US2733057A

US2733057A - Continuous mining machine having

Info

Publication number: US2733057A
Authority: US
Publication date: 1956-01-31
Anticipated expiration: 1973-01-31

Description

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CONTINUOUS MINING MACHINE HAVING ADJUSTABLE TUBULAR CUTTERS Filed Oct. 8, 1952 6 Sheets-Sheet 2 H. D. LETTS CONTINUOUS MINING MACHINE HAVING ADJUSTABLE TUBULAR CUTTERS Jan. 3l 1956 6 Sheets-Sheet 3 Filed Oct. 8, 1952 l ig. ,6

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H/S A ORNEYS Jan. 31, 1956 H. D. LETTs 2,733,057

CONTINUOUS MINING MACHINE HAVING ADJUSTABLE IUBUIAR cUTTERs Filed Oct. 8, 1952 6 Sheets-Sheet 6 INVENT Haro/d D. Le

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RNE YS United States y Patent T CONTINUOUS VMINING MACHINEHAVING ADJUSTABLE TUBULAR CUTTERS Harold D. Letts, Zelienople, P a.,assignor of one-half to Howard B. Salkeld, Zelienople, Pa.

Application Octobers, 1952, SerialNo. 315,874 8 Claims. (Cl. .2M-.7)

'This invention relates to a machine .forcontinuously mining coal and like minerals and particularly such a machine that is adapted lto constant advance.

Ordinarily, a vein of coal is undercut or vkerfed and then exploded into smaller portions which are relayed to the mouth of the mine. Such a technique is slow and cumbersome. Consequently, various machines have been suggested for continuously mining coal in order to avoid these intermittent and time-consumingsteps. N one, however, has been completely satisfactory. .One objection is that the action of many of the prior so-called kcontinuous mining machines is limited to a given position. ,That is, such machines are really stationary and therefore restricted to mining only an area Within reach. Upon exhausting such an area, the prior art machines must be moved, often laboriously, to a new station Where, with the machine once more stationary, the mining operation is resumed.

Another objection to yprior .mining machines is that they are incapable of adjusting lateral .slopes in the direction of a vein of coal, that is, to an oblique direction which is neither horizontal nor vertical. It frequently happens that a vein being mined jis horizontal `for only a given distance after which it may turn vertically or tilt in such an oblique direction. Previous mining machines, due in many instances to their rigid and actually stationary operation, cannot be quickly adapted to follow a vertical change of direction of a coal vein. And in no instance is it known where anymining machine can be adapted to follow such an oblique or skewed path.

The present machine solves these problems and Ipresents as well other novel features hereafter described. In particular, the present machine embodies in -one form the cooperable action of a plurality of parallel, tubular cutters with a cutter chain. The tubular cutters .are placed side-by-side, while the cutter chain traverses a path which is transverse to the 'tubular cutters and conforms substantially with their transverse outline. In this manner, the tubular cutters and cutting chain b ore a hole which is substantially oblong in .cross-section. Ordinarily, the machine contains a conveyor `to receive the coal as it is discharged from the tubular cutters and then to transport the mined coal to the rear of the machine. ln this manner, the operation of the machine is truly continuous since the cuttersconstantly advance and the coal is simultaneously carried away.`

In another embodiment, the tubular 'cutters are supported at the leading ends of alpair of housings or frames mounted on the mining machine. ",The housings are individually pivota'ble so that the direction of mining may be changed either vertically or in an oblique directionl depending on whether both or only one of the housings is pivoted.

Other advantages and novel features are apparent from the .following description and drawings of alpresently preferred embodiment wherein:

Figure `l is a plan-view showing ageneral'arrangement of parts;

l 2,733,057 Patented .Jan..3 1, v 1.95.6

vFigure Slis asideelevation `.of 'Figure 1;

Figure 3 is an end view of .Figure 1 taken on .the line IIL-III;

Figures 4 through 9 ,Figure l1., and Figure .12 .arcsectons of Figure l1 taken on lines having -a Roman numeral which corresponds, respectively, to .the Arabic numeral of the resulting ligure;

Figure 10 is a section of Figure 2 :taken on the line Figure 13 is a section ofFigure 1 corresponding to Eigure 4 but showing one 'tubular cutter raised with .respect to the other;

Figure 14 illustrates front and side elevations of the cutting means on theleading edges o'f the tubular cutters;

' Figure 15 is a diagram schematically `illustrating a hydraulicsystem used .to pivot vvthe housings or frames;

rFigures .16, '17 .and 18 are longitudinal sections .of a tubular cutter illustrating various positions a pilot cutter may take;

Figures 19, '20,` and 2'1 are end views of a tubular cutter showing modications of means to support a tubular cutter *about a mining shaft; and

Figures .22I 23, and 24are vertical longitudinal sections of Figures 19, 20, and 2l, respectively, with only the outer half shell of the tubular cutter removed.

