WO2003076761A1

WO2003076761A1 - Drill member for rock drilling and a method for manufacturing the drill member

Info

Publication number: WO2003076761A1
Application number: PCT/SE2003/000361
Authority: WO
Inventors: Johan Linden
Original assignee: Sandvik AB
Current assignee: Sandvik AB
Priority date: 2002-03-12
Filing date: 2003-03-05
Publication date: 2003-09-18
Anticipated expiration: 2004-09-12
Also published as: SE523940C2; SE0200728L; SE0200728D0; AU2003252825A1

Abstract

According to the present invention a thread joint of steel for percussive drilling is provided where flushing water is used, comprising at least one external thread (14) as well as an internal thread (12). The thread (16) comprises thread flanks (21,22) and thread bottoms (23) and thread crests (24) provided between flanks. Said members (19) consist of at least two different materials. The member is performed in a composite component (15). The thread bottoms (23) and the thread crests (24) consist of low alloyed steel. The invention further relates to a method for manufacturing the drill member.

Description

DRILL MEMBER FOR ROCK DRILLING AND A METHOD FOR MANUFACTURING THE DRILL MEMBER

Background of the invention

The present invention relates to a drill member for rock drilling and a method for manufacturing a drill member in accordance with the preambles of the appended independent claims.

Prior art

At percussive top hammer drilling in rock a drill string is intended to be fastened to a shank adapter in a drilling machine via one end surface of a rod or a tube. The other end of the rod or the tube is threaded either to another rod or another tube or a drill bit for percussive drilling. The rod or the tube can also be fastened to the shank adapter or another part with the aid of threaded sleeves. A flushing channel runs through the entire drill string in order to lead flushing medium to the drill bit for removal of drill cuttings.

During drilling the drill string, i.e. bits, rods, tubes, sleeves and shank adapters, are subjected to corrosive attacks. This applies especially at drilling underground where water is used as flushing medium and where the environment is moist.

Corrosive attacks are especially serious at the most highly stressed parts, i.e. at thread bottoms and reductions. In combination with pulsating strain, caused by impact waves and bending stresses, so-called corrosion fatigue arises. This is a usual cause for breakage of the drill string. Generally a low alloyed case hardened steel is used in the drill member. The reason for this is that abrasion and wear of the thread portions have for long been limiting the life spans. As the drilling machines and the drill members have improved these problems have diminished and corrosion fatigue become a limiting factor. The case hardening gives compressive stresses in the surface, which has a certain effect on the mechanical part of the fatigue. The corrosion resistance of the low alloyed steel is however poor and for that reason corrosion fatigue and breakages still occur easily. In US-A-4,872,515 or US-A-5,064,004 a drill member is shown where a threaded portion has been provided with a metallic material, which is softer than the steel of the drill member. Thereby is intended to solve the problem of frictional damages (pitting) in the threads by covering at least the parts of the thread of the drill member that cooperate with other parts of the threaded connection.

One method of eliminating corrosion fatigue is to make the rods in stainless steel such as in SE-A-0000521-5. The stainless steel is however relatively soft and consequently has inferior wear resistance than a carburized rod, i.e. it wears out relatively quickly. Through SE-C2-515 195 and SE-C2-515 294 thread joints for percussive rock drilling are shown. By covering the thread bottoms of the cylindrical external thread with at least one layer of a material with different electrode potential than the underlying steel an increased tool life for the threaded connection is attained.

Objects of the invention

One object of the present invention is to considerably improve the resistance to corrosion fatigue in a drill member for percussive rock drilling.

Another object of the present invention is to considerably improve the resistance against corrosion fatigue at sections with reduced thickness of the material in a drill member for percussive rock drilling.

Still another object of the present invention is to considerably improve the resistance to corrosion fatigue in thread bottoms in a threaded portion in a drill member for percussive rock drilling.

Still another object of the present invention is to provide a method for manufacturing a drill member with improved resistance against corrosion fatigue for percussive rock drilling.

Brief description of the drawings

These and other objects have been achieved by a thread joint and a drill member with features according to the characterizing portions in the appended independent claims with reference to the drawings.

Fig. 1A shows a tube and Fig. 1 B shows a rod, both in perspective views. Fig. 2 shows a blank for extrusion in a perspective view. Fig. 3 shows an extruded rod in a perspective view.

Fig. 4 shows an axial cross-section of a part machined from the rod in Fig. 3. Fig. 5A shows an axial cross-section of a male portion according to the present invention after machining of the part according to Fig. 4.

Fig. 5B shows an enlarged sectional view of the thread in Fig. 5A. Fig. 6 shows a drill rod according to the present invention in an axial cross- section.

Fig. 7 shows an axial cross-section of a female portion according to the present invention.

