GB2063421A - Flexible Shaft for a Roof Drill - Google Patents

Abstract

A system for drilling holes in the roof of a mine has a flexible shaft 16 comprising a cylindrical outer casing 100 formed by a spring member 102 wound in helical configuration, and a flexible inner assembly that includes an elastomeric core 104 and a series of radially rigid reinforcing segments 110 extending end to end along the length of the flexible shaft. The flexible shaft has improved radial dimensional stability as well as reduced tendency to elongate or otherwise distort. The drive 14 includes the shaft gripping assembly 50 carried by a thrust piston 32. Fluid pressure applied to a flexible sleeve 68 urges a collet 82 to grip the flexible shaft 16, the resulting twisting of the helical outer casing 100 causing the shaft to become rigid at its upper end. <IMAGE>

Description

SPECIFICATION Drilling System This invention relates to drilling systems and shafts therefor and, more particularly, to drilling systems particularly suited for drilling holes in the roof of a mine.

In the mining industry, falls of mine roofs account for a large percentage of the fatalities that occur in coal mines. Thus, roof control has been a major safety and production consideration.

Roof fall fatalities have been greatly reduced in cases were the mine roof is supported with roof bolts that are inserted into holes which are drilled into the mine roof using a drill bit that is attached to a rigid shaft. As the holes become progressively deeper, the mine worker adds extension sections to the drill shaft. Such an operation requires the worker to be at the head of a roof drilling machine for starting the hole and for adding extension sections.

A variety of proposed drilling systems seek to eliminate these hazards. U.S. Patent 4,057,11 5 discloses a roof drill system employing a flexible drill shaft composed of inner and outer oppositely wound helical springs, together with a driver mechanism that includes a rotatively driven shaft gripping chuck which applies torque to the flexible shaft, causing the outer spring to contract inwardly and the inner spring to expand outwardly so that the shaft between the driver mechanism and the drill bit becomes substantially rigid while the portion of the drill shaft below the gripping chuck remains flexible. In particular applications, the drive mechanism provides a drive torque of 300 foot pounds (407 Nm) and a thrust of 5000 pounds (1 524N), with the shaft being driven at 750 rpm.Thrust is cyclically applied to the shaft in a shaft gripping and releasing cycle that is repeated about once a second.

It has been found that drill shafts with inner and outer oppositely wound steel springs (of the type shown in U.S. Patent 4,057,11 5) have a tendency to elongate and adjacent turns of one or both springs to separate with resulting reduced shaft driving effectiveness.

In accordance with a feature of the invention, there is provided a flexible shaft for a roof drill or the like that includes an elongated cylindrical outer casing composed of a spring member wound in helical configuration, and a flexible inner assembly that includes a series of radially rigid reinforcing segments extending the length of the flexible shaft. A transition member secured to the outer casing at one end of the shaft receives a drill bit or the like. The flexible shaft in accordance with the invention has improved dimensional stability as well as reduced tendencies to elongate or otherwise distort that have been experienced with shafts of the type shown in U.S.

Patent 4,057,11 5.

In a particular embodiment, a greater than seam height drill system includes a torquer/thruster mechanism with a shaft gripping mechanism having a through passage that defines an axis and receives the drill shaft. A first drive unit drives the shaft gripping mechanism in rotation about the passage axis and a second drive unit drives the shaft gripping mechanism in a thrust direction parallel to the passage axis. The shaft gripping mechanism is arranged to periodically grip the shaft so that a torsional drive supplied to the shaft by the first drive unit and thrust is concurrently applied to the shaft by the second drive unit. The outer casing of the flexible drill shaft is formed of a spring wire of rectangular cross section that is wound in helical configuration so that the edges of adjacent turns of the helix abut.The flexible inner assembly includes an elongated flexible tubular core member with a series of cylindrical rings disposed along the length of the core member in end to end abutting relation. In one embodiment the cylindrical rings have parallel inclined end surfaces which enhance the radial stability characteristics. In another embodiment the cylindrical rings have torque transmitting projections at each end which are received in nesting interengagement with projections of adjacent rings. Other interengaging surface configurations, such as stepped shoulders, may also be utilized including configurations that provide both radial stability and torque transmission embodiment.

A shaft in accordance with the invention for use in a greater than seam height roof drill has improved radial stability and resistance which enhances the uniformity and adequacy of the gripping engagement of the shaft by the drill's torquer/thruster mechanism.

