Stabilising band for a roller assembly

Abstract

The invention relates to a stabilising band for a roller assembly of the type used in the drilling industry. The roller assembly includes a roller pin mounted within a bore of a roller and the stabilising band is configured so as to fit tightly about the roller pin with a minimal running fit and within an annular groove formed in a wall of the bore of the roller.

Description

FIELD OF THE INVENTION

The present invention relates to a stabilising band for a roller assembly.

BACKGROUND OF THE INVENTION

During drilling operations, a drill bit is subject to wear and thus the dimension of the drill hole will vary over time. To ensure that the dimension of the drill hole is held true, rotary roller reamers are located in the drill string above the drill bit and are used to ream out the drill hole to the required dimension. The inclusion of rotary roller reamers in the drill string enables the drill bit to be used for a longer period without changeover and this prevents considerable costly downtime.

A rotar roller reamer typically includes a number of roller assemblies mounted about its periphery. Each roller assembly will normally include a crushing roller mounted on a roller pin so as to rotate thereabout.

However, the working environment of a rotary roller reamer (and thus these roller assemblies) is very harsh, and any parts that require relative rotation (such as between each crushing roller and its roller pin) need to be adequately sealed to prevent the ingress of any contaminants and to maintain any internal lubricants in an acceptable state. Accordingly, a seal is typically provided at or adjacent to either end of the roller. Such a seal may adopt numerous different forms but may be a conventional o-ring seal. It is recognized that in some situations, for example when the roller assembly is subject to high impact compression, resulting movement of the roller pin may cause the integrity of these seals to be lost.

The present invention aims to facilitate maintenance of the integrity of the seals.

SUMMARY OF THE INVENTION

According to the present invention there is provided a stabilising band for a roller assembly, the roller assembly having a roller pin mounted within a bore of a roller body, the stabilising band being configured so as to fit tightly about the roller pin with a minimal running fit and within an annular groove formed in a wall of the bore of the roller body.

Preferably, the roller pin is rotatably mounted within the bore of the roller body.

The stabilising band may be endless or may be broken (discontinuous) and will preferably float within the groove, in that it may either be rotatable with the roller pin or with the roller body.

Such a stabilising band is preferably made of a material that is reasonably hard and has a relatively low coefficient of friction. This material may be a fluoropolymer selected from the range of polytetrafluorethylenes (PTFE) marketed by DuPont under the TEFLON® trade mark. However, more preferably, such a material will be strengthened by the addition of filler, such as with a glass, bronze or nickel filler. Ideally, the material will be a bronze filled PTFE.

In this form, the stabilising band tends to assist in maintaining the rotation of the roller pin substantially stable about its longitudinal axis and along its entire length. In this respect, in some situations, the seals between the roller pin and the roller will be somewhat sensitive to end-to-end bounce of the roller pin. Such bounce would normally be expected to incur due to the reasonably severe impact compression encountered by the roller assembly during operation. The use of a stabilising band of this type will thus assist with the smooth operation of the roller assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away view of a rotary roller reamer incorporating a stabilising band in accordance with an embodiment of the invention;

FIG. 1A is an enlarged view of the central portion (i.e. the pocket and the roller assembly) of the rotary roller reamer shown in FIG. 1;

FIG. 2 is a partial assembly view of a roller assembly adjacent to a reamer body having multiple pockets;

FIG. 3 is a central longitudinal cross sectional view of the roller assembly shown in FIG. 2 mounted in a pocket of a rotary roller;

FIG. 3A is a part cross sectional view of one end of the roller assembly along a line offset from the centre line of the rotary roller reamer;

• • FIG. 4 is a longitudinal cross sectional view of the pocket of the rotary roller reamer shown in FIG. 3;

FIGS. 5 to 8 are perspective views of the first retaining means;

FIGS. 9 to 11 are perspective views of the second retaining means;

FIG. 12 is a side view of the crushing roller;

FIG. 13 is a longitudinal cross sectional view of the crushing roller shown in FIG. 12;