.Referring to .the drawings, this embodiment includes, as ygenerally shown, a continuously movable base 30, -a mining head '31 and a conveying system 32.

The movable base comprises endless tractor treads 33 having a front axle'34 and a rear -axle 35. The axles are held apart by side beams .36 outside the treads -as shown in V Figure 7. A pair o'f -housings or frames 3.7 and 38 extend lengthwise of the base 30 along the sides and pivot about the rear axle on bearings 39 as illustrated in Figure v10. Each housing is constructedin the same manner and iineludes arearward compartment 40 having an arm portion 41 projecting 'forwardly ofthe base. The rearward compartment contains the drive means for'the tractor treads 33 and 'the mining head 31. Electric motors 42 and 42a secured to the floors of the rear compartments 40 ,receive .current through a flexible cable 43 which approaches motor 42from one side andcrosses between the flights of the conveying system 32 to service the other motor 42a. `B.y kmeans of

conventional gearing

44 and 45, each motor drives a rear shaft 46 and -a main drive shaft 47a or Zi7b which extends past the leading end of its housing. The shafts 46 47a, .and 47b are `.-journaled in conventional bearings (not shown) which are secured to the sides of the housings. AA .medial Aportion of each main drive shaft operates a ,gear reduction 'box 48 by intermeshing gears 49 and V50. A sprocket 51 ofthe gear box drives the `rear axle .35 .by a chain 52 and sprocket 5 3'ixed to ,thataxle A 4hydraulic cylinder 54 supports each housing forwardly of the rear axle and pivots the 'housing thereabout. As illustrated in vFigure 7, a standard 55 secured to fthe side'beam 36 carries each hydraulic cylinder whose piston bears against the underside of the arrn portion 4:1:of the housing. A scoop plate generally shown at 56 .includes ftwo arcuate wings 57 and '5S which lcurve outwardly away `from the 'conveying system 32 'at the side and inwardly toward the conveying system at the bottom. The forward ends :of the wings terminate at a point adjacent the rear yof the mining head 3i and have a plu rality of hinged plates 59 arranged in fish-scale fashion. That is, the `plates pivot about a common axis and adjacent `plates partially overlap. Yrthe hinged plates en-y able lthe'scoop yto adapt itself to changing Vground con-v Y' coal discharged by `the mining V'head Yand direct Lit onto the conveying system. As shown in Figure 11, each spring 60 bears against opposing pockets 61 and 62 which are secured, respectively, to a side of the projecting arm 41 and a side of a wing of the scoop 56.

Considering now the mining head, this apparatus includes tubular cutters 63 supported about

mining shafts

64a and 64b and a cooperating cutting chain 65. The construction of each tubular cutter is the same, and they are preferably of equal diameter. The

mining shafts

64a and 64b extend in parallel fashion from their

corresponding housings

37 and 38 wherein they are rotated by the

main drive shafts

47a and 47b, respectively. Since the main drive shafts must rotate in the same direction to propel the cutting chain 65 as hereafter described, and since the tubular cutters 63 are preferably driven in opposite directions to urge the mined coal toward the center of the machine, diierent drive arrangements are used to rotate the mining shafts from the main drive shafts. As shown in Figure 6, the main drive shaft 47a rotating in the direction of the arrow 66 drives the mining shaft 64a in an opposite direction by cooperating spur gears 67 and 68. On the other hand, the main drive shaft 47b rotating in the same direction as the main drive shaft 47a drives the mining shaft 64b in a similar direction by a silent chain drive shown generally at 69. As a result, the main drive shafts as between themselves rotate in the same direction, but the tubular cutters being supported over the mining shafts rotate in opposite directions with respect to each other. In either type of drive arrangement for the mining shafts, relatively large bearings 70 and 71 (Figure l2) straddle the spur gears or silent chain drive to support the mining shafts in cantilever fashion. The bearings in turn are supported by the sides of the housing. Each mining shaft terminates in suitable cutting means to form a pilot cutter. In Figure 3, this pilot cutter is shown as a conventional convolute boring surface 72 having carbide cutting teeth 73.

