Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3726562 A
Publication typeGrant
Publication dateApr 10, 1973
Filing dateApr 7, 1971
Priority dateApr 7, 1971
Publication numberUS 3726562 A, US 3726562A, US-A-3726562, US3726562 A, US3726562A
InventorsWharton G
Original AssigneeWharton G
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Mining machine including means for utilizing vacuum at working face and methods of operation thereof
US 3726562 A
Abstract
Apparatus for mining coal or other mineable material, of the continuous or mobile type, having a cutter head operative to engage and work the mine face, and having associated therewith one or more vacuum lines or air suction conduits which are critically oriented relative to the working face and the cutter head. A main vacuum line may be employed to pneumatically convey the freshly mined, lump size coal to ground level, or to a subsurface grinder, or other site remote from the mine face. One or more auxillary vacuum lines may be positioned to terminate adjacent the mine roof and floor, and in close proximity to the working face, to scavenge methane, carbon dioxide, carbon monoxide and coal dust.
Images(2)
Previous page
Next page
Description  (OCR text may contain errors)

United States Patent 1 [111 3,726,562 Wharton, III 5] Apr. 10, 1973 [5 MINING MACHINE INCLUDING 3,362,752 1/1968 MEANS FOR UTILIZING VACUUM AT WORKING FACE AND METHODS OF OPERATION THEREOF Densmore ..299/18 Primary Examiner-Ernest R. Purser Attorney-Sidney W. Russell [5 7] ABSTRACT Apparatus for mining coal or other mineable material, of the continuous or mobile type, having a cutter head operative to engage and work the mine face, and having associated therewith one or more vacuum lines or air suction conduits which are critically oriented relative to the working face and the cutter head. A main vacuum line may be employed to pneumatically convey the freshly mined, lump size coal to ground level, or to a subsurface grinder, or other site remote from the mine face. One or more auxillary vacuum lines may be positioned to terminate adjacent the mine roof and floor, and in close proximity to the working face,

to scavenge methane, carbon dioxide, carbon monoxide and coal dust.

6 Claims, 4 Drawing Figures PATENTEB APR 1 0197s sum 2 0F 2 INVENTOR W GEORGE C.WHARTON,I1I

ATTORNEY MINING MACHINE INCLUDING MEANS FOR UTILIZING VACUUM AT WORKING FACE AND METHODS OF OPERATION THEREOF BACKGROUND OF INVENTION AND PRIOR ART This invention relates to the art of mobile coal mining machines. More particularly, the invention is addressed to mining apparatus having, in operative combination therewith, means to apply vacuum to selected areas adjacent to or in the vicinity of the working face whereby the atmosphere within the tunnel may be used as a motive fluid for a variety of useful functions including the transfer of freshly mined lump size coal away from the working face, for example, to ground level, and the concomitant removal of methane and coal dust.

In coal mining operations, the problems of methane, CO CO and coal dust accumulation have always been serious. The explosion and health hazards are obvious. Naturally, there have been many prior art proposals to deal with these problems. The utilization of vacuum or air suction systems within a coal mine is, broadly speaking, not new in the art. For example, Ziemba et al. U.S. Pat. No. 3,387,889, discloses an air pump acting through a forwardly mounted duct to suckup and remove coal dust from the floor of the tunnel in the vicinity of the cutter heads. The patentees system is incapable of conveying the coal cuttings per se, which are of relatively large size, say of the order of one to two inches on the average, as resulting from the disintegrating action of the typical cutter head. Also, the location of the suction duct adjacent the mine floor is ineffectually suited for methane removal, inasmuch as methane, being lighter than air, tends to accumulate is higher concentrations at the mine roof.

Densmore U.S. Pat. No. 3,225,678 teaches a similar arrangement. White U.S. Pat. No. 2,100,178 proposes to alleviate build-up of coal dust by enclosing a mechanical conveyor with a vacuum hood. Reeder U.S. Pat. No. 2,375,689 discloses the use of a grinding wheel which pulverizes the coat at the face of the vein to a finely divided state. The grinding wheel is enclosed by a hood to which air suction is applied and the finely pulverized coal dust is conveyed through a conduit to storage area remote from the working face. The disadvantages of such arrangement are at least two-fold. It results in the generation of excessive and hazardous quantities of coal dust at the face, and the mine operator must limit himself to production of pulverized coal only, as distinguished from the generally more desirable lump size coal. None of these conventional schemes have been completely successful even for their limited purposes. And, as far as I am aware, the prior art has not revealed a means for pneumatically conveying lump size coal cuttings directly from the cutter head to a site remove from the mine face, nor has the prior art evolved a satisfactory means specifically designed for rapid and efficient methane, CO, and CO removal.