Detailed description of the invention

The invention relates to a drill member for rock drilling and a method for manufacturing a drill member with a flushing channel for percussive drilling with at least one reduction or a portion 40, 40' with relatively thin thickness of the material, which partly is performed in homogenous stainless steel in order to considerably improve the resistance against corrosion fatigue. In addition, the flushing channel is in one case performed in the same stainless steel and therefore corrosion fatigue therein no longer occurs during rock drilling. According to the invention a drill member is provided for percussive drilling, that is, a male portion 19 (Fig. 5A) or a female portion 26 (Fig. 7) equipped with an external thread 16 and an internal thread 16', respectively. The threads shown are so called cylindrical trapezoidal threads but other thread shapes may be used, for example conical threads or rope threads or a combination of these. With reference mainly to Figs. 5A and 5C the drill member 19 has a through flushing channel 20, through which a flushing medium, generally air or water, is led. The thread 16 comprises thread bottoms 23 and thread crests 24, with thread flanks 21 , 22 provided therebetween. The thread bottoms 23 and the thread crests 24 are both performed in low alloyed steel. The thread 16 has a depth D, which is defined as the perpendicular distance between the thread bottom 23 and the thread crest 24 and the low alloyed portion of the thread has a thickness T after machining. The depth D is generally in the range of 1-4 mm and the outer diameter of the rod is 20-70 mm. The ratio T/D is >1.0, preferably 1.1-4.0, preferably 2.0-2.5. In a preferred embodiment a trapezoidal thread (T38) with a depth D = 2-2.5 mm and a low alloyed steel with a thickness T of 2-8 mm, preferably around 4 mm is used. In other words, the stainless steel is radially spaced from the bottom of the thread or reduction 40 by a distance A, which is >0 mm, preferably <8 mm, most preferably 2-6 mm.

By making the thread bottoms 23 in both embodiments in low alloyed steel the corrosion fatigue will occur relatively soon in the low alloyed steel. However, when cracks derived from corrosion fatigue reach the stainless, underlying steel, further crack propagation will be stopped. Thereby, the male portion 19 obtains great resistance against corrosion fatigue. The stainless steel has a composition which gives a PRE value >10, preferably 12-17. PRE means Pitting Resistance Equivalent and describes the resistance of the alloy against pitting corrosion. PRE is defined according to formula PRE =Cr+3.3(Mo+W)+16N where Cr, Mo, W and N corresponds to the contents of the elements in weight percent.

The low alloyed steel in the shell 18 has a hardness >500 Vickers, most preferably 650-800 Vickers whereby good wear resistance will be obtained. The hardness can be obtained by making the component in tough hardened steel, by carburizing the surface or surface hardening by for instance induction heating. The low alloyed steel preferably has a composition in weight%

C 0.1-0.7

Si 0.1-1 Mn 0.2-2

Cr <5

Ni <5

Mo <2 the rest being Fe and inevitable impurities.

Male portions or drill members according to the invention are made as follows. In Fig. 1 A a tube 11 is shown and in Fig. 1 B a rod 12 is shown. The tube 11 and the rod 12 are fitted with fine tolerances, for example by shrink fit, into each other to form a blank 13 such as is apparent from Fig. 2 and are fixed by circumferential welds 14 at the ends of the blank. In addition the welds 14 give a protection against oxidation at the interface between the tube 11 and the rod 12 at the subsequent heating. The blank 13 is extruded in hot condition to a composite component 15 with a diameter that is adapted to the desired dimension of a thread 16 for percussive rock drilling (see Fig. 5A). With "composite component" is here meant an extruded tube or an extruded rod of at least two different materials.

The composite component in the shown embodiment is made of a rod 15 with a core 17 of stainless steel and a shell 18 of low alloyed steel. From this rod a conventional external thread or male thread 16 for percussive rock drilling is turned, such that both thread bottoms and thread crests and reductions 40 are obtained in the low alloyed shell 18. Alternatively, the core 17' may consist of low alloyed steel and the shell 18' of stainless steel (Fig. 7). From this rod a conventional inner thread or female thread 16' for percussive rock drilling is turned, such that both thread bottoms and thread crests and reductions 40 are in the low alloyed core 17'. The core 17' comprises a through-going flushing channel 20'. The entire thread should consist of a homogenous low alloyed steel to reduce the risk for the thread loosening from the stainless part. The machined ends are carburized in order to give hardness and wear resistance to the flanks of the thread 16, 16'. Coating these portions in order to avoid carburization thereof protects the stainless steel. The machined ends are then friction welded to a hexagonal rod or to a round rod of low alloyed or preferably of stainless steel (see Fig. 6) to a drill rod 25 which finally is hardened and annealed. Alternatively the threaded end could be welded directly to a rolled rod if the weld and the rod become strong enough. Then there is no need for hardening or annealing of the drill rod.