Each tubular cutter is supported concentrically about its mining shaft. Preferably, this support includes a helicoid sheet which spirals about the shaft and extends radially from the mining shaft to the tubular cutter. In this manner, in addition to supporting the tubular cutter about its shaft, the helicoid sheet helps to fracture the cylinder of coal cut by the tubular cutter and simultaneously advance the broken portions through the tubular cutter onto the conveying system as the cutter rotates. The leading edges of the helicoid sheet may have cutting teeth 74 as shown in Figures 3 and 12. More than a single helicoid sheet may also be used. The form illustrated in the drawings (except for Figures 19 through 24) includes, for example, two

helicoid sheets

109a and 109b spaced substantially 180 degrees from each other to form a double-thread construction.

The leading edges of the tubular cutters may also have cutting teeth 75. The teeth have carbide tips and are removably inserted in receiving blocks 76 fixed to the shell of the tubular cutter as shown in Figure 14. Successive teeth preferably point in different directions so that the cut made by the tubular cutter exceeds the thickness of its shell. A circumferential ridge 77 spirals rearwardly on the exterior of each tubular cutter to force backwardly any coal chips or dust which becomes lodged between the outside of the tubular cutter and the hole it is boring. In this manner, clogging or fouling of the tubular cutters is prevented.

While the direction of the hole cut by the mining machine is solely dictated by the desired operation of the machine, it has been found that the present machine best follows the action of the mining head and -in line with the hole thereby cut when the

mining head shafts

64a and 64b are in substantially the same vertical plane as the corresponding tractor treads 33, and when a plane cotangent with the bottoms of the tubular cutters is substantially coplanar with the bottom flights of the tractor treads.

A cutting chain 65 is stationed behind the tubular cutters and travels a continuous path transverse to the mining shafts. As illustrated in Figure 5,

sprockets

78 and 79 keyed to the

main drive shafts

47a and 47b, respectively, propel the cutting chain which passes beneath guide strips 80 spaced from the

wings

57 and 58 of the scoop 56 by supporting arms 81. In this connection, it will be noted that the spring 60 which urges the scoop 56 away from the projecting arm 41 also serves thereby to tension the cutting chain 65. The teeth 82 of the chain preferably point in different directions as in the case of the teeth on the leading edges of the tubular cutters. The cooperable action of the tubular cutters and the cutting chain provides substantially an oblong hole.

Referring principally to Figures 9 and 10, the conveying system, generally shown at 32, includes

vertical guide walls

83 and 84 extending lengthwise of the movable base 30 of Figure l. The walls have bearing inserts 85 which space and support the walls on the front and rear axles 34 and 35.

Platforms

86 and 87 are fixed as by welding to adjacent sides of the

walls

83 and 84. A scraper conveyor, shown generally at 88, includes a chain 89 and crossarms 90. The conveyor rides over the platforms pushing the coal before it on the upper ght to discharge the coal eventually into a shuttle car 91 or portable conveyor. The scraper conveyor turns about a rear axle 92 and a front axle 93. The motor 94 in Figure 1, carried by a ledge 95 secured to the guide wall 83, drives the rear axle by a conventional sprocket and chain arrangement. This motor may be energized by splicing to the exible cable 43. The rear axle 92 is journaled in the

guide walls

83 and 84 while the front axle 93 is joumaled in the forward ends of the side beams 36. The

platforms

86 and 87 cause the conveyor flights to straddle the front and rear axles of the movable base 30.

