US3614162A

US3614162A - Mining-machine cutting structure

Info

Publication number: US3614162A
Authority: US
Inventors: George R Teeter
Original assignee: George R Teeter
Current assignee: Joy Manufacturing Co; Citibank NA; Joy Technologies Inc
Priority date: 1968-12-24
Filing date: 1968-12-24
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: CA929967A

Abstract

A mining-machine cutting structure and more particularly a mining head having cutting means consisting of a single centrally located cutter supporting chain and cutter-supporting rotary elements extending outwardly from the sides of the cutting chain.

Description

United States Patent George R. Teeter 111 Glenview Ave., Oil City, Pa. 16301 786,650

Dec. 24, 1968 Oct. 19, 1971 Inventor Appl. No. Filed Patented MINING-MACHINE CUTTING STRUCTURE 17 Claims, 8 Drawing Figs.

[1.8. CI 299/67, 299/84, 299/87 Int. (I .E2lc 25/06, E2 lc 35/20 Field of Search 299/64, 67, 76, 80, 82-84; 198/9; 37/190 References Cited UNITED STATES PATENTS 3/1922 Porter 299/67 Besteland Joy Joy Gonski Kilbourne. Kilbourne. Prox FOREIGN PATENTS U.S.S.R.

Primary Examiner-Ernest R. Purser Attorney-E. Wallace Breisch 37/ 1 90 299/83 299/83 299/59 X 299/76 X 299/64 X 299/92 ABSTRACT: A mining-machine cutting structure and more particularly a mining head having cutting means consisting of a single centrally located cutter supporting chain and cuttersupporting rotary elements extending outwardly from the sides of the cutting chain.

PAIENTEDBCT 19 I97! SHEET 1 BF 5 3, 614,162

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PATENTEUUBI 19 ISII 3.614.182

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SHEET 5 UF 5 IN VE/VTOR GEORGE E. TEE TEE MINING-MACHINE CUTTING STRUCTURE In a continuous mining apparatus of the type employed in this invention a disintegrating head mechanism is used to dislodge mineral from a mine vein and is operable to provide mine passageway or room into which the apparatus advances and mining progresses. The disintegrating head mechanism is pivotably mounted on a mobile base to swing in a vertical plane between the mine roof and floor and includes a rotary drum cutting-head assembly arranged on a horizontal transverse axis and having teeth or bits which tear away and dislodge and mineral. The apparatus also includes a conventional loading head for gathering the loose mineral on the mine floor and moving it rearwardly and inwardly toward the forward receiving portion of the conveying means of the apparatus. The rotary drum cutting-head assembly hasend portions thereof which can be selectively extended or retracted to, respectively, dislodge mineral from the ribs and comers of a mine passageway and reduce the effective length of the cutting head assembly to provide clearance at the sides of the assembly.

The present invention contemplates improvements over such known types of mining apparatus, for example; a reduction gearing arrangement for driving the cutter head assembly thereby allowing the use of a smaller diameter drive shaft; an improved rotary drum cutter head assembly configuration which allows the use of a centrally located relatively wide endless circulating cutter chain; a cooperation between the cutter chain and the conveying means which aids in the rapid conveyance of the dislodged mineral; and an improved structure for extending and retracting the end portions of the rotary drum cutting-head assembly.

These and other objects and advantages of this invention will become more readily apparent from the following description and drawings in which:

FIG. 1 is a perspective view of a mining machine embodying the principles of this invention;

FIG. 2 is a plan view of the mining machine shown in FIG. '1;

FIG. 3 is a side elevational view of the mining machine shown in FIG. 2;

FIG. 4 is a schematic representation of the gearing arrangement of this invention which rotatably drives a rotary drum cutter head assembly;

FIG. 5 is an enlarged view, partly in section, taken on line 55 of FIG. 1 and showing a main gear casing and a portion of the cutter head assembly embodying the principles of this invention;

FIG. 6 is an enlarged view, partly in section, of a cutter head assembly of this invention;

FIG. 7 is an enlarged view, partly in section, showing the bevel gear casing which is shown in phantom in FIG. 5; and FIG. 8 is a schematic representation of the hydraulic circuit for extending and retracting end portions of the rotary drum cutting-head assembly.

