US2891778A

US2891778A - Long wall mining apparatus having a seam embracing channel

Info

Publication number: US2891778A
Application number: US628875A
Authority: US
Inventors: Milik Rudolf
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-12-17
Filing date: 1956-12-17
Publication date: 1959-06-23
Anticipated expiration: 1976-06-23

Description

R. MILIK LONG W LL MINING APPARATUS HAVING A SEAN! EMBRACING CHANNEL Filed Dec. 17, 1956 11 Sheets-Sheet 1 WM, f

June 23, 1959 R. MlLlK 2,891,778

LONG WALL MINING APPARATUS HAVING A SEAM EMBRACI NG CHANNEL Filed Dec. 17, 1956 11 Sheets-Sheet 2 Fig.3.

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LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL I Filed Dec 17, 1956 11 Sheets-Sheet 4 III,

M W; db M-M ATTOPA Efi June 23, 1959 R. MILIK 2,891,778

LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL Filed Dec. 17, 1956 11 Sheets-Sheet 5 Fig .14

Fig 15. A '1 I I 1 $23 25 22 25 2a A v I A 27%W5p 23 //VVE/V7'0/ Z R. MILIK W (a u W j Arron/5g;

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LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL Filed Dec. 17, 1956 11 Sheets-Sheet e WM, W KM, ATTW/VEK';

June 23, 1959 R. MILIK 2,891,778

LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL Filed Dec. 17, 1956 11 Sheets-Sheet 7 //VVE/V7'OEQ R. MILIK M, We f ATTOENE" June 23, 1959 R. MlLlK 2,891,778

LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL Filed Dec. 17, 1956 .wvs/vrae R. M l L l K 11 Sheets-Sheet 8 I R. MlLlK June 23, 1959 LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL Filed Dec. 17, 1956 l1 Sheets-Sheet 9 WVE/VTOR R. M l L I K Afro/ems)? June 23, 1959 R. MILIKI 2,391,773

I LONG WALL MINING APPARATUS HAVING A SEAM EMBRACING CHANNEL Filed Dec 17, 1956 11 Sheets-Sheet 1o Fig.25.'

5 (J/m14L ATTORNEM" June23, 1959 v R. MlLlK 2,891,778

LONG WALL MINING APPARATUS x-mvmc: A SEAM EMBRACING CHANNEL Filed Dec. 17, 1956 11 Sheets-Sheet 11 INVEN TOP 5 5M, 7 u WM ATTORNE Y5 United States Patent 2,891,778 Patented June 23, 1959 LONG WALL lVflNlNG APPARATUS HAVING A SEAM EMBRACING CHANNEL Rudolf Milik, London, England Application December 17, 1956, Serial No. 628,875

16 Claims. (Cl. 262-29) This invention relates to the mining of minerals and in particular the mining of coal underground, and one of the objects of the invention is to provide improved mining apparatus especially, but not exclusively adaptable for working thin seams.

Another object of the present invention is to provide improved apparatus for mining the whole of an extended area or length of the seam face (of whatever thickness) which is attacked by cutting means which have a general direction of advance toward or into the seam.

A further object of the invention is to provide such improved mining apparatus which is applicable to both advance and retreat methods of mining.

Another object of the present invention is to provide for continuous conveyance of the mineral as it is cut from the seam by the same apparatus as effects seam cutting.

A still further object of this invention is to provide improved mineral cutting and conveying apparatus constructed to permit of passing an appreciable volume of manner, to hug closely to the convexly curved face created by this mode of working, hereinafter referred to as arc-face mining.

With a view to the achievement of the foregoing and other objects, and in order that the invention may be more readily understood reference will now be made to the accompanying drawings which illustrate various features of the invention.

In the drawings:

Figure 1 is a plan view showing diagrammatically a typical layout for arc-face mining, operating on the advance mining principle,

Figures 2, 3, 4 and 5 are cross sections showing how seams of difierent thicknesses may be attacked,

Figures 6 and 7 are a plan view and cross section respectively showing how cutting picks may be mounted on a travelling chain,

Figures 8 and 9 are views similar to Figures 6 and v 7 respectively showing how cutting picks may be mounted on atravelling rope.