The hydraulic cylinder 54 may be operated by the system schematically shown in Figure l5. This apparatus may be housed between the vertical guide walls and preferably near the forward end of the machine to be sufficiently above the conveyor 88 to avoid interference. A pump 94 driven by a motor 95 draws hydraulic tluid from a reservoir 96 and discharges it through a line 97 to a relief valve 9S and then to a solenoid-operated, threeway valve 99. Ordinarily, the fluid flows through the return line 100 to the reservoir. When it is desired to pivot a housing, an operator depresses the push button 101 forming a part of the control panel 102 of Figure l. This operates the solenoid valve through the electrical lead 103 thereby closing the return line 100 and opening the valve 99 to the hydraulic cylinder 54. The hydraulic pressure developed is conventionally used to pivot the housing about the rear axle as previously described. The mining machine may be horizontally steered by conventionally braking one of the tractor treads.

Various modifications are possible with the mining head. As shown in Figures 16, 17, and 13, the pilot cutter 72 at the leading end of the mining head shaft 164 may precede, be substantially flush with, or succeed the cutting teeth 75 on the leading edge of a tubular cutter 63. These variations are ordinarily dependent on the properties of the coal being mined. Further, the means for supporting a tubular cutter about a mining shaft may take many forms. Ordinarily, such supporting means need only permit the ow of the material mined through the tubular cutter since continued mining forces previously mined coal through the cutter. Accordingly, straight radial arms extending from the mining shaft to the cutter may be employed. However, it is much preferred to aid the ow of coal through the tubular cutter. To this end,helicoid sheets which spiral about the mining shafts are used. Either the previously described doubleahrcadconstruction :It-0911 and 510911 as shownin figure i6 -or fthe single-thread construction iM illustrated in lFigu'reS -19 vand 22, .resembling zan Archimedes screw, may :be :used The former :construction :is preferred since .it proivides smoother and more :efficient operation. For .example, when .the .leading v.edges of .fthe .-helicoid :sheet have cutting teeth 74 as vin :Figure .3, twice as :much cutting force is exerted by v.the :helicoid sheets 10.9.a .and .109b of AFigure 1'6 as compared to the .-helicoidsheetf104 of Fig- -ure In :any case, the .helicoid `sheets also .have ythe ladded advantage of helping to .fracture the coal as .it is .introduced into :and tumbles ythrough the 'tubular cutters.

When the properties of the scoal are such that relatively v:large lumps :are formed, any helicoid sheet 'construction :can tbe :changed .to `that A.of 'Figures 20 'and 23. In fths case,'just.a helicoid strip .105 fisused. The outer edge of vthe strip bears against Aa tubular cutter 163, while .t'he'strip lis `rigidly spaced Sfrom sthe rmining .shaft .264 by .radial :arms 110.6. This .arrangement facilitates :the .flow `of .larger lumps of coal.` ,Figures .21 rand .24 illustrate :a .still further type of supporting means for the tubular cutters. 'This type embodies -a :plurality of `sheets lil? -which .extend .radially from the shaft 36.4 `to `the tubular .cutter 263. The leading edges or" eachsheet 167 .'slant rearwardly and contain vcutting teeth :11)8. The advantage "of lthis construction is :that as thecoaladvancesinto the tubular cutter, it ,becomes wedged between the edges .of ithe'sheets 1.07 and the tubularcutterl. :Continued mining action aided 'by Ythe teeth 108 fractures the coal into smaller portions which are thereby .more easily :processedby the machine.

In an overall operation, an operator walks behind the continuously advancing 'machine and controls :the actions of rthe various parts .through -a -control panel 102. The control circuits which :are of .standard ydesign reach the machine through `a liiexible 'conduit ll. In the embodiment shown, the pilot `cutters lat the leading ends of the mining shafts 64a and'64b .-iirst'bore linto .the coal or like mineral. The diameter of .the pilot cutter .exceeds that of .its :shaft so that an annular Iarea is formed about the shaft. Accordingly, .when the teeth .7S yof the tubular .cutters iirst bore Vinto the zcoal, the .cross sectional area yof a .tubular cutter around ,its `mining shai't .is somewhat Agreater than the cross sectional area =of the lcylinder of .coal-.cut This .annular area provides :room to which the :coal may break and, coupled with the lnatural -tendency of the mined coal to crumble, aids in reducing the `coal qto lsmaller portions. As .the tubular cutters continue to rotate, the coal .'tumbles therethrough vaided :byxthefhelh rcoid -sheets which may also further fracture Lthecoa'l as Aby strik-ing one lump against another. .The .tubular cut-. Vters grotate toward each other at Athe .bottom so that the coal :C .as in Figure 3 is -urged toward -the center. The cutting -chain 65 removes the triangular portions vbetween the tubular .cutters -leit @untouched by their action. This cooperable action between the :cutters Aand :chain rprov'ides a substantially oblongfhole. :Since the teeth '7S on adjacent tubular vcutters overlap as lthe vcutters rotate, the cutting .chain 65 mounted as described :serves lthe additional purpose of synchronizing the rotation of each cutter to prevent .the teeth from striking against one another. The scoop L56 receives the coal from the cutters and `cuttingl chain and directs .it onto the 'conveyor .88. The co'iled spring 6i) maintains the scoop 1in a downward vposition and vthereby also automatically `tensions the cutting chain. The conveyor .moves the Icoal fto the rear of the 'machine where it is dumped :into a shuttle car 91 or .onto a'portable conveyor and then carried away.

