Method of separating the upper coal in seams

A method in underground coal mining for separating the upper coal of the seam from the roof during the advancement of the upper sliding cap of a support frame, wherein the front edge of the cap is forced in a plane of the cap between the upper coal to be separated and the rock from which the coal is to be separated. During the advancement of the sliding cap, the sliding cap is alternatingly moved backwardly and forwardly, so that the from edge of the sliding cap separates the upper coal during its forward movement. Alternatively or additionally, when the front edge of the sliding cap contacts the upper coal, alternatingly higher and lower pressure can be admitted to the sliding cap in order to obtain a shaking effect. In this combined method, the sliding cap is advanced, the shaking procedure is carried out as the front edge contacts the upper coal, and the sliding cap is subsequently moved backwardly. The cycle is then repeated several times.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method in underground coal mining for 
separating the upper coal of a seam from the roof during the advancement 
of the upper sliding cap of a support frame, wherein the front edge of the 
cap is forced in a plane of the cap between the upper coal to be separated 
and the rock from which the coal is to be separated. 
2. Description of the Prior Art 
In underground mining, coal may be extracted in accordance with the 
longwall working method utilizing, for example, a coal plane which is 
moved at a certain height level between roof and footwall. In the ideal 
case, the coal is always separated to the level of the roof. However, in 
practice, geological disturbances may have the result that upper coal or 
residual coal remains attached to the roof. With advancing extraction, 
each individual support frame must be advanced in the longwall by 
actuating, for example, a walking legs mechanism which connects the 
support conveyor with the support frame. This advance movement is impaired 
or prevented by any upper coal remaining attached to the roof because the 
front edge of the cap of the support frame presses in the plane of the 
roof between the upper coal and the rock and the pressure may not be 
sufficient for separating the upper coal. 
In order to facilitate the separation of the upper coal from the roof, the 
cap may include a wedge-type arrangement. 
Similar problems occur in shield-type support frames with packing caps 
which are advanced together with the support conveyor in order to close 
open spaces. This is because any remaining residual coal may block the 
advancement of the packing or sliding cap. To ensure that this cap 
contributes to the separation of the upper coal, this cap can be provided 
with a separating wedge or a tearing ledge. However, it happens again and 
again that the force available for advancing the cap is not sufficient for 
separating the upper coal. 
It is, therefore, the primary object of the present invention to further 
develop a method of the above-described type in such a way that the 
separation of the upper coal is facilitated or made possible, without 
requiring complicated or expensive apparatus. 
SUMMARY OF THE INVENTION 
In accordance with a first embodiment of the present invention, the sliding 
cap is moved several times back and forth during the advancement thereof 
in such a way that the cap is thrust between the upper coal and the rock 
during several successive advance movements of the cap. 
In the past, the hope was that the advancement of the sliding cap will 
cause the front edge of the cap to separate the upper coal. In accordance 
with the present invention, on the other hand, the sliding cap is moved 
back and forth so that the cap punches its way forwardly. 
Particularly if the sliding cap is advanced synchronously with the 
advancement of a support conveyor by means of a synchronization control, 
it is advantageous to superimpose a thrust control over the 
synchronization control. This thrust control moves the sliding cap during 
its advancement back and forth with a frequency which can be selected. The 
frequency may be given by a manual control. The frequency is related to 
the amplitudes of the forward and backward strokes of the sliding cap. The 
sliding cap may be provided with a bearing ledge or the like. In this 
method, the sliding cap punches its way forwardly until synchronized 
movement with the support conveyor has been reached. 
For an automatic separation of the upper coal by means of the sliding cap, 
the relative position between the walking legs of the support frame and 
the sliding cap is determined by means of distance sensors in connection 
with an electronic circuit. When the determined relative position 
corresponds to a desired value or a desired value range, a distance 
synchronization between sliding cap and walking legs is carried out. When 
the determined relative position does not correspond to the desired value 
or a desired value range, the electronic control initiates a cyclical 
forward and backward movement of the sliding cap. This cyclical forward 
and backward movement of the sliding cap is carried out until the 
determined relative position finally corresponds to a desired value or a 
desired value range. 
It may happen that the upper coal is so firmly attached to the rock that it 
cannot be separated even when several thrust attempts are carried out. 
Therefore, it may be advantageous to stop the attempted separation of the 
upper coal after a certain period of time has transpired. In this 
situation, the upper coal must be separated by a suitable hand tool. 
