in the working face. On the contrary, a uniform spray mist is produced and the spray jets are directed towardsthe cutting head. The process of the invention arises from the discovery that when water is atomised with air it forms a spray mist which is entrained by the rotation of the cutting head. The surprising feature is the formation in and beyond the cutting paths of an ignition-suppressing microclimate, so long as the parameters are maintained as specified. The spiral/helical vane is a contributoryfactor.The spray mist is preferablyformed with an airvolume of 0.2 to 1 m3/min per cutter, and the mixture of water and air is preferably expelled at a stream velocity of 25 to 35 mls in the nozzle cross-section.

The disposition of the nozzles depends on the design ofthe gallery driving machine. For use on a machine having a vertically swivelling and horizontally swinging cutting arm and a mushroom-shaped cutting head with a spiral vane along which the cutters are arrayed, the nozzles are disposed on a ring adapted to be disposed round the cutting arm and to be secured non-rotatablyto the cutting arm. On the otherhand,foruse on a gallery driving machine having a vertically swivelling arm on which a cutting roll is journalled, the cutting roll having a helical vane along which cutters are arrayed, the nozzles are disposed on an elongate carrier adpated to extend alongside the cutting roll and to be secured non-rotatably to the arm.The elongate carrier is preferably fork-shaped, with a first nozzle carrying strip adapted to be disposed above the cutting roll and a second nozzle carrying strip adapted to be disposed below the cutting roll. Spray is provided from the nozzles on the first or second nozzle carrying strip, depending on whetherthe cutting roll is swivelling up or down.

The accruing advantages are to be seen in that by adopting the teaching of the invention when operating a part-section gallery driving machine of the type described the ignition offiredamp is adequately suppressed without resorting to complicated single-cutter spraying. The nozzles are mounted at a distance from the cutters so thatthe incidence of blockages is therefore rare. This permits the use of small nozzle diameters and low atomisation pressures. The process of the invention produces a spray mist which maintains an ignition-suppressing microclimate within and beyond the cutting path area. Underthe positive influence of the helical/spiral vane and the cutters arrayed thereon, a microclimate which suppresses the ignition offiredamp extends a surprising distance around the cutting head.This controlled climate extends from the working face back beyond the cutting head to the dust barrier formed by the provision of curtain sprays. By virtue of this controlled climate, the safety margin is very high, even when firedamp escapes from the blisters frequently encountered in geological strata laden with firedamp.

The process of the invention will now be described with reference to accompanying drawings showing, purely by way of example, embodiments of spray devices for carrying outthe process. In the drawings: Figure lisa diagrammatic side elevation of a gallery driving machine of the type having a verticaily swivelling and horizontally swinging cutting arm with a mushroom-shaped cutting head, fitted with oneform of spray device; Figure2 is an enlarged detailed elevation ofthe ringed partof Figure 1; and Figure3 is a fragmentary side elevation showing anotherform of spray device of the invention on a vertically swivelling arm of a gallery driving machine having a cutting roll journal led thereon.

Figure 1 shows a gallery driving machine 1 having a crawlertraction unit 2, a turret 3, a cutting arm 4 which can swivel vertically and swing horizontally, and a mushroom-shaped cutting head 5with a spiral vane 6 which carries at least thirty cutters 7 (see also Figure 2), which have a cutting speed of 0.5 to 4 mls at the most, preferably between 2 and 3 m/s, and generate a cutting path 9 on the working face 8 as rockand/orcoal are dislodged. A nozzle ring loins disposed round the forward end ofthe cutting arm 4 and secured thereto non-rotatably, and a plurality of nozzles 11 are uniformly spaced round the ring 10. A mixture of waster and air is sprayed through these nozzles 11 at a pressure 1 to 2 bars above atmospheric.The mixture of water and air is supplied to the nozzle ring through a duct 12. The spray jet 13 emerging from each of the nozzles 11 is directed towardsthe cutting head 5. The spraying produces a spray mist with a drop size analysis between 1 and 100 sLm in a volume allowing 0.2to0.5 llmin per cutter in contact with the working face 8.

Figure 3 shows a spray device in accordance with the invention for use with gallery driving machine having a cutting roll 14. The cutting roll 14is journalledon a vertically swivelling arm 15, and the periphery of the cutting roll is occupied bya helical vane 6 along which cutters 7 are set. The cutting roll attacks the working face 8,thereby generating a cutting path 9. The nozzles 11 in the spray device of the invention are disposed on an elongate carrier 16 which extends alongside the cutting roll and is securednon-rotatablyto the arm. The elongate carrier 16 isfork-shaped and has a first nozzle carrier strip 1 6a disposed above the cutting roll 14 and a second nozzle carrier strip 1 6b disposed belowthe cutting roll. The mixture of water and air is fed to the spray devicethrough a duct 12. The spray jets 13 emerging from the nozzles are directed towards the cutting roll 14. The spraying produces a spray mist with a drop size analysis between 1 and 100 m in a volume allowing 0.2 to 0.5 llmin per cutter in contact with the working face 8.

Claims

1. A process for reducing the ignition riskwhen driving galleries in underground mineworkingswith the aid of a machine having at least one cutting head carrying cutters, in which process a mixture of water and air is sprayed from nozzles and the newly exposed part of the working face around the cutting head is drenched with the resulting mist, the mixture of water and air being sprayed from stationary nozzles mounted on the machine at a distance from the cutting head, to form a spray mist with a drop size analysis between 1 and 100 ijm, and in atotal volume allowing 0.

2 - 0.5 I/min per cutter in contact with the working face, the spray jets emerging from the nozzles being directed towards the cutting head 2.A process as in Claim 1, wherein the spray mist isformed with an airvolume of 0.2to 1 m3/min per cutter and the mixture of water and air is expelled at a stream velocity of 25 to 35 mls in the nozzle cross-section.

3. A device for carrying out the process as in Claim 1 or Claim 2 adapted for use on a gallery driving machine having a vertically swivelling and horizontally swinging cutting arm and a mushroom-shaped cutting head with a spiral vane along which cutters are arrayed, the nozzles being disposed on a ring adapted to be disposed round the cutting arm and to be secured non-rotatablytothe cutting arm.

4. Adeviceforcarrying outtheprocessasin Claim 1 or Claim 2, adapted for use on a gallery driving machine having a vertically swivelling arm, at least one cutting rolljournalledthereinwitha helical vane along which cutters are arrayed, the nozzles being disposed on an elongate carrier adapted to extend alongside the cutting roll and to be secured non-rotatably to the arm.

5. A device as in Claim 4, wherein the elongate carrier is fork-shaped, with a first nozzle carrying strip adapted to be disposed above the cutting roll and a second nozzle carrying strip adapted to be disposed belowthecutting roll.

6. A process for reducing the ignition riskwhen driving galleries in underground mine workings substantially as hereinbefore described with reference to the accompanying drawings.

7. Adeviceforreducing the ignition riskwhen driving galleries in underground mine workings substantially as hereinbefore described with reference to Figures 1 and 2 the accompanying drawings.

8. A device for reducing the ignition riskwhen driving galleries in underground mine workings substantially as hereinbefore described with reference to Figure 3the accompanying drawings.

9. A gallery driving machine fitted with a device for reducing the ignition riskwhen driving galleries in underground mine workings as in anyone of Claims3to5,7and8.