"Figures 10 and "11 are perspective views of parts of duct' sections of, two difierent forms,

Figures 12 and 13 are transverse sectional views conveyor principle,

Figure 14 is a transverse sectional view through a form of duct section suitable for use when out coal is discharged on the pusher principle,

Figure 15 is a transverse sectional view through a form of duct section suitable for use when cut coal is discharged on the belt conveyor principle,

Figure 16 is a view similar to Figure 15, showing an alternative form of duct section adapted for belt conveyor coal discharge and illustrating a modified method of shearing an overcut and undercut seam,

Figure 17 is a plan view of the form of duct shown in Figure 16, looking in the direction of arrow XVII of, but at right angles to Figure 16,

.Figure 18 is a detail view showing modified means for enabling belt driving ropes to span adjacent duct sections, I

Figure 19 is a transverse sectional view showing how a belt conveyor run within a duct section is connected to a belt driving rope in a tunnel guide extending longitudinally along the exterior of a duct section,

Figure 20 is a longitudinal sectional view, on.1ine XXXX of Figure 19,

Figure 21 is a front view of a portion of a coal-cutting and shearing chain,

Figure 22 is a plan view looking in the direction of arrow XXII, Figure 21, p,

Figure 23 is a diagram relating to the traverse. of a cutter, hereinafter more particularly described.

Figure 24 is a plan view of a driving head as used one in each of the two parallel roads flanking the seam being attacked, and

Figures 25 and 26 are cross sections on lines XXV- XXV and XXVI-OCVI respectively of Figure 24.

Figures 27 to 29 are enlarged views of the top lefthand corner of the diagrammatic Figure 14 to illustrate constructional features, Figure 27 being a cross section on the same plane as Figure 14, with the duct 15C being shown in phantom for clarity, Figure 28 being a plan view from above looking in the direction of arrow XXVIII in Figure 27, and Figure 29 being a cross section similar to Figure 27 but taken along line XXIX-- XXIX in Figure 28.

It will be assumed that arc-face mining is adopted, and one example of mining apparatus, applied to coal mining on the so-called advance mining principle, is shown in Figure 1; my improved mining apparatus is equally applicable to retreat mining.

In the layout shown in Figure 1 parallel entry roads 1, are driven in from a gate room 3 to flank part of a comparatively thin coal seam 4, say sixteen to twentyfour inches deep. The exposed face of a comparatively thin seam 4, say eight to eighteen inches deep, may simply be undercut and overcut to make incisions 5, as shown in Figure 3, or if desired may also be cut into by further incisions 5 (Figures 2, 4 and 5). The incisions 5 may be of any suitable width, say one to-seven inches, and of suitable depth, for instance from three to thirty inches, determined mainly by the nature of the deposit, so as to leave ribs 6 of say two to ten inches thick.

-An example of such a slightly thicker seam face is shown in Figure 2, whilst Figure 4 illustrates a medium thickness seam, of say twenty to fifty inches deep, incised to form thicker ribs, and Figure 5 illustrates incision spacing suitable for seams from three feet or more in depth.

The incisions 5 may be made by means of picks 7 mounted on a chain, as in Figures 6 and 7 or on a rope or cable, as in Figures 8 and 9. In the chain cutter shown in Figures 6 and 7 the picks 7 are detachably secured to blocks 8 hooked to C-shaped links 9 which together with connecting links 10 constitute an endless chain; the

picks 7 are staggered angularly, as in known practice, to embrace a 90 cutting are 11. The C-shaped links 9 have lips 12 adapted to hold and guide the chain in relation to C-sectioned runways 13 provided in the rims 14, or in similar runways provided on a duct section 15. In the rope or cable cutter shown in Figures 8 and 9, picks 7 are mounted in split collars 16 clamped to a rope or cable 17, the collars having lipped ridges 18 to engage runways 13 on a duct section 15'.

Examples of duct sections suitable for supporting chain or rope cutter assemblies are illustrated in Figures and 11. In the former only the rims 1 support cutter assemblies so that the duct section provides a single compartment. A single compartment duct section of this form is especially suitable for attacking thin seams, as exemplified in Figure 3, and its manner of use is illustrated in Figure 12. It will be noted that the coal seam undercut and overcut by the rim-supported cutter-assemblies is sheared off by vertical blades 19 forged integral with or attached to connecting links it of a chain cutter.