When it is desired to steer the machine vertically, the operator need only hydraulically .applypivoting .pressure to both of the vhousings as gpreviously explained. e if, however, it .is .desired to follow an-obliquc direction that is neither horizontal nor vertical, only one housngis pin oted, .or .onehousing is pivoted .more than the other, vto station the Vtubular cutters as-shown inFigure .13. This :position .of `the .fcutters aided V.by .conventional :horizontal steering n ieans previously mentioned enables .the .direction .of `mining to `proceed in the .oblique or skewed path. Moreover, the lmachine can recover from yan .oblique lchange of direction .and resume "its rformer direction =or veer oit instill another direction. The compressibility of .the coiled spring A60 :and the .natural .play ybetween sthe .cantiliver -mining :shafts 64a `and 64b ,permit elevation tot .one end of -the A.cutting chain and of one housing with respect to the other without interfering with y.their .co-

`While .the `vforegoing disclosure :describes ra presently preferred .embodiment and some ymodifications thereof, .it Vis understood .that 'the present invention y,may Vbe practiced lin .other forms l.and with still other modifications within the scope of .the following claims.

Iclairn:

1. A mningrmachine including a movable base, frames supported by .the base yandihaving a 4shaft-driven'rotatable tubular cutter extending .forwardly-of the -base, means rto move vertically'the-forwardtend of Aeach .frameindividual-- ly with .respect to the .base whereby .the ltubular :cutters may be placed at different verticalelevations causing the direction of boring 4-to proceed ina skewed direction, the tubularcutters having van endless band drivingly connected with the .tubularcutters and traveling in kan encompassing path around .thedrivingshafts for the .tubular cutters preventing separation of .the fsarne whereby the cooperable action of the `tubular .cutters .with the :endless band .cuts substantially an .oblonghole 2. .A .continuous :mining lmachine .adapted yfor :constant advance ,including .a movable .-hase having .front and rear axles, .a continuous conveyor l:mounted over .the base :and extending .longitudinally thereof, .means to drive .the Vconveyor, amusing-mounted on -the base-on .eachside 'of the conveyor .and extending forwardlyfof :the base., each houslng containing driving means .including :means .to .drive the .movable base, fmeans .to pivot'each :housing labout .fthe rear 4axle,.and :amining lheadsupported by Vthe leadingv ends of .the .housings lincluding a .mining .shaft `projecting 'from each housing .in .parallel relation and rotated .inopposite directions .by .the .driving .means in fthe housings, each shaft .terminating in cuttingmeans tto .form .a pilot cutter., a pair .of closely .spaced v.tubular .cutters :each 'concentric with a .diiierentshafg means .to support eachtubularcutter aboutits concentric shaft, said supporting means being adapted lboth to .assist n .ffracturing .the .material :mined and .to advanceit .through the tubular cutteronto the vconveyor, a cutting chain stationed behind the tubular cutters and adapted to travel a continuous path 1transversezto the shafts,said chain having linear upper and lower ights conforming substantially to the perimeter of the associatedl tubular cutters, .means .to ,move the chain :through said path, and 'afscoop pivotable about-the frontzaxle and extending beneath the cutting chain to :the Vrear of .thetu' bular cutters to .guide the materialfdischarged from the tu-4 bularcuttersonto the conveyor.

