Coal extraction in a longwall working

Coal is extracted in a longwall working with two subsidiary galleries disposed respectively at the ends of the longwall coal-face. The coal is obtained at the longwall face, is loaded and removed with the aid of a continuous conveyor acting as a longwall-heading conveyor which delivers into one of the subsidiary galleries. In order to extract the coal a plurality of long drill-holes, respectively spaced from the coal-face and from each other by a spacing which corresponds to the effective force of an explosive charge provided with a fuse-cord, are bored in the coal starting from one of the subsidiary galleries. Each of the drill-holes extends the full effective length of the coal face and is loaded with such an explosive charge, and then filled with water under pressure. The charges are exploded in succession, starting with the drill-hole adjacent the coal-face, whereupon the coal so acquired is loaded and removed by the continuous conveyor. The conveyor is operative at all points along the coal-face simultaneously, and is a worm conveyor with a worm associated with a channel open along its length to the coal-face.

BACKGROUND OF THE INVENTION 
The invention relates to a method of extracting coal in a longwall working 
in which the coal is obtained at the longwall face, is loaded and is 
removed with the aid of a continuous conveyor, acting as a 
longwall-heading or face conveyor, into one of two subsidiary galleries. 
In addition, the invention relates to worm conveyor to carry out such a 
method. 
Such methods of extracting coal are applicable to level and to inclined 
stratifications, because in such stratification conditions gravity is not 
adequate to remove the coal and hence the heading conveyor has to be 
employed as a continuous conveyor. A continuous conveyor is required for 
the continuous removal of the coal because it is only by such means that 
it is possible to achieve a narrow space which accommodates the conveyor 
and enables securing of the roof. The length of the longwall face 
extending between the two subsidiary galleries is basically optional; it 
may run to several hundred meters, but if residual pillars are left, upon 
the pulling-in of a spur of coal, for instance for the driving forward of 
heading packs, and in other special cases it can become reduced to 
substantially smaller lengths. Subsidiary galleries are therefore also 
typified by subsidiary spaces involved at the end of the longwall and, for 
example, ventilated by air outlets. 
The extraction methods indicated in the foregoing are in themselves already 
known. The coal is obtained, loaded and removed principally by mechanical 
means. Mechanical coal extraction proceeds by machine, mostly with a 
slicing or cutting action and hence with an essentially point-by-point 
attack on the longwall face, bearing in mind its length. However with the 
cutting type of extraction, the extraction machine as a rule also performs 
the loading work. With the slicing type of extraction an additional 
loading operation is required, mostly with the aid of a further machine. 
By way of face conveyors, chain scraper conveyors are almost exclusively 
employed because the bottom-channel run of such conveyors is sufficiently 
resistant and can therefore be utilized as a track for the machines 
employed in the longwall heading. 
The essentially point-by-point attack along the longwall face is 
unfavourable because the extraction rate is dependent solely on the width 
of the extraction machine, which determines the depth of penetration into 
the body of coal, and on the speed of advance of the machine. Therefore 
increase in the extraction rate demands correspondingly increased 
installed performance of the extraction machine. The power demand of chain 
scraper conveyors is also unusually high because such conveyors are 
energy-wise unfavourable due to friction between the chain belt and the 
channels. 
At the basis of the invention is the object of extending the extraction, 
loading and removal of the debris in the heading to the entire longwall 
face and, in so doing, to make the chain scraper conveyor superfluous as a 
track for an extraction machine. 
SUMMARY OF THE INVENTION 
According to the invention, the foregoing object is achieved through a 
technique whereby, to extract the coal from one of two subsidiary 
galleries, long drill-holes are bored in the coal at a spacing from the 
longwall face corresponding to the effective force of an explosive charge 
provided with fuse-cord, are loaded with the charge, are acted upon by 
water under pressure and are fired, whereupon the coal acquired from the 
explosion is loaded and removed at all points along the longwall 
simultaneously and continuously by the use of a worm conveyor with a 
worm-associated channel open to the coal-face. 
Among factors at the basis of the invention is a recognition that the 
lengths hitherto attained by long drill-holes can be increased 
considerably while still ensuring a specific effective force. As practical 
tests have shown, with already known drilling equipment it is possible to 
produce long drill-holes with a uniform burden and extending over lengths 
of 50 meters and more. According to the length of the longwall and in 
accordance with one embodiment of the invention, the long drill-holes are 
bored until they penetrate to the second subsidiary gallery or are driven 
until they penetrate to a region in the heading advanced into the body of 
coal; in the latter case, the drill-hole concerned is continued by a 
further drill-hole started at the advanced region, so as to be able to 
extract the entire longwall face. 
