Patent Description:
Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes. For the latter application, drill strings are typically used in which a plurality of rods are interconnected to advance the drill bit and increase the depth of the hole. In 'top hammer drilling' a terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes. Guide adapters may be included between the first drill rod and the drill bit to improve the straightness and quality of the hole drilled.

Drill rods, that are connectable to neighbouring drill rods and the drill bit or guide adapter, can have a shoulder. If a guide adapter is included, it will also have a shoulder. The shoulder is formed as a radially flared extension of the main length section of the drill rod or on guide adapter to provide increased efficiency in energy transfer between the drill rod and the drill bit or guide adapter or between the guide adapter and the drill bit. The shoulder on the first drill string rod that joins to the drill bit or guide adapter and the shoulder on the guide adapter is exposed to high levels of wear as the hole collapses and rock cuttings gather behind the drill bit. The problem with this is that as the shoulder wears the strength of the coupling will weaken prematurely. Additionally, as the shoulder wears away the contact area between the drill string rod and the drill bit or guide adapter or between the guide adapter and the drill bit decreases and therefore the transfer of the energy between the drill bit or guide adapter and rod or between the guide adapter and drill bit decreases, if the transfer of energy is not efficient energy will be wasted and the drilling efficiency will be compromised.

<CIT> discloses a rock drill bit having retrac teeth, <CIT> discloses an impact type drilling brazing tool, <CIT> discloses a drill bit with a detachable head, <CIT> discloses a rock drilling tool and reamer for percussive drilling, <CIT> discloses a drill string rod with guidance shoulder, <CIT> discloses a sucker rod, <CIT> discloses a plural part earth bit, <CIT> discloses a two piece drill bit, <CIT> discloses a method for drilling and a device therefore, <CIT> discloses a two-part drilling tool, <CIT> discloses a drill rod with a detachable bit.

Therefore, there exists a need for a drilling assembly design where the wear to the shoulder on the drill string rod and / or on guide adapter is reduced. One known solution is to hard face the peripheral edge of the shoulder; however, this adds considerably additional costs to the production of the drill string rod or guide adapter. Accordingly, there exists a need for a drilling assembly design where the wear to the shoulder of the drill rod and / or guide adapter is reduced without adding significant addition production costs.

It is an objective of this invention to provide a novel and improved percussive drilling assembly and apparatus where the shoulder on the first rod that is connected to the drill bit or guide adapter is less prone to wear and / or where the shoulder on the guide adapter that is connected to the drill bit is less prone to wear.

The objective is achieved by providing a drilling assembly according to claim <NUM> or claim <NUM>.

Advantageously, if the shoulder of the drill rod is at least partially encased inside the mounting sleeve of the drill bit or guide adapter the shoulder and / or if the shoulder of the guide adapter is at least partially encased inside the mounting sleeve of the drill bit it is protected from exposure to wear from rock cuttings. This is beneficial as it reduces the risk of premature failure of the drill rod and / or guide adapter. Further, as the shoulder is no longer subject to being worn away, the contact area between the shoulder and the mounting sleeve is constant, which means that there is no reduction in the efficiency of the energy transfer between the two parts so a higher level of drilling efficiency is maintained.

Preferably, at least <NUM>%, more preferably at least <NUM>%, even more preferably at least <NUM>%, even more preferably at least <NUM>%, most preferably at least <NUM>% of the length of the peripheral surface of the shoulder is encased inside the mounting sleeve. If less than <NUM>% of the length of the peripheral surface of the shoulder is encased, then the level of protection will not be sufficient to gain the benefit of reducing wear to the shoulder. By increasing the proportion of the shoulder that is encased inside mounting sleeve the higher the level of protection to wear will be achieved.

Preferably, the mounting sleeve on the drill bit and / or the guide adapter has a connecting section, having a first wall thickness at its thinnest point, for securing to the male connecting means on the drill rod and an encasing section, having a second wall thickness at its thickest point, for the shoulder of the drill rod to fit inside, wherein the second wall thickness is less than the first wall thickness.

Advantageously, the inside geometry of the female sleeve on the drill bit or guide adapter must be able to encase the shoulder from wear.

Preferably, the second wall thickness is at least <NUM>. If the second wall thickness is less than <NUM> there is an increased risk of cracking in this region.

Preferably, the encasing section has a length L<NUM> and the shoulder has a length L<NUM>, wherein L<NUM> is at least <NUM>%, more preferably at least <NUM>%, more preferably at least <NUM>%, even more preferably at least <NUM>%, most preferably at least <NUM>% of L<NUM>.