.3. A machine for lcontinuously mining .coal and like minerals vthat is adapted vfor constant advance including: a movable base having .tractor treads traveling about;front and rear axles, .vertical-guide walls .extending longitudinally of .the base andmountedfthereon, acontinuous-conveyor stationed between the walls .and mounted over' the base for individual movement, :means Ato drive-fthe conveyor,..=a fhousing on each=side1of vthe conveyor ipivota'lly mounted about the rear axle and extending forwardly of the base, each housing containing electrical driving means including means to drive the tractor treads, means to support each housing forward of the rear axle and to pivot each housing separately thereabout, and a mining head supported by the leading ends of the housings including a mining shaft projecting from each housing in parallel relation, means to drive each mining shaft in opposite directions including a main drive shaft extending lengthwise of each housing and driven in turn by the electrical driving means, cutting means on the forward ends of the mining shafts to form pilot cutters, a pair of closely spaced tubular cutters having cutting means at their leading edges, cach cutter having the same diameter and being concentric with a different shaft, a plane cotangent with the bottoms of the tubular cutters being substantially coplanar with the bottom llights of the tractor treads, means to support each tubular cutter about its concentric shaft including a helicoid sheet spiraling about the mining shaft, and extending radially from the shaft to the tubular cutter, an endless chain having cutting teeth stationed behind the tubular cutters and driven by the main drive shafts, said chain being adapted to travel a continuous path transverse to the mining shafts wherein the upper and lower flights of the chain are spaced apart a distance substantially equal to a diameter of a tubular cutter whereby the cooperable action of the pilot cutter, tubular cutters, and cutting chain results in substantially an oblong hole, a scoop pivotable about the front axle and extending beneath the cutting chain to a point adjacent the rear of the tubular cutters to guide the material discharged from the tubular cutters onto the conveyor, and resilient means urgi ng the scoop downwardly.'

4. A machine for continuously mining coal and like minerals that is adapted for constant advance and for allowing a winding vein thereof, including: a movable base having endless tractor treads traveling about front and rear axles, vertical guide walls extending longitudinally of the base and mounted thereon, a continuous conveyor stationed between the walls and mounted over the base for individual movement, means supported by a guide wall to drive the conveyor, a housing on each side of the conveyor pivotally mounted about the rear axle and extending forwardly of the base, each housing containing electrical driving means including means to drive the rear axle, hydraulic means to support each housing forward of the rear axle and to pivot each housing thereabout, whereby pivoting both housings equally changes the path of mining in a vertical direction and pivoting the housings unequally changes the path of mining in an oblique direction that is neither horizontal nor vertical, and a mining head supported by the leading ends of the housings including a mining head shaft projecting from each housing in parallel relation, each mining head shaft being in substantially the same vertical plane as a corresponding tractor tread, means to drive each mining head shaft comprising a main drive shaft extending lengthwise and forwardly of each housing and driven in turn in the same direction by the electrical driving means, means mechanically joining one main drive shaft to a mining head -shaft to drive the latter in an opposite direction, means mechanically joining the remaining main drive shaft to the remaining mining head shaft to drive the latter-in the same direction, cut-` ting means on the forward ends of the mining head shafts to form pilot cutters, a pair of contacting tubular cutters having cutting means at their leading edges, each tubular cutter having the same diameter and being concentric with a different mining head shaft, a plane cotangent with the bottoms of the tubular cutters being substantially coplanar with the bottom flights of the tractor treads, means to support each tubular cutter about its concentric shaft including a helicoid sheet spiraling about the mining head shaft and extending radially from the shaft to the tubular cutter whereby said supporting means both assists in fracturing the cylinder of coal-initially cut by each tubularV cutter and to advance the resulting fractured portions through the tubular cutter, an endless cutting chain stationed behind the tubular cutters and driven by the portions of the main drive shafts extending forwardly of the housings, said chain being adapted to travel a continuous path transverse to the mining head shafts wherein the upper and lower ights of the chain are spaced apart a distance substantially equal to a diameter of a tubular cutter whereby the cooperable action of the pilot cutters, tubular cutters, and cutting chain results in substantially an oblong hole which is at least as large as the largest crosssection of the machine, a scoop pivotable about the front axle and extending beneath the conveyor and cutting chain to a point adjacent the rear of the tubular cutters to guide the material discharged from the tubular cutters and cutting chain onto the conveyor, and guide strips supported by the scoop to space the bottom ight of the cutting chain from the upper ight, and resilient means urging the scoop downwardly away from the housings to tension the cutting chain and maintain the scoop in a downward position.