These long drill-holes can be closed off at each end by a water infusing 
probe and so acted on by the water pressure. On the one hand, through this 
the suppression of dust is facilitated, and on the other hand the effect 
of the charge is improved because of the incompressibility of water. This 
explosive charge comprises the explosive contained in the core of the 
fuse-cord, the explosive being initiated by an exploder arranged at one 
end of the fuse-cord. Additionally the fuse-cord for its part may initiate 
charges contained in several cartridges that are fastened at spaced 
intervals along the fuse-cord. Such an explosive charge can be drawn 
inward upon the withdrawal of the drill-rod against the direction of 
attack of the long drill-hole. 
The gathering of the extracted coal takes place on the one hand by means of 
the laterally open channel of the worm conveyor into which the coal, 
according to one embodiment of the invention, is impelled by the 
explosion. The channel in this case is moved forward towards the coal. In 
another embodiment of the invention, to secure the roof the explosive 
charge and/or its effective force are so calculated that the coal is 
loosened and by means of its residual connections supports the area of the 
yield until the coal is removed. In all cases the flanks of the conveyor 
worm are also pressed into the coal. The result of this is that the 
loading and removal of the shattered coal takes place simultaneously along 
the entire length of the longwall. Through this it is possible to make do 
with a very narrow conveying area and to keep the space of the heading 
which is opened up during extraction and is initially not extended so 
small that it is possible fully to secure the roof. 
The invention possesses the advantage of an extraction system that at all 
points along the heading and at every instant copes with all the work 
required. The method according to the invention also possesses adequate 
flexibility as regards different seams, i.e. it can according to the 
occasion adapt to different stratification circumstances. In addition, the 
method according to the invention requires a relatively small work force 
and furthermore possesses the advantage that the power outputs of the 
machines to be installed are overall considerably reduced. At the same 
time, the rates of extraction attained and the utilisation-index of the 
longwall equipment are very high. 
Steel worms to pick up and load debris on to a conveyor belt disposed to 
the rear are already known in loading machines. In addition, an extraction 
method is known in which, by means of a steel worm, drilled-out material 
is removed that is acquired by a bit located on the tip of a drill-rod 
forming the worm shaft. Worm-associated channels are not, however, 
provided here, so that already known worm conveyors are not regarded as 
conveying equipment for use along the longwall heading. 
The extraction to plan of coal by longwall working with the assistance of 
shot-firing is admittedly also already known. But because of unsolved 
loading and transporting problems, the application of this method of 
extraction has been restricted to cases of steeply tilted stratification 
or, with level and sloping stratification, shot-work has been limited to 
the extraction of short fractional lengths along the longwall face. Thus, 
it is, for example, a known technique to extract, through blasting by 
means of long drill-holes, the coal to be found in the so-called machine 
"stables" which have to be driven for the chain scraper conveyor and the 
extraction machine. Insofar as long drill-holes have otherwise been 
employed to extract coal in a level stratification, here what applies is 
pillar work, in which short lengths of the working face are present and 
the transport and extension problem plays no part ("Nobel-Heft" January 
1973, 26, 32). 
Other objects and features of the present invention will appear more fully 
below from the following detailed description considered in connection 
with the accompanying drawings, which disclose preferred embodiments of 
the invention. It is to be expressly understood, however, that the 
drawings are designed for purposes of illustration only and not as a 
definition of the limits of the invention, reference for the latter 
purpose being had to the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 is a top view with an interrupted presentation of a longwall heading 
with level stratification. The longwall face is denoted by 1 and is worked 
in the direction of the arrow a. For removing the coal, a continuous face 
conveyor 2 is used which by means of a chute 3 provides transport out to a 
loading conveyor 4 which is laid along a subsidiary gallery 5. The loading 
conveyor 4 passes the coal extracted in the heading to a roadway conveyor 
6. 
The heading is enlarged by extension plates 7 and is worked by packing the 
goaf with fragmented debris, the "old ground" being shown at 8. 
From a second subsidiary gallery 9, with the aid of a drilling machine 10, 
long drill-holes 11, 12 and 13 are bored till they penetrate into the 
subsidiary gallery 5. The spacing of the long drill-holes 11 to 13 from 
each other or from the longwall face 1 corresponds to the burden, and is 
shown at B in the upper part of FIG. 2. 