Other features and advantages of the invention will be seen as the following description of particular embodiments progresses, in conjunction with the drawings, in which: Fig.1 is an elevational view, with parts broken away, of a drill system in accordance with the invention; Fig. 2 is a side elevational view, with parts broken away, of a portion of the flexible shaft employed in the drill system of Fig. 1; Fig. 3 is a perspective view of cylindrical segment components of the flexible shaft shown in Fig. 2; Fig. 4 is a perspective view of another form of cylindrical segments for use in a drill system in accordance with the invention; and Fig, 5 is a sectional view taken along the line 5-5 of Fig. 1.

The drill system shown in Fig. 1 is a greater than seam height drill designed for remote drilling of a hole 10 in the roof 12 of a mine. The drill system includes a hydraulically actuated head 14 having an axially extending passage through which flexible drill shaft 1 6 extends. Connected to the upper end of shaft 1 6 by means of coupling chuck 18 is drill bit 20.

Drive head 14 is mounted on a conventional bolter chassis or other carrier by support arms diagrammatically indicated at 22, 23. Vacuum hood 24 at the top of drive head 14 is arranged to be seated against the mine roof 12, as indicated in Fig. 1. The shaft drive mechanism includes piston housing 30 in which thrust piston 32 is disposed for limited axial movement. Piston 32 has lower head surface 34 defining the upper wall of chamber 36 and uppper head surface 38 (of smaller area than head surface 34) that defines the lower wall of chamber 40. Piston 32 carries suitable seals as diagrammatically indicated at 42. Shaft gripping assembly 50 is carried by piston 32 and driven in rotation by a main driver (not shown).Thrust bearings 52 and radial bearings 54, 56 support the gripping assembly for rotation relative to piston 32 and the gripping assembly carries circumferential seal units as diagrammatically indicated at 58, 60 and 62.

Shaft gripping assembly 50 includes a housing member 64 that receives a bladder assembly 66 consisting of a flexible sleeve 68 sealed at either end to upper and lower support rings 70, 72 respectively. Mounted within bladder assembly 66 is an alloy steel collet 74 that includes upper flange 76, elongated hollow cylindrical body 78 in which are four slits 80 which extend along helical paths about the longitudinal axis of collet 74 to provide a set of four gripping leaves 82.

Lower hydraulic fluid passage 90 is in communication with piston chamber 36, and piston 32 includes passage 92 which communicates with passage 94 through gripper housing 64 into the chamber 96, the inner boundary of which is defined by flexible sleeve 68. Upper hydraulic fluid passage 98 is in communication with upper piston chamber 40.

Further details of flexible shaft 1 6 may be seen with reference to Fig. 2. Welded to transition chuck 1 8 is outer casing member 100 in the form of a helical band 102 of spring steel. Band 102 is substantially rectangular in cross section and has a thickness dimension of 0.125 inch (3.18 mm) and a width dimension of 0.375 inch (9.53 mm).

The subassembly of spring band 102 and chuck 1 8 is centerless ground along its entire length except for the flange at the head end of the chuck to a diameter of 1.04 ince (26.43 mm). Disposed within casing 100 is a flexible assembly of an elongated elastomeric tubular core member 104, of rubber for example, which defines a through passage 106 that extends from a fitting (not shown) at the lower end of shaft 16 to a passage extension in chuck 18 that has outlet ports 108 immediately below bit 20. Disposed along the length of core member 104 is a stacked series of cylindrical steel rings 110, each having a length oi 0.44 inch (11.18 mm), an outer diameter of 0.75 inch (18.06 mm) and a wall thickness of 0.083 inch (2.11 mm). The end surfaces 112, 114 of rings 110 are inclined, as indicated in Figs. 2 and 3, and enhance radial stability.In an alternate embodiment, as indicated in Fig. 4, the upper and lower edges 112', 114, of cylinders 110' have teeth 116 that nest in engagement and enhance the torque transmitting characteristics of the reinforcing assembly of the rings 110' and core member 104'.

A cross sectional view of the shaft and gripping mechanism is shown in Fig. 5.