The duct section 15A (Figure 11) is sub-divided by partitions or floors 20 arranged intermediately of the upper and lower flanges or walls of the section. These partitions or floors 20 also have C-sectioned rims 14A for supporting cutter assemblies to provide a duct section suitable for attacking a seam in the manner indicated in Figure 4. Another partitioned duct section 15B is illustrated in Figure 13, wherein a central cutter supporting rim 14B is set back from the rims 14. The duct sections illustrated in Figures 10 to 13 are shown without mechanical conveyor means therein and are particularly though not exclusively suitable for use where the duct serves as a shaker or vibratory conveyor.

Larger duct sections

15C, 15D are illustrated in Figures l4, 15 respectively, which show arrangements wherein no supports are provided during working operations for intermediately disposed chain cutters; these cutters are sufliciently supported when in operation by the incisions they make. Starting grooves are made by the use of hand or mechanical tools in the working face to support the intermediately disposed cutters at the commencement of a cutting operation. Alternatively longitudinally spaced brackets may be provided supporting these cutter assemblies. In Figure 14 pusher elements 21 attached to the chain links 10 push broken coal along the floor of the duct section and return unhindered beneath the roof thereof. Figures 27 to 29 show how chain links 10A, to which the pusher elements 211 are attached or with which they are integrally formed, are provided with lips 12A which engage the C-sectioned runways 13 provided in the rims 14 of duct section 15C, in a manner similar to the guiding of the C-shaped links 9 which carry the pick blocks 8 by lips 12 as shown in Figure 7. The lips 12A, which alternatively could be provided on pusher elements 21 if these are separate from chain links 10A, have a limited movement with runways l3 and thus prevent undue drooping of pusher elements 21 when the picks 7 are not cutting; when the picks 7 are cutting, they would be held substantially level and close to the top of the duct section 15C as shown in Figure 14. One or more intermediate or connecting links it may be interposed between cutter-carrying links 9 and pushercarrying links 19A. An endless conveyor belt 22 is secured to wire cables 23 guided in

longitudinal grooves

24, 25 in the floor and roof respectively of the duct sections, in a manner illustrated in Figures l5, l6 and 19.

Passageways 26 may be provided for delivering water to fine orifices 27 through which it issues in spray or jet form for dust-laying purposes.

Figure 1 illustrates also an installation for arc-face mining in which a sectional duct is employed, the duct sections beingarticulated so as to conform to the curvature .of the working face of the seam. A reciprocatory mo tion is imparted to the sectional duct to shake it bodily over the seam face by synchronised shaker motors 28 mounted on wheeled platforms 29 which may be made to run along tracks 30 laid in the entry roads 1, 2. One or more endless cutter assemblies supported on the sectional duct are continuously and unidirectionally circulated by means of chain or rope drums 31 rotated by flamcproof electric motors 32 carried on platforms 29. Mined coal is adapted to be discharged from one end of the sectional duct on to a belt conveyor 33 set in entry road 2, and goaf filling is effected by the aid of another belt conveyor 4 in entry road ll.

The sectional duct is advanced in pace with the cutting away of the seam by moving the platforms 29 along the tracks 3t? in entry roads 1, 2 and the degree of curvature of the arc-faces is determinable by calculations involving among other factors, the distance between the entry roads It and 2, the maximum economical pull on the duct by the platforms 29 and the depth of seam being attacked.

Flexible trunking 35 connects a suction plant 36 to one end of the sectional duct, so that a large volume of air can be sucked therethrough, over the exposed face of the seam. Dust entrained by this air is removed by a separator 37.

in attacking a seam face by the arc-face mining method, cutting could be commenced at the seam face exposed in say a gate road by reciprocating one or more flexible implement carriers endwise and simultaneously pulling the opposite ends of the carriers along parallel side roads extending from the gate road and flanking the seam. This seam face is usually straight (viewed in plan) and the corners of the seam at the road junctions would first be attacked, but gradually the arc-face would be created. It may, however, be preferable to drive between the side roads a tunnel of pro-arranged curved form (viewed in plan) and to commence arc-face cutting simultaneously over the entire seam face exposed in the tunnel. One advantage of this procedure is that the overall length of the flexible implement carrier can remain unchanged, whereas if cutting is commenced at a straight face adjustment of the carrier length would be necessary.

