Boring or penetrating the earth – Bit or bit element – Impact or percussion type
Patent
1997-03-26
2000-09-19
Schoeppel, Roger J.
Boring or penetrating the earth
Bit or bit element
Impact or percussion type
175430, 175432, 175434, E21B 1036
Patent
active
06119798&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to inserts of cemented carbide bodies and rock drill bits preferably for percussive rock drilling.
In U.S. Pat. No. 4,598,779 is shown a rock drill bit that is provided with a plurality of chisel-shaped cutting inserts. Each insert discloses a guiding surface that is relatively sharply connected to cutting edges. A relatively sharp connection is disadvantageous when using cemented carbide. That is, flaking may occur during severe rock drilling due to tension in the connections, such that straight holes may not be achieved in the long run. Also the shape of the known insert is not optimized for maximum wear volume. U.S. Pat. No. 4,607,712 discloses a rock drill bit which has a plurality of cutting inserts. The working part of each insert has a semispherical basic shape, to which has been added extra volume of cemented carbide. However, the prior art insert does not sufficiently support against the wall of the bore such that straight holes may not be achieved. Furthermore, connections between the components of the working part are relatively sharp thereby producing the above-mentioned tensions detrimental for hard cemented carbide. In addition, the spherical basic shape holds a relatively small volume of cemented carbide.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to avoid or alleviate the problems of the prior art. One object of the invention is to increase the wear resistance of cemented carbide bodies preferably for use in tools for rock drilling and mineral drilling. The wear resistance of the cemented carbide body can be increased by increasing the body volume in the area exposed to wear. In order to reach a distinct increase of the wear resistance, the volume of the area exposed to wear has to be increased essentially. A distinct increase of the wear resistance can be obtained when increasing the volume of the outer zone which is exposed to wear when the tool is in operation by at least 50%, probably 100% or more. Inserts in percussive drill bits wear most in the area which comes in contact with a hole wall and in the top of the insert where the rock has to be broken. In order to increase the wear resistance of an insert, the volume of the outer zone has to be increased in the area coming in contact with the wall and in the top. Prior art tools normally have inserts with an axial-symmetric top design (left part of FIG. 12). An increase of the outer zone which is exposed to wear often leads to a non-axial symmetric top. Due to the nature of the wear, which depends on the rock properties and the drilling conditions, the wear appears pronounced in the area coming in contact with the wall or in the top area where the rock is broken. It is important to respect this fact and increase the volume of the outer zone most where the inserts wear most.
Both longer life and higher penetration rate can be achieved because the optimal geometrical structure will not be destroyed as fast. An important advantage of the invention is a higher precision when using the material in drill bits. The enlargened volume of wear resistant material and thus the high wear resistance of the outer zone in the area exposed to wear, provides for straighter holes and much better diameter tolerances of the drilled hole. Also the intervals of regrinding can be prolonged; this leading to less efforts and dangers to the driller.
A still further object of the present invention according to a dependent claim where a polycrystalline diamond coating is provided on at least the working portion of the insert is to enhance the life of the insert although the PCD-coating may have cracked or flaked off.
The objects of the present invention are realized by an insert and a rock drill bit that has been given the characteristics of the appending claims.
BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1-5 show an insert suitable to drill under conditions where the wear of the insert is concentrated in the area close to the wall.
FIG. 1 shows an insert according to th
REFERENCES:
patent: 4572307 (1986-02-01), Tunell
patent: 4598779 (1986-07-01), Liljekvist et al.
patent: 4607712 (1986-08-01), Larsson
patent: 4724913 (1988-02-01), Morris
patent: 5248006 (1993-09-01), Scott et al.
Fischer Udo
Hartzell Torbjorn
Karki Kauko
Sandvik AB
Schoeppel Roger J.
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