A central flushing channel is drilled. Alternatively, a tube can replace the rod 12 such that the finished extruded composite component 15 is made of a tube such that one doesn't have to drill a hole. In the latter case the extrusion blank 13 shall have a hole for a mandrel and therefore the rod that will constitute the core instead may be a tube blank or a solid rod that is drilled. Both the male portion 19 and the female portion 26 comprise impact transferring surfaces, that is, the end surface 19A and the bottom surface 26A, respectively.

Extrusion blanks 13 were manufactured at tests from tubes 11 of low alloyed steel, with composition 1 , outer diameter 77 mm and inner diameter 53 mm and stainless rod 12, with composition 2 and diameter 53 mm. The blanks were heated to 1150°C and were extruded to a rod with outer diameter of 43 mm. The diameter for the stainless steel was 30 mm. Investigations in optical microscope showed that the metallurgical bond between the low alloyed and the stainless steel was good. From the rods obtained through this procedure male portions 19 were manufactured by means of conventional machining. The thread was of the type T38 with outer diameter 38 mm and had the depth D 2.35 mm. The distance A was 3 mm and the thickness T was 5.35 mm, wherein T/D became about 2.3. These male portions were then case hardened, during which the end surfaces of stainless steel were covered by protective paint for avoiding the effects of the carbon containing gaseous atmosphere. The male portions were then friction welded to respective ends of a rolled rod 25, which included a flushing channel. Subsequently a flushing channel was drilled in each male portion and all rods were hardened from 1030°C.

The invention relates primarily to drifter rods, i.e. rods with male portions at both ends. One can however imagine also to make drill tubes or MF rods by the method according to the present invention. The latter has both male and female portion (MF=Male-Female).

The entire thread is thus performed in low alloyed steel and the stainless steel does not reach the bottom of the thread in the radial direction. In this way the stainless steel constitutes a barrier for corrosion fatigue when the corrosion induced cracks have grown through the low alloyed steel.

Claims

1. An member for percussive rock drilling where flushing water is used, comprising sections with reduced thickness of the material, at least one thread (16; 16"), said thread (16;16') comprising thread flanks (21,22) and thread bottoms (23) provided between flanks and thread crests (24), said member (19,26) consisting of at least two different materials, characterized in that the member is performed in a composite component (15) and in that the thread bottoms (23) and the thread crests (24) consist of low alloyed steel and in that the member comprises a flushing channel (20;20').

2. The member according to claim ^characterized in that a stainless steel is radially spaced from the bottom of the thread by a distance (A).

3. The member according to claim 2, characterized in that the distance (A) is >0 mm and <8 mm.

4. The member according to claim 2, characterized in that the distance (A) is 2-6 mm.

5. The member according to claim ^characterized in that one material (17;18') has a composition which gives a PRE value >10, preferably 12-17 and in that the low alloyed steel (18; 17') has a hardness >500 Vickers, most preferably 650- 800 Vickers.

6. The member according to claim 5, characterized in that the low alloyed steel has the composition in weight%

C 0.1-0.7 Si 0.1-1

Mn 0.2-2

Cr <5 Ni <5

Mo <2 the rest being Fe and inevitable impurities.

7. The member according to claim ^characterized in that the member (19;26) comprises a core (17;17') and a shell (18;18'), wherein anyone of the core and the shell consists of stainless steel while the other consists of low alloyed steel.

8. The member according to claim ^characterized in that the member (19;26) is firmly connected to an end of a rod or a tube of low alloyed or stainless steel and forms a drill rod (25) and in that the drill rod comprises a through-going flushing channel (20;20').

9. Method for manufacturing a drill member for percussive rock drilling, said member comprising sections with reduced thickness of the material, at least one thread

(16;16'), said thread (16;16') comprising thread flanks (21,22) and thread bottoms (23) and thread crests (24) provided between the flanks, said members (19;26) consisting of at least two different materials, characterized in that the method comprises the following steps: - providing a core (17; 17') and a shell (18; 18'), wherein the core and the shell consisting of different materials,

- fitting the core (17;17') into the shell (18;18') with close fit in order to create a blank (13),

- welding the ends of the blank (13) in order to fix the core relative to the shell, - extruding the blank (13) in hot condition to a composite component (15) and

- forming a thread (16; 16') for percussive rock drilling from the composite component (15) or a portion thereof, such that thread bottoms (23) and thread crests (24) are obtained in the low alloyed steel.

10. The method according to claims 9, characterized in that the method comprises the following further step: - friction welding the composite component or a portion thereof to a drill rod (25) of low alloyed or stainless steel.