A continuous mining machine generally designated at 10, which embodies the principles of this invention, may assume various forms but, for illustrative purposes, herein comprises a crawler base 14 carrying a frame 16 on which a forwardly extending mining boom 18 is pivotably mounted at the forward end of the frame 16 to swing up and down between a mine roof 20 and a mine floor 22. A cutting head assembly 24 extends transversely of boom 18 and is rotatably secured thereto at the forward end thereof. Pivotably mounted at the forward end of frame 16 and extending forwardly therefrom beneath the boom 18 is a conventional loading head 26 having oscillatory gathering arms 28 for engaging mined mineral and moving such mineral rearwardly and inwardly toward well-known conveying means 30 of the mining machine 10. Conventional fluid jacks 32 serve to swing the boom 18 in a vertical plane about the pivot axis thereof and the loading head 26 is tilted about the horizontal axis thereof by fluid jacks 34. Fluid jacks 32 and 34 have one end thereof secured to the forward end of frame 16 and have the other end thereof secured to respective rearward lever ends of boom 18 and loading head 26.

The cutting head assembly 24 is driven from motors 36, which are suitably rigidly secured by brackets 38 to boom 18. The drive from motors 36 is delivered through speed-reducing transmissions 40 to a pair of universal drive shafis 42. In-

asmuch as the gearing arrangement from both drive shafis 42 to the. cutting-head assembly 24 is identical, the discussion hereinafter will refer to the drive train from a single drive shaft 42.

The end of drive shaft 42 is suitably coupled to a stub shaft 44 by coupling means 46. Shaft 44 has a bevel gear 48 at the forward end thereof which is in toothed engagement with another bevel gear 50. The bevel gear 50 is drivingly secured to a shaft 52 which extends transversely inward of machine 10 and is suitably rotatably supported by a bevel gear casing 54 mounted on the boom 18. Bevel gear casing 54 is suitably secured to a side portion of a main gear casing 56. Casing 56 is contained within a forward area of boom 18 and is securely fastened to the inner sides thereof in any suitable manner.

The shafl 52 has a spur gear 58 at the inner end thereof which is in toothed engagement with a transversely aligned spur reduction gear 60. Gear 60 is in a driving relationship with a coaxially aligned spur gear 62. Spur gear 62 is in toothed engagement with a transversely aligned spur reduction gear 64. Gear 64 is in a driving relationship with a coaxially aligned spur gear 66. Gear 66 is in toothed engagement with a transversely aligned spur reduction gear 68. Gear 68 is in driving engagement with a splined portion of a cutting head assembly drive shaft 70. Shaft 70 extends through gear 68 in a transverse direction with relation to the longitudinal axis of mining machine 10. Gears 58-68 and a portion of shaft 70 are captively and rotatably received by gear casing 56. g

It is to be noted that there are two gears 68 equally spaced on opposite sides of the longitudinal centerline of machine 10, therefore the total driving force supplied to the cutter head assembly 24 by the motors 36 is applied to the shaft 70 at spaced points (gears 68). With such an arrangement no more than one-half of the total driving force is normally applied to any given portion of the shaft 70 thus avoiding the overstressing of a cutter head assembly drive shaft as is common with prior art machines.

Shaft 70 is rotatably supported by tubular gear casing extensions 72 which extend outwardly (i.e. transversely from the centerline of machine 10) from a forward portion 74 of gear casing 56. As hereinafter described in detail shaft 70 rotatably drives: an endless circulating belt-type continuous hinge cutter chain 76 which has a width thereof approximately equal to a transverse measurement of casing portion 74 taken at the forward end thereof; hollow cylindrical rotary drum cuttingheads 78 which extend outwardly from respective sides of portion 74; and hollow cylindrical rotary drum cutting-head extensions 80 which are slidably partially received within respective heads 78 and are selectively hydraulically extendable outwardly therefrom.

