US3617093A

US3617093A - Mining machine drum cutter extension means

Info

Publication number: US3617093A
Application number: US72239A
Authority: US
Inventors: Glenn A Daily
Original assignee: Individual
Current assignee: Joy Manufacturing Co; Citibank NA; Joy Technologies Inc
Priority date: 1970-09-14
Filing date: 1970-09-14
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02

Abstract

A mining and loading apparatus and more particularly a continuous-mining apparatus having improved drum cutter extension means for dislodging mineral from a solid mine vein. This drum cutter incorporates a double passageway head shaft for activating hydraulic cylinders to extend and retract extensible drum portions of the drum cutter.

Description

United States Patent Inventor Glenn A. Daily RD. 1, Utica, Pa. 16362 Appl. No. 72,239 7 Filed Sept. 14, 1970 Patented Nov. 2, 1971 Continuation of application Ser. No.

7 86,648 Dec. 24, 1968, now abandoned.

MINING MACHINE DRUM CUTTER EXTENSION MEANS 13 Claims, 5 Drawing Figs.

[1.8. CI 299/80, 299/67, 299/87 Int. Cl ..E21c 27/24, E2lc 35/20 Field of Search 299/64, 67, 75, 80

[56] References Cited UNITED STATES PATENTS 3,305,273 2/1967 Kilbourne 299/80 X FOREIGN PATENTS 889,803 2/1962 Great Britain 299/80 182,641 8/1966 U.S.S.R........ 299/80 Primary Examiner-Ernest R. Purser Attorney-E. Wallace Breisch ABSTRACT: A mining and loading apparatus and more particularly a continuous-mining apparatus having improved drum cutter extension means for dislodging mineral from a solid mine vein. This drum cutter incorporates a double passageway head shaft for activating hydraulic cylinders to extend and retract extensible drum portions ofthe drum cutter.

PATENTEDunv 2 I97l I SHEET 10F 3 IN VEN TOR 4. DAILY PATENTEUun v 2 l9?! SHEEI 2 UF 3 IN VENTOR.

GLENN A. DAILY PAIENTEMnv 2 ran SHEET 3 or 3 MINING MACHINE DRUM CUTTER EXTENSION MEANS This application is a continuation of application, Ser. No. 786,648, filed Dec. 24, 1968 and now abandoned.

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 the 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 has end portions thereof which can be selectively extended or retracted to, respectively, dislodge mineral from the ribs and corners 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, an improved structure and hydraulic circuit 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. I is a perspective view of a mining machine embodying the principles of this invention;

FIG. 2 is an enlarged view, partly in section, taken on line 2-2 of FIG. 1 and showing a main gear casing and a portion of the cutterhead assembly embodying the principles of this invention;

FIG. 3 is an enlarged view, partly in section of a cutterhead assembly embodying the principles of this invention;

FIG. 4 is an enlarged detail view of hydraulic pressure fluid supply passageways and sealing means of this invention; and

FIG. 5 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, with which an outboard oil seal and oil supply means of this invention is associated, may assume various forms but for illustrative purposes, herein comprises a crawler base 14 carrying a frame I6 on which a forwardly extending mining boom 18 is pivotably mounted at the forward end of frame l6to swing up and down between a mine roof and a mine floor. 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 a well-known conveying means 30 of the mining machine 10. Conventional fluid jacks (not shown) serve to swing the boom 18 in a vertical plane about the pivot axis thereof and tilt the loading head 26 about the horizontal axis thereof. The fluid jacks have one end thereof secured to the forward end of frame l6 and have the other ends thereof secured to respective rearward ends of boom 18 and loading heads 26.

The cutting head assembly 24 is driven in any suitable manner from motors 36, which are suitably rigidly secured by brackets 38 to boom 18. Such a driving arrangement is shown and illustrated in U.S. Pat. application, Ser. No. 786,650, filed Dec. 24, I968, assigned to the same assignee as is this invention.

The drive from motors 36 rotatably drives a cutting head assembly drive shaft 70. Head drive shaft 70 extends transversely of the longitudinal axis of mining machine and is captively and 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 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.

As hereinafter described in detail head drive 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 7 4 taken at the forward end thereof; hollow cylindrical rotary drum cutting heads 78 which extend outwardly from respective sides of portion 74; and hollow cylindrical rotary drum cutting head extension 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. 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 motion reversing 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 easing 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.