The aforesaid problems have been rendered all the more difficult of solution in view of recently enacted federal mine safety legislation imposing much more stringent safety standards on mine operators. Permissible concentrations of methane and dust have been drastically reduced. Ventilation requirements have been substantially increased, for example, a minimum air flow of 3,000 CFM is required at the working face.

0 tends to scatter methane and coal dust in its artificially induced travel rearward toward the nearest air outlet, as well as to dry up the mine and increase the explosion potential.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of my invention to provide a method and means for pneumatically conveying lump size coal cuttings directly from the cutter head to a site remote from the mine face, preferably to a surface located storage area.

It is another primary object of my invention to furnish a method and means for efficiently scavenging freshly liberated methane and accumulations of CO and CO from the region of the mine face and transporting same by a confined stream of air, isolated from the surrounding atmosphere, to the exterior of the mine.

A further object of my invention is to provide a method and means for removing coal dust from the immediate vicinity of the mine face and pneumatically transporting same to a local storage zone or to a ground level storage area.

Another object of my invention is to induce a sufficient magnitude of air flow, at and across the mine so that brattice cloth curtains and blowers stirring up face dust and further drying up the mine would be eliminated.

Yet another object of my invention is to provide a locally positioned coal grinding means disposed a short distance from the mine face, and desirably carried by or integral with the mining machine itself, which receives the coal cuttings carried through a main suction line and reduces the size of the cuttings to about one inch uniform or less l" X 0).

A still further object, related to that immediately preceding, is to introduce the resulting ground coal into the discharge side of an air blower and pneumatically conveying the coal, under positive pressure, to the mine surface or to a cyclone discharge onto a belt conveyor.

These and other objects and advantages of my invention will become apparent to those skilled in the art in light of the detailed description to follow.

One embodiment of my invention is directed to a mining machine, comprising in combination, a mobile cutter head support means, a cutter head extending forwardly of said support means for mine face engagement, said cutter head being operative to engage the mine face and to fracture mine material therefrom in the form of lumps having a size of from about 1 inch to about 2 inches, a vacuum shield means proximately spaced from and at least partially enclosing said cutter head, an air suction conduit connecting with said shield means, air pump means connecting with said air suction conduit, whereby ambient air entering said shield means picks up said lumps directly as they are disintegrated from the mine face by said cutter head and the lumps are pneumatically conveyed through said suction and crusher to receptacle means remote from the mine face.

Another embodiment of the invention is addressed to a mining machine comprising a mobile cutter head support means, a controllable cutter head extending forwardly of said support .means for mine face engagement, said cutter head being operative to engage the mine face and to fracture mine material therefrom, and a methane scavaging system comprising an air suction conduit having an open end positioned immediately to the rear of said cutter head and proximately spaced from the mine roof, air pump means connecting with said sir suction conduit, whereby methane freshly liberated from the mine face is immediately picked up by an ambient air stream entering said suction conduit and transported through said suction conduit to a site remote from the mine face, and into the flow of air being discharged from the mine.

A more specific embodiment of the invention relates to a combination of the immediately preceding two embodiments.

In a method aspect, the invention relates to an improvement in the art of mining coal including the step of disintegrating coal from a mine face in the form of lumps having a size of from about 1 inch to about 2 inches, which improvement comprises intercepting said lumps before the latter strike the mine floor and, without effecting any further size reduction thereof, introducing the lumps into a confined stream of air, isolated from the surrounding atmosphere, and pneumatically conveying the lumps to a locus remote from the mine face.

Another method embodiment of the invention is directed to establishing a zone of subambient air pressure in the region immediately adjacent the mine face and closely spaced from the mine roof and in open fluid communication with the surrounding atmosphere, sweeping the mine roof with a current of air passing into said zone of subambient air pressure, admixing methane freshly liberated from the mine face with said current of air, and passing the resultant mixture as a confined stream, isolated from the surrounding atmosphere, to the exterior of the mine.