FIG. 14 is an end view of the crushing roller shown in FIG. 12;

FIGS. 15 to 17 are views of the roller pin;

FIG. 18 is a cross sectional view showing connection of the first retaining means to the connector screw which extends from the enlarged head of the roller pin;

FIG. 19 is cross sectional view showing insertion of the retaining plug in the connector screw slot of the first retaining means;

FIG. 20 is a partial cross sectional view showing insertion of a roller cartridge (i.e. the assembled roller assembly) into a pocket of the rotary reamer;

FIG. 21 is a perspective view of the stabilization band shown in FIG. 1A;

FIG. 22 is a front view of the stabilization band shown in FIG. 21;

FIG. 23 is a side view of the stabilization band shown in FIG. 21; and

FIG. 24 is a cut-away view of another from of roller assembly incorporating stabilising rings in accordance with an embodiment of the invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 1A illustrate a rotary roller reamer 10. The rotary roller reamer 10 has a male end 12 and a female end 14. The rotary roller reamer 10 is arranged to be attached to a drill string (not shown). As shown in this embodiment, the male end 12 is located at the down hole end of the rotary roller reamer 10 and the female end 14 is located at the up hole end of the rotary roller reamer 10. It will of course be appreciated that the configuration or nature of the respective ends of the rotary roller reamer 10 may vary.

The rotary roller reamer 10 includes a tubular reamer body 16 which includes three circumferentially spaced pockets 18. Located within each pocket 18 is a roller assembly or roller cartridge 20. The pockets 18 as illustrated are equally spaced about the periphery of the reamer body 16 and are located in a section 16a of the body 16 that has a larger outer diameter than the remainder of the body 16. Although three pockets 18 are illustrated, it will be appreciated that arrangements with different numbers of pockets 18 and spacings are envisaged.

FIG. 2 better illustrates the pockets 18 formed in the reamer body 16. This figure also illustrates the cut away sections or mud ways 17 formed between adjacent pockets 18.

FIG. 2 illustrates the roller assembly 20 in a disassembled condition. The roller assembly 20 includes a roller pin 22, a crushing roller 24, a first retaining means 26, a second retaining means 28, a retaining screw 29, a first thrust ring 30, a second thrust ring 32, a pair of seals 34a, 34b, a pressure equalisation means 36, a fastener 38, a pair of self locking pins 38a, a connector screw 70 and a retaining plug 72.

When the components of the roler assembly 20 are assembled together they form a single cartridge which can be secured, using the fastener 38, in the pocket 18 of the rotary roller 10. During use, the crushing roller 24 is arranged to rotate about the roller pin 22 so that it can be used to ream the sidewalls of the drill hole through which the rotary roller reamer 10 is passed. The nature of each of the components of the roller assembly 20 and the pockets 18 formed in the reamer body 16 will now be described in more detail.

FIGS. 3, 3A and 4 best illustrate the configuration of each of the pockets 18 and the engagement of the roller assembly 20 within its respective pocket 18. Each pocket 18 includes a lower tapered. socket 40, a primary cavity 42, a secondary cavity 44 and an upper tapered socket 46. The lower tapered socket 40 is located at the down hole end of the rotary roller reamer 10, whilst the upper tapered socket 46 is located at the up hole end of the rotary roller reamer 10. The lower tapered socket 40 is arranged to receive the second retaining means 28, whilst the upper tapered socket 46 is arranged to receive the first retaining means 26. The primary cavity 42 is arranged to receive the roller pin 22 and the crushing roller 24 which is mounted thereon. The primary cavity 42 is sized and configured to provide operating clearance for the crushing roller 24 during use of the rotary roller reamer 10. The secondary cavity 44 forms a seat for the head 22a of the roller pin 22.