Outwardly adjacent to spacer sleeves 96 and keepers 98, internally splined rotary drum cutting head driving sleeves I00 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 10) are rotatably supported by roller bearings 102. Bearings 102 are fixedly secured about the outer periphery of casing extension portions 72 adjacent the inner ends thereof.

Outwardly adjacent to sleeves 100, lock nuts 104 are threadably received on shaft 70. When lock nuts I04 are positioned around shaft 70 and tightened into bearing against sleeves 100 at the outer surface thereof: engaging sleeves I00;

spacer sleeves

90, 92 and 96, roller bearing 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 lock nuts I04 transferring thrust from shaft 70 through the sleeves I00 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 ends thereof and a reduced diameter portion thereof forms a chain end supporting seat I08 which extends axially from flange 106 toward the centerline of machine 10. Further description of seats I08 and the purpose therefor is shown and illustrated in the hereinbefore mentioned U.S. Pat. application Ser. No. 786,650.

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 lntemally splined rotary drum cutting head extension sleeves 112 project radially inwardly from the inner periphery of head extensions 80 and are located outwardly adjacent the inner ends thereof. Sleeves 112 have the radially innermost surfaces thereof in splined engagement with shaft 70 such that head extensions 80 are rotatably driven from shafl 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 innerrnost surfaces thereof in sliding relationship with the outer periphery ofshaft 70.

Shaft 70 is splined along the outer surfaces thereof from a point intermediate the axial ends thereof inwardly to the lock nuts 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 115 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. 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. But holder 120 and cutter bits 122 are secured to caps 124 in a suitable spaced orientation to one another.

An elongated hydraulic fluid conducting tube 128 which has an outer diameter thereof less than the inside 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 10 and in approximate radial alignment with the lock nuts 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 suitably 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 sufficient pressure develops therein to cause check valves to open. The pressure fluid then flows through valves 130 into cylinders 134 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 to 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 ofa plurality of ports 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 head 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 valves 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 138, such an inward movement of piston heads 136 causes the cutting heads extensions 78 to retract inwardly from the extended position thereof.

Hydraulic pressure fluid is selectively supplied to the internal passageway of tube 128 or external passageway 142 through respective gear casing extension portion 72 right hand and left hand respectively, passageways generally indicated at 146 and 148. As viewed in FIG. 2, passageway 146 is located within the left gear casing extension portion 72 and passageway 148 is within the right extension portion 72.

Passageways

146 and 148 extend radially inwardly from the rearward ends of extension portions 72 to a point intermediate the inner and outer diameter of portions 72 whereat

passageways

146 and 148 turn approximately 90 and extend outwardly (i.e., away from the centerline of machine 10 parallel to the axis of shaft 70) to a point inwardly adjacent the outer ends of extensions 72. From such a

point passageways

146 and 148 extend radially inwardly and open end at the inner periphery of extension 72. Each

passageway

146 and 148 communicate with an annular grooves in the outer periphery of a respective drive shaft keeper 98. Each groove 160 is in communication with annular grooves 164 located at the inner periphery of keepers by means of a plurality of circumferentially spaced passageways 162 which extend radially between grooves 160 and 164. Grooves 160 and 164 are in a staggered relationship to one another such that one end of passageways 162 open ends at an outer portion of groove 160 and the other end thereof open ends at an inner end portion of groove 164.

Grooves 164 are in communication with grooves 166 located at the inner periphery ofspacer sleeves 96 by means of a plurality of circumferentially spaced passageways 165. Passageways 165 open end at the outer periphery of a spacer sleeve 96 in communication with a groove 164 and extends radially inwardly therefrom to a groove 166.

With such a groove and passageway arrangement as hereinabove-described hydraulic pressure fluid is supplied to tube 128 for extending rotary drum cutting heads 80 in a manner hereinbefore described by flowing pressure fluid through passageway 146 into groove 160, through passageways 162 into groove 164, through passageway 165 into groove 166 and through at least one tube 168 which extends radially inwardly of shaft 70 and communicates between 166 and tube 128. Similarly, pressure fluid is supplied to passageway 142 to retract rotary drum cutting heads 80 in a manner hereinbefore described by flowing pressure fluid through passageway 148 into groove 160, through passageways 163 into groove 164, through passagways 165 into groove 166 and through at least one passageway 170 which extends radially inwardly of shaft 70 and has the radial outer end thereof communicating with groove 166 and the radial inner end thereof open ended in passageway 148.