in some coal mines the proportion of methane gas released from the cut seam may be relatively small and the existence of a stream of air induced within the sectional duct for ventilating purposes provide for a suitable pressure differential as between the lower pressure inside the duct and the higher pressure outside of the duct. These conditions ensure that no leakage of diluted methane gas can take place from within the duct to the cross-tunnel in front of the seam and the entry roads 1, 2 in communication therewith, and under these conditions there is no need to seal the rims 14 of the duct to prevent outward leakage of a gaseous medium from within the duct. Where the amount of occluded methane gas is high, however, it may be necessary or desirable to provide flexible sealing strips 38 on the rims 14, as shown in Figure 16, which illustrates a sloping roof duct similar to that shown in Figure 12. The construction of duct section shown in Figures 16 and 17 also illustrates the use of gearing for raising and lowering the rear of the duct, to compensate for unevenness of the mine floor and/or undulation of the seam. Such gearing comprises a casing 39 on the duct and a telescopic shoe 40 adapted for relative movement by screw jacks 41 to which the required rotation is imparted by rope drums 42. The operating rope may be common to a number or to all of the gearings provided on the duct; one such gearing may be provided for each duct section.

As the cutter-supporting duct advances into the seam there is always a possibility of roof subsidences and this, if excessive, may result, even with a sloping roof duct in the duct being forced down tightly. With seams of at least moderate height such roof subsidence may be met by the use of pit props and other shoring, but in thin seams some other method of roof control is desirable. A

suitable roof control means i s shown inFigures l6 and 17, where a series of elevatable beams 43, for instance one foreach. duct section, extend into the space between the sloping duct roof and the top of the tunnel in which the duct operates. These ,beams 43 surmount telescopic 'pillars 44 extensible hydraulically by'means of cylinder units 45 mounted on brackets 45A which attach the pillars 44 to the duct sections.

The belt conveyor drive ropes 23 may be accommodated in tunnels 46 of the bulbous form in cross section located onjthe exterior of the duct sections over slots 47 through which extend the shanks of slippers 48 secured to said drive .ropes 23. The rope tunnels 46 of adjacent duct sections may abut end to end as shown in Figure .17 or be joined by tubular connectors 49 as shown in Figure 18.

Figures 21 and 22 illustrate more clearly the form of chain cutter shown in Figure 16, and this will be seen to comprise pick boxes 50 (carrying staggered picks 51) mounted on one of a pair of spaced links 52. These pairs of spaced links 52 alternate with single links 53,. to which they are pivotally connected by pins 54 and the links 53 support shearing cutters 55 arranged in series such that each successive cutter projects slightly more than the preceding cutter, so as to provide a broaching action.

Figuref2 3 ,is a diagrammatic layout illustrating pick cutting action, A indicating the length of seamface being worked. Assuming A to be say 200 feet and the speed .of'the cutter chains as 200 feet per minute, then if the rate of advance of the cutting equipment equals 1 /2 inches per minute, the zig-zag line a, b represents .the to-and-fro movement of any given cutting pick during that period of advance. I

A suitable mobile power unit of which one is used in each of the entry roads 1, 2 (Figure l) is illustrated in Figures 24 to 26. This power unit comprises aplatform 29 swivel mounted on a post 56 carried on a chassis 57 mounted rolling or sliding along the track rails 30. On the platform 29 is a superstructure 58 supportingan end drum 59 around which passes the coal conveyor belt 22 which is shown passing into the sectional duct 60. One end ofthe sectional duct 60 .(constructed, for-example, of sections similar to those illustrated inFigures l6 and 1-7) is seen protrudingfrom the cross tunnel 61,fand the lower run of the belt 22 is guided, as it emerges from the ,duct 60 in a level course by the jockey :roller 62 revolubly mounted in the superstructure 58, the coal conveyed bythis lower belt run being dropped on to the upper run of a discharge conveyor 63. This endless cutter chain which traverses the top :and bottom rims ofthe duct sections, as previously described, is moved by a sprocketed drum 64 journalled in the superstructure 58 and driven by an electric motor 65 through reduction gearing 66, the lower stretch of the cutter chain being guided in a level course by a jockey-wheel 67. The belt drum 59 is driven by a separate electric motor 68 and associated reduction gearing .69." v

.. What I claim is? 1 .1. Mining apparatus comprising an elongated structure of generally channel form supported onone sideto present its open "mouth" to a mineral seam to be cut and cutters mounted an'e'ast along the'top and bottom edges of said channel structure, mineral conveying means within said structure, and means for driving said conveying means.

