Boring or penetrating the earth – Bit or bit element – With helical-conveying portion
Reexamination Certificate
2001-02-07
2002-09-17
Pezzuto, Robert E. (Department: 3671)
Boring or penetrating the earth
Bit or bit element
With helical-conveying portion
C175S415000
Reexamination Certificate
active
06450272
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drill for drilling in stone and, particularly, in concrete, and which is inserted in a mechanized hand-held tool and is subjected to rotational and percussion movements for cutting abrasive material.
2. Description of the Prior Art
The drills of the type described, because they are used for removal of abrasive material, require that the parts, which are inserted in the drill head, be made of hard metal. The insertable parts are fixedly secured in the drill head. Usually, the parts, which are formed as hard metal plates, are inserted in axially extending mortises formed in the drill head and are soldered to the drill head. Such a drill is disclosed, e.g., in German Publication DE 20 08 825. In the drill disclosed in DE 20 08 825, the bits smoothly pass into associated helix ridges of a helix used for removal of the drilled or cut material. To insure a more reliable securing of the hard metal plates in the drill head, according to European Publication EP 09 47 662 A1, the hard metal plates have additional prismatic projections which engage in corresponding recesses provided in the drill.
The drawback of such attachment of hard metal plates in axial mortises consists in that the hard metal plates easily break out upon a possible radial hooking of the places, in particular when the drill strikes a reinforcing metal. An encounter of the drill with reinforcing metal, because of a limited flexural strength of a hard metal plate due to its small thickness, results in generation of a localized tensile stresses in boundary surfaces of the mortises in which the portion of a respective plate engages. The localized tensile stresses of the boundary surfaces facilitate the breaking out of the hard metal plate. Also, the axially extending boundary surfaces are subjected to an excessive fatigue, which is caused by shear stresses resulting from the drill being subjected to axial percussions. A further drawback of the above-described attachment of hard metal plates consists in that the provision of mortises for receiving the hard metal plates reduces free space available for removal of the drilled-off material.
German Publication DE 43 39 245 discloses forming an entire drill head of a hard metal and securing the drill head to the drill body only over the end surface of the drill head which extends substantially perpendicular to the rotational axis of the drill. The solid hard metal head has a compact, substantially convex, polygonal shape with the lengths of its sides being substantially the same. Because of its shape, the solid hard metal head has a high inner stiffness and does not require provision of axially extending boundary surfaces which would facilitate breaking out of the bits. Rather, the boundary surface, which extends in the radial direction, is subjected to a compression pulsating load. However, the remaining superimposed torsional stresses can result in a torsional fatigue of the radial edge of the boundary layer. To prevent hooking in reinforcing metal, which leads to increased torsional stresses, usually, auxiliary cutting edges are provided between the main cutting edges and which are arranged exclusively on the radial edge of the head and are axially offset backward. The auxiliary cutting edges, due to their penetration resistance and mass inertia, prevent the main cutting edges from penetrating deeply into the reinforcing metal by temporarily lifting the drill from the reinforcing metal. The manufacturing and economical drawbacks of this drill result from a large volume of the solid hard metal head when the drill is designed for drilling large-diameter bores.
European publication EP 88 44 48 discloses a solid hard metal head with an “X”-shaped arrangement of four cutting edges, with the main cutting edges and the auxiliary cutting edges, which are formed as side cutting edges, being arranged, respectively, diametrically opposite each other and with respective main and auxiliary cutting edges forming an angle that deviates from 90°. The “X”-shaped, solid, hard metal head has essentially a rotationally symmetrical, crosswise, axially mirror symmetrical, prismatic shape. The base surface is provided with deep, concave, obtuse-angled notches which extend radially inward along one-third of the base surface parallel to the cutting edges over the longer surfaces. The notches serve for removal of the cut abrasive material. The side cutting edges trail the main cutting edges in the rotational direction, forming with the respective main cutting edges acute angles. As a result, a large recess on each of the short sides of the base surface is limited by the radial edge region and serves for removal of some of the cut abrasive material in front of the respective auxiliary or side cutting edge. Because in EP 88 44 48, the head is secured to the drill body only over its end surface, torsional stresses, which are generated upon hooking of the drill with the reinforcing metal, result in the torsional fatigue of the head end surface. Another drawback of this head consists in that because of an obtuse angle, in the rotational direction, between the auxiliary cutting edge and trailing the auxiliary cutting edge, the main cutting edge, a large rotational angle is needed in order to overcome the mass inertia. However, practically, it is impossible to form such an angle in low-speed, large-diameter drills.
German Publication DE 197 07115 discloses a drill with an even number, but more than two, of radial, arranged rotationally symmetrical, bits and having a prismatic, solid, hard metal head, with the bits not being formed as separates plates but forming an integral part of the head. The head is secured in corresponding grooves having axially extending surfaces and formed in the drill body. The head is secured to the drill body over the head end surface and along the surfaces of the grooves. The securing the head over its end surface and along the surfaces of corresponding mortises insures, even in large diameter drills, break-proof securing of the bits, and the danger of the bits breaking out is substantially reduced even if the drill encounters a reinforcing metal. However, the drawback of this drill consists in that providing axial mortises on opposite sides of each bit reduces free space for forming respective recesses necessary for removal of the drilled-off abrasive material.
Accordingly, an object of the present invention to provide a rock drill without the drawbacks of conventional prior art rock drill.
Another object of the present invention is to provide a rock drill with break-proof securing of the hard metal bits and which would provide a sufficiently large space for removal of the drilled or cut-off abrasive material, while insuring a high drilling efficiency.
SUMMARY OF THE INVENTION
This and other objects of the present invention are achieved by providing a rock drill in which the solid hard metal head is secured to the drill body over the end surface of the head and is additionally secured to the drill body over portions of the side surfaces associated with respective bits, located in a radially outer region of the head, extending substantially parallel to a rotational axis of the drill, and extending into mortises formed in the drill body, with the side surfaces including first surfaces, which are associated with at least some of the bits and are subjected to pressure acting in a rotational direction of the drill during operation of the drill.
According to the present invention, the solid hard metal head in addition to being secured to the end surface of the drill body, which lies perpendicular to the rotational axis, is secured to the drill body along a portion of the side surfaces of the bits which lie in the outer radial region of the drill head and extend, advantageously, parallel to the rotational axis. The side surfaces of at least some of the bits support the respective bits in the rotational direction, i.e., they are subjected to a certain pressure. As a result, a break-proof attachmen
Hauptmann Udo
Hofmann Karl-Heinz
Pröls Tim
Starkmann Josef
Hilti Aktiengesellschaft
Pezzuto Robert E.
Sidley Austin Brown & Wood LLP
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