CA2074076A1

CA2074076A1 - Drilling tool for percussive and rotary drilling

Info

Publication number: CA2074076A1
Application number: CA002074076A
Authority: CA
Inventors: Karl-Axel Stjernstrom; Stig Uno Lof
Original assignee: Individual
Current assignee: Uniroc AB
Priority date: 1990-01-17
Filing date: 1991-01-17
Publication date: 1991-07-18
Also published as: DE69102993T2; JPH05503556A; FI98155B; EP0511298B1; AU642708B2; WO1991010805A1; FI923240A; ATE108861T1; DE69102993D1; FI98155C; EP0511298A1; FI923240A0; AU7228091A

Abstract

A drilling tool for percussive and rotary drilling in advance of a trailing casing tube (20) has a reamer (15) pivotally journalled on an eccentric shaft (12) rearwardly of a centric pilot bit (11). The reamer (15) has an eccentric portion (32) carrying axially directed hard metal button inserts (36-40) grouped within an acute angle (V) of a circle sector centered on the drilling axis (C). The inserts comprise primary inserts (36-38) with a radial reach defining the full diameter of the drilled hole and inner secondary inserts (39, 40) closer to the shaft (12). The reamer (15) is pivotable on the shaft (12) between a projected and a retracted position. When projected, the group of button inserts (36-40) ream up the hole from the diameter drilled by the pilot bit (11) to the full diameter of the hole enabling the casing tube (20) to advance. In the retracted position the drilling tool (10) can pass through the casing tube (20). A duality of inserts (36, 39) leading in the rotational direction act jointly to break the rock in said direction substantially tangentially relative to the shaft (12). The rock cuttings from the button inserts (36-40) are subjected to enhanced flushing action. Optionally such flushing action is further supported by a groove (52) on the rotationally leading flank of the reamer (15). A cutting edge (54) on the groove (52) is reinforced by stellite and improves drilling of claybound ground.

Description

WO91/10805 PCTtSE91/000~

2~7~07~

Drillinq tool for percus~ive and rotary drilling The present invention relates to a drilling tool ~or percussive and xotary drilling in advance of a trailing cas-ing tube, in which tool a pilot bit via an intermediate eccent-ric shaft is carried by a guide body, which is rotatably cen-tered in and by the mouth of said casing tube on the rotatio-nal axis of said tool during drilling, and is coupled to drive means in said casing tube for actuation o~ said tool, a tubular reamer has an sccentxic protruding portion carrying on one axial face thereof hard metal button inserts, and the reamer is pivotally mounted on said eccentrie shaft between on the one hand a projected position, in which said eccentric portion with the button inserts thereon are adapted to ream up the hole from the initial diameter produced by said pilo~
bit to the ~ull diameter of the hole enabling the casing tube to be advanced thereinto, and, on the other hand, a retracted position, in which the drilling tool can be passed through said casing tube.
The drive means usually comprise a drill string which within a string of interconnected casing tubes carries a down-hole drill for direct actuation of the drilling tool by way of impacts and rotation as described for example in US patent 3,848,683 (Figs. 6-8) or, when tophammer drive is practiced, has the drill string directly coupled to the tool for actua-tion thereof. The latter drive is exemplified by US patent 3,753,470 (Figs. 1-3). In both drilling applications tools provided with hard metal button inserts of cemented tungsten carbide have been in extensive use ~or more than a decade.
one such drilling tool is described in US patent 4,440,244.
In drilling with tools o~ the above type noxmally the reamer element is su~jected to the heaviest load and has a shorter operatio~al life as compared to the other tool ele-ments. It is generally expected that in the average two ~UB~TI~UTE S~EET