Annular static seals such as rings 180 are suitably received in suitable grooves between the outer periphery of drive shaft keepers 98 and the inner periphery of gear casing extension portions 72 and between the inner periphery of spacer sleeves 96 and the outer periphery of shaft 70. Selfpressurizing expanding, type seal rings 182 are suitably received in suitable grooves between the inner periphery of keepers 98 and the outer periphery of spacer sleeves 96. Seal rings 180 and 182 are positioned adjacent both sides of

respective grooves

160, 166 and 168 to prevent pressure hydraulic fluid from flowing out of the sides of such grooves. It is to be noted that rings 182 must be of a self-pressurizing expanding type because of the rotating movement of sleeves 96 with respect to the stationary keepers 98.

It is to be noted that because the seal rings 180 and 182 are located outwardly of roller bearings 94 the replacement of such seals is relatively simple, for the bearings 94 need not be disturbed and the casing extension portions 72 can remain in place during the removal of worn seal rings 180 and 182 and the insertion of replacements. It is additionally noted that by the use of

grooves

160, 164 and 166 of substantial axial dimension, a relative movement between adjacent passageways of an amount substantially equal to the width of such grooves is possible without impairing the continuous flow of hydraulic pressure fluid to and away from

passageways

146 and 148. Also the staggering of grooves 160 and 164 is desirable so as keep the reduction of the cross-sectional area of keepers 98 at a minimum at any particular point.

Hydraulic fluid is drawn from a suitable fluid reservoir 149 by mans of a pump 184. Hydraulic fluid passes through pump 184 and is furnished under pressure to a valve 186 which selectively channels the fluid to either

passageway

146 or 148. As is well known, fluid flowing through one passageway of such a circuit displaces fluid from the cylinders 134 through the other passageway, through the valve 186 and into the reservoir 149.

A preferred embodiment of this invention having been hereinbcfore described and herewith illustrated it is to be realized that variations in the specific structure are envisioned and contemplated as further embodiment 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.

What is claimed is:

1. A mining machine cutting structure comprising: a support member; an elongated mining head member mounted at the forward end of said support member for powered rotation about a longitudinal axis of said head member and having axially extensible and retractable end portion; said mining head member including a longitudinally extending tubular head shaft transmitting power for said powered rotation, said support member having extension portions for supporting said head shaft at axially spaced portions thereof; and elongated member coaxially received within said head shaft and inwardly spaced from at least a portion of the inner surface thereof to form an elongated chamber in conjunction therewith, said elongated member having an axial bore extending therein; each of said extension portions having a passageway therein, said passageways communicating at one end thereof with said axial bore and said chamber, respectively, and said passageways, at the other ends thereof, adapted to be selectively connected to individual ones of a pressure fluid source and a fluid reservoir; and fluid operable extensible means connected to said reciprocable end portions and operatively connected to said chamber and said bore for the selective extension and retraction of said reciprocable end portions.

2. A mining machine cutting structure as specified in claim 1 wherein said fluid operably extensible means comprise a pair of axially spaced extensible hydraulic cylinder assemblies secured within each end of said head shaft, each of said cylinder assemblies having respective pistons, rods, rod ends and head ends.

3. A mining machine cutting structure as specified in claim 2 wherein each of said head ends have a pilot-operated check valve mounted thereon communicating through said check valve with said axial bore, each of said rod ends communicating with said chamber, and control portal means communicating between said check valve and said chamber for the receiving a flow of unlocking pressure fluid into said check valve.

4. A mining machine cutting structure as specifiedin claim 1 additionally including bearing means disposed intermediate said support member extension portions and said head shaft at said axially spaced portions.

5. A mining machine cutting structure as specified in claim 4 including sealing means disposed intermediate said support member extension portions and said head shaft axially outwardly of each of said bearing means and each of said passageways extending through respective ones of said sealing means.

6. A mining machine cutting structure as specified in claim 1 wherein said bore supplies pressure fluid for the extension of said end portions and said chamber provides pressure fluid for the retraction of said end portions.