At the longitudinal centerline of machine 10 a cutter chain drive sprocket 82 is in splined engagement with shaft 70. Drive sprocket 82 has a plurality of teeth 84 around the outer periphery thereof which drivably engage the cutter chain 76 as hereinafter described. A suitable rear idler sprocket 86 which is rotatable on a shaft 88 and extends transversely of the forward boom area provides well-known tensioning and motionreversing means for the cutter chain 76 to form a continuous orbital path therefor.

Spacer sleeves 90 are positioned along shaft 70 intermediate sprocket 82 and adjacent gears 68 so as to maintain a spaced relationship between sprocket 82 and gears 68. On the outer sides of gears 68 (outer being away from sprocket 82 along the centerline of shaft 70) spacer sleeves 92 are positioned along shaft 70 to provide a spaced relationship between gears 68 and roller bearings 94 which additionally surround shaft 70. Roller bearings 94 provide a rotational relationship between the main gear casing 56 and shaft 70 inwardly adjacent the outer ends of casing extension portions 72. A spacer sleeve 96 is positioned along shaft 70 outwardly adjacent the bearings 94. The outer diameter of spacer sleeve 96 is less than the outer diameter of bearing 94. Annular drive shaft keepers 98, which are rigidly secured to the outer ends of casing extension portions 72 and project radially inwardly from the inner periphery thereof, have the inner surfaces thereof in rotatable contact with the outer surface of spacer sleeves 96.

Outwardiy adjacent to spacer sleeves 96 and keepers 98, internally splined rotary drum cutting-head driving sleeves 100 are in splined engagement with shaft 70. Sleeves 100 are rigidly secured to the rotary drum cutting-heads 78 intermediate the axial ends thereof and project radially inwardly from the inner periphery thereof. With such sleeves 100 the rotary drum cutting-heads 78 are rotatably driven from shaft 70 at a rate thereof equal to the rate of cutter chain drive sprocket 82 and cutter chain 76. The inner end of cutting heads 78 (inner end being that end closest to the longitudinal centerline of machine are rotatably supported by roller bearings 102. Bearings 102 are fixedly secured about the outer periphery of easing extension portion 72 adjacent the inner ends thereof.

Outwardly adjacent to sleeves 100, locknuts 104 are threadably received on shaft 70. When locknuts 104 are positioned around shaft 70 and tightened into bearing against sleeves 100 at the outer surface thereof: engaging sleeves 100; spacer sleeves 90, 92 and 96, roller bearings 94; and drive sprocket 82 are releasably secured with respect to shaft 70 thereby preventing any motion thereof in the axial direction. Transverse movement of shaft 70 with respect to machine 10 is prevented by locknuts 104 transferring thrust from shaft 70 through the sleeves 100 and the remainder of the cutter heads 78 to the bearings 102.

Each rotary drum cutting-head 78 has a radially outwardly extending flange 106 at the inner and thereof and a reduced diameter portion thereof forms a chain end-supporting seat 108 which extends axially from flange 106 toward the centerline of machine 10. Seats 108 extend under a portion of the outer edges of the endless circulating cutter chain 76 and with such a location act to support the bight portion of the cutter chain 76 at the edges thereof where it is trained about the rotary drum cutting-heads 78. The rotational speeds of the cutter chain 76 and the seats 108 are equal and therefore there is no movement of cutter chain 76 with respect to the seats 108 during the time chain 76 is supported by seats 108. Because of this lack of relative movement there is no wearing between the respective contact surfaces of seats 108 and chain 76.

The cutter chain drive sprocket 82 is dimensioned to provide root surfaces 110 thereof which lie in approximately the same cylindrical surface as the contact surfaces of the spaced seats 108. With such root surfaces 110, each link in the bight portion of chain 76 is supported at three areas, namely: end supports at the contact surfaces of the spaced seats 108; and a central support at the root surface 110 of the drive sprocket 82. With such a support arrangement the deflection of chain 76 is minimized and the maximum bending moment due to cutting loads is reduced over that deflection and bending movement which would develop under the same loading if the chain 76 has only one or two areas of support. This support arrangement allows the use of cutter chains having a greater chain width to pitch length ratio than previously permitted, for example a chain width to pitch length ratio of 4 to l, or more. Such a large width to length ratio permits the construction of a chain width large enough for the purposes of this invention as hereinafter set forth while maintaining a sufficient flexibility to avoid unreasonably large chain drive sprocket diameters. If the chain width to pitch length ratio is less than 4 to l, the required chain width would yield a pitch length requiring sprockets too large to be used in a cutter head such as hereinbefore described.

