CUTTER FOR BORING HEAD

Abstract

A cutter for a boring head having a shaft is mountable at a saddle. A roller body is rotatably mounted about the shaft via bearings housed at a cavity located radially between the shaft and the roller body. A lubrication fluid is configured to flow internally within the shaft via a first and second passageway. An elongate overflow chamber is provided in fluid communication with the passageways to receive thermally expanded lubrication fluid from the cavity.

Claims

1. A cutter for a boring head, the cutter comprising: a shaft having a longitudinal axis mountable at a saddle of a boring head; a roller body rotatably mounted about the shaft and having cutting elements provided at an external face; bearings mounted within an annular cavity located radially between the shaft and the roller body; a first passageway centred on the axis of the shaft and extending axially through the shaft from a first end; a second passageway extending transverse or perpendicular to the first passageway to provide a fluid link between the first passageway and the cavity; and an elongate overflow chamber centred on the axis of the shaft and formed as an elongate axial extension of the first passageway to extend axially through the shaft beyond the second passageway as a blind bore, the chamber having an unoccupied internal volume along its axial length configured to receive a lubrication fluid from the annular cavity.

2. The cutter as claimed in claim 1, wherein the axial length of the chamber is in the range 1.5 to 5.0 times a diameter or width of the chamber in a radial direction.

3. The cutter as claimed in claim 2, wherein the range is 2.5 to 3.5.

4. The cutter as claimed in claim 1, wherein the first passageway and the chamber are substantially cylindrical.

5. The cutter as claimed in claim 4, wherein a diameter of the first passageway is greater than a diameter of the chamber.

6. The cutter as claimed in claim 1, wherein an axial length of the first passageway is greater than the axial length of the chamber.

7. The cutter as claimed in any claim 1, wherein an axial junction of the first passageway and the chamber includes an abutment or a step that projects radially inward towards the axis.

8. The cutter as claimed in any claim 1, further comprising a first plug removably mounted in the first passageway to close an open end of the first passageway and a second plug removably mounted in the second passageway.

9. The cutter as claimed in claim 8, wherein the first and second plugs each have at least one communication bore arranged to provide a fluid flow path between the cavity and the respective first and second passageways.

10. The cutter as claimed in any claim 1, further comprising at least one communication bore extending through the shaft to allow the transfer of the lubrication fluid between the chamber and the cavity.

11. The cutter as claimed in claim 10, comprising a plurality of communication bores extending transverse or perpendicular to the chamber from one end of the chamber axially furthest from the second passageway.

12. The cutter as claimed in any claim 1, wherein a volume of the chamber is less than an unoccupied free volume of the cavity.

13. The cutter as claimed in claim 12, wherein the volume of the chamber (203) is in the range 5 to 50% of the unoccupied free volume (400) of the cavity (219).

14. The cutter as claimed in claim 13, wherein the range is 10 to 25%.

15. A boring head comprising a plurality of cutters, each of the cutters including a shaft having a longitudinal axis mountable at a saddle of a boring head, a roller body rotatably mounted about the shaft and having cutting elements provided at an external face, bearings mounted within an annular cavity located radially between the shaft and the roller body, a first passageway centred on the axis of the shaft and extending axially through the shaft from a first end, a second passageway extending transverse or perpendicular to the first passageway to provide a fluid link between the first passageway and the cavity, and an elongate overflow chamber centred on the axis of the shaft and formed as an elongate axial extension of the first passageway to extend axially through the shaft beyond the second passageway as a blind bore, the chamber having an unoccupied internal volume along its axial length configured to receive a lubrication fluid from the annular cavity.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0024] FIG. 1 is an external perspective view of a cutter mounted at a boring head according to a specific implementation of the present invention;

[0025] FIG. 2 is a cross sectional perspective view of the cutter of FIG. 1 in a first plane;

[0026] FIG. 3 is a cross sectional perspective view of the cutter of FIG. 1 in a second plane;

[0027] FIG. 4 is a cross sectional perspective view of the cutter in the same plane as FIG. 2;

[0028] FIG. 5 is a cross sectional perspective view of the shaft (journal) part of the cutter of FIGS. 1 to 4 according to a specific implementation of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0029] Referring to FIG. 1, a boring head 106 comprises a plurality of cutters 100 (alternatively termed reaming heads). Each cutter 100 comprises a rotatable frusto-conical roller body 101 mounted on a central shaft (or journal) 102. A plurality of annular rows of cutting inserts 103 project from an external face of the roller body 101 configured to work the rock as a roller body 101 rotates about the shaft 102. Shaft 102 is in turn mounted at a saddle 104 rigidly mounted at the boring head 106. Accordingly, each reaming head 100 is configured to rotate about axis 105 extending through the mounting shaft 102 with the axis 105 aligned transverse to the face of the boring head 106 from which the saddle 104 projects.