Another embodiment of the invention is drawn to the removal of carbon dioxide, carbon monoxide, dust etc. on the mine floor.

DESCRIPTION OF THE DRAWINGS The structure and mode of operation of the mining machine may be more clearly understood by reference to the accompanying drawings, which illustrate a preferred embodiment of the invention, and in which:

FIG. 1 is a plan view of the mining machine of this invention;

FIG. 2 is a side elevation view of the mining machine of this invention;

FIG. 3 is an enlarged side elevation view of the cutter head-vacuum shield assembly;

FIG. 4 is an enlarged side elevation view of hydraulic cylinder-lever arm assemblies for raising and lowering the auxiliary methane and dust removal suction lines.

DESCRIPTION OF THE INVENTION With reference now to FIGS. 1 and 2, numeral 10 denotes, in general, a continuous or mobile low silhouette mining machine or coal cutting machine. As illustrated, it is of the so-called trackless type, movement thereof being effected by ground engaging wheels 11, although of course this could as well be a track type machine. Except for my inventive modifications thereof, the mining machine is otherwise conventional and well-known in the art and, therefore, a detailed discussion thereof is unnecessary. Extending forwardly of the machine is a pivotal arm or boom 12 upon which, at the forward or outboard end thereof, is rotatably mounted a rotary cutting head 13. Cutter 13 is, in this particular embodiment, a conical or so-called burster type of cutter head. The cutter head size or diameter may be varied to suit certain conditions. Arm 12 is operably connected to a cutter head power transmission and positioning mechanism 14, here illustrated diagrammatically. The mechanism 14 is pivoted at pivot point 15 to permit rotation of arm 12 in a vertical plane. Hydraulic cylinders 16 are operative to rotate arm 12 in a horizontal plane. Cutter 13 is thus enabled to traverse the mine face both horizontally and vertically. The apparatus thus far described is conventional in the art.

My inventive improvements thereover will now be described:

A. Coal Conveying System As indicated in FIGS. 1 and 2, cutter head 13 is operably engaging the working face 17 whereby to fracture or disintegrate coal therefrom in the form of lumps having a size, typically, of from about 1 inch to about 2 inches. As best shown in FIG. 3, a vacuum shield or shroud means 18 at least partially encloses, and preferably encloses at least the major portion of, cutter head 13. The vacuum shield means 18 is desirably constructed of a heavy duty resilient material, such as rubber or plastic, in order that it will flexibly deform to conform with the contour of the working face 17 as arm 12 sweeps through a horizontal arc and/or through a vertical arc. The outboard ends of vacuum shield 18, which are most closely adjacent to working face 17, do not effect a tight seal therewith in order to allow a relatively free entrance for the inflow of air. If desired, the outboard edge of shield 18 may be provided with notches, serrations, orifices or the like, to assure a minimum pressure drop. It will be observed that shield 18 serves two important functions. The first is to define a restricted zone of vacuum immediately about cutter head 13. The second is to intercept substantially all of the freshly mined coal lumps before the latter strike the mine floor and to channel the lumps directly into main air suction conduit 19.

The main air suction conduit 19 connects with shield 18 and thence extends rearwardly of the mining machine to connect with a combined air pump and grinder unit 20 carried by the mining machine. The unit 20 preferably comprises cyclone separator means on the suction side of the air pump, and coal grinding means receiving the resulting disengaged lumps of coal, the grinding means being adapted to reduce the size of the coal lumps to about 1 inch uniform or less. Following size reduction, the coal particles are reintroduced by air lock means into conveying air on the pressure or discharge side of the air pump. Units of this type are known in the art and are available commercially, for example, one suitable design is the Airveyor transfer unit manufactured by Fuller Company. The reduced size coal particles are then pneumatically conveyed under super-atmospheric pressure through the discharge conduit 21 all the way out of the mine to a storage area located at ground level, or to a belt loading point where coal is separated from the air by a cyclone system.