7. In a mining machine of the type having a forwardly extending support member with an elongated mining head member transversely mounted at the forward end of said support member for powered rotation about the central longitudinal axis of said head member and in which said support member includes a casing rotatably supporting an elongated head shaft transmitting power for said powered rotation mounted within outwardly extending casing extension portions encompassing axially spaced portions of said head shaft the improvement wherein; said head shaft has an axial through bore; an elongated member within said shaft inwardly spaced from at least a portion of the inner surface of said bore forming a pair of axial passageways within said bore, each of said casing extension portions has a passageway therein communicating selectively at one end with an external source of pressure fluid and a fluid-receiving tank alternatively, and the other ends of said casing passageways communicating with fluid tight means in turn communicating with individual ones of said pair of axial passageways respectively.

8. In a mining machine as specified in claim 7 the further improvement wherein; bearing means are mounted within said casing extension portions inwardly adjacent the outer ends of said casing portions to support said shaft and wherein said fluidtight means comprises sealing means encompassing said shaft located axially outwardly of each of said bearing means and mounted at least partially within the outer ends of said casing portions to provide liquid-tight relationship between said shaft and said casing portions.

9.'In a mining machine as specified in claim 8 the further improvement wherein each of said sealing means is interposed between a spacer sleeve secured in fluidtight relationship on the outer surface of said head shaft and an annular keeper member secured within the outer end of each of said casing extension portions in fluidtight relationship therewith and said keeper member and said sleeve had intercommunicating passageway means therein.

10. in a mining machine as specified in claim 9 the further improvement wherein said passageway means in said keeper member comprises an external peripheral groove and an internal peripheral groove in said keeper member communicating with each other through at least one radial opening open ended in both grooves and said passageway means in said spacer sleeve comprise a groove in the internal peripheral surface thereof communicating with the external surface of said sleeve through at leas one radial opening in said sleeve.

11. In a mining machine as specified in claim 9 the further improvement wherein said spacer sleeves rotate with said shaft and said keepers are held stationary by said casing extension.

12. In a mining machine as specified in claim 7 the further improvement wherein said bore has an extensible hydraulic cylinder assembly secured withing each end thereof, said cylinder assemblies having respective pistons, rods, rod ends and head ends, each head end having a pilot operated check valve mounted thereon and communicating through said valve with one of said axial passageways, each said rod end communicating with the other of said axial passageways, and each said pilot operated check valve communicating with said other passageway through a control portal for receiving unlocking pressure fluid.

13. In a mining machine as specified in claim 12 the further improvement wherein a pair of cutter-carrying drums is mounted on axially spaced portions of said head shaft and said drums have axially slidable drum extension portions mounted therein, each said drum extension portion being secured to a respective one of said rod ends to be selectively moved axially thereby, said axial movement being effected by said selective connecting of said casing extension passageways with said source of fiuid pressure and said tank, respectively.

Claims

4. A mining machine cutting structure as specified in claim 1 additionally including bearing means disposed intermediate said support member extension portions and said head shaft at said axially spaced portions.

7. In a mining machine of the type having a forwardly extending support member with an elongated mining head member transversely mounted at the forward end of said support member for powered rotation about the central longitudinal axis of said head member and in which said support member includes a casing rotatably supporting an elongated hEad shaft transmitting power for said powered rotation mounted within outwardly extending casing extension portions encompassing axially spaced portions of said head shaft, the improvement wherein; said head shaft has an axial through bore; an elongated member within said shaft inwardly spaced from at least a portion of the inner surface of said bore forming a pair of axial passageways within said bore, each of said casing extension portions has a passageway therein communicating selectively at one end with an external source of pressure fluid and a fluid-receiving tank alternatively, and the other ends of said casing passageways communicating with fluid tight means in turn communicating with individual ones of said pair of axial passageways respectively.

9. In a mining machine as specified in claim 8 the further improvement wherein each of said sealing means is interposed between a spacer sleeve secured in fluidtight relationship on the outer surface of said head shaft and an annular keeper member secured within the outer end of each of said casing extension portions in fluidtight relationship therewith and said keeper member and said sleeve had intercommunicating passageway means therein.

13. In a mining machine as specified in claim 12 the further improvement wherein a pair of cutter-carrying drums is mounted on axially spaced portions of said head shaft and said drums have axially slidable drum extension portions mounted therein, each said drum extension portion being secured to a respective one of said rod ends to be selectively moved axially thereby, said axial movement being effected by said selective connecting of said casing extension passageways with said source of fluid pressure and said tank, respectively.