The lower part of FIG. 2 is a longitudinal section taken through the long 
drill-hole 11. According to this presentation, the explosive charge with 
which the drill-hole is loaded consists of fuse-cord 15 and a string of 
explosive cartridges 16 which are fastened at equal intervals along the 
fuse-cord 15. This explosive charge and the drill-hole is subjected to 
water pressure with the aid of two water infusing probes, 17 and 18 
respectively, which are fastened into the ends of the long drill-hole 11. 
In the embodiment illustrated in this figure, each burden is dealt with by 
a single long drill-hole, 11 or 12 or 13. Dependent on the thickness of 
the seam, however, several long drill-holes can also be made for each 
burden, distributed across the thickness of the seam 19. In the embodiment 
shown the long drill-holes 11, 12 and 13 are disposed of, by exploding the 
charges, in succession. The coal extracted during this procedure is loaded 
and removed by a worm conveyor, which constitutes the longwall-heading or 
face conveyor 2. 
The worm conveyor 2 has a channel which, as shown in FIG. 3, consists of an 
angle-unit 20. The angle-unit has a lower plate 21 which, facing the 
coal-body, is provided with a cutting edge 22 so as, when so required, to 
slice away coal left behind on the floor 23 when the channel 20 is 
shifted. In addition, the channel 20 has a plate 24 running substantially 
at a right angle to the plate 21 and intended to give protection against 
the catapulting of fragmented debris into the area shown at 25 in FIG. 3. 
This plate can be made to match the thickness of the seam at any time by 
means of a flexible upper strip 26 of, for example, rubber or plastic. 
Work to extend the longwall-heading gives support to the roof 28, after its 
exposure by the completed explosion, by means of the roofing plates 27. 
The roofing plates 27 or the cap units of a step-by-step roof-supporting 
device can be made to match the burden and are therefore longer than the 
usual cap units. 
The channel 20 is moved forward with the aid of advancing cylinders 29. As 
the amount of explosive or the burden can be chosen in such a way that 
either the coal is only loosened, i.e. still with its connections supports 
the roof, or is flung on to the conveyor 2, the worm conveyor performs 
loading and conveying work at all points along the heading simultaneously 
to dispose of the loosened heap. 
The worm conveyor 2 consists of sectional lengths, which in FIG. 4 are 
denoted generally by 30 to 32. Each sectional length consists of a channel 
length 33, 34 or 35 and a corresponding length of worm shafting 36, 37 or 
38. On the worm shafting there is a complete steel helix 39. Each length 
of worm shafting 36 possesses, according to the embodiment shown, two 
bearings 40 and 41. Adjacent to the bearings universal joints 43 are fixed 
to the lengths of shafting. The universal joints couple the worm shaftings 
36 to 38 in such a way that the individual lengths 33 to 35 can be angled 
with respect to each other in both horizontal and vertical planes. 
Each universal joint 43 has a central ring 44 and two forks, 45 and 46 
respectively, which in each instance are attached to the ends of the 
associated universally-jointed shaftings 36 and 37 or 38. The ring 44 is 
connected to the forks 45, 46 by pivot pins 47 and 48, the axes of which 
intersect at right angles in the well-known manner of a Hooke's joint. 
The bearing pedestals 40 and 41 and also the universal joints 43 are of 
such dimensions that they constitute only trivial obstacles to the flow of 
coal produced along the channel 20 by the worm conveyor. The drive means 
for the worm conveyor is housed conventionally in the longwall-heading or 
in the gallery and is not shown in the drawings. 
FIG. 1 shows a longwall-heading with the longwall working equipment 
omitted. As the direction of the subsidiary galleries 9 and 5 indicate, in 
both cases shown in this figure extraction proceeds by the retreating 
system in the direction of the arrow a. 
According to the upper presentation in FIG. 1, the long drill-holes 11 to 
13 are driven as far as a region 50 included in the heading. The region 50 
is merely driven into the coal. Each drill-hole is continued by means of 
drill-holes 51 to 53, which are started at the region 50 or in the gallery 
9 and are accordingly driven forward to the region 50 or to the gallery 9, 
as the case may be. The explosive charges are drawn into the respective 
drill-holes when the drill-rod is withdrawn. 
In the lower embodiment of FIG. 1, the long drill-holes are continued by 
long drill-holes which reach up to a further region 54, advanced into the 
coal-body. These long drill-holes 51 to 53 are continued by means of 
further long drill-holes 56 to 58, which reach up to a region 55. 
Continuations are provided by means of long drill-holes 59 to 61, which 
penetrate as far as the gallery 9. 
The burdens are broken away individually by firing of the respective long 
drill-holes. It is preferable that the next burden should be broken away 
after the removal of the heap. However, one can also break away several 
burdens in succession and only then undertake removal action.