Conduits 19 and 21 are formed of flexible hose material, such as plastic or rubber corrugated hose with or without wire reinforcing and desirably are of light weight construction. For most applications, a hose diameter of about 8 inches will be suitable for the main suction and discharge conduits. It is contemplated that, as the mining machine advances additional sections of conduit 21 will be laid in at periodic intervals, say, every 20 to 40 feet.

B. Methane Removal System With reference to FIG. 4, an enlarged hood member 22 is carried by a pivoted support arm 23 which, in turn, is pivotally connected to arm 12 at pivot point 24. A hydraulic cylinder 25 is pivotally connected to support arm 23 at pivot point 26 and to arm 12 at pivot point 27. An auxiliary air suction conduit 28 connects hood 22 with main conduit 19 at tee 29. Cylinder 25 is powered from the main hydraulic system and, acting through arm 23, is operative to vary the elevation of hood 22 relative to arm 12 so that hood 22 is maintained in a constant proximately spaced relationship with mine roof 30 regardless of the elevation angle of arm 12. Hood 22 may be spaced a distance of from about one-fourth inch to about 1 inch below roof 30. The invention further contemplates the use of automatic control means to regulate cylinder 25 in order to maintain such constant spacing. The air suction conduit 28 can be a flexible hose similar to main conduit 19 but, in general, will be of smaller diameter, for example, 4 inches.

Methane gas which is freshly liberated from the working face will tend to accumulate at roof 30. The hood 22 and suction conduit 28 act to establish a zone of subambient air pressure in the region immediately adjacent and to the rear of the mine face 17 and closely spaced from the mine roof 30. This, in turn, causes a current or stream of air to sweep the mine roof, picking up and admixing with the liberated methane, the resultant mixture then being passed through conduit 28, thence through main conduit 19, and finally discharged to the exterior of the mine through conduit 21.

C. Dust Removal System Again with reference to FIG. 4, an enlarged hood member 32 is carried by a pivoted support arm 33 which, in turn, is pivotally connected to arm 12 at pivot point 34. A hydraulic cylinder 35 is pivotally connected to support arm 33 at pivot point 36 and to arm 12 at pivot point 37. An air suction conduit 38 connects hood 32 with main conduit 19 at tee 29. Cylinder 35 is likewise powered from the main hydraulic system and, acting through arm 33, is operative to vary elevation of hood 32 relative to arm 12 whereby the hood 32 is maintained in a constant proximately spaced relationship with mine floor 40 regardless of the elevation angle of arm 12. The hood 32 may be spaced a distance of from about one-fourth inch to about 1 inch above floor 40. Automatic control means may be provided to maintain such constant spacing. The air suction conduit 38 can be a flexible hose similar to main conduit 19, but, in general, will be of smaller diameter, for example, 4 inches. The hood 32, in conjunction with conduit 38, functions to establish a zone of subambient air pressure in the region immediately below and to the rear of cutter head 13 whereby ambient air entering hood 32 sucks up coal dust, fines, carbon dioxide and carbon monoxide, and pneumatically conveys them through conduits 38, 19 and 21, ultimately to be deposited in a storage area at ground level.

With regard to the vacuum removal system which has been described in the foregoing, it is contemplated that air removal be accomplished at a rate of about 3,000 CFM. The latter is replaced in a continuing inward flow by 3,000 CFM from the mine forced ventilation supply. Further, via the present system, the mine air can be continuously freshened and replaced, even during a breakdown and repair, simply by permitting the air suction mechanism to continue to run.

Numerous other embodiments and variations of the basic invention described herein above will suggest themselves to the routineer. To highlight but a few such variants, all of which are encompassed by the appended claims except as otherwise specifically excluded, 1 point to the following:

1. The air pump may be mounted on a vehicle separate from the mining machine proper or it may be located at a fixed station within the mine to be moved forward from time to time, or at ground level;

2. The coal grinder may be dispensed with, in which case the coal lumps as delivered to storage will be of random size within the range of from about 1 inch to about 2 inches;

3. In a less preferred embodiment, the freshly mined coal may be loaded into a local following shuttle car or hopper car, rather than being air lifted all the way to ground level. Even here, however, my invention does eliminate the usual swinging boom, mechanical flight conveyor or loader, with its gathering arms, along with the dust generated by such apparatus, and it also affords means for continuous vacuum removal of methanes, dust, CO, and CO. Further, the sudden forward and backward lunges of the conventional loader are eliminated.