~ 2 reamers will be worn out for each expended pilot bit, and two pilot bits for each guide body. It is therefore important that attempts to increase the operational life be directed primarily to the xeamer so as to prolong the useful time cy-cle between serviciny and change of worn tool elements.
It is an object o~ the invention to increase in drill ing tools of the above type the life expectancy of the reamer primarily by improving the grouping and rock crushing action of its button inserts. Another object is to gain by the cho-sen rock breaking action that the produced rock debris tends to become more coarse in grain. Another object in connection therewith is to enable the produced coarser rock cuttings to be removed by more efficient ~lushing whereby secondary crush-ing of the debris by the inserts is reduced. A further object is to improve reamer work and flushing during drilling of tough clayey ground. These objects are attained by the fea-tures stated in the appended claims.
An embodiment o~ the invention and a modification thereof will be described hereinafter with reference to the appended drawings, wherein Fig. l shows, partly in section, the drilling tool in its drilling position in front of a cas-ing tube to be driven down concurrently. Fig. 2 shows the tool of Fig. l in retracted position while bPing passed through the casing tube~ Fig. 3 shows the forward portion o~
the tool in Fig. l seen from the rear. Fig. 4 shows a some-what enlarged side view o~ the reamer in Fig. 3. Fig. 5 shows on a stlll larger scale a view from below of the reamer in Fig. l seen on the line 5-5 thereof. Figs. 6-8 are sections in the scale of Fig. 4 seen on the respective lines 6-6, 7-7, and 8-8 in Fig. 5. Fig. 9 shows enlarged a modified embodi-ment of the reamer depicted in a side Yiew slmilar~to Fig. 3.
Fig. lO is a view showing the modified reamer o~ Fig. 9 from below in a presentation similar to Fig. 5 but also indicating in sec~ion the eccentric shaft carrying the reamer.
In analogy with the above cited patent re~erences, the drilling tool in Fig. 1 comprises a pilot bit ll, a reamer 15 and a guide body 18. In practicing tophammer drilli~g the slightly modified guide body thus would be connected directly to a drill string. In the downhole drive example chosen in SUBSTIT~TE SI~EET

WO91/tO805 PCT/SE91/00034 3 2~7~0~
Fig. 1 the drill indicated at 22 is connected to be rotated within the casing tube 20 by the drill string 21 in unison with the guide body 18 while delivering impacts to the lat-ter.
The cy~indrical guide portion 19 of the guide body 18 is rotatably journalled in and centered by a casing shoe 23 ~orming the mouth of the casing tube 20 at the lower end thereof. The casing shoe 23 has a somewhat smaller i~ner di-ameter than the casing tube 20 and forms at the ~ransition thereto an annular shoulder 24, against which a rear ~lange 25 on the guide body 18 abuts in order to transmit impact energy thereto so as to drive down the casing tube 20.
Straight axial flushing grooves 26, for example three in num-ber, are provided on the guide portion 19 and extend through the rear flange 25 for purposes of expelling flushing medium and drill cuttings from the hole to the interior of the cas-ing tube 20. At least one of the grooves 26 should during drilling be positioned to receive flushing medium from the broad spacing radially behind the reamer 15. Preferably the guide portion has an annular groove 27 formed centrally there~
around for egualizing the ~lushing medium ~low emitted through the axial grooves 26. Flushing medium is supplied via passages 28 in the drill string 21 and guide body 18 and is supplied to the hole via a central passage 23 in the pilot bit 11.
The pilot bit 11 has an intermediate eccentric shaft 12 rearwardly prolonged by a threaded end 13 concentric with the pilot bit 11. The end 13 is received in centered threaded engagement with the guide body la and the intermediate eccen-tric shaft 12 carries pivotally the reamer 15 between a pro-jected drilling position according to Fig. 1 and a retracted position shown in Fig. 2. The drilling position, in which the pilot bit 11 toyether with the reamer 15 are adapted to drill a hole larger than the outer diameter o~ the casing tube 20, is defined by an inclined abutment 16 at one end of a ledge 51 at the rear of the pilot bit 11. Abutment 16 transmits ~ia a cooperating inclined lug 17 on the reamer 15 ~he joint ro-tation of the cirill string 21, guide body 18 and pilot bit 11 on to the reamer 15 and urges the latter axially against the guide body 18 in order to eliminate play during transmission Sl~BST~tlJl'E SHEET

