The invention relates to a down-the-hole drilling device according to the preamble of the independent claim directed thereto.

A way to carry out earth drilling in a developed manner with respect to traditional technique is known e.g. from Finnish Patent No. 95618. A drilling head in a drilling unit of the drilling apparatus that exists inside a casing pipe or in other words a so called earth pipe or casing pipe presented in this patent is formed of a first frame part and an annular second frame part, the drilling surfaces of which being provided with drilling organs, such as drill bits or like, of the first and second drilling means or in other words of a center drill or a pilot and a reaming drill or a reamer. In this solution the first frame part forming the pilot, is being released from the second frame part forming the reamer, in order to pull the same alone off from a drilled hole after the drilling situation.

The solution in question is provided with an arrangement, which locks the said drilling means together for a drilling situation unrotatively in respect with each other and in both directions longitudinally, in which context as an advantageous embodiment e.g. a bayonet coupling has been used. After many years of experience, the drilling device according to the above mentioned patent has proved very efficient in practise and also very easy to be adjusted for different kinds of drilling purposes. Currently the kind of drilling devices of this type or so called drill bits are widely used successfully. However, the drilling surface of drill bits of customary type are especially designed for drilling rock, which is a disadvantage when a drill bit will mainly be used for drilling different kinds of soil layers other than rock. A rock drill bit design is especially poor when drilling in hard clay and sand, because the impact will only reflect backwards in the drill bit due to a large and flat drilling surface thereof. A consequence of the above is that the penetration is slow, and the echoing impact energy has the tendency to break the drill bit.

An improvement in this respect is presented in international patent application PCT/FI2015/050090. This design has proven to be especially effective in clay and sand formations. However, in the drilling there have occurred jamming and vibration issues in boulders and moraine formations due to the long distance between the cutting inserts e.g. carbide buttons being submerged onto the drilling surface of the pilot. One design of this kind is shown in figure la. Because the drill bit needs to be able to drill efficiently in all ground formations, the depth of flushing grooves on the drilling surface has been diminished. This has, however, also decreased the benefit gained in clay and sand drilling .

It is an aim of the down-the-hole drilling device according to the present invention to bring about a decisive improvement particularly in the problems described above in drilling different types of soil and thus to raise essentially the level of prior art. In order to carry out this aim, the down-the-hole drilling device according to the invention is mainly characterized by what has been presented in the characterizing part of the independent claim directed thereto. As the most important advantages of the down-the-hole drilling device according to the invention may be mentioned simplicity of constructions and operating principle enabled by the same. The above are first of all thanks to the fact that the applicability of the drilling device, being found profitable in practice as such, can be further improved by making possible drilling with the same drilling device construction that has an efficiently operating drilling surface for a wide variety of soil types.

By adding a narrow protrusion essentially at the trailing edge of one or more grooves of the flushing channel assembly on the pilot drill bit surface, an optimized cutting effect can be achieved even with smaller sized grooves of the flushing channel assembly. Thanks to the narrow protrusions, the cutting effect can be restored even though the grooves of the flushing channel assembly on the drilling surface have been narrowed as shown in figure lb compared to the customary design as shown in figure la. Thanks to a protrusion being essentially narrow, it can easily penetrate to the soil by the hammering motion, which is why the cutting inserts can be placed further apart from each other than in customary designs. Thanks to the protrusions being placed in the trailing edges of the one or more flushing grooves, soil being cut by the protrusions is directed straight into the grooves of the flushing channel assembly, being thus efficiently flushed away.

One benefit of the present invention is also the very easy manufacturing of drill bits provided with the protrusions according to the invention, while, however, in principle customary drill bits can still be used without major modifications. The protrusions can easily be machined, processed or installed onto the drilling surface of the pilot during normal manufacturing process thereof, wherein no additional manufacturing steps are needed.

So, thanks to the invention, with a minor increase in the manufacturing costs, a drilling device of basically customary type can be significantly improved, which enables efficient use of the drill bit in every soil type or ground condition etc. Thanks to the invention, there is not a need for different types of drill bits for different ground conditions or soil types in order to drill efficiently. Moreover the increased efficiency will lower the cost per drill meter by enabling finishing the hole faster. This will also save time for the end user, lower fuel consumption during the drilling and cut down C0 ₂ emissions.

Other advantageous embodiments of the down-the-hole drilling device according to the invention have been presented in the dependent claims directed thereto.

In the following description the invention is being illustrated in detail with reference to the appended drawings, in which in figures la and lb

are shown a face view of a drilling device of customary type and a face view of an advantageous drilling device according to the invention, wherein only some of the cutting inserts are shown, in figure 2

is shown a longitudinal cross section of a customary down-the-hole drilling device with a casing shoe, and in figure 3

are shown face views and perspective views of different kinds of drilling devices according to the invention, wherein the cutting inserts and shanks have been left out.

The invention relates to a down-the-hole drilling device 1 for drilling to be performed with a casing pipe 2, wherein the drilling device comprises in its drilling head I with reference to figure 2: a drilling arrangement having first drilling means 4 for drilling a center hole and second drilling means 5 for reaming the center hole for the casing pipe 2; and a flushing flow arrangement 6 for feeding of a pressurized flushing medium onto a drilling surface P of the drilling arrangement by a feed flow arrangement 6a and for discharging the same from the drilling surface together with drilling waste backwards with respect to the drilling direction by an exhaust flow arrangement 6b. The casing pipe 2 is arranged to be pulled into the hole to be drilled by power influence F directed thereto from the drilling arrangement. The feed flow arrangement 6a is arranged to lead the flushing medium for drilling onto the drilling surface PI of the first drilling means 4 at a flushing channel assembly 6al therein in essentially radial direction r. The drilling surfaces PI, P2 of the first and second drilling means 4, 5 are provided with cutting inserts 10a submerged therein. The drilling surface PI of the first drilling means 4 i.e. the pilot comprises a protrusion assembly PT in order to enhance drilling efficiency and to guide drilling waste at the flushing channel assembly 6al.