In accordance with a second embodiment of the present invention, high 
pressure and low pressure are alternatingly applied several times on the 
sliding cap when the advancement of the sliding cap is stopped by upper 
coal. This alternating application of pressure results in a shaking or 
vibration effect during which the front edge of the sliding cap 
permanently rests against the upper coal. This shaking effect can be 
obtained by a special hydraulic control unit which is integrated into the 
hydraulic system for the advancement of the sliding cap. The frequency of 
the pressure application and/or the duration of the pressure application 
and/or the magnitudes of the low pressure and of the high pressure can be 
suitably adjusted. 
In accordance with a third embodiment of the present invention, the methods 
of the first and second embodiments are combined. In accordance with this 
third embodiment, the sliding cap is thrust against the upper coal during 
the advancement of the sliding cap. Subsequently, alternating low and high 
pressures are applied to the sliding cap in order to obtain the shaking 
effect. This shaking effect may continue for a predetermined period of 
time. Subsequently, the sliding cap is moved back by a certain distance. 
The above-described cycle is then repeated. Accordingly, in combination 
with the synchronization control, the sliding cap carries out alternating 
movements for thrusting forwardly and for separating the upper coal until 
the distance synchronization between support conveyor and sliding cap has 
been reached. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the drawings and descriptive matter in which there are 
illustrated and described preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 2 of the drawing, a shield-type support frame 1 is 
connected in the region of the footwall of the longwall through a 
connecting rod 102 to a support conveyor 103, only illustrated 
schematically. A hydraulically movable packing cap or sliding cap 104 is 
coupled through a synchronization control to the support conveyor 103, so 
that, with advancing working at the coal face K, the support conveyor 103 
is advanced through connecting rod 102 by means of a hydraulic system, not 
illustrated in detail, and the sliding cap 104 is synchronously advanced 
with the support conveyor 103. The sliding cap 104 has the purpose to 
uphold the roof and to close empty spaces. 
As illustrated in the lower portion of FIG. 2, upper coal or residual coal 
R may remain attached to roof H. For separating this upper coal R, the 
sliding cap 104 has at its front edge a tearing ledge 105 which is pushed 
in the plane of the upper side of the sliding cap 104 between the rock and 
the upper coal R, so that the upper coal R is separated and the path is 
cleared for the advancing sliding cap 104. When the upper coal R has been 
separated, sliding cap 104 can uphold the exposed roof H. Sliding cap 104 
is now approximately at the same level as the support conveyor 103. 
In order to advance the sliding cap 104, a certain pressure is applied to a 
hydraulic cylinder which is coupled to the sliding cap. If this pressure 
is not alone sufficient to separate the upper coal R from the roof H, the 
method in accordance with the present invention is utilized. 
The present invention is directed to altogether three different embodiments 
which are explained in more detail as follows. 
The support conveyor 103 is advanced in the direction of arrow P. At the 
same time, sliding cap 104 is advanced. However, the advancement of the 
sliding cap 104 is not continuous, but rather is carried out with forward 
and backward movements. During the backward movement of the sliding cap 
104, the front edge of the tearing ledge 105 is moved a certain distance 
away from the upper coal R. During the forward movement of the sliding cap 
104, the front edge of the tearing ledge 105 is thrust between the roof H 
and the upper coal R. The tearing ledge of the cap 104 acts on the upper 
coal R with an energy which depends upon the mass of the sliding cap, the 
force supplied for moving the sliding cap and the speed of the sliding 
cap. The backward movement and the subsequent forward movement of the 
sliding cap are repeated several times, so that the sliding cap punches 
its way forward as it separates individual pieces of the upper coal. 
The control of this punching movement is not illustrated in detail. In 
accordance with a feature of the present invention, the control can be 
carried out manually by appropriately actuating the hydraulic cylinder 
coupled to sliding cap 104. However, an automatic control can be provided. 
This automatic control operates by means of distance sensors, not shown, 
which determine the relative position of the support conveyor 103 and the 
sliding cap 104. The control causes a cyclical forward and backward 
movement of the sliding cap 104 until the relative position between 
support conveyor 103 and sliding cap 104 corresponds to a predetermined 
desired position. 
A second embodiment of the method for separating the upper coal R from the 
roof H in accordance with the present invention provides that the sliding 
cap 104, after having been pressed against the upper coal R, carries out a 
shaking movement with its tearing ledge 105. This shaking movement is 
carried out by alternatingly applying a relatively low pressure and a 
relatively high pressure to the hydraulic system which operates the 
sliding cap 104. The low pressure is lower than the pressure with which 
the sliding cap 104 is advanced when no obstacle, i.e., upper coal, is 
present. The higher pressure mentioned above, on the other hand, is 
greater than the pressure applied when no obstacle is present. During this 
shaking procedure, the front edge of the tearing ledge 105 remains in 
contact with the upper coal R until the upper coal R is separated. Of 
course, the shaking procedure is carried out only for a limited period of 
time. If the upper coal R is not separated from the roof after a certain 
period of time, it may become necessary to use a hand tool for separating 
the upper coal. 