The hollow cylindrical rotary drum cutting-head extensions 80 are dimensioned to have an inner portion thereof slidably received within an outer portion of respective cutting heads 78 (inner and outer being respectively, toward and away from the centerline of machine 10). lntemally splined rotary drum cutting-head extension sleeves 122 project radially inwardly from the inner periphery of head extensions and are located outwardly adjacent the inner ends thereof. Sleeves 1 12 have the radially innermost surfaces thereof in splined engagement with shaft 70 such that head extensions 80 are rotatably driven from shift 70 at a rate thereof equal to the rate of rotation of cutting heads 78. Rotary drum cutting-head extension keeper sleeves 114 project radially inwardly from the inner periphery of head extensions 80 and are located intermediate the axial ends thereof. Sleeves 114 have the radially innermost surfaces thereof in sliding relationship with the outer periphery of shaft 70.

Shaft 70 is splined along the outer surfaces thereof from a point intermediate the axial ends thereof inwardly to the locknuts 104. An end cap 116 is secured to the outer end of shaft 70 and extends radially outwardly therefrom. End cap 116 limits the axial movement of head extensions 80 with respect to cutter heads 78 to that distance from the outermost splined area of shaft 70 outwardly to the end cap 116, for when the head extensions 80 extend outwardly such a distance the keeper sleeve 114 contacts end cap 116 thereby preventing any further outward movement.

Well-known screw-type continuous conveyor scrolls 118 are secured to the outer periphery of rotary drum-cutting heads 78 and to well-known scroll-supporting sheaths which are secured to outer end portions of the rotary drum cutting-head extensions 80. Such sheaths 115 allow the extension and retraction of head extensions 80 while still maintaining a substantially continuous conveying scroll 118 with respect to the scroll 118 on heads 78. Scrolls 118 and the cutting chain 76 have a plurality of suitable bit holders 120 secured adjacent the outer peripheral edges thereof in a suitable spaced orientation to one another. A cutter bit 122 is inserted in each bit holder 120. Cutter bits 122 may be of any suitable type and as shown are plumb bob deep-penetrating point attack conical bits. The scrolls 118 are suitably arranged to convey a portion of mineral mined by bits 122 inwardly from such bit locations toward the cutting chain 76. End cutter caps 124 are suitably secured to the outer ends of head extensions 80. Bit holders 120 and cutter bits 122 are secured to caps 124 in a suitable spaced orientation to one another.

To mine mineral from a mineral face 126, the operator of the machine 10 initially pivots the boom 18 upwardly toward the mine roof 20. After such initial pivoting the cutter head assembly 24 is sumped inwardly to begin a cut in the face 126. After the sumping is completed the boom 18 is drawn downwardly toward the mine floor 22 until the shear cut of the face 126 is complete. During the sumping and shearing phase it is important that the mined mineral be conveyed rearwardly of the face 126 for if the mineral is not quickly removed the efficiency of the cutter head assembly 24 is greatly reduced and, additionally, an inordinate amount of undesirable mineral fines is produced.