Preferably, the shoulder has an outer diameter D<NUM> and encasing section has an inside diameter D<NUM>, wherein D<NUM> is within the range of <NUM>-<NUM>%, preferably <NUM>-<NUM>% of D<NUM>.

If the outer diameter of the shoulder is too large compared to the inside diameter of the encasing section the fit between the shoulder and the mounting sleeve will be too tight and it will make uncoupling of the parts difficult. If the outer diameter of the shoulder is too small compared to the inside diameter of the encasing section the wall of the mounting sleeve in the encasing section will become too thin which increases the risk of cracking in this section.

Preferably, the clearance between the peripheral surface of the shoulder and an internal surface of the encasing section is between <NUM>-<NUM>. If the clearance is too small the fit between the shoulder and the mounting sleeve will be too tight and it will make uncoupling of the parts difficult. If the clearance is too large the wall of the mounting sleeve will become too thin which increases the risk of cracking in this section and the connection between the two surfaces will not be sufficient to maximize the transfer of energy between the two connecting parts.

Optionally, the peripheral surface of the shoulder and the internal surface of the encasing section are substantially cylindrical. The cylindrical profiles could either have uniform diameters along their axial lengths or could be stepped, so that at the peripheral surface of the shoulder and the internal surface of the encasing section have at least two sections, each section having a different diameter compared to the other sections but having a uniform diameter along the axial length of each section. The profile of the peripheral surface of the shoulder is designed to match and fit inside the profile of the internal surface of the encasing section.

Alternatively, the peripheral surface of the shoulder and the internal surface of the encasing section have a conical shape. The profile of the peripheral surface of the shoulder is designed to match and fit inside the profile of the internal surface of the encasing section.

Preferably, the junction between the edges of the peripheral surface and the first annular side surface and between the edges of the peripheral surface and the second annular side surface on the shoulder are chamfered or rounded off. Advantageously, this reduces the risk of chipping and breakage in these regions.

Preferably, the length of the shoulder is between <NUM>-<NUM>, more preferably between <NUM>-<NUM>. If the length of the shoulder is too short there is an increased risk of chipping or cracking occurring to the shoulder. If the length of the shoulder is too long unnecessary expense is added. The most preferred length of the shoulder will depend on the thread size being used.

Optionally, the male connecting means on the drill rod is a spigot having an externally threaded section and a non-threaded shank positioned axially between the threaded section and the shoulder and wherein the mounting sleeve on the drill bit or guide adapter is internally threaded. This mounting option is preferred for larger drill bits.

Optionally, the male connecting means on the drill rod is conical and non-threaded and the mounting sleeve on the drill bit or guide adapter is internally conical and non-threaded, forming a tapered connection. This type of connection would typically be used for smaller drill bits.

Preferably, the first annular side surface of the shoulder abuts an annular endmost surface on the connecting section of the mounting sleeve on the drill bit or guide adapter. Advantageously, this will mean that the shoulder is encased inside the drill bit or guide adapter.

Preferably, the drill bit or guide adapter has an outer diameter, D<NUM> at its annular rearward end in the section surrounding the encasing section, wherein D<NUM> is at least <NUM>% greater than the outer diameter, D<NUM>, of the shoulder, preferably D<NUM> is at least <NUM> greater than D<NUM> up to a maximum of the diameter of the drill bit or guide adapter at its largest cross section. This will provide the protection to the shoulder.

It should be understood that the shoulder could be either the shoulder on the drill rod or on the guide adapter and the mounting sleeve could be either on the drill bit or the guide adapter.

Another aspect of the present invention relates to a drill bit or guide adapter having a mounting sleeve that has a has a connecting section, having a first wall thickness, T<NUM>, at its thinnest point, for securing to the male connecting means on the drill rod and an encasing section, having a second wall thickness, T<NUM>, at its thickest point, for the shoulder of the drill rod to fit inside, wherein the second wall thickness, T<NUM>, is less than the first wall thickness, T<NUM>.

<FIG> shows a percussive drilling assembly <NUM> whereby a first drill rod <NUM> is releasably coupled to a drill bit <NUM> of conventional design. The percussive drilling assembly <NUM> is especially used for top hammer drilling. Shockwaves generated by a surface piston (not shown) are translated through the mated surfaces from the drill rod <NUM> to the drill bit <NUM>. The drill rod <NUM> comprises an axially extending main length section <NUM> that is terminated at one end by a male end <NUM> and at a second opposite end by a female end <NUM> having a longitudinal axis <NUM>. The drill rod <NUM> is capable of being coupled end-to-end with other adjacent drill rods <NUM> to form a drill string (not shown).