WO91/1080S r~ PCT/SE91/00034 of impact energy therefrom. Upon turning of the drill string 21 180 degrees relative to the reamer 15, the straight rear portion o~ the reamer lug 17 moving along the ledge 51 is met by an axial abutment 14 thereat, Fig. 3, diametrically oppo-site to the inclined abutment 16. When brought together, the axial abutment 14 and the lug 17 define the retracted posi-tion, Fig. 2, in which the drilling tool lO can be raised through and lowered down through the casing tube 20.
The reamer 15, Fig.5, is a tubular substantially cylln-drical steel body 30 centered on axis K and provided along a parallel axis E with an eccentric through bore 3l whereby the reamer 15 is pivotally journalled on the eccentric shaft 12 of the pilot bit ll. By the bore 31 the reamer body 30 be-comes an eccentric symmetrically disposed with respect to a central plane through the axes K-E and having a radially pro-truding eccentric portion 32. That portion 32 has a.circular crest centered on an axis C coplanar with plane K-E and being the rotational axis of the guide body l8 and the entire tool lO. The crest of ~he eccentric ~ortion 32 is geometrically faced by an acute angle V of maximally about 36 degrees ex-tending from the axis C and ~orming therewith a circle sector symmetrically divided by the plane K-E-C. At its crest the portion 32 is bevelled forming an inclined conical surface 33 with axis C as center. Sur~ace 33 carries primary but~on in-serts 36,37,38 of hard metal which are inclined outwardly relative to the drilling axis C and whose radial reach de-finer during drilling the full diameter of the hole. The prl-mary button inserts, 37, Fig. 6, are preferably inclined 35 degrees relative to axis C and are grouped as close to one another as is permissible with respect to the necessary operational strength for the but~ons, by experience at a dis-tance between them of about 1.5 times their diameter. In hard rock it is preferred to have three primary but~ons 36-38 on surface 33 as shown, while in softer ground the number can be reduced to two. The outer pariphery of surf ace 33 outside angl~ V is rounded to con~orm with ~he mantle of reamer body 30 centered on axis E. The maximally possible value for angle V is limited by geometrical considerations depending on the size of the ~ull diameter drilled, the necessary ~ize of the SUB~TI~UTE SHEEr . WO91/10805 PCT/SE91/000~
~7~7~
shaft 12 for transmitting the impact energy required, and the demand that the primary inserts 36-38 on eccen~ric portion 32 upon retraction thereof should be retractable through the casing tube 20.
The reamer portion 32 has a plane axially direc~ed front face 34 into which the bevelled surface 33 merges along a circular line centered on drilling axis C. Front face 34 extends from the lug 17 to a diametrically opposed abutment 35 on a axially protruding portion 42 by which the reamer li rests against the back of the pilot bit 11, and which extends peripherally back to the lug 17. The front face 34 carries secondary hard metal button inserts 39,40 placed on the same radius fxom axis C within the sector angle V and staggered radially inwardly of the primary button inserts 36-38. The arrangement for working hard rock will as shown be two secon-dary inserts 39,40 inwardly o~ three primary ones 36-38 or, for softer ground, one secondary inside two primar~, in both cases in a symmetrical disposition xelative to the middle plane K-E-C. To allow for closely concentrated grouping of the inserts the secondary inserts 39,40 have a somewhat smaller diameter than the primary onès 36-38 and their last-ing attachment to the reamer 15 is assured by on the one hand inclining the secondary inserts somewhat less, for examp~e only 10 degrees, than the primary ones 36-38 inclined at 35 degrees, and on the other hand by disposing the secondary inserts radially at a sufficient distance from the inner boundary of the bevelled surface 33.
The flushing passage 29 wi~hin the eccentric shaft 12 of the pilot bit ll has a through crosshore 43 through which flushing medium is led to an inner supply groove 44 in the eccentric bore 31 o the reamer 15. Therefrom are branched two axially forwardly directed flushing grooves 45,46 ex-tending to the :Eront face 34 and opening towards respectively the abutment 35 and the lug 17. From the suppl~ groove 44 there preferably ex~end two rearward}y directed oblique channels 47,48 to the diamwetrically somewhat reduced rear portion 49 of the reamer 15. One of them, 47, Figs. 4,5, emerges some distance behind the area of the front face 34 between the inserts 36,3g and the ~butments 35,14. The other, SU~STITUTE 9HET