To aid in the conveying of mined mineral rearwardly from the face 126 the width of the cutter chain 76 is substantially equal to the width of the conveying means 30 and, additionally, the cutter chain 76 and conveying means 30 are substantially symmetrical about the longitudinal centerline of machine 10. With such an arrangement, as the cutter head assembly 24 is lowered during the shear cut, a cooperation between the bottom reach of the cutter chain 76 and the conveying means 30 develops because the bottom reach of the cutter chain 76 and the conveying means 30 are progressing in the same direction, namely away from the face 126. Such cooperation removes mined mineral quickly from the face area because the chain 76 acts to propel or push the mined mineral directly onto the conveying means 30 at a faster rate than if the only way to direct the mined minerals to the conveying means 30 were by means of the oscillatory gathering arms 28 and the scrolls 1 18. The cutter chain 76 may be of any suitable construction which incorporates hingedly connected links and is adapted to be driven by a central drive sprocket, as

for example that cutter chain shown and illustrated in U.S. Pat. application No. 786,649, filed Dec. 24, 1968 and assigned to the same assignee as is this invention.

An elongated hydraulic fluid tube 128 which has an outer diameter thereof less than the insider diameter of shaft 70 is mounted within shaft 70 in spaced relationship with the inner diameter thereof. As shown the axial ends of tube 128 are symmetrical with respect to the centerline of machine and in approximate radial alignment with the locknuts 104 which are positioned around the outer periphery of shaft 70 as hereinbefore described. Pilot-operated check valves 130 are received within respective end portions of shaft 70 and have the inlet connections thereof secured to the axial ends of tube 128 and the outlet connections thereof secured to the head ends of hydraulically extensible cylinder assemblies 132 which are additionally partially received within shaft 70. The outer periphery of valves 130 and assemblies 132 is less than and spaced from the inner periphery of shaft 70.

Assembly 132 can be of any suitable construction and as shown comprises: a hydraulic cylinder 134 which has the outer ends thereof (outer being defined as away from the centerline of machine 10 along the axial centerline of shaft 70) sealingly secured to the end cap of shaft 70; a piston head 136 which is reciprocably received within cylinder 134; and a piston rod 138 which has the inner end thereof firmly secured to piston head 136 and the outer end thereof secured to the end cutter cap 124 at the inner surface thereof.

With such a construction of assembly 132 as hereinabove described, to extend the rotary drum cutting-head extensions 80 from an unextended position thereof, hydraulic pressure fluid is initially supplied as described hereinafter to tube 128. The pressure fluid continues flowing in tube 128 until such time that a sufiicient pressure develops therein to cause check valves 130 to open. The pressure fluid then flows through valves 130 into cylinders 34 thereby urging piston heads 136 forwardly from an unextended position thereof. Because the piston heads 136 are directly connected to respective cutting heads 78 by means of the piston rod 138, such a forward move of piston heads 136 causes the cutting heads 78 to extend outwardly from the unextended positions thereof. Any hydraulic fluid in the portion of cylinders 134 outward of the piston head 136 is expelled from cylinders 134 by means of a plurality of ports 140 located at the outer end of cylinders 134. Such fluid is expelled through ports 140 into an annular passageway 142 which is defined by the annular space between the outer peripheries of cylinders 134, check valves 130 and the fluid tube 128 and the inner periphery of shaft 70. Fluid flowing through passageway 142 is expelled therefrom through casing retraction passageways as hereinafter described.

When the head extensions 78 are extended to a desired position, the pressure fluid supply to tube 128 is discontinued thereby resulting in valves 130 closing and, because the fluid in cylinders 134 intermediate valves 130 and piston heads 136 is incompressible, the head extensions 78 are locked into position with respect to any inward movement thereof.

To retract the rotary drum cutting-head extension 78 from an extended position thereof hydraulic fluid is supplied to passageway 142. Fluid initially flows through passageway 142 into ports 140 and continues to flow until such time that a sufficient pressure develops within passageway 142 to open the valves 130 by means of applying pressure to such valves 78 through external portals 144 thereof. When such values 130 are open the pressure buildup within cylinder 134 outward to piston head 136 urges the piston head 136 inward from the extended position thereof. Because the piston heads 136 are directly connected to respective cutting heads 78 by means of piston rods 133, such an inward movement of piston heads 136 causes the cutting heads to retract inwardly from the extended position thereof.