4. My invention is readily adaptable to other forms of cutter heads, such as drum cutters, endless chain cutters, multiple such units, and the like. The necessary modification of the cutter head vacuum shield will be a matter of mechanical design within the skill of the ar tisan.

5. Although I have described my apparatus in connection with the mining of coal, that being its primary and preferred utility, it is apparent that my invention may be utilized to mine any mineral material, for example, salt, lead, zinc, copper, asbestos, etc., limited only by the hardness of the matrix involved.

By way of summary, my invention offers a number of substantial advantages over systems of the prior art. Pneumatic transport of lump size coal cuttings directly from the cutter head to a remote receptacle means eliminates the conventional conveyors and mechanical loaders along with the additional dust generated thereby. In the embodiment where the coal is air-lifted to ground level storage, it further eliminates the conventional shuttle car which, as well recognized by those skilled in the art, entail heavy capital and labor costs. The invention provides continuous and efficient removal of methane gas CO and CO from the region where these tend to accumulate in highest concentrations. It further provides continuous and efficient removal of coal dust from the region where it tends to build up in greater quantities. if affords the mine operator great flexibility in selecting the size of coal which he wishes to market. And most importantly, in view of the more severe ventilation requirements imposed by recent mine safety legislation, the invention affords a facile and economic means for developing and maintaining a localized high volume air flow across the working face, the mine roof and mine floor, and exhausting same to a safe location, without scattering dust and gas. This has the ancillary advantage of reducing the load requirements of the main shaft ventilating fans and, in some cases, such fans may be altogether eliminated or at least reduced in number and/or size. Further, fresh air will flow into the entire working face area of the place, ventilating it naturally and without a dust raising wind which is the case today by forced air induction behind a line curtain along the rib.

Lastly, it is believed that a skilled operator will be able to mine out a parting as he works down from the top of the seam and with some remotely controlled current of air passing into said second zone, admixing for mine face engagement, said cutter head being operative to engage the mine face and to fracture mine material therefrom in the form of lumps, a vacuum shield means proximately spaced from and substanvalves, disposed rearwardly in the discharge line,

deposit this parting or separation in the seam onto a separate belt, or into a worked out area of the mine itself.

I claim as my invention:

1. in the mining of coal including the step of disintegrating coal accompanied by the liberation of methane from the mine face, the improvement which comprises establishing a zone of subambient air pressure in the region immediately adjacent the mine face and closely spaced from the mine roof and in open fluid communication with the surrounding atmosphere, sweeping the mine roof with a current of air passing into said zone, admixing said liberated methane therewith, removing said methane by application of suction at a point adjacent the mine roof, maintaining a second zone of subambient air pressure in the region immediately adjacent the mine face and closely spaced from and in open fluid communication with the surrounding atmosphere, sweeping the mine floor with a tially enclosing said cutter head and also substantially contacting said mine face, a first air suction conduit connecting with said shield means, air pump means connecting with an air suction whereby ambient air entering said shield means picks up said lumps directly as they are disintegrated from the mine face by said cutter head and the lumps are pneumatically conveyed through said first suction conduit, receptacle means to receive said lumps remote from the mine face, an upper methane scavenging system comprising a second air suction conduit having an open end positioned immediately to the rear of said cutter head and proximately spaced from the mine roof, whereby methane freshly liberated from the mine face is immediately picked up by an ambient air stream entering said second suction conduit and transported through said second conduit to a site remote from the mine face, and a lower third air suction conduit having an open end positioned immediately to the rear of said cutter head and proximately spaced from the mine floor, whereby ambient air entering said third conduit picks up dust and remaining noxious fumes and pneumatically conveys the latter through said third conduit to a site remote from the mine face.

3. The apparatus of claim 2 wherein said cutter in cludes means adapted to fracture said mine material in lumps of from about 1 inch to about 2 inches in size.

4. The apparatus of claim 3 wherein said machine includes receptacle means remote from the mine face and said receptacle means includes grinding means adapted to reduce the size of said lump to less than 1 inch.

5. The apparatus of claim 4 wherein said grinding means is carried by said moble cutter head support means.

6. The apparatus of claim 2 further characterized in the provision of means to vary the elevations of said second and third air suction conduits.