WO91/10805 ~ PCT/SE91/000 48, emerges also in rearwardly spaced relation at the plane of symmetry, Fig. 6. Through the channels 47,48 ~lushing medium is emitted to produce ejector action whereby flushing o~ the hard metal inserts 36-40 i.s enhanced.
During drilling the tool lO rota~es counterclockwise when viewed from the underside in Fig. l as indicated by the arrow 50 in Fig 5. The pilot bit ll drills, pre~erably like-wise by the aid of hard metal button inserts, a pilot hole that is reamed up by the reamer button inserts 36-40 to a full diameter big enough to enable the casing tube 20 to be driven down concurrently while drilling is in progress. In the closely united group of reamer inserts 3~-40 with all of them having their central axes within the limits of sector angle Y, the secondary button inserts 39,40 are retracted and are trailing in the rotational direction 50 in a staggered way relative to the leading first primary insert 36 and its followers 37,38. Thereby the duality of leading button inserts 36,39 jointly attain a rock ~reaking action directed somewhat inwardly in the rotational direction, i.e. in substance tangentially relative to the shaft 12, and towards the abutments 14,35, Figs. 3~5. This is the area swept by flushing medium (water,air,mist,or foam) f rom groove 45 and after reversal of the flow by the ledge 51 on the pilot bit 11 the debris loaded flushing medium low escapes rearwardly throu~h the broad clearance between the leading flank of the reamer 15 and the drilled full diameter hole. Simultaneously cleaning by flushing medium of the group of button inserts 36-40 is further enhanced by flushing medium emanating from the flushing groove 46, the ejector channels 47,48, and the debris laden retreating ~lushing medium flow from the perimeter of the pilot bit ll.
A separate trailing button insert 41, Fig 5,8, can be provided for working any residual rock fragments remaining in the radial spaci~g left between the primary 36-38 and secon-dary 39,4~ inserts. The trailing insert 4l is disposed straightly axially, is set across the inner borderline of the bevelled sur~ace 33 and is spaced angularly for example 37.5 degrees relative to ~lane K-E-C and axis C.
SUB~Tnn3T SHÆET

WO91/1080$ PC~/SE91/000~
7 207~7~, For purposes of drilling for example a 115 mm hole it is recommended to choose diameter 14.5 mm for the primary button inserts, diameter 10.0 ~n for the secondary, and 12.7 for the trailing insert.
In the embodiment of Figs. 8,9, a combined f lushing and digging groove 52 is provided Oll the reamer flank that f aces the rotational direction 50. The groove 52 extends shovellike towards the rear of the reamer 15, terminating on the reduced rear mantle portion 49 of the reamer body 30 some distance in f ront of flushing channel 47. The rotatio~ally leading border-line 53 o~ the groove 52 in the example shown is somewhat inclined away from the rotational direction 50, while its opposed straight ed~e 54 is reinforced by hard metal, pref-erably by application or stellite. The flushing medium stream issuing from groove 45 is reversed by ledge 51, catches from the area in front of the duality of leading button inserts 36,39 the normally coarse rock debris brokan out jointly by them, and expels the debris laden flushing medium through the reamer groove 52. The shovellike action of the groove 52 enhances the flow and so does its rein orced edge 54 by push-ing and drivin~ the cuttings in the rotational direction 50 for more easy removal. The concentrated ~lushing-away of debris from the area in front of the inserts 36,39 assures a reduced tendency towards secondary crushing of the cuttings, which due to the close adjacency of the foremost inserts 36,39 tend to become more coars grained than in conventional reaming. A flow enhancing action is also due to the rear-wardly ejected ~lushing fluid stream issuing from the channel 47 upstream of the groove 52.
Experience shows hat drilling in claybound ground be-comes more easy due to the cutting action of the radially protruding trailing edge 54 of groove 52, whereby the inburs~
of tough clay is severed and flushed away portionwise. The tendency towards plugged flushing passages is thus reduced.
In case of need the cutting edge 54 can be formed somewhat inclined, preferably helically with a steep pitch in the counterrotationa~ direction to assure better clay removal.
SUBSTlTlJTE SHEET

