Boring or penetrating the earth – Bit or bit element – Impact or percussion type
Reexamination Certificate
2001-02-14
2003-04-22
Will, Thomas B. (Department: 3671)
Boring or penetrating the earth
Bit or bit element
Impact or percussion type
C175S394000
Reexamination Certificate
active
06550555
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a drill bit for drilling rock, having an elongated shank and at least one cutting plate at one end, the cutting plate having at least one end cutting edge running from the periphery to the rotary axis of the drill. The cutting edge is formed with the formation of a wedge angle &ggr; of an adjoining flank and rake face, the flank enclosing a clearance angle &bgr; and the rake face enclosing a rake angle &agr; with a plane E perpendicular to the rotary axis D, and the wedge angle &ggr;=180°−(&agr;+&bgr;)
Drills for drilling rock generally consist of a cylindrical steel shaft formed with helically twisted flutes for the disposal of the drillings, a chucking part or shank end for attachment in the drill, and a drill bit head at the other end. The drill bit head is formed by one or more cutting plates connected to the steel shaft, as a rule by brazing, and made of a wear-resistant material such as hardmetal.
Such drill bits are required to have as high a drilling capacity (drilling progress per unit of time) as possible, on the one hand, and as long a tool life as possible, on the other hand.
The end of the tool life of the drill bit is generally determined by the maximum permissible width of the wear mark along the cutting edge at the rake faces and flanks of the end cutting edges. The maximum permissible width of the wear mark is about ⅔ of the thickness of the cutting plate.
The wear mark results from roughening of the rake faces and flanks on account of friction with the removed material particles. In addition, high temperatures occur in the cutting-edge region due to the friction and lead to a diffusion of the metal particles from the cutting-edge region into the removed material particles. As a result, the cutting edge is weakened and, if the maximum permissible width of the wear mark is exceeded, failure of the cutting plate rapidly occurs.
In addition, if the maximum permissible width of the wear mark is exceeded and if the inadmissible dulling of the cutting edge associated therewith occurs, the material is only removed to a greatly reduced extent. The energy introduced by the drilling tool is increasingly converted into heat by the increased friction, so that the drill bit may heat up to the temperature at which the brazing filler metal with which the cutting plate is soldered in place melts. A loss of brazing of the cutting plate and thus failure of the drill bit is the result.
Since the cutting speeds in the peripheral region of the drill bit are markedly higher than in the center region, in particular the cutting-edge regions at the periphery of the cutting plate are subjected to increased wear.
The most widespread conventional drills for drilling rock have, as drill bit head, a cutting plate having two end cutting edges which adjoin one another in a roof shape and in each case have a constant clearance angle &bgr; and wedge angle &ggr; along their profile from the periphery to the center of the drill bit.
In this case, the clearance angle &bgr;is normally within a range of between 20° and 30°, whereas the rake angle is in the order of magnitude of about 60°, so that a constant wedge angle of between 90° and 100° is obtained.
In these conventional drills having constant clearance angles and wedge angles over the length of the end cutting edges, the end of the tool life is determined by the maximum permissible width of the wear mark at the peripheral region of the cutting plate. The maximum permissible width of the wear mark, on account of the higher cutting speed in this region, is reached much earlier than in the center region. The latter, of course, could actually continue to be used.
German Utility Model DE 298 19 388 U1 describes a hard metal cutting plate for use on a rock drill bit, in which cutting plate the clearance angle of the end cutting edge decreases with increasing distance from the rotary axis of the drill bit. Due to that construction, the support of the cutting edge, in particular at the peripheral region of the drill bit, is certainly improved and thus the risk of fracture of the cutting plate is reduced.
On account of the large wedge angle, however, the maximum permissible width of the wear mark is reached relatively quickly and the drilling capacity which can be achieved is not very high.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a drill bit for drilling rock which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which has a high drilling capacity and in which the period until the maximum permissible width of the wear mark is reached, in particular at the peripheral regions of the end cutting edges, is increased.
With the above and other objects in view there is provided, in accordance with the invention, a drill bit for drilling rock, comprising:
an elongated shaft having a forward end and defining a rotary axis of the drill bit;
at least one cutting plate disposed at the forward end of the elongated shaft, the cutting plate being formed with a rake face and a flank enclosing a wedge angle &ggr; therebetween and defining a cutting edge extending from a periphery to the rotary axis of the drill bit;
the flank enclosing a clearance angle &bgr; with a plane extending perpendicular to the rotary axis and the rake face enclosing a rake angle &agr; with the plane;
wherein &agr;+&bgr;+&ggr;=180°, and the clearance angle &bgr; increases, at least in segments thereof, with an increasing distance from the rotary axis, and the wedge angle &ggr; decreases, at least in segments thereof, with an increasing distance from the rotary axis.
In other words, the objects of the invention are satisfied in that the clearance angle &bgr; of the cutting edge, at least in sections, increases with increasing distance from the rotary axis D and the wedge angle &ggr;, at least in sections, decreases with increasing distance from the rotary axis D.
This achieves the effect that good support of the drill bit point is achieved by a large wedge angle &ggr; in the region of the rotary axis D of the drill, whereas the smaller wedge angle &ggr; in the region of the drill bit periphery ensures that the maximum permissible width of the wear mark, compared with prior art drills having a constant clearance angle &bgr; and wedge angle &ggr;, is not reached until later, so that the wear in the center and in the peripheral region is made more uniform and thus the tool life is increased.
In accordance with an added feature of the invention, the clearance angle &bgr; increases continuously and the wedge angle &ggr; decreases continuously. In this way, the cutting edge is subjected to uniform stress. No load peaks occur, which could cause premature failure of the cutting edge by fracture.
In accordance with an additional feature of the invention, the clearance angle &bgr; increases from approximately 30° at the rotary axis D to approximately 40° at the periphery of the drill bit, and the wedge angle &ggr; decreases from approximately 90° at the rotary axis to approximately 50° at the periphery of the drill bit.
In accordance with another feature of the invention, the cutting plate is a single cutting plate formed with two straight cutting edges enclosing a point angle &dgr; of about 130° with one another.
The configuration according to the invention is used especially frequently and advantageously in drills which are provided with a single cutting plate with two straight end cutting edges that enclose the point angle &dgr; of about 130°.
In practice, it has proved to be especially advantageous for a uniform high cutting capacity to provide a clearance angle &bgr; of about 30° and a wedge angle &ggr; of about 90° in the region of the rotary axis D, and to provide a clearance angle &bgr; of about 40° and a wedge angle &ggr; of about 50° in the peripheral region of the drill.
In accordance with a concomitant feature of the invention, each of the cutting edges is formed in two
Huber Ronald
Krenn Franz
Alpen-May-Kestag GmbH
Greenberg Laurence A.
Locher Ralph E.
Petravick Meredith C.
Stemer Werner H.
LandOfFree
Drill bit for drilling rock does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Drill bit for drilling rock, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Drill bit for drilling rock will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3010117