I. I l k

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US24004 *May 17, 1859 Appabatus for cooling beer
US2375689 *Dec 27, 1943May 8, 1945David H ReederApparatus for mining coal
US3005627 *Aug 5, 1958Oct 24, 1961William TinlinTunneling machine having suction exhaust means
US3260548 *Mar 11, 1965Jul 12, 1966Consolidation Coal CoMethod and apparatus for continuously mining and transporting coal
US3362752 *Aug 17, 1965Jan 9, 1968Joy Mfg CoMining apparatus and method
US3387889 *Nov 3, 1966Jun 11, 1968Anthony J. ZiembaCoal dust removal and conveyance system
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3856357 *Aug 22, 1973Dec 24, 1974Wharton GCombination rotor-box cutter mining machine and method of mining
US3897110 *Jun 18, 1974Jul 29, 1975Coal Industry Patents LtdMining equipment
US3993355 *Nov 17, 1975Nov 23, 1976Cunningham Kelly GMining machine having pneumatic conveyance and cutter head floor driven about anchor
US4548442 *Dec 6, 1983Oct 22, 1985The Robbins CompanyMobile mining machine and method
US5112111 *Dec 10, 1990May 12, 1992Addington Resources, Inc.Apparatus and method for continuous mining
US5192115 *May 28, 1991Mar 9, 1993The Robbins CompanyTramming mobile mining machine
US5192116 *May 28, 1991Mar 9, 1993The Robbins CompanyGantry-type mobile mining machine
US5234257 *Oct 11, 1991Aug 10, 1993The Robbins CompanyMobile mining machine having tilted swing axis and method
US5261729 *Nov 20, 1991Nov 16, 1993Mining Technologies, Inc.Apparatus for continuous mining
US5364171 *Oct 21, 1993Nov 15, 1994Mining Technologies, Inc.Apparatus and method for continuous mining
US5913372 *Mar 13, 1998Jun 22, 1999M-L, L.L.C.Oil and gas well cuttings disposal system with continuous vacuum operation for sequentially filling disposal tanks
US7637038 *Mar 15, 2006Dec 29, 2009Bauer Maschinen GmbhFoundation construction device for making trenches in soil
US7798247Nov 9, 2005Sep 21, 2010Sandvik Mining And Construction OyArrangement for sucking dust
CN101099025BNov 9, 2005Nov 3, 2010山特维克矿山工程机械有限公司Dust suction method relating to drilling arrangement and drilling arrangement
CN101915107A *Sep 2, 2010Dec 15, 2010郑州煤矿机械集团股份有限公司Method for arranging coal mine large-mining-height working surface equipment
CN102080555A *Jan 26, 2011Jun 1, 2011郑州煤矿机械集团股份有限公司Double-stage side guard device applicable to transition support of large coal mining height fully-mechanized face
CN102080556A *Jan 26, 2011Jun 1, 2011郑州煤矿机械集团股份有限公司Transitional bracket for mechanized large mining height working face of coal
CN102080557A *Jan 26, 2011Jun 1, 2011郑州煤矿机械集团股份有限公司Split type side guard device applicable for transition support of large coal mining height fully-mechanized face
CN102108875A *Jan 26, 2011Jun 29, 2011郑州煤矿机械集团股份有限公司Single-stage side protective device applicable to high working surface transition support in mechanized mining and deep mining of coal
CN102116155A *Jan 26, 2011Jul 6, 2011郑州煤矿机械集团股份有限公司Method for supporting and coalmining in transition section of large-mining-height working face
WO1985002653A1 *Nov 15, 1984Jun 20, 1985Robbins CoMobile mining machine and method
WO1999046475A1 *Nov 23, 1998Sep 16, 1999Dietzen Gary HOil and gas well cuttings disposal system with continuous vacuum operation for sequentially filling disposal tanks
WO2006051168A1 *Nov 9, 2005May 18, 2006Sandvik Tamrock OyArrangement for sucking dust
Classifications
U.S. Classification299/12, 299/18, 299/67, 299/75
International ClassificationE21C41/00, E21C27/20, E21C35/22, E21C35/00, E21C27/00, E21C41/18
Cooperative ClassificationE21C35/223, E21C27/20
European ClassificationE21C27/20, E21C35/22D