2. Mining apparatus as claimed in claim 1, wherein the cutters are mounted for movement relatively to said top and bottom edges of the channel structure and in a direction normal to the general direction of bodily advance of the structure.

3. Mining apparatus as claimed in claim 1, including power means at opposite ends of the structure and movable in parallel paths flanking said seam for efiecting bodily advance of the structure into the seam.

4. Mining apparatus as claimed in claim 1 wherein said structure comprises open-end articulated sections.

5. Mining apparatus as claimed in claim 1, including means for imparting to the structure a limited bodily endwise reciprocatory movement.

6. Mining apparatus as claimed in claim 1, wherein, said sectional structure has an inclined roof, and including means for raising and lowering the rear of the structure, roof control means comprising extensible columns anchored to the structure and roof supporting beams carried by said columns and extending over the inclined roof of said structure.

7. Mining apparatus comprising an elongated channel structure supportable on one side on the mine floor adjacent a mineral seam to embrace the working face of said seam by the open mouth of said channel structure, said structure having continuous guideways on the two rims \thereof, a flexible cable carried by said guideways and incorporating cutting implements, power means at opposite ends of said structure for imparting circulatory motion to said cable to traverse upper and lower runs along said rim guideways, power means to move the structure bodily as the cutting implements cut mineral from the seam and conveyor means within said channel for discharging cut mineral. I

8. Mining apparatus comprising a structure constituted of a plurality of sections of open-end channel form, each supported on one side to present its open mouth to the working face of a mineral seam to be cut, adjacent channel sections being pivotally joined to enable the articulated structure to take up an arcuate form, power means attached to at least the opposite ends of said structure and mounted :for transport parallel one to the other to advance said structure bodily toward the seam as the Working face is cut away, cutters movably mounted on at least the contiguous top and bottom edges of the articulatedchannel sections and conveying means movably mounted within the structure for discharging cut mineral.

9. Mining apparatus comprising an elongated air-impervious channel structure supported with its mouth embracing the seam face and constituting with the seam face a closed tubular path, cutting implements mounted for movement on and in relation to said channel structure, means efiecting movementiof said cutting implements, means conveying mined mineral through said channel structure, means for advancing said channel structure into the space left by mined mineral, and means for forcing ventilating air through the interior of said air-impervious channel structure. 7 e

10. Mining apparatus comprising an articulated sectional structure of channel form supportable with its open mouth facing a mineral seam, having at least one horizontal and longitudinal partition and having open-side tubular guideways extending coextensive with each of the rims of said channel structure mouth and with the outer .edge of said at least one partition, an endless flexible cable having runs thereof supported in said guideways, radiating pick cutters attached to said cable for cutting kerfs as the cable runs traverse said guideways, blade cutters attached to said cable and extending substantially perpendicular for shearing inter-kerf ribs of mineral, power means for continuously circulating said cable to traverse said pick and blade cutters to and fro over the front of said structure, conveying means circulating through each compartment of the longitudinally partitioned channel structure, and power means advancing said structure toward the seam in step with mineral cutting and conveying operations.

11. Mining apparatus comprising an elongated channel structure supportable on one side on the mine floor adjacent a mineral seam to embrace the working face of said seam by the open mouth of said channel structure, said structure having continuous guideways on the tworims thereof, a flexible cable carried by said guideways,,

radiating pick cutters on said cable for kerf cutting, blade:

cutters on said cable extending perpendicular to the seam for shearing inter-kerf mineral, power means at opposite ends of said structure for imparting circulatory motion to said cable to traverse upper and lower runs along said rim guideways, power means to move the structure bodily as the cutting implements cut mineral from the seam and pusher elements on said cable and projecting into said channel for discharging cut mineral from one end of said channel.