The lower tapered socket 40 includes a semi-circular truncated conical seat of less than or equal to 7° angle to a normal axis of the socket 18 (i.e. the axis normal to the longitudinal axis of the rotary roller reamer 10). As illustrated, this angle is approximately 3°. The lower tapered socket 40 is tapered so that the larger diameter of the socket 40 forms part of the floor 18a of the pocket 18. Tangential to the conical seat is an entrance guide way 40a having sides matching the taper of the conical seat.

Formed in the lower part of the lower tapered socket 40 and coincident with the floor 18a of the pocket 18, is a semi-circular recess 40b. This recess 40b is a security recess which is arranged to receive a complimentary shaped lug 28k formed on the second retaining means 28. The function of the security recess 40b and the lug 28k will be discussed in more detail subsequently.

Installed in a portion of the floor 18a of the lower tapered socket 40 so as to be positioned below the head 22a of the roller pin 22 are four carbide inserts 18b. The carbide inserts 18b are provided to prevent wear of the floor 18a of the pocket 18 due to movement of the head 22a during use of the rotary roller reamer 10.

The primary cavity 42, as clearly illustrated in FIG. 4, is necked down as compared to the external diameter of the reamer body 16. Additionally, the floor 18a of the primary cavity 42 steps downwardly in a direction towards the centre line of the reamer body 16. Thus, the primary cavity 42 has a depth in a direction normal to the longitudinal axis that is sufficient to provide working clearance for the crushing roller 24. Additionally, the external diameter of the reamer body 16 in this area is reduced or “necked down” as compared to the external diameter of the reamer body 16 in the areas adjacent to the lower and upper tapered sockets 40, 46. This necked down configuration of the reamer body 16 provides stress relief in the area of the pockets 18.

The secondary cavity 44 is formed with a flanked trapezium shape which narrows at the down hole end of the cavity 44.

The upper tapered socket 46 includes a semi-circular truncated conical seat of less than or equal to 7° angle to the normal axis of socket 46. As illustrated, this angle is approximately 3°. The upper socket 46 is tapered so that the smaller diameter of the socket 46 forms part of the floor 18a of the pocket 18. The seat extends for approximately 270° arc length, with the remainder of the arc length opening into the secondary cavity 44. Located substantially centrally of the upper tapered socket 46 is a post 52. The post 52 includes a bore 54 which is threaded so that it can receive the fastener 38. Altematively, as illustrated, a threaded insert 54a may be located in the bore 54.

FIGS. 5 to 8 illustrate the first retaining means 26. The first retaining means 26 is formed as a first plug 26 and is arranged to be received within the upper tapered socket 46. The first plug 26 is formed as a frustum. The frustum has an angle of less than or equal to 7° to its central longitudinal axis and includes a base 26a and a top 26b. As illustrated, the frustum has an angle of approximately 3°. The base 26a is arranged to be positioned lowermost in the lower tapered socket 46. The base 26a has an outer diameter which is smaller than the outer diameter of the top 26b. The underside of the base 26a is shaped to engage with the floor 18a of the pocket 18 in the area of the upper tapered socket 46. In particular, the base 26a is shaped so that it will mate with the post 52.

The first plug 26 includes a fastener-receiving cavity 26c that opens through a sidewall 26d and also into the base 26a of the first plug. The cavity 26c is configured so that the fastener 38 can be positioned within and so that the leading end 38b of the fastener 38 can be secured within the bore 54 formed in the post 52. An aperture 26e is located in the top 26b of the first plug 26 and is configured so that the working end of a tool can be passed there through. This enables the fastener 38 to be screwed into and out of the bore 54 of the post 52.

Formed in the top 26a of the first plug 26 is a pair of bores arranged to receive the self locking pins 38a. The self locking pins 38a are configured to properly locate and lock the fastener 38 within the fastener-receiving cavity 26c.