[0030] Referring to FIG. 2, roller body 101 comprises a first annular end 214 and a second annular end 215 with an internal facing surface 212 extending between ends 214, 215. Roller body 101 is accordingly formed as a hollow body having an annular wall indicated generally by reference 216 defined between internal facing surface 212 and an external facing surface 213 from which project the annular rows of cutting inserts 103. Roller body 101 is mounted about an external surface 221 of shaft 102 so as to surround external surface 221 between a first 200 and second 220 end of shaft 102. Roller body wall 216 comprises a series of annular recesses 205, 206, 207 that collectively define a bearing cavity 219 positioned radially between shaft 102 and roller body 101. Recesses 205, 207 are configured to mount two respective sets of roller bearings whilst annular recess 206 is configured to mount a plurality of ball bearings that, together with the roller bearings, define a collective bearing assembly to rotatably mount roller body 101 at shaft 102.

[0031] A first and second sealing assembly indicated generally by reference 204 is provided at the first and second ends 214, 215 of roller body 101 adjacent the shaft first and second ends 200, 220. The annular seal assemblies 204 comprise a series of O-rings and metal sealing rings/gaskets to provide a fluid tight seal to enclose and seal the bearing cavity 219. Seal assemblies 204 are configured to withstand an internal pressure within bearing cavity 219 of in the region of 0.3 to 0.4 MPa. That is, seal assemblies 204 are effective to prevent the loss of a lubrication fluid (typically grease) that occupies bearing cavity 219 to lubricate the rotational frictional contact of the bearings between the shaft 102 and roller body 101.

[0032] Shaft 102 comprises a first passageway 201 centred on axis 105 and formed as a cylindrical bore extending from shaft first end 200 to an approximate mid-length region of shaft 102. That is, an axial length of first passageway 201 is equal to approximately half the full axial length of shaft 102 between ends 200, 220. A second passageway 202 extends transverse to the first passageway 201 (and axis 105). Second passageway 202 provides a communication link between first passageway 201 and bearing cavity 219 such that a first end 217 of the second passageway 202 is provided in communication with first passageway 201 whilst a second end 218 of the second passageway 202 is provided in communication with bearing cavity 219 at the axial mid-region of the shaft 102 and roller body 101 corresponding to central annular recess 206. An elongate overflow chamber 203 is formed as a cylindrical bore and an axial extension of first passageway 201. That is, first passageway 201 and chamber 203 are coaxially aligned to be centred along shaft longitudinal axis 105. An axial length of chamber 203 is less than a corresponding axial length of first passageway 201 such that chamber 203 does not extend to emerge at the shaft second end 220 and is formed as a blind bore terminating within shaft 102 at an axial position corresponding to sealing assembly 204 (at shaft second end 220). Forming chamber 203 as a blind bore (having a termination end within the shaft) is advantageous to maximise the strength of the shaft 102 when mounted within saddle 104 to withstand the significant loading forces in use. A diameter of chamber 203 is less than a corresponding diameter of first passageway 201 so as to create an annular step 211 that projects radially inward towards axis 105 at the junction between the first passageway 201 and chamber 203. In particular, the annular step 211 is positioned at a first end 300 of chamber 203 and a second end 303 of first passageway 201, referring to FIG. 3. A first end 302 of first passageway 201 is open at shaft first end 200. Chamber 203 comprises second end 301 formed as a conical-shaped recess resultant from the two-stage manufacturing of the axially aligned first passageway 201 and chamber 203.

[0033] A first ball plug 208 is accommodated within first passageway 201 an end of which is seated onto the annular step 211. A corresponding second ball plug 209 is accommodated within second passageway 202. Referring to FIG. 5, each plug 208, 209 comprises a plurality of communication bores 500, 501 that provide fluid communication pathways between bearing cavity 219 and the first and second passageways 201, 202 and overflow chamber 203.