12. Mining apparatus comprising a structure constituted of a plurality of sections of openend channel form, each supported on one side to present its open mouth to the working face of a mineral seam to be cut and each having open-side guides along top and bottom rim edges, adjacent channel sections being pivotally joined to enable the articulated structure to take up an arcuate form, power means attached to at least the opposite ends of said structure and mounted for transport parallel one to the other to advance said structure bodily toward the seam as the Working face is cut away, a flexible cable movable through saidsrnim edge guides, means for continuously traversing said cable, pick cutters radiating from said cable for cutting top and bottom kerf, blade cutters extending from said cable for shearing inter-kerf mineral, and conveying means movably mounted within the structure for discharging cut mineral.

13. Mining apparatus comprising an articulated sectional structure of channel form supportable with its open mouth facing a mineral seam, divided into at least two horizontal and longitudinal chambers by at least one partition and having open-side tubular guideways extending coextensive with each of the rims of said channel structure mouth and with the outer edge of said at least one partition, an endless flexible cable having runs thereof supported in said guideways, radiating pick cutters attached to said cable for cutting kerfs as the cable runs traverse said guideways, blade cutters attached to said cable and extending substantially perpendicular for shearing inter-kerf ribs of mineral, power means for continuously circulating said cable to traverse said pick and blade cutters to and fro over the front of said structure, an endless belt conveyor arranged with upper and lower runs adjacent the roof and floor respectively of each said chamber, means for circulating said belt through each chamber of the partitioned channel structure, and power means advancing said structure toward the seam in step with mineral cutting and conveying operations.

14. Mining apparatus, comprising, in combination, an articulated sectional duct comprising a plurality of openend air-impervious channels whose mouths combine to embrace an extended working face of a mineral seam and which constitute an airway extending over the whole of said Working face, each of said channels having guides at least along top and bottom rims thereof, so that said guides of adjacent channels constitute continuous guideways extending the full length of the sectional duct; an endless flexible cable supported in part by said continuous guideways and carrying projecting cutting implements, power operated means at opposite ends of said duct imparting unidirectional circulatory movement to said cable to traverse said cutting implements relatively to the length of the duct, power means movable along parallel roads flanking the seam to advance the articulated duct bodily into the space left by mineral cut away by said cutting implements, conveyor means movably mounted within and through said duct for continuously removing mineral cut by said cutting implements, and air extractor means connected to said duct for continuously ventilating the working face of said seam.

15. Mining apparatus comprising an elongated structure of generally channel form resting on a fiat lower side to present its open mouth to the face of a mineral seam, said structure having an inclined roof and consisting of a plurality of interconnected open-end sections articulated collaterally to admit planar disalignment to fit the arcuate face created during working, means for raising and lowering the rear of the structure, roof control means comprising extensible columns anchored to the structure, roof supporting beams carried by said columns and extending over the inclined roof of said structure, a flexible cable supporting cutting implements for traversing at least the longitudinal mouth rims of the structure, power means for continuously traversing said flexible cable and cutting implements, power means for advancing said structure in step with the cutting away of the seam, and a conveyor moving within said structure to discharge cut mineral at one end thereof.

16. Mining apparatus comprising in combination, an articulated sectional duct comprising a plurality of openend air-impervious channels whose mouths combine to embrace an extended working face of a mineral seam and which constitute an airway extending over the whole of said working face, each of said channels having first guideways extending along top and bottom rims thereof and sets of second guideways extending along the floor and roof of each channel, so that the guideways of adjacent channels constitute continuous guideways extending the full length of the sectional duct, an endless flexible cable supported in part by said first guideways, pick cutters radiating from said cable for kerf-cutting, blade cutters extending perpendicular from the cable for shearing interkerf mineral, power-operated means at opposite ends of said duct imparting unidirectional circulatory movement to said cable to traverse said cutters relatively tothe length of the duct, endless ropes extending through said second guideways, an endless belt conveyor attached to said endless ropes, means for continuously traversing said ropes and with them said belt through said duct for continuously removing mineral cut by said cutters, power means movable along parallel roads flanking the seam to advance the articulated duct bodily into the space left by mineral cut away by said cutting implements, and air extractor means connected to said duct for continuously ventilating the working face of said seam.

References tilted in the file of this patent UNITED STATES PATENTS 753,092 Neukirch Feb. 23, 1904 1,588,987 OToole June 15, 1926 1,622,837 Pearce Mar. 29, 1927 1,741,112 Holmes Dec. 24, 1929 2,105,504 Ramsay Jan. 18, 1938 2,105,505 Ramsay Jan. 18, 1938