Claims

C l a i m s

1. A drilling tool for percussive and rotary drilling in advance of a trailing casing tube (20), in which tool (10) a) a pilot bit (11) via an intermediate eccentric shaft (12) is carried by a guide body (18), which is rotatably cen-tered in and by the mouth (23) of said casing tube (20) on the rotational axis (C) of said tool (10) during drilling, and is coupled to drive means (21,22) in said casing tube (20) for actuation of said tool (10), b) a tubular reamer has an eccentric protruding portion (32) carrying on one axial face thereof hard metal button inserts (36-40), and c) the reamer (15) is pivotally mounted on said eccentric shaft (12) between on the one hand a projected position, in which said eccentric portion (32) with the button inserts (36-40) thereon are adapted to ream up the hole from the ini-tial diameter produced by said pilot bit (11) to the full diameter of the hole enabling the casing tube (20) to be advanced thereinto, and on the other hand a retracted posi-tion, in which the drilling tool (10) can be passed through said casing tube (20), c h a r a c t e r i z e d t h e r e b y, that said reamer (15) on its eccentric portion (32) comprises a duality of adjacent radially spaced button inserts (36,39) leading in the rotational direction (50) during drilling of said tool (10) with the radially inner (39) of them trailing in said direction immediately behind he outer (36), said duality of botton inserts (36,39) thereby being adapted jointly to break rock in forward direction substantially tangentially relative to said shaft (12).

2. A drilling tool according to claim 1, w h e r e i n said button inserts (36-40) on said protruding portion (32) comprise radially outward primary button inserts (36,37,38) defining during drilling the full diameter of the hole, and secondary button inserts (39,40) disposed radially inwardly thereof, said primary and secondary button inserts (36-40) forming a closely united group with the button centers there-of falling within an acute angle (V) of a circle sector extend-ing from said rotational axis (C) and defining the perimeter of said eccentric reamer portion (32).

3. A drilling tool according to claim 1 or 2, w h e r e i n said reamer (15) on the flank thereof that faces the rotational drilling direction (50) is provided with a groove (52) extending axially in rearward direction rota-tionally in front of said button inserts (36-40) and adapted to lead away flushing medium and drill cuttings expelled from said inserts (36-40).

4. A drilling tool according to claim 3, w h e r e i n said groove (52) forms a an axial cutting edge (54) adjacent to and in front of said outer leading button insert (36).

5. A drilling tool according to claim 4, w h e r e i n said groove (52) is reinforced by hard metal material along said cutting edge (52).

6. A drilling tool according to claim 2, w h e r e i n said closely grouped primary and secondary button inserts (36-40) are outwardly inclined relative to said rotational axis (C), said secondary inserts (39,40) being less inclined and having a somewhat smaller diameter than said primary in-serts (36-38).

7. A drilling tool according to claim 2 or 3, w h e r e i n a supply groove (44) for flushing medium is provided within said reamer (15), a forwardly directed flush-ing groove (45) extends from said supply groove (44) and opens towards the area rotationally in front of said duality of button inserts (36,39).

8. A drilling tool according to claim 3, w h e r e i n a supply groove (44) for flushing medium is provided within said reamer (15) and an inclined axially rearwardly directed flushing channel (47) extends from said supply groove (44) radially in outward direction to the rear of said groove (52) whereby flushing medium ejected through said channel (47) is adapted to enhance removal of flushing medium through said groove (52) by ejector action.

9. A drilling tool according to claim 6, w h e r e i n said primary an secondary button inserts (36-40) are disposed with their centers symmetrically grouped within said acute sector angle (V) and comprise three outer primary button in-serts (36,37,38) with the intermediate one of them on the plane of symmetry of said sector and two inner peripherally staggered secondary button inserts (39,40) spaced from said plane.

10. A drilling tool according to claim 9, w h e r e i n said secondary button inserts (39,40) are spaced in radial direction inwardly of said primary button inserts (36-38) and a separate trailing button insert (41) on said reamer (15) outside said sector angle (V) is set to work any remaining rock in the radial spacing between said primary and secondary button inserts (36-40).