The third embodiment of the present invention constitutes a combination of 
the two above-described methods. The punching movement of the sliding cap 
104 described above is superimposed by a shaking movement. If, during the 
cyclical advancement of the sliding cap, the front edge of the tearing 
ledge 105 makes contact with the upper coal R, the above-described shaking 
procedure is initiated for a certain period of time, unless the first 
contact of the tearing ledge with the upper coal separates the upper coal. 
If the upper coal is not separated, the shaking procedure is concluded 
after a certain period of time has elapsed and the sliding cap 104 is 
again moved back by a certain distance and, subsequently, is again moved 
forwardly until the front edge of the tearing ledge makes contact with the 
upper coal R. This combined punching and shaking procedure is carried out 
until synchronization with the advance movement of the support conveyor 
103 is reached. 
In the following, an example of a shaking control unit in accordance with 
the present invention shall be described. This example is capable of 
carrying out the second method described above and parts of the third 
method described above. 
As illustrated in FIG. 1 of the drawing, the shaking device includes a 
double-acting cylinder 1 whose piston rod 2 moves the sliding cap of the 
shield-type support frame illustrated in FIG. 2. This movement is carried 
out in synchronization with the advancement of the support conveyor 103. 
The unit for the synchronization control is not illustrated in detail but 
is denoted by reference symbol S. The unit acts on two hydraulic lines 3 
and 4, wherein line 3 is 3 is connected to the piston space 5 and line 4 
is connected to annular space 6 of cylinder 1. By admitting pressurized 
fluid to the annular space 6, the sliding cap is retracted by means of 
piston rod 2. If pressurized fluid is admitted to piston space 5 through 
line 3, the piston 2 moves the sliding cap toward the coal face K. In 
doing so, a certain pressure is reached in line 3. 
If the forward edge of the cap makes contact with an obstacle, for example, 
residual coal which has remained attached to the roof, the piston rod 2 
comes to a standstill if the residual coal is not pushed off by the cap 
which is moved forwardly with normal force. As a consequence, the pressure 
in line 3 rises. 
A three/two-way valve 7 of a shaking control 8 includes a first larger 
control area 7a and a second smaller control area 7b. An adjustable 
compression spring pretensions the valve 7 in the zero position 
illustrated in FIG. 1. When normal pressure is present in line 3 during 
the advancement of the piston rod 2, the pressure acting through control 
line 10 on the control area 7a is not sufficient to switch the valve 
against the force of compression spring 9. However, when the pressure in 
line 3 is increased as the residual coal stops the advancement of the 
piston rod 2, valve 7 is suddenly opened and spring 9 is compressed when a 
certain limit value of valve 7 adjusted by means of compressions spring 9 
has been reached. As a result, the increased pressure in line 3 and in 
branch line 11 connected to line 3 is built up suddenly in the piston 
space 5 of cylinder 1 through valve 7, a line 12 and a check valve 13. 
This increased pressure provides the front edge of the sliding cap, 
constructed as a tearing ledge, with increased force between the residual 
coal which has remained attached to the roof and the rock. 
The increased pressure in line 12 additionally acts on control area 7b of 
valve 7 through control line 15 which contains a throttle 14. Together 
with the pressure generated by compression spring 9, this increased 
pressure is sufficient to switch back valve 7, so that line 12 is again 
connected to a return tank T, as is control line 15, however, the latter 
connection being effected with a time delay caused by throttle 14. 
If the obstacle of residual coal is still present, the above-described 
conditions again prevail and the above-described procedure is repeated 
with a frequency which can be adjusted by throttle 14. Accordingly, the 
front edge of the sliding cap acts on the residual coal at the contact 
point alternatingly with high and low pressure, i.e., in a pulse-like 
manner. This makes it possible to separate the residual coal. 
A control line 16 connects line 4 to check valve 17 which can be unlocked. 
Check valve 17 prevents the pressure from decreasing in the piston base 5 
and in line 3 during the shaking procedure. During manual operation, 
piston rod 2 is retracted by applying pressure to the annular space 6 
through line 4. By unlocking check valve 17 through control line 16, the 
pressure prevailing in piston space 5 can be released into line 3. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.