As an advantageous embodiment of the down-the-hole drilling device according to the invention with reference to the exemplary design as shown in figure 2, the drilling head I of the drilling device 1 consists of a first frame part 4a and a second frame part 5a, wherein the drilling surfaces PI, P2 of the first and second drilling means 4, 5 are formed of end surfaces of the frame parts. The essentially rotationally symmetrical first and second drilling means 4, 5 are coupled with each other on the first hand at least during a drilling situation in a power transmitting manner by means of a coupling arrangement, in order to carry out co-operation thereof for a rotational motion, a feeding motion and/or a hammering motion and on the other hand removably in order to enable removal of the first drilling means 4 from a drilled hole.

The drilling device is provided with a casing shoe 8 for pulling the casing pipe 2 into the hole by means of a shoulder arrangement L enabling an independent rotational movement of the casing pipe 2 and the drilling device 1 with respect to each other and restricting mutual longitudinal s movement thereof, wherein the exhaust flow arrangement 6b comprises one or more longitudinal s return flow channels 6b' on the side surface of the first drilling means 4 for removing drilling waste between the first and second drilling means 4, 5 inside the casing pipe 2. The first frame part 4a comprises a centric duct 6a" for delivering of the flushing medium therefrom through one or more essentially longitudinal feed channels 6a' onto the drilling surface PI of the first drilling means 4 at one or more grooves of the flushing channel assembly 6al, the flow cross section of which gets wider in radial direction r toward the outer periphery of the first frame part 4a. With reference to figures lb and 3 the protrusion assembly PT is arranged in connection with a trailing edge of one or more grooves of the flushing channel assembly 6al. The trailing edge means, as shown in figure lb, the rear edge of the grooves with respect to the rotation direction w in drilling. As a furthermore advantageous embodiment of the down-the-hole drilling device according to the invention, with reference to the exemplary designs as shown in figure 3, length of the one or more protrusions of the protrusion assembly PT corresponds in a direct (see figures lb, 3a, 3c) , an angled (see figure 3b) or an arched manner essentially to the length of the one or more grooves of the flushing channel assembly 6al.

As a furthermore advantageous embodiment of the down-the-hole drilling device according to the invention, a protrusion of the protrusion assembly PT has a constant cross section perpendicular to its longitudinal direction thereof over the whole length thereof. The embodiments in figures 3b and 3c comprise furthermore supplementary flushing grooves 6a2 on the bottoms of the flushing grooves 6al.

As a furthermore advantageous embodiment of the down-the-hole drilling device according to the invention, cross section of a protrusion of the protrusion assembly PT perpendicular to its longitudinal direction diminishes toward cutting edge CE thereof. As a furthermore advantageous embodiment of the down-the-hole drilling device according to the invention, a protrusion of the protrusion assembly PT has rounded or conical cutting edge CE in a plane perpendicular to its longitudinal direction. Furthermore as an advantageous embodiment of the down-the-hole drilling device according to the invention, a protrusion of the protrusion assembly PT comprises essentially narrow protrusions that continue in an arched (see figure 3d) or in an angled manner uninterruptedly over the center part of the first drilling surface PI that is free of the flushing grooves 6al .

Furthermore as an advantageous embodiment of the down-the-hole drilling device according to the invention, a protrusion of the protrusion assembly PT is made of or coated with an essentially harder material, like carbide, tungsten carbide, titanium oxide etc., than the drilling head of the drilling device, such as the first frame part 4a. In this context the protrusion assembly may also comprise hard material inserts submerged onto the first frame part's drilling surface or replaceable single part or multi-part protrusions that are installed in place e.g. by pushing them in radial direction by exploiting slide grooves on the drilling surface.

The height of the protrusions of the protrusion assembly PT is e.g. between 0,5 - 15 mm and in most common applications typically between 1 - 8 mm. The height of the protrusions in typical applications is, however, essentially lower than the height of the cutting inserts or at least it doesn't exceed the height of the cutting inserts . On the other hand, instead of the type of embodiments shown in the drawings, it is naturally possible to use as the drilling device also other drilling devices that are applicable for the same purpose, in which a casing pipe may be exploited in connection with the drilling that is drawn into the ground unrotatively without or with a casing shoe. The casing pipe can naturally also be pulled into the hole ether by the second frame part i.e. the reamer (as in figure 2) or by the first frame part i.e. the pilot, in which case the reamer as a "reaming ring", may be situated further back in the longitudinal direction than the reamer presented in figure 2. It is not that significant for the down-the-hole drilling device according to the invention, either, how the first and second drilling means are coupled with each other, so that a wide variety of different solutions can be exploited as the power transmission assemblies between the same in addition to a bayonet coupling. Also the height of the protrusions of the protrusion assembly may vary depending e.g. on the drilling circumstances and on the size of the drilling device, in which context the exemplary limits given above for the height of the protrusions are simply examples of values suitable for most typical drillings.