The sidewall 26d of the first plug 26 also includes an elongate connector screw slot 26f which enables the first plug 26 to be connected to a connector screw 70 which extends from the enlarged head 22a of the roller pin 22. The connector screw slot 26f includes a threaded upper portion 26′f which is arranged to receive a threaded retaining plug 72 (FIG. 19). Prior to receiving the retaining plug 72, the threaded upper portion 26′f is sized to enable the head 70a of the connector screw 70 to pass there through. In this manner, the head 70a of the connector screw 70 can be inserted into the connector screw slot 26f and then the shank of the screw 70 can be moved along the length of the slot 26f. The connection between the screw 70 and the first plug 26 will be described in more detail subsequently.

As best illustrated in FIG. 3, the fastener 38 is a socket head fastener. The head of the fastener 38 is arranged to be located within an upper portion of the cavity 26c so that when the fastener 38 is screwed into the post 52, the first retaining means 26 is drawn into the lower tapered socket 46 and when the fastener 38 is unscrewed, the first retaining means 26 is lifted out of the upper tapered socket 46. The configuration of the sidewalls of the lower tapered socket 46 and the shape of the head 22a of the roller pin 22 facilitate this action of the first retaining means 26. As the first retaining means 26 (first plug 26) is connected to the roller pin 22, movement of the first plug 26 in and out of the upper tapered pocket 46 will result in movement of the entire roller cartridge 20 in and out of the pocket 18.

FIGS. 9 to 11 illustrate the second retaining means 28. The second retaining means 28, or second plug, is formed as a frustum. The frustum has an angle of less than or equal to 7° to its central longitudinal axis. As illustrated, this angle is approximately 3°. The second plug 28 has a base 28b, a top 28c and a sidewall 28d. The base 28b has a larger external diameter than the top 28c and is arranged for positioning lowermost within the upper tapered socket 40. A bore 28e is formed in a flat portion of the sidewall 28d of the second plug 28. The bore 28e extends substantially perpendicular to the central longitudinal axis thereof. The bore 28e is arranged to receive a second end 22b of the roller pin 22. The bore 28e is sized for a sliding fit with the second end 22b of the roller pin 22.

A threaded aperture 28f is formed in the base 28b of the second plug 28. The threaded aperture 28f is arranged to receive a retaining screw 29 which locates the second end 22b of the roller pin 22 within the second plug 28. The engagement of the retaining screw 29 with the roller pin 22 will be described in more detail subsequently.

Formed in the sidewall 28d of the second plug 28 is a minor bore 28j. The function of the minor bore 28j will be explained subsequently.

As mentioned previously, the second plug 28 has a lug 28k formed on the lower part thereof. The lug 28k is arranged to engage within the security recess 40b formed in the lower tapered socket 40. This engagement serves to better retain the roller assembly 20 within the pocket 18.

FIGS. 12 to 14 illustrate the crushing roller 24. The crushing roller 24 is formed as a hollow cylindrical member having a central bore which is sized to receive the shank of the roller pin 22. The crushing roller 24 has reduced diameter portions at each end for primary engagement of the crushing roller 24 with the walls of the well bore. A secondary engagement diameter is formed therebetween and is studded with a plurality of buttons 60 (not shown in FIGS. 12 to 14). The buttons 60 are preferably domed shaped tungsten carbide buttons that are each mounted within an aperture 62. The carbide buttons 60, in accordance with a preferred embodiment, are arranged in four rows of eight and are set on a left-hand 3.31699″ pitch helix. Each row is separated by 90° of angular rotation and the starting point for each row commences in a progressive step equal to 0.125× 1/9^th of the helical datum curve length. Each button 60 is spaced at 1/9^th of the helical curve length.

It will be appreciated by those skilled in the art that the above arrangement of buttons 60 on the crushing roller 24 provides a very efficient use of the carbide buttons and thus significantly less carbide is used. This reduction in carbide use is also expected to reduce the torque loading in the drill string. It will further be appreciated that other arrangements of the carbide buttons on the crushing roller are envisaged. Advantageously, the carbide buttons are arranged so that during use they provide substantially complete coverage of the portion of the wall of the well or drill hole being reamed. In other words, the contact area of the various carbide buttons with the portion of the drill hole being reamed overlaps.

