Rack-driven mining machine with pivotal guide shoe

Described is a mining machine of the type which moves along a track or conveyor provided with a gear rack and wherein a driven gearwheel on the machine engages the rack to move the machine along the track. At least one skid is pivotally connected to the mining machine and bears upon and is guided by the rack, the pivotal connection of the skid to the machine being intermediate the ends of the skid. The gearwheel is fixedly mounted on the mining machine and extends through an opening in the skid to mesh with the gear rack whereby rotation of the gearwheel will cause the machine to traverse the track. The axis of rotation of the gearwheel lies in a vertical plane through which the pivotal axis of the skid extends whereby the skid can articulate along the rack without affecting the engagement of the gearwheel with the rack.

BACKGROUND OF THE INVENTION 
While not limited thereto, the present invention is particularly adapted 
for use with longwall mining machines and coal plows. In the mining of 
coal veins by the longwall mining method, a cutting machine is employed 
that cuts along the longwall face of the coal seam while moving 
longitudinally along the longwall face on a conveyor or track spaced 
therefrom. A suitable cutting machine for performing this operation 
usually consists of a machine body movable along the conveyor, and one or 
more support arms pivotally attached to the body and carrying rotating 
cutting tools. 
A longwall mining machine of this type can be advanced by means of a winch 
arrangement comprising a chain wheel which is in engagement with a chain 
looped about a guide wheel and anchored at its opposite ends to the ends 
of the longwall face. With this arrangement, rotation of the chain wheel 
by a drive motor will cause the mining machine to advance along the track 
on which it is mounted. In other cases, however, movement of the mining 
machine along the face being mined is achieved by means of a gearwheel on 
the mining machine which engages a rack extending along the track. Such 
mining machines are shown, for example, in U.S. Pat. Nos. 1,710,801 and 
1,638,507. 
In a rack-driven mining machine of the type described above, it is 
difficult to produce the forward thrust required for a mining operation. 
These difficulties are due mainly to the undulating, uneven mine floor 
which impairs meshing of the driving gearwheel with the teeth of the gear 
rack. This is particularly true in the case of long mining machines where 
the undulating condition of the floor impedes the transmission of 
substantial thrust forces. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a new and improved propelling 
system for a longwall mining machine is provided utilizing a rack and 
driving gearwheel arrangement which facilitates good meshing engagement of 
the gearwheel with the rack under all mine floor conditions and enables 
the generation of particularly large forward thrust forces. 
In carrying out the invention, the driving gearwheel which engages the 
aforesaid rack extends through an opening in a skid which bears upon the 
rack and which is pivotally connected to the mining machine along an axis 
which extends through the axis of rotation of the driving gearwheel. In 
this manner, and since the skid constantly bears on the rack even in the 
case of undulating floors, the distance between the rack and the axis of 
the driving gearwheel will always remain constant, or substantially 
constant. 
Consequently, the teeth of the gearwheel mesh with the rack throughout 
their entire depths and are capable of transmitting large driving forces 
which produce the desired forward thrust. It is advantageous if the mining 
machine is directly supported and guided on the rack by means of the 
skids. In this way, the skids improve the retention of the driving wheel 
in the rack geeth and changes in the distance between the axis of rotation 
of the driving gearwheel and the teeth of the rack are avoided. 
In a preferred embodiment of the invention, skids of the type described 
above are provided on opposite ends of the mining machine and each is 
provided with a driving gearwheel. The gearwheels, in turn, are driven by 
fluid motors connected in parallel to a winch pump. Due to the parallel 
connection of the fluid motors acting on the driving gearwheels which are 
spatially separated from each other, the load is divided between the two 
driving gearwheels; and the desired large forward thrust can be produced 
even when one or both of the gearwheels does not completely mesh with the 
gear rack. 
The mining machine frame is conveniently provided in the region of its two 
skids with detachably-disposed axial journals for supporting the driving 
gearwheels that mesh with the gear rack. Detachably-disposed axial 
journals also support the intermediate gears between the fluid drive 
motors and the gearwheels which engage the rack. This facilitates easy 
replacement of the wheel gears. 
A further improvement of tooth engagement between the gearwheel and its 
associated rack is achieved by securing the gearwheel on shaft journals by 
means of adjustable bearings. The adjustable bearings improve the contact 
pattern of the driving gear system and linear contact between gear teeth 
and the rack is achieved even if the axis of rotation of the driving 
gearwheel is not exactly parallel to the horizontal plane through which 
the rack extends. 
Advantageously, the driving gearwheel meshes with the gear rack through an 
opening in an associated skid. The driving gearwheel is then positioned in 
a substantially protected position within the skid and is covered in the 
region in which it engages the rack. Wipers of resilient material are 
provided at opposite ends of each skid to clear the rack of debris.