Hydraulic pressure fluid is selectively supplied to tube 128 or passageway 142 by any suitable means for example such means as fully illustrated and described in U.S. Pat. application No. 786,648, filed Dec. 24, 1969, and assigned to the same assignee as is this invention in which hydraulic pressure fluid flows from any suitable external fluid reservoir (tank 149) to passageways generally indicated at 146 or 148, to, respectively, extend or retract the rotary drum cutting-head extensions in a manner hereinbefore described. The passageways 146 and 148 are located in the gear casing extension portions 72 in a manner fully illustrated in the abovementioned application No. 786,648.

It is to be noted that cutter chains designed according to the principles of this invention can be used on mining machines of a type other than the rotary drum mining machine 10 hereinbefore described, for example one or two of such chains can replace the multiple cutter chains of a ripper bar miner of the type illustrated in U.S. Pat. No. 2,650,813.

Preferred embodiments of the mining machine of this invention having been hereinbefore described and herewith illustrated it is to be realized that variations in the specific structure are envisioned and contemplated as further embodiments of the principles of this invention. It is therefore respectfully requested that this invention be interpreted as broadly as possible and limited only by the scope of the appended claims.

I claim:

1. A mining machine cutting-structure comprising: a support member; an elongated mining head member mounted at a forward end of said support member for powered rotation about a longitudinal axis of said head member; said head member having cutting means consisting of a single, centrally located, cutter-supporting chain and cutter-supporting rotary elements extending outwardly from the sides of said chain and beyond the sides of said support member, respectively; and the cutters on said rotary elements and on said chain being movable in orbits closely adjacent to each other along said axis the full length of said head member to cut clearance for said head member during movement of said head member into a bedded deposit of material to be mined.

2. A mining machine cutting-structure as set forth in claim 1 wherein said chain is supported for movement through an elongated orbital path and driven gear means are operatively supported by said support member within said orbital path to drive said head member for said powered operation.

3. A mining machine cutter structure as set forth in claim 1 additionally comprising, a head shaft extending along said longitudinal axis and drivingly connected to said chain and said rotary elements; driven gear means operatively supported by said support member to drive said head shaft; and said gear means comprising two gear trains applying equal rotational forces to said head shafl at locations equally spaced on opposite sides of the longitudinal centerline of said support member.

4. A mining machine cutter structure as set forth in claim 2 additionally comprising: a head shaft extending along said longitudinal axis and drivingly connected to said chain and said rotary elements; said head shaft being driven by said gear means; and said gear means comprising two gear trains applying equal rotational forces to said head shaft at locating equally spaced and opposite sides of the longitudinal centerline of said support member.

5. A mining machine as set forth in claim 3 wherein said chain is centrally driven and centrally supported by a single drive sprocket carried and driven by said head shaft intermediate said cutter-supporting rotary elements, and adjacent end portions of said rotary elements supportingly engage edge portions of said chain.

6. A mining machine cutter structure as set forth in claim 3 wherein each of said gear trains have at least three speedreduction steps.

7. A mining machine cutting-structure as set forth in claim 1 wherein said chain is centrally driven and centrally supported by a single drive sprocket intermediate between said cuttersupporting rotary elements, and adjacent end portions of said rotary elements supportingly engage edge portions of said chain.

8. A mining machine cutting-structure as set forth in claim 1 wherein said cutter supporting rotary elements are driven by a hollow head shaft extending along said longitudinal axis and additionally comprise: axially movable cutter-supporting extensions slidably mounted on axial end portions of said hollow head shaft said head shaft being coaxial with respect to said longitudinal axis of said head member; and a pair of axially spaced extensible hydraulic cylinders carried with each end portion of said head shaft and connected to the respective extensions for moving said extensions.

9. A mining machine cutting-structure as set forth in claim 8 wherein each of said cylinders communicates with a controlled source of pressure fluid through a pilot-operated check valve.

10. A mining machine cutting-structure as set forth in claim 8 wherein a liquid-conducting tube coaxially mounted within said head shaft and radially spaced inwardly from the interior surface of said head shaft forms an internal and an external liquid-conducting passageway, said internal passageway communicates with the head ends of said cylinders and said external passageway communicates with the rod ends of said cylinders and said source of pressure fluid selectively communicates with one of said passageways and the other of said passageways simultaneously communicates with a nonpressurized liquid-containing reservoir.