Located between each of helically spaced rows of buttons 60 are flutes 64. There are four flutes 64 and they are generated on the same helical datum path as the apertures 62. The flutes 64 are arranged to enable increased mud flow past the crushing roller 24 and to increase the clearance through which the crushing residue from the rotary roller reamer 10 can pass.

The inclusion of primary engagement diameters at the respective ends 24a, 24b of the crushing roller 24 enables the rotary roller reamer 10 to be bi-directional (i.e. either up hole or down hole in its application). Seven holes 62a are located in each primary diameter for the insertion of further domed tungsten carbide buttons 60a. The holes 62a are equally spaced and circumferentially drilled on the surfaces normal to the roller central axis.

As illustrated in FIG. 12, a further hole 62b drilled through to the central bore is formed in each of the primary engagement diameters. Each hole 62b is tapped with a female thread and is arranged to receive a pressure plug 63. Each hole 62b has the dual function of a grease injection port and a purge port. The use of the pressure plugs 63 will be described in more detail subsequently.

As illustrated in FIG. 13, a pair of seal retention grooves 66 is formed within the wall of the central bore of the crushing roller 24 and are arranged to receive respective seals 34a, 34b. As shown, the seals 34a, 34b are simple o-rings. However, the use of other types of seals is envisaged.

Also shown in FIG. 13 are further annular grooves 24c intermediate the ends of the bore of the crushing roller 24. Each groove 24c is arranged to receive a stabilizing band 75. As best illustrated in FIG. 21, each stabilization band 75 is a band which is broken at point A to provide a gap between the respective ends 75a, 75b of the band. The ends 75a, 75b terminate at an angle of about 45° (See FIG. 23). Termination at other angles is envisaged.

Each stabilization band 75 is sized to provide a minimal running fit about the shank of the roller pin 22 and to float within its respective groove 24c. In this embodiment metric fit D9h8 is adopted. The stabilization band 75 may either be rotatable with the roller pin 22 or with the crushing roller 24.

Such a stabilizing band 75 is preferably made of a material that is reasonably hard and has a relatively low coefficient of friction. Such a material may have a Shore D hardness of about 67, a static coefficient of friction of about 0.09 and a dynamic coefficient of about 0.13. This material may be a fluoropolymer selected from the range of polytetrafluorethylenes (PTFE) marketed by DuPont under the TEFLON® trade mark. However, more preferably, such a material will be strengthened by the addition of filler, such as with a glass, bronze or nickel filler. Ideally, the material will be a bronze filled PTFE.

In this form, the stabilizing band 75 assists in maintaining the rotation of the roller pin 22 substantially stable about its longitudinal axis and along its entire length. In this respect, in some situations, a seals 34a, 34bmay be somewhat sensitive to end-to-end bounce of the roller pin 22, such as would normally be expected due to the reasonably severe impact compression encountered by the roller assembly 20 during operation. The additional use of a stabilizing band 75 of this general type will thus assist with the smooth operation of the roller assembly 20.

FIGS. 15 to 18 illustrate the roller pin 22. The roller pin 22 includes a central longitudinal bore 22c (best shown in FIGS. 3 and 15) that opens through the lower end 22b. The bore 22c in the shank of the roller pin 22 forms a lubricant reservoir. A side port 22d extends between the lubricant reservoir 22c and a primary lubricant distribution groove 22e. The primary lubricant distribution groove 22e extends longitudinally of the roller pin 22. As best shown in FIGS. 16 and 17, the primary lubricant distribution groove 22e is formed in a “figure 8” configuration.

It will be appreciated that the lubricant reservoir 22c enables a lubricant to be stored in the roller pin 22 and subsequently supplied, via the side port 22d, to the distribution groove 22e during rotation of the crushing roller 24 about the roller pin 22. The lubricant is distributed over the shank of the roller pin 22 as the crushing roller 24 rotates thereabout. The seals 34a, 34b retain the lubricant on the shank of the roller pin 22.