5. A mining head adapted to be mounted forwardly of a mining machine including a plurality of drive shafts, a tubular cutter drivingly connected to each drive shaft, means for vertically moving the tubular cutters individually or together with one another with respect to the machine band receiving means on each drive shaft, and an endless band common to the band receiving means and traveling transversely around the shafts in engagement therewith whereby the vertically movable tubular cutters are maintained in a closely spaced cooperating relation preventing separation thereof.

6. A mining head adapted to be mounted forwardly of a mining machine including a plurality of substantially parallel drive shafts, a tubular cutter drivingly connected to each drive shaft, means for vertically independently tilting the drive shafts with respect to one another and to the machine, band receiving means on each shaft, and an endless band common to the band receiving means and having cutting means traveling in a path transversely around the drive shafts in engagement with the band receiving means whereby the cooperable action of the tubularcutters with the endless band cuts a hole and the band maintains the tubular cutters in closely held together cooperating relation so that the cutters are prevented from separating and the hole cut is uniformly substantially oblong.

7. A mining head adapted to be mounted forwardly of a mining machine and act as a directional control including: a pair of closely spaced tubular cutters arranged in parallel relation, a pair of shafts terminating in cutting means to form pilot cutters, means to support a tubular cutter about a shaft, driving means to rotate the shafts, vertically acting lift means for independently vertically tilting the forward end of each shaft with respect to the mining machine, sprockets drivingly connected `to the shafts, a common cutting chain trained about the sprockets and mounted transversely of the shafts and propelled by said driving means, and means to space apart the upper and lower ights of the chain a distance substantially equal to a diameter of a tubular cutter whereby the cooperable action of the pilot cutters, tubular cutters, and cutting chain cuts a single hole and the engagement between the sprockets and the trained cutting chain maintains the tubular cutters in closely held together cooperating relation even during such vertical tilting so that the hole is substantially oblong and adapted to receive the mining machine.

8. In a machine for continuously mining coal and like minerals, a mining head adapted to act as a directional control, including: la pair of closely spaced tubular cutters of substantially equal diameters, said cutters being normally arranged in parallel relation and having cutting teeth at their leading edges, a pair of mining shafts, means to support each tubular cutter about a mining shaft, said supporting means being adapted both to assist in fracturing the cylinder of coil initially cut by each tubular cutter and to advance the resulting fractured portions through the tubular cutter, cutting means on the leading end of each shaft to form a pilot cutter, driving shafts to `rotate the mining shafts toward each other, independently tilting means to vertically tilt the forward end of each mining shaft with respect to the mining machine while the machine is advancing, and including separately operable jack means, sprockets on the driving shafts, an endless chain provided with cutting teeth, said chain engaging the sprockets and encompassing the driving and mining shafts in restrained relation, a coal scoop adapted to be carried by the mining machine below the cutting chain for gathering mined coal and guiding it rearwardly, guiding means on the scoop to receive the lower iiight of the chain and space it from the upper llight a distance substantially equal to a diameter of a tubular cutter, and resilient means urging the scoop downwardly from the mining machine to tension the cutting chain whereby the cooperable action of the pilot cutters, tubular cutters, and cutting chain cuts a single hole and the cutting chain synchronizes the tubular cutters in adjacent cooperating relation even when the mining shafts are unequally vertically tilted so that the hole is substantially oblong and adapted to receive the mining machine as it advances regardless of the angle of advance.

References Cited in the le of this patent UNITED STATES PATENTS Stanley Aug. 29, Kuhn et al Aug. 3, McKinlay Oct. 19, Morgan Feb. 2l, McKinlay Sept. 3, Humbcl Nov. l5, McKinnon June 20, Levin Oct. 23, Galuppo et al. .lune 15, Compton July 31, Snyder et al Nov. 16, Graham Nov. 16,

FOREIGN PATENTS Germany May 3, Great Britain Aug. 6, Great Britain June 10,

OTHER REFERENCES Coal Age May 13, 1926, pages 667-670.