[0034] Referring to FIG. 3, a pair of further communication bores 210a, 210b extend perpendicular to axis 105 between the second end 301 of chamber 203 and one end of the bearing cavity 219 adjacent seal assembly 204 provided at the roller body second end 215. Communication bores 210a, 210b are configured to provide a further fluid communication pathway between the annular bearing cavity 219 and the internal passageways 201, 202 and chamber 203 within shaft 102. According to the specific implementation, a diameter of communication bores 500, 501, 210a, 210b is less than the diameters of the cylindrical first and second passageways 201, 202 and chamber 203. First passageway end 302 is sealed via a sealing plug 304 that forms an axial extension of first plug 208. Accordingly, lubrication grease introduced into bearing cavity 219 is sealed internally within cutter 100 via plug 304 and seal assemblies 204.

[0035] Referring to FIG. 4, chamber 203 comprises an axial length A that is greater than its diameter D so as to be elongate. According to the specific implementation length A is approximately three times diameter D. First passageway is also elongate having an axial length B being greater than its diameter D. According to the specific implementation, chamber axial length A is less than first passageway axial length B as defined between chamber ends 300, 301 and the passageway ends 302, 303. Additionally, chamber axial length A is greater than a length C of second passageway 202 that extends in a radial direction between first passageway 201 and chamber cavity 219.

[0036] Moreover, chamber diameter D is less than first passageway diameter D. Additionally, chamber diameter D is less than a corresponding diameter D of second passageway 202. Accordingly, an internal volume of chamber 203 between ends 300, 301 is less than an internal volume of first passageway 201 but is greater than an internal volume of second passageway 202 without plugs 208, 209 accommodated within the respective passageways 201, 202.

[0037] In use and referring to FIGS. 2 to 5, overflow chamber 203 is unobstructed so as to be internally empty to define a free reservoir volume to receive thermally expanded lubrication fluid from the bearing cavity 219. With the roller bearings and the ball bearings (illustrated schematically by respective references 401, 402) accommodated within cavity 219 at the corresponding regions of recesses 205, 207, 206, a free volume 400 is defined as the unoccupied volume within the bearing cavity 219 as defined by roller body internal surface 212 and the shaft external surface 221. The free volume 400 surrounding the bearings 401, 402 is occupied by the lubrication grease. The grease is initially introduced into cavity 219 using an elongate delivery tool (not shown) inserted into the unoccupied first passageway 201 and chamber 203. The rod-shaped tool is inserted into chamber 203 so as to prevent the lubrication fluid from flowing into this internal region of shaft 102 and to direct it exclusively into the bearing cavity 219 where it is desired. That is, the fluid is supplied to bearing cavity 219 via an internal duct within the delivery tool extending through first and second passageways 201, 202 and bypassing chamber 203. The plugs 208, 209, 304 are then inserted in position as illustrated in FIGS. 2 to 5. Chambers 203 is provided in fluid communication with the free volume 400 (and the lubrication fluid) via communication bores 500, 501 and 210a, 210b. During use and rotation of roller body 101 about axis 105 and shaft 102, the lubrication grease is heated from ambient to approximately 160 C. causing the fluid to expand within free volume 400 and elevate the internal pressure against the seal assemblies 204.

[0038] The grease expands within free volume 400 and is capable of flowing internally within the shaft 102 via communication bores 500, 501 and 210a, 210b. The unoccupied free space within chamber 203 is approximately 10 to 25% of the free volume 400 and is based, in part, on the thermal expansion coefficient of the lubrication fluid and in particular the volume of the fluid at the operating temperature of the cutter (approximately 160 C.). The free-flow of fluid between the chamber 203 and cavity 219 maintains the pressure within cavity 219 below the maximum pressure of the seal assemblies 204 which may be typically 0.3 to 0.4 MPa. The thermally expanded and heated fluid is accordingly configured to collect in the reservoir chamber 203 to relieve the pressure within cavity 219 and avoid seal failure and loss of lubricant from cutter 100. The present configuration is also advantageous avoid the return flow of contaminated lubricant that may otherwise occur with conventional arrangements that employ elastomeric reservoirs or wells. The overflow chamber 203 comprising multiple fluid flow inlets and outlets (501, 210a, 210b) is advantageous to provide the reliable and unhindered free-flow of lubricant between chamber 203 and cavity 219 resultant from lubricant expansion and contraction.