In operation, drive unit 14 is positioned against mine roof 12 and held in position throughout the drilling operation. Shaft 1 6 is fed up through the stationary head 14 so that bit 20 is in engagement with the mine roof. Air (or water) is supplied up through the hollow center 106 of shaft 16 for cooling bit 20 and flushing chips down through the bore hole 10 which are collected in vacuum head 24 and exhausted through passage 120. Gripper assembly 50 is driven continuously in rotation. Hydraulic fluid is applied to the lower piston chamber 36 through passage 90 while back pressure is applied to the upper piston chamber 40.The hydraulic fluid flows through passages 92 and 94 into the chamber 96 and forces flexible sleeve 68 against collet body, in turn forcing the collet leaves 82 inwardly against shaft casing 100, thus positively gripping shaft 1 6 and driving it in rotation. The resulting rotational force applied to shaft casing 100 causes a twisting of the outer casing so that it contracts inwardly against the radially rigid cylindrical segments 110 of flexible inner assembly, causing the upper end of shaft 16 to become a substantially rigid structure while the lower portion of shaft 16 below the gripping mechanism remains flexible.

The buildup of hydraulic pressure in chamber 36 overcomes the back pressure in upper chamber 40 and piston 32 is driven upwardly in a shaft thrusting stroke. When the upper limit of travel of piston 32 is reached, hydraulic pressure in chamber 36 is vented, releasing the clamping pressure on gripping leaves 82 and allowing the collet 74 to expand and release shaft 1 6. The hydraulic pressure in upper piston chamber 40 drives piston 32 downwardly to its lower limit position where the torquing and thrusting is repeated by again applying hydraulic fluid through passage 90 to lower chamber 36.

As the coil of outer casing 100 is twisted, it applies constricting and contracting forces on the passive column of cylindrical rings 110. That column of rings 110 is subjected to axial compressive forces with abutting end surfaces 112, 114 of the rings 110 increasing the rigidity of the reinforcing column while the radial stability of the rings 110 limit the inward deflection of the outer casing 100 under the pressure of clamping collet leaves 82 such that the dimensional stability of the shaft along its entire length is enhanced as well as the uniformity of the clamping action of the collet as the shaft is advanced through the drive head 14 in the drilling operation.

Claims (9)

Claims

1. A flexible shaft for use with a torquer/thruster mechanism for a greater than seam height roof drill or the like which includes a shaft gripping mechanism having a through passage that defines an axis and arranged to engage a flexible shaft in driving relation, drive means for driving said shaft gripping mechanism in rotation about said passage axis and in a thrust direction parallel to said passage axis, and means for actuating said shaft gripping mechanism to engage said shaft whereby torsional drive and thrust are concurrently applied to said shaft, said flexible shaft comprising a transition member at one end of said flexible shaft for receiving a drill bit or the like, an elongated cylindrical outer casing secured to said transition member and composed of a spring member wound in helical configuration, and a flexible inner assembly including a series of radially rigid reinforcing segments disposed within said outer casing and extending along the length of said flexible shaft, the lay of said helical spring member being such that rotation of said shaft by said gripping mechanism for driving said transition member causes axial contracting and radial constricting action of said outer casing against outer surfaces of said reinforcing segments effective to firmly seat end surfaces of said reinforcing segments against end surfaces of adjacent said reinforcing segments and provide a rigid shaft section between said shaft gripping mechanism and said transition member which the remainder of said shaft remains flexible.

2. The apparatus of claim 1 wherein said segments are cylindrical rings.

3. The apparatus of claim 2 and further including an elongated flexible inner core member disposed within said stack of cylindrical rings.

4. The apparatus of claim 3 wherein said elongated flexible member is hollow.

5. The apparatus of any preceding claim wherein said reinforcing segments have radial stability enhancing surfaces for interengagement with cooperating surfaces of adjacent segments.

6. The apparatus of any of claims 1-4 wherein said reinforcing segments have torque transmission enhancing surfaces for interengagement with cooperating surfaces of adjacent segments.

7. The apparatus of any preceding claim wherein said outer casing is formed of a spring wire of rectangular cross section that is wound in helical configuration so that the edges of adjacent turns of the helix abut, and said flexible inner assembly includes an elongated flexible tubular core member, said segments being cylindrical rings disposed along the length of said core member in end to end abutting relation.

8. The apparatus of claim 7 wherein the axial length of each said reinforcing segment and the axial length dimension of said spring wire cross section are similar in magnitude.

9. Apparatus substantially as herein described with reference to and as shown in the accompanying drawings.