WO1995033911A1

WO1995033911A1 - Drill bit

Info

Publication number: WO1995033911A1
Application number: PCT/NO1995/000090
Authority: WO
Inventors: Tor Berge Gjersvik
Original assignee: Lyng Drilling Products A/S
Priority date: 1994-06-07
Filing date: 1995-06-01
Publication date: 1995-12-14
Also published as: NO179954C; NO942101L; NO942101D0; NO179954B

Abstract

A drill bit for drilling in soil and rock formations, etc., where the drill bit is provided with ribs (3), having a trailing lateral surface (4) which defines the full diameter of the drill bit. Materials (8, 9), having greater wear resistance than the body (2) are inserted in the lateral surfaces (4), which materials (8, 9) comprise at least an element (8) of synthetic polycristalline diamond.

Description

DR I LL B I T

The present invention relates to a drill bit, as stated in the introductory part of claim 1.

Drill bits for drilling in formations in the ground comprise cutting elements which are fixed to either a body of steel or preferably an infiltrated matrix of tungsten carbide. The body has ribs to which the cutting elements are fixed. The ribs terminate at their trailing end in a lateral surface defining the diameter of the drill bit in question.

It is important that the portions of the ribs, defining the lateral surface of the drill bit, have a correct and precise gauge. The maximum acceptable deviation is 1/16", that is when the lateral surfaces of the drill bit are worn down so much that the diameter is reduced by 1/16" or more, the deviation is too big, and the drill bit has to be replaced. It has also been shown that the life span of the drill bit primarily is dependent upon the ability of the ribs to withstand wear on the gauge.

Previoulsy, the side edges of the drill bit have been strengthen by locating inserts of hard metal. This is known from US-patent 4 640 375. These hard metal inserts are situated perpendicular to the axis of the drill bit. When the lateral surfaces around these hard metal inserts wear, the hard metal inserts will exert a shear action, which increases the friction against the formation where the drilling is performed. This is caused by a sharp edge arising against the rotation direction of the drill bit, and this edge shears into the formation. Through uneven wear, the drill bit may also be a deviated by the frictional increase. The drill bit will then tend to not be directable in a controlled way.

In an other embodiment, it is known to locate natural diamonds and/or thermal stable diamond (TSD) in the lateral surface of the drill bit. These have a surface that is substan¬ tially less than that of the hard metal inserts, which causes less friction after the drill bit is exposed to wear. However, friction is still a problem causing abrasive wear of the outer surfaces of the drill bit, and may lead to reduced directional control of the drill bit. It is therefore an object with present invention to provide a device of the above mentioned kind, which after wear of the drill bit do not cause shear action which is known to occur using hard metal inserts and the friction problems which is known to occur using inserts of natural diamonds and/or thermal stable diamonds. The object of the invention is acheived with a device having features as stated in the characterizing part of Claim 1. The invention will now be further explained by an example of an embodiment, and with reference to the accompanying drawings, in which fig. 1 is a perspective view of a drill bit according to the present invention, fig. 2 is an axial section of the drill bit of fig. 1, fig. 3 is a cross section taken along the line III-III in fig. 1, and fig. 4 is an axial section through a core drill bit according to the present invention. Referring first to fig. 1, a drill bit is shown, which is generally identified by reference numeral 1. The drill bit 1 comprises a body 2 of infiltrated tungsten carbide of a per se known type. Along the body 2, and integrated therewith, are ribs 3, extending from full diameter in an area 4 in the rear of the drill bit and to an area 5 by the front part of the drill bit. Along the ribs are fixed cutting elements 6 extending from the front of the ribs and down to full diameter. In a per se known manner, the drill bit 1 is provided with orifices 7 in the front for the provision of drillling mud. Between the lateral surfaces 4 of two diametrically opposite ribs 3 there is a distance which exactly correspond to the diameter of the drill bit. This diameter is measured between what is considered as durable material in order to withstand abrasive wear of the lateral surfaces 4. According to the invention, this material is formed from elements of polycrystalline diamond (PCD). This material is synthetic diamonds comprising a matrix of diamond and cobalt. The elements 8 may be of a material which correspond to the material that is preferred in the elements 6. With reference to fig. 3 there is shown the location of the elements 8, compared to the lateral surface 4. The lateral surface 4 is curved in order to follow the drill diameter. The elements 8 are situated with an angle towards the direction of rotation. This angle α may lie in the range 0-20°, preferrably 8°. The elements 8 are situated so that they incline at an angle towards the direction of rotation. Thereby the wear will first occur in the trailing edge of the elements 8. This means that a sharp edge against the direction of rotation will not emerge, and thereby following shear action in the rotation. In use, this location causes the elements 8 to be exposed to a compressive force. They are more resistant to this compressive force than to the shear force, which is present in known hard metal inserts located perpendicular to ^■ the axis of the drill bit. By the fact that PCD is a material with a very low friction, the friction will be reduced by wear, due to the basic material in the lateral surfaces 4 will get a reduced diameter compared to the inserted PCD-bits, in contrast to known drill bits, which get an increased friction at the lateral surfaces by wear. The low friction also means that the temperature will be lower, and as a result, a better durability will be acheived. The lower coefficient of friction also implies a lower torque, so that the forces supplied to the drill bit, to a greater extent will be used for shearing at the elements 6, while in present drill bits being used to overcome the increasing friction of the lateral surfaces 4.

Furthermore, natural diamonds are situated in the rear of the elements 8. Fig. 4 shows an axial section through a core drill bit according to present invention. The core drill bit 1 is provided with cutting elements 6 in a per se known manner. Further, according to the invention, wear elements 8 are situated on the lateral surfaces 4. In this embodiment, elements 8 are also situated on an inner lateral surface 10 of the core drill bit 1.

Claims

Claims:

1. A drill bit for drilling in soil and rock formations, etc., which drill bit is provided with ribs (3) having a trailing lateral surface (4) which defines the full diameter of the drill bit, and wherein materials (8, 9) having a greater wear resistance than the body (2) are inserted in the lateral surfaces (4), characterized in that the materials (8, 9) comprise at least an element (8) of synthetic polycrystalline diamond.

2. A drill bit according to claim 1, characterized in that said elements (8) are inclined in an angle a towards the direction of rotation of the drill bit (1).

3. A drill bit according to claim 1-2, characterized in that the angle α is in the range from 0° to 20°.

4. A drill bit according to claim 1-3, characterized in that said elements (8) are inclined in an angle 8° towards the direction of rotation of the drill bit (1).

5. A drill bit according to claim 1-4, characterized by elements (9) of natural diamond situated on the lateral surfaces (4), behind the elements (8).

6. A drill bit according to claim 1-5, wherein said drill bit is a core drill bit, characterized in that elements (8) of synthetic polycrystalline diamond are also situated on an inner lateral surface (10) of the drill bit (1).