A second side port 22i is located adjacent the second end 22b of the roller pin 22 and intersects with the lubricant reservoir 22c. The side port 22i opens into a groove 22j. The function of the groove 22j and the side port 22i will be described below.

Also formed adjacent the second end 22b of the roller pin 22 is a transverse retaining slot 22g. The retaining slot 22g is arranged so that the leading end of the retaining screw 29 in the second retaining means 28 can be located in the retaining slot 22g. In this manner, the roller pin 22 can be oriented relative to the second retaining means 28. The use of a retaining slot 22g enables limited rotation of the roller pin 22 after connection to the second plug 28.

As best shown in FIGS. 3 and 20, the pressure equalization means 36 is positioned against a counter bore formed in the lubricant reservoir 22c. When the roller cartridge 20 is located in the pocket 18, the portion of the lubricant reservoir 22c to the right side (as shown in FIG. 3) of the pressure equalization means 36 opens into the bore 28e of the second plug 28. The second side port 22i of the roller pin 22 opens into the groove 22j (FIG. 20) which intum aligns with the minor bore 28j formed in the second plug 28. The minor bore 28j of the second plug 28 opens to the area surrounding the crushing roller 24. Thus, it will be appreciated that there is a pressure flow path from the area surrounding the crushing roller 24 to pressure equalization means 36.

The pressure equalization means 36 acts to ensure that the pressure of the lubricant within the bearing cavity (i.e. the clearance between the roller pin 22 and the crushing roller 24) is substantially equal to the pressure of the drilling mud which completely envelopes the rotary roller reamer 10 during a reaming operation. It is important to equalize this pressure so as to prevent the seals 34a, 34b from blowing in or out.

The pressure equalization means may take the form of a filter 36. In one embodiment, the filter 36 may be a sintered metal filter. The sintered metal filter may have an alloy composition of 68% copper, 27% nickel and 5% tin and a micron capture equal to or about 30 μm. The pressure equalisation means may adopt other configurations.

As best illustrated in FIGS. 3, 18 and 19 the head 22a of the roller pin 22 is shaped to mate with the sidewall 26b of the first plug 26. Thus, the head 22a is configured as a flanked trapezium shaped solid with a conical cut in its outer face.

The head 22a includes a blind bore 22f which is coincident with the elongate axis of the roller pin 22. The bore 22f is threaded to enable connection of the connector pin 70 thereto. This connection will be described in detail subsequently.

The first thrust ring 30 is formed as a solid ring of low friction metal or reinforced polymer which bears against the roller side face of the head 22a of the roller pin 22 and the face of the first end 24a of the crushing roller 24. The first thrust ring 30 is designed to accept the vertical thrust imparted from the sidewalls of the drill hole on the crushing roller 24 as a result of the rotating upward travel of the rotary roller reamer 10. The first thrust ring 30 is a sacrificial thrust ring.

The first thrust ring 30 has an internal o-ring seal 30a arranged to provide a small amount of shock absorption between the inside diameter of the thrust ring 30 and the shank of the roller pin 22. The o-ring seal 30a also acts as a barrier to the flow of drilling mud.

The second thrust ring 32 is a solid ring of low friction metal or reinforced polymer which bears against the second end 24b or the crushing roller 24 and the face of the second plug 28. The second thrust ring 32 is designed to accommodate the vertical thrust imparted from the sidewalls of the drill hole on the crushing roller 24 as a result of the rotating downward travel of the rotary roller reamer 10 within the hole being drilled. The second thrust ring 32 is a sacrificial thrust ring.

The second thrust ring 32 has an internal o-ring seal 32a arranged to provide a small amount of shock absorption between the inside diameter of the thrust ring 32 and the shank of the roller pin 22. The o-ring seal 32a also acts as a barrier to the flow of drilling mud. The o-ring seals 32a, 32b are preferably made of a fluoroelastomeric compound.