With reference now to the drawings, and particularly to FIGS. 1 and 2, the 
longwall mining machine itself is identified generally by the reference 
numeral 1. The mining machine travels along a face conveyor or track 2 and 
supports a side bracket 3 (FIG. 2) on the stowing side of the machine. The 
bracket 3, in turn, carries a channel 5 which is open at the top to 
accommodate an electrical supply cable for the mining machine, not shown. 
A gear rack 6, divided into individual sections 6a, is located between the 
face conveyor or track 2 and the side bracket 3. The conveyor 2 is divided 
into trough portions connected end-to-end; the lengths of the individual 
portions 6a corresponding to half the length of each trough portion of the 
conveyor assembly. Furthermore, each of the rack portions 6a is offset by 
half its length with respect to the joints of the conveyor trough portions 
and is pivotally connected to adjacent rack portions and to the side 
bracket 3 by means of bolts 7 extending transverse to the longitudinal 
extent of the conveyor 2 (See FIG. 4). Each end of the frame 8 of the 
machine 1 is provided with a skid 9 on the working face side of the 
machine, the skid bearing by means of a roller 10 on the conveyor 2 when 
the machine moves to the right or left as viewed in FIG. 1. Each end of 
the frame 8 on the stowing side of the machine is also provided with a 
skid 11, each skid being pivotally mounted on bolts 12 carried on frame 
shoulders 13 (See FIG. 4). Bolts 12 also extend transversely to the 
longitudinal extent of the conveyor 2. As best shown in FIG. 4, both skids 
11 on the stowing side of the machine surround the rack 6 which is 
situated between the side bracket 3 and the conveyor 2. The skids 11 bear 
on, and are supported by, the rack 6 and guide the mining machine 1 as it 
traverses the conveyor 2. 
As is best shown in FIG. 1, the body of the mining machine 1 is formed from 
individual modules. These include two cutter heads 14 on opposite ends of 
the machine, each cutter head including a pivotal support arm 15 and a 
cutter drum 16 which is supported on the end of the arm 15. Another module 
17 comprises a winch; and next to the winch is a driving motor 18. An 
intermediate module 19 is provided for the power line and control elements 
of the mining machine. All of the modules are flange-mounted upon each 
other to form a rigid body which bears on the frame 8 and is connected 
thereto. The winch module 17 incorporates a fluid circuit, not shown, 
comprising a fluid pump and a fluid motor. A second fluid motor in module 
20 is connected in parallel to the fluid pump. Each of the two fluid 
motors is provided with a gear 21 carried on a shaft 22. The rotating 
motion of the two fluid motors is transmitted through gears 21 and 23 to 
each of the gearwheels 24 which mesh with the rack 6. 
As shown in FIG. 4, the rack 6 includes side members 6b rigidly joined to 
each other by cross-shafts 25. The teeth of the two driving gearwheels 24 
engage successive ones of the shafts 25 on the rack 26 and propel the 
mining machine along the track 2. 
With reference to FIG. 3, it can be seen that the gearwheels 24 are 
rotatably supported on shaft journals 27 which are detachably mounted on 
the machine frame by means of screw fasteners 28. The same is true of 
gears 23. It can be seen that the gearwheel 24 is mounted on the frame 
shoulder 13 previously described. Each driving gearwheel 24 is supported 
by a self-aligning tapered roller bearing 29. The gearwheels, therefore, 
can adjust themselves over a limited range with respect to their axes of 
rotation such that their teeth flanks make contact over the entire width 
of the cross-shafts 25. Annular gaskets 30 and 31 surround the shaft 
journals 27 to provide a seal on one side of each gearwheel 24; while a 
cap 33 protects the bearings on the other side of the gearwheel. 
Since the fluid motors driving the gearwheels 24 are connected in parallel 
to the same fluid pump, they engage the rack with approximately identical 
tooth pressures. The gearwheels 24 are situated directly above the skids 
11 on the stowing side of the machine (FIG. 5) so that engagement of the 
two driving gearwheels 24 with the cross-shafts 25 cannot be impaired by 
irregularities of the floor or by an undulating floor. The axes of the 
shaft journals 27 are situated in a common vertical plane with the bolts 
12 which pivotally connect the skids 11 to the frame shoulder 13. Since 
the skids 11 are positively connected to the rack 6 by virtue of flanges 
34 which extend under the rack, the gearwheels 24 maintain constant 
contact with the teeth or cross-shafts 25 of the rack and this engagement 
is not endangered even on an uneven floor. 
The longwall mining machine illustrated in FIGS. 1 and 2 can, of course, 
traverse along the working face 26 shown in FIG. 2 with only a single 
driving gearwheel 24 if this is permitted by the conditions of the seam 
being mined. In this case, not only the module 20 but also the 
intermediate gear 23 and one of the driving gearwheels 24 will be omitted. 
The machine frame 8 which is also constructed in module form can be 
adapted for machines of different lengths. It is possible to attach the 
rack 6 on the stowing side and/or on the working face side of the machine 
and to equip the mining machine with correspondingly-arranged driving 
gearwheels 24. 
The skids 11 on the stowing side are shown in sectional form in FIGS. 4 and 
5. These skids grip beneath the rack 6 by means of flanges 34 and are 
provided with an opening 35 through which the driving gearwheel 24 meshes 
from above with the cross-shafts 25 of the rack 6. Both skids 11 guide the 
mining machine in the vertical and in the horizontal directions and are 
carried in slots 37 in the frame shoulder 13. In this respect, the bolts 
12 which extend transversely to the mining machine extend through the 
frame shoulder 13 and through a bore 38 in a flange 36 on the skid. The 
bolt 12 is situated in a common vertical plane with the shaft journal 27 
of the gearwheel 24. As a result, pivotal movement of the skid with 
respect to the bolt 12 will not affect the meshing engagement of the 
gearwheel 24 with the rack. Strippers 39 (FIG. 5), which consist of 
resilient material such as rubber or plastic, are mounted on both end 
faces of the skids and slide on the rack 60 so that the top rack surface 
which functions as a traveling path for the skids is kept free of debris. 
Although the invention has been shown in connection with certain specific 
embodiments, it will be readily apparent to those skilled in the art that 
various changes in form and arrangement of parts may be made to suit 
requirements without departing from the spirit and scope of the invention.