Rotary percussion drill with a hard material bit

Abstract

A rotary-percussion drill, includes a hard material bit (2, 2′) having at least one cutting edge (3, 3′), and a shaft having an end (7, 7′) with an axial base surface (6, 6′) provided with a chamfer (8, 8′) at least on its outer radial rim, the bottom surface (4, 4′) of the bit (3, 3′) which lies opposite the cutting edge (3, 3′), being secured to the base surface (6, 6′) of the shaft end (7, 7′) by brazing alloy in a material-locking manner.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a rotary-percussion drill with a brazed hard material bit, in particular, to a rotary-percussion drill having a diameter from 4 mm to 45 mm for use with rotary-percussion hand-held power tools.[0003]2. Description of the Prior Art[0004]Usually, rotary-percussion drills of a type described above are provided, at the drill shaft end, with a chisel-shaped hard material plate that is brazed to the shaft end axially at its bottom and also over two opposite side attachment surfaces which are received in a receiving slot extending diametrically in the shaft end. Different heat expansion coefficients of the shaft end and the hard material bit in a direction normal to the axial direction, which are caused by large temperature differences which occur during butt-brazing and during percussion drilling, lead to high internal stresses, in particular in the brazing alloy that connects in a material-lo...

AI Technical Summary

Benefits of technology

[0014]Advantageously, in a radially middle region of the sector of two diametrical free surfaces, there are provided two additional radial chamfers between each two circumferentially adjacent blades. Thereby, a relatively large receiving capacity for the tolerated amount of the brazing alloy is provided, without the brazing alloy being squeezed radially outwardly, which improves removal of abrasively removed drillings, and, thereby, the drill feed.

Problems solved by technology

Different heat expansion coefficients of the shaft end and the hard material bit in a direction normal to the axial direction, which are caused by large temperature differences which occur during butt-brazing and during percussion drilling, lead to high internal stresses, in particular in the brazing alloy that connects in a material-locking manner the bit with the shaft end.

High internal stresses can cause failure of the drill.

In principle, a small thickness of the brazing alloy layer increases the connection strength of the material-locking connection, however, it also increases internal stresses in the brazing alloy and the hard material bit.

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