1 l. A mining machine cutting-structure as set forth in claim 1 wherein the width of said chain is greater than one half the axial length of one of said cutter supporting elements.

12. A mining machine cutting-structure as set forth in claim 1 wherein said cutter-carrying-supporting elements comprise a pair of generally cylindrical rotary drums each having a conveyor scroll mounted thereon, and each conveyor scroll having a discharge opening at the axially innermost end thereof to permit at least a portion of mined material to be discharged substantially directly onto a respective side portion of said cutter chain.

13. A mining machine comprising: a mobile frame member a gathering head mechanism extending forwardly from one portion of said frame member; an elongated orbitally movable flight conveyor having upper and lower runs supported by said frame member and said head mechanism with a forward portion of said conveyor being cooperable with said head mechanism to permit the upper run of said conveyor to move rearwardly thereof; an elongated boom pivotally connected to said frame and extending forwardly thereof to pennit movement of said boom through a vertical are; a mining head rotatably carried at the forward end of said boom and extending transversely thereof; said mining head having a central endless cutter supporting and conveying means movable through an elongated orbit with respect to said boom, said cutter supporting and conveying means having upper and lower runs with respect to said boom with the lower run thereof moving rearwardly thereof; and said cutter supporting and conveying means having a plurality of adjacent members each of a width at least substantially equal to the width of said flight conveyor and with at least the rearward portion of the orbit thereof overlying the forward portion of the orbit of said conveyor.

14. A mining machine as specified in claim 13 wherein said cutter supporting and conveying means has said lower run overlying said gathering head at least one half the length of said gathering head measured longitudinally of the machine.

15. A mining machine as specified in claim 13 wherein the central axis of orbits of said flight conveyor and said cutter supporting and conveying means lie in a common vertical plane.

16. A mining machine as specified in claim 13 wherein the central axis of orbits of said flight conveyor and said cutter supporting and conveying means comprises a single chain and said adjacent members are respective ones of links of said chain.

17. A mining machine as specified in claim 13 wherein the rate of orbital movement of said flight conveyor is less than the rate of orbital movement of said cutter supporting and conveying means.

Claims

3. A mining machine cutter structure as set forth in claim 1 additionally comprising, a head shaft extending along said longitudinal axis and drivingly connected to said chain and said rotary elements; driven gear means operatively supported by said support member to drive said head shaft; and said gear means comprising two gear trains applying equal rotational forces to said head shaft at locations equally spaced on opposite sides of the longitudinal centerline of said support member.

6. A mining machine cutter structure as set forth in claim 3 wherein each of said gear trains have at least three speed-reduction steps.

7. A mining machine cutting-structure as set forth in claim 1 wherein said chain is centrally driven and centrally supported by a single drive sprocket intermediate between said cutter-supporting rotary elements, and adjacent end portions of said rotary elements supportingly engage edge portions of said chain.

11. A mining machine cutting-structure as set forth in claim 1 wherein the width of said chain is greater than one half the axial length of one of said cutter supporting elements.

13. A mining machine comprising: a mobile frame member a gathering head mechanism extending forwardly from one portion of said frame member; an elongated orbitally movable flight conveyor having upper and lower runs supported by said frame member and said head mechanism with a forward portion of said conveyor being cooperable with said head mechanism to permit the upper run of said conveyor to move rearwardly thereof; an elongated boom pivotally connected to said frame and extending forwardly thereof to permit movement of said boom through a vertical arc; a mining head rotatably carried at the forward end of said boom and extending transversely thereof; said mining head having a central endless cutter supporting and conveying means movable through an elongated orbit with respect to said boom, said cutter supporting and conveying means having upper and lower runs with respect to said boom with the lower run thereof moving rearwardly thereof; and said cutter supporting and conveying means having a plurality of adjacent members each of a width at least substantially equal to the width of said flight conveyor and with at least the rearward portion of the orbit thereof overlying the forward portion of the orbit of said conveyor.