The assembly process for a roller assembly 20 is as follows. A first thrust ring 30 is slid along the shank of the roller pin 22 until it abuts the head 22a of the roller pin 22. A crushing roller 24 with seals 34a, 34b and stabilization bands 75 in position and carbide tips 60 fitted, is then slid onto the shank of the roller pin 22 until the first end 24a of the crushing roller 24 abuts the first thrust ring 30. The filter 36 is then seated against the counter bore of the lubricant reservoir 22c.

At this stage, grease is injected into the crushing roller 24 via one of the holes 62b (“the first hole 62b”). The grease is injected until grease flows through the hole 62b (the “second hole 62b”) in the other primary engagement diameter of the crushing roller 24. A pressure plug 63 is then installed to seal off the second hole 62b.

Grease injection is continued until lubricant flows through the lubricant reservoir 22c and out through the pressure equalization filter 36. At this point, the grease injection equipment is removed and a pressure plug 63 is fitted in the first hole 62b.

The second thrust ring 32 is then positioned on the shank of the roller pin 22 until it abuts with the second end 24b of the crushing roller 24. Finally, the second plug 28 is slid onto the end of the roller pin 22 so that the trailing end of the second thrust ring 32 is located flush against the flat portion of the sidewall 28d of the second plug 28. The retaining screw 29 is then located in the threaded aperture 28f and screwed inwardly so that it locates within the retaining slot 22g formed in the shank of the roller pin 22.

The fastener 38 is then inserted in the fastener-receiving cavity 26c of the first plug 26 and held in position by the self locking pins 38a.

A steel ball 71 is then dropped in the blind bore 22f. A connector screw 70 is then screwed into the bore 22f until it is firmly set against the steel ball 71. This action ensures a constant depth of engagement of the first plug 26 to the roller pin 22. The head 70a of the connector screw 70 is then passed through the upper portion 26f of the connector screw slot 26f in the first plug 26.

Connection between the first plug 26 and the roller pin 22 is maintained by inserting a retaining plug 72 in the threaded upper portion 26f of the connector screw slot 26f. The retaining plug 72 prevents the head 70a of the connector screw 70 from inadvertently withdrawing from the connector screw slot 72.

The positioning of the connector screw 70 in the connector screw slot 26f of the first plug 26 is best illustrated in FIG. 18. The insertion of the retaining plug 72 in the threaded upper portion 26f of the connector screw slot 26f is best illustrated in FIG. 19.

As will be apparent, the connection between the head 22a of the roller pin 22 and the first plug 26 is such as to allow limited articulation of the first plug 26 relative to the roller pin 22, whilst still ensuring proper alignment of the plug 26 relative to the roller pin 22 when the roller cartridge 20 is fitted into a pocket 18 of the rotary roller reamer 10.

Once the components of the roller assembly 20 have been assembled, the roller cartridge, as it is then known forms a single cartridge which is ready for insertion into a pocket 18 of the rotary reamer 10.

A roller cartridge 20 is fitted within a pocket 18 of the rotary roller reamer 10 as follows. Firstly, the roller cartridge 20 is held horizontally so that the second plug 28 is located in a forward position facing the end of the lower tapered socket 40. The roller cartridge 20 is then tilted towards the floor 18a of the pocket 18. It is then lowered into the pocket 18 until the second plug 28 contacts the floor 18a of the pocket 18. The roller cartridge 20 is then slid forward and down into the pocket 18 until the second plug 28 is seated in the lower tapered socket 40.

During positioning of the second plug 28 in the lower tapered socket 40, the first plug 26 aligns itself relative to the roller pin 22 and the upper tapered socket 46 so that it is properly positioned within the pocket 18 ready to be fastened in position by the fastener 38. This “self aligning” characteristic of the first plug 26 is a consequence of the nature of the connection between the first plug 26, the connector screw 70, the steel ball 71 and the head 22a of the roller pin 22.

