Boring or penetrating the earth – Bit or bit element – Bit with leading portion forming smaller diameter initial bore
Reexamination Certificate
1998-11-05
2001-04-10
Lillis, Eileen D. (Department: 3673)
Boring or penetrating the earth
Bit or bit element
Bit with leading portion forming smaller diameter initial bore
C175S381000, C175S385000, C175S405000, C408S204000, C408S224000, C279S019500
Reexamination Certificate
active
06213230
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a drilling tool especially for the rotary percussion drilling of preferably rock.
Drilling tools and especially rock drills are used for making perforations in concrete or masonry and, in particular, are also designed for use in drilling hammers. To make relatively large perforations, so-called drill crowns, such as are represented by way of example in DE 3,322,887, are generally used. Such a drill crown consists of a pot-shaped housing with hard-metal cutting bits arranged on the end face. A concentrically inserted centering drill serves for centering, especially during the initial drilling of the rock material.
Furthermore, to make generally relatively small perforations, so-called perforation drills have become known, these generally consisting of a solid drill head, the drill shank being provided with an integral or separate conveying helix (DE 2,856,205 A1; DE 3,614,010 A1). The rock drill according to DE 2,856,205 having a pot-shaped cross-drilling head also has a separately insertable centering drill.
Both with drill crowns and with perforation drills having exchangeable centering drills, there is the problem of placing the centering drill securely, but also exchangeably in a bore in the drilling tool. For this purpose, this bore for receiving the centering drill is designed generally conically, in order to receive a likewise conical centering drill shank. However, exchange after a lengthy operation of the drilling tool may present problems, since the clamping effect of the conical faces is so great that the centering drill cannot be removed without further action. For this purpose, DE 3,322,887 provides, for example, a transverse bore, in which the end of the centering drill projects. The centering drill can then be pressed out by means of a separate tool. However, such a transversely extending recess at the end of the conical seat in the drill crown shank constitutes a disturbance of cross section which not only impairs the transmission of percussion movements but also adversely weakens the cross section of the tool shank.
Furthermore, DE 3,322,887 has, on the centering drill, a retaining element which is designed as a separate ring. However, this device serves merely to prevent the centering drill from falling out inadvertently. Normally, the centering drill is seated firmly in the drill crown as a result of the conical frictional connection.
A further known solution according to German Utility Model GM 1,992,344 provides for the centering drill of a drill crown to be fastened axially non-displaceably within the drill crown shank by means of a bayonet-like connection. For this purpose, the centering drill has, at the rear end of its chucking shank, a flattening which cooperates with a bolt located eccentrically in a transverse bore. An additional groove approximately perpendicular to the flattening is connected to the transverse bolt in the manner of a bayonet fastening by a rotation of the drill. The centering drill shank is thereby secured axially non-displaceably against falling out.
The general prior art also includes fixing the centering drill in a drill crown by means of a transverse screw. In this case, the centering drill is recessed in the drill longitudinal direction in the region of the penetrating screw, so that, where appropriate, an axial movement of the drill is allowed.
The subject of Utility Model DE-U1-85 21 577 also shows a drill crown, with an axially movable centering drill, laterally arranged setscrews projecting into the receiving bore for the centering drill. In this case, the centering drill is designed as a known “SDS drill” which has longitudinal grooves for separate rotational takeup as well as axial securing by means of elements which in each case are separate. Such a tool, admittedly, allows a cost-effective use of a known SDS drill. However, the mechanical outlay on the shank of the drill crown is considerable.
The disadvantage of the known solutions having an axially movable centering drill is also that, during rotary percussion drilling, the centering drill executes relative to the remaining tool longitudinal and rotational oscillating movements which, under high stress, lead to destruction of the holding means for the centering drill. In particular, for example, the thread of a transverse holding pin is destroyed relatively quickly as a result of these oscillations. Also, in the case of percussion stress with an axially displaceable centering drill, the multiplicity of individual parts used according to Utility Model GM 85 21 577 are exposed to high wear.
Furthermore, the fixed attachment of the centering drill, for example by means of a conical seat, has the disadvantage that the drilling capacity is markedly reduced, in comparison with an embodiment in which the centering drill can also be set in axial oscillating movement as a result of percussion stress.
SUMMARY OF THE INVENTION
The object on which the invention is based is to avoid the disadvantages of the previously explained prior art and, in particular, to provide a mounting for a centering drill in a drilling tool, which mounting is intended especially for rotary percussion use and has long service lives, easy exchangeability of the centering drill and an improved drilling capacity.
The invention is based on the essential notion that a drilling tool especially for the rotary percussion drilling of rock is to be provided in an advantageous way with an exchangeable centering drill which is designed as a wearing part. At the same time, the centering drill itself is to be mounted axially movably within its receiving bore, in order to be able to be subjected to percussion stress, according to the invention the centering drill being secured against falling out via a preferably bar-shaped or tubular holding element. For this purpose, there is located in the drilling tool a recess or bore which is arranged transversely to the axial drilling direction and into which the holding means penetrates symmetrically relative to the longitudinal axis of the drilling tool, viewed centrally or in cross section, and cooperates with a likewise central, preferably symmetrical recess on the centering drill shank, which recess completely passes through the latter, in such a way that, despite axial movability, the centering drill is prevented from falling out and, at the same time, rotational takeup is implemented. This constitutes an especially simple and cost-effective solution, since the bar-shaped or tubular holding means serves at the same time as a rotational takeup and axial securing of the centering drill. For the exchange of the pin-like holding means, the latter can easily be removed from the transverse bore. Because of the inventively continuous recess in the centering drill shank, which has, for example, the shape of a symmetrical slot or is formed by a bore which is larger by comparison with the cross section of the holding means, the centering drill can execute longitudinal oscillating movements in the axial direction relative to the remaining drilling tool. Owing to the central arrangement of the penetration on the centering drill shank, a weakening is certainly produced in the drill crown shank, but it is symmetrical and, by contrast with an asymmetrical weakening such as is the case in a range of known embodiments, it effects symmetrical profiles of impulsive force and/or shockwaves both in the drill crown shank and in the centering drill, with the result that it is possible to achieve a comparatively high drilling performance. Moreover, the service life of the components is increased by the purely symmetrically occurring loads. The bore for receiving the centering drill is preferably designed in such a way that the bore bottom serves at the same time as a stop for the centering drill end, in order to transmit the axial percussions of the drilling tool to the centering drill. This avoids a reduction in the drilling capacity, such as occurs in an embodiment having a stationary centering drill. The centering drill, including its hol
Hawera Probst GmbH
Kinberg Robert
Lee Jong-Suk
Lillis Eileen D.
Spencer George
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