<FIG> shows the male end <NUM> of the drill rod <NUM> comprising a male connecting means <NUM>, in this case in the form of a spigot <NUM> and a shoulder <NUM> that projects radially outward relative to the main length section <NUM>, that extends over a fraction of the axial distance of the main length section <NUM>. The shoulder <NUM> comprises a peripheral surface <NUM> that extends axially along the length of the shoulder <NUM>, a first annular side surface <NUM> at the forwardmost end of the shoulder <NUM> that abuts the drill bit <NUM> adjacent to the male connection means <NUM>, alternatively called an annular abutment surface, and a second annular side surface <NUM> that flares radially from the main length section <NUM>. The main length section <NUM>, has an outer diameter D<NUM>, the shoulder <NUM> has a length L<NUM> and an outer diameter D<NUM>. The drill rod <NUM> has an internal bore (not shown) that extends axially through the main length section <NUM>, optionally the bore has a uniform diameter over its entire axial length.

Preferably, the corner or junction between the edges of the peripheral surface <NUM> and the first annular side surface <NUM> and between the peripheral surface <NUM> and the second annular side surface <NUM> on the shoulder <NUM> are chamfered.

<FIG> shows the cross section of the drill bit <NUM> as known in the prior art and <FIG> shows the cross section of drill bit <NUM> according to one embodiment of the present invention. In both versions the drill bit <NUM> comprises an axially forwardmost drill head of convention design for example comprising a rock crushing means, most typically this is a plurality of wear resistant cutting buttons projecting axially forward from the drill head (not shown); a plurality of grooves extending in the axial direction of the drill bit used for the removal of sludge and drill cuttings (not shown)); and a mounting sleeve <NUM> that comprises an internal cavity <NUM> extending axially from the axially rearward endmost surface <NUM> to receive the male connecting means <NUM> of the drill rod <NUM>.

In the version known in the prior art shown, as shown in <FIG>, the mounting sleeve <NUM> has a connecting section <NUM> suitable for coupling to the male connecting means <NUM> of the drill rod <NUM>.

<FIG> shows the drill bit <NUM> known in the prior art (as shown in <FIG>) releasably connected to the drill rod <NUM> wherein the first annular side surface <NUM> shoulder <NUM> of the drill rod <NUM> abuts the annular endmost surface <NUM> of the drill bit <NUM> such that a "shoulder contact" is formed.

In the version according to one embodiment of the present invention, as shown in <FIG>, the mounting sleeve <NUM> is modified so that it has a connecting section <NUM> suitable for coupling to the male connecting means <NUM> of the drill rod <NUM> and additionally also has an encasing section <NUM> suitable for the shoulder <NUM> of the drill rod <NUM> to fit inside. The connecting section has a wall thickness T<NUM> at its thinnest point, that is thicker than the wall thickness T<NUM> of the encasing section <NUM>, at its thickest point. Preferably, T<NUM> is at least <NUM>% greater than T<NUM>.

<FIG> shows the drill bit <NUM> according to an embodiment of the present invention whereby the modified drill bit <NUM>, as shown in <FIG>, is releasably coupled to the drill rod <NUM> so that the shoulder <NUM> of the drill rod <NUM> is at least partially encased in both the radial and axial directions inside the drill bit <NUM>. In other words, the drill rod <NUM> is at least partially enclosed inside the drill bit <NUM> in both radial and axial directions, so that the drill rod <NUM> is inserted inside at least part of the drill bit <NUM>. The first annular side surface <NUM> of the shoulder <NUM> on the drill rod <NUM> now abuts an annular endmost surface <NUM> of the connecting section <NUM>. Preferably, at least <NUM>%, more preferably at least <NUM>%, more preferably at least <NUM>%, even more preferably at least <NUM>%, most preferably at least <NUM>% of the length L<NUM> of the shoulder <NUM> is encased or enclosed inside the mounting sleeve <NUM> within the encasing section <NUM>.

The encasing section <NUM> has a length L<NUM>. Preferably, the length of the encasing section L<NUM> is at least <NUM>% of the length of the shoulder L2, more preferably at least <NUM>%, more preferably at least <NUM>%, even more preferably at least <NUM>%, most preferably at least <NUM>%. Preferably, L<NUM> is <NUM> to <NUM>, more preferably about <NUM>.