A hex driver is then inserted through the aperture 26d in the first plug 26 and the fastener 38 is screwed into the threaded bore 54 of the post 52 formed in the floor 18a of the pocket 18. As the fastener 38 is screwed into the bore 54 the first plug 26 is drawn into the upper tapered socket 46. FIG. 20 illustrates a roller cartridge 20 being fitted into a pocket 18 of a rotary roller reamer 10.

It will be appreciated by those skilled in the art that different numbers of pockets 18 may be provided on the reamer body 16. Additionally, although the pockets 18 are described as being equally spaced about the periphery of the reamer body, this need not always be the case. They may for example be spaced by an exponential or logarithmic value.

It will also be appreciated that the crushing roller 24 may include different arrangements and numbers of primary engagement diameters (i.e. may adopt a multi step form), carbide buttons; flutes and helixes.

Shown in FIG. 24 is another form of roller assembly 100. The roller assembly 100 generally includes a roller pin 120 and a crushing roller 140. The crushing roller 140 includes a body having a bore formed therein that is sized to snugly receive therein the shank of the roller pin 120.

At each end of the bore there is an annular groove in which a seal 220 is arranged to be located. It will be appreciated by those skilled in the art that the seals 220 may adopt different forms and that the annular grooves may be located adjacent to the end of the bore of the roller pin 120.

Also shown in FIG. 24 are further annular grooves intermediate the ends of the bore of the roller pin 120. Mounted within each of the annular grooves is a stabilising band 260. The stabilising bands 260 are identical to the stabilising bands 75 shown and described previously in relation to FIG. 3.

Although the roller assemblies described previously include a fixed roller pin (i.e. non-rotating) and a crushing roller that rotates thereabout, it will be appreciated that the stabilising bands of the present invention may be incorporated in arrangements wherein the roller pin is not fixed.

It should be appreciated that stabilizing bands in accordance with the present invention may find application in many different forms of roller assemblies. Accordingly, reference to the term “roller assembly” should not necessarily be restricted to roller assemblies of the type used in rotary roller reamers.

It should be noted that these embodiments have been described by way of example only, and modifications within the spirit and scope of the present invention are envisaged.

Claims

1-15. (canceled)

16. A stabilizing band for a roller assembly, the roller assembly having a roller pin mounted within a bore of a roller, the stabilizing band being configured so as to fit tightly about the roller pin with a minimal running fit and within an annular groove formed in a wall of the bore of the roller, said stabilizing band being broken so as to provide a gap between respective first and second ends of the stabilizing band.

17. A stabilizing band according to claim 16 wherein the first and second ends each terminate at an angle of about 45°.

18. A stabilizing band according to claim 16 wherein the gap extends for approximately 15° of arc of the stabilizing band.

19. A stabilizing band according to claim 16 wherein it is configured to float within the annular groove so that it may either be rotatable with the roller pin or with the roller.

20. A stabilizing band according to claim 16 made of a material that is reasonably hard and has a relatively low coefficient of friction.

21. A stabilizing band according to claim 20 wherein the material has a Shore D hardness of about 67.

22. A stabilizing band according to claim 20 wherein the material has a static coefficient of friction of about 0.09.

23. A stabilizing band according to claim 20 wherein the material has dynamic coefficient of friction of about 0.13.

24. A stabilizing band according to claim 16 made from a fluoropolymer material.

25. A stabilizing band according to claim 24 wherein the fluoropolymer material includes a filler.

26. A stabilizing band according to claim 25 wherein the filler is a glass, bronze or nickel filler.

27. A stabilizing band according to claim 16 made from a bronze filled PTFE.

28. A roller assembly including a roller pin, a roller, at least one seal and at least one stabilizing band configured to fit tightly about the roller pin with a minimal running fit and within an annular groove formed in a wall of a bore of the roller, said stabilizing band being broken so as to provide a gap between respective first and second ends of the stabilizing band.

29. A roller assembly according to claim 28 wherein the roller pin is fixed and the roller is arranged to rotate thereabout.

30. A roller assembly according to claim 28 including two seals and two stabilizing bands.