The encasing section <NUM> has an inside diameter D<NUM>. Preferably the outer diameter D<NUM> of the shoulder <NUM> is within the range of <NUM>-<NUM>% of D<NUM>, more preferably <NUM>-<NUM>%. The clearance <NUM>, which is the radial distance between the peripheral surface <NUM> of the shoulder <NUM> and an internal surface <NUM> of the encasing section <NUM>, is preferably between <NUM>-<NUM>. The drill bit <NUM> has an outer diameter, D<NUM> at its annular rearward end, in the section surrounding the encasing section <NUM>. Preferably, D<NUM> is at least <NUM>% greater than D<NUM>. Preferably, D<NUM> is at least <NUM> larger than D<NUM>, up to a maximum of the diameter of the drill bit <NUM> at its largest cross section.

In one embodiment, the peripheral surface <NUM> of the shoulder <NUM> and the internal surface <NUM> of the encasing section <NUM> are both substantially cylindrical as shown in <FIG>. If the shoulder <NUM> and encasing section <NUM> are substantially cylindrical they could either have a uniform diameter along there is a stepped profile such that the peripheral surface <NUM> of the shoulder <NUM> and the internal surface <NUM> of the encasing section <NUM> have at least two sections, each section having a different diameter compared to the other sections, but having a uniform diameter along the axial length of each section.

<FIG> shows an alternative embodiment wherein the peripheral surface <NUM> of the shoulder <NUM> and the internal surface <NUM> of the encasing section <NUM> have a conical shape, having either straight or curved profile.

In one embodiment, as shown in <FIG>, <FIG>, <FIG> and <FIG> the coupling between the drill bit <NUM> and the drill rod <NUM> is formed by the threaded connection. In this embodiment the male connecting means <NUM> on the drill rod <NUM> is a spigot <NUM> that projects axially forward from the shoulder <NUM>. The spigot <NUM> has an externally threaded section <NUM> and a non-threaded shank <NUM> positioned axially between the threaded section <NUM> and the shoulder <NUM>. To couple with this the cavity <NUM> inside the mounting sleeve <NUM> on the drill bit <NUM> is internally threaded <NUM>.

<FIG> shows an alternative embodiment, wherein instead of a threaded coupling, a tapered connection is formed. In this embodiment the male connecting means <NUM> on the drill rod <NUM> is conical and non-threaded and mounting sleeve <NUM> is internally conical and non-threaded, so that the parts are held together by friction.

Any other suitable connecting means could also be used. Any type of connecting means could be combined with any of the profiles of the shoulder <NUM>.

Claim 1:
A drilling assembly (<NUM>) for percussive drilling, comprising a drill bit (<NUM>) and a drill rod (<NUM>);
the drill rod (<NUM>) comprising a hollow elongate main length section (<NUM>) extending axially between a male end (<NUM>) and a female end (<NUM>); the male end (<NUM>) comprising a male connecting means (<NUM>) and a radially projecting shoulder (<NUM>) that axially separates the main length section (<NUM>) and the male connecting means (<NUM>); the shoulder (<NUM>) comprising a peripheral surface (<NUM>) having a greater outer diameter (D<NUM>) than the outer diameter of the main length section (D<NUM>), a first annular side surface (<NUM>) that abuts the drill bit (<NUM>) and a second annular side surface (<NUM>) that flares radially from the main length section (<NUM>);
the drill bit (<NUM>) comprising a mounting sleeve (<NUM>) for connecting to the drill rod (<NUM>);
wherein the peripheral surface (<NUM>) of the shoulder (<NUM>) on the drill rod (<NUM>) is at least partially encased in both radial and axial directions inside the mounting sleeve (<NUM>) of the drill bit (<NUM>);
wherein the first annular side surface (<NUM>) of the shoulder (<NUM>) on the drill rod (<NUM>) abuts an annular endmost surface (<NUM>) on a connecting section (<NUM>) of the mounting sleeve (<NUM>) on the drill bit (<NUM>);
wherein the mounting sleeve (<NUM>) on the drill bit (<NUM>) the connecting section (<NUM>), has a first wall thickness (T<NUM>) at its thinnest point, for securing to the male connecting means (<NUM>) on the drill rod (<NUM>) and an encasing section (<NUM>), having a second wall thickness (T<NUM>) at its thickest point, for the shoulder (<NUM>) of the drill rod (<NUM>) to fit inside, wherein the second wall thickness (T<NUM>) is less than the first wall thickness (T<NUM>);
characterized in that:
the peripheral surface (<NUM>) of the shoulder (<NUM>) and an internal surface (<NUM>) of the encasing section (<NUM>) are substantially cylindrical; and
wherein at least <NUM>% of a length (L<NUM>) of the peripheral surface (<NUM>, <NUM>') of the shoulder (<NUM>, <NUM>') is encased inside the mounting sleeve (<NUM>).