GB2033454A - A rock drilling tool - Google Patents

Abstract

A rock drilling bit has at least two inserts having chisel-like cutting edges and a flushing bore (6) which extends from a flushing-bore chamber (7) and opens into the front side (1) of the bit. The inserts 2, 3, 4 taper in a direction towards the center of the bit, and the chisel-like cutting edges of at least two mutually radially opposing inserts (3, 4) are of mutually different lengths. The flushing bore (6) opens out at a location eccentrically of the center of the front surface (1) of the bit between said two inserts 3, 4. The flushing bore (6) extends in a preferred embodiment of the bit obliquely in relation to the axis of the bit, i.e. forms an angle with said axis. <IMAGE>

Description

SPECIFICATION A rock drilling tool The present invention relates to a rock drilling tool having a bit with a so-called solid center and at least two inserts having chisel-like cutting edges, and a flushing hole which extends from a flushing-hole chamber and opens out at the front side of the bit, the inserts being arranged in recesses end-milled in the bit and extending inwardly from the periphery of said bit and being open outwardly towards the periphery thereof and towards its front but being closed towards the center of said bit.

Boring bits having a solid center and endcut insert positions exhibit a number of advantages over bits having side-milled insert positions of conventional type with central studs; for example they are more reliable and the hard metal inserts are more reliably anchored against the center by soldering with reduced solder-stresses in the hard metal inserts as a result of reduced cutting length of the inserts and an increased cutting width, and a longer useful life in respect of drilling rock tending to reduce the diameter of such inserts, owing to the greater insert breadths and the increased depth to which the drill can be passed into readily-split types of rock, as a result of the larger center hole.One disadvantage with known boring bits having a solid center, however, is that the large center hole does not permit the rock to be satisfactory crushed or broken-up at the center of the bit in the case of certain, tougher types of rock.

An object of the invention is to provide a rock drilling tool having a bit with which all the advantages afforded by known bits having a solid center are retained and the disadvantage of poor crushing at the drill center in tougher kinds of rock is eliminated.

The rock drilling tool according to the invention is characterized in that the inserts taper in a direction towards the center of the bit, and in that the chisel-like cutting edges are of different length in respect of at least two mutually radially opposed inserts and the flushing hole opens out eccentrically in the front surface of the bit between said two inserts.

As a result of the novel design of the inserts having cutting surfaces of different magnitude and tapering in towards the center of the bit, it is possible to place the inserts nearer the center of the bit and to position the flushing hole eccentrically, thereby reducing the "dead" area in the center of the bit, which enables the tool to be passed into the rock more readily and the rock to be broken up at the center of the bit without leaving a center flash, even in the case of hard and tough types of rock, while improving the sludgespace. The inserts can also be made broader on their peripheral sides, so as to increase the wear strength of the bit towards its peripheral surface, and to provide better coverage of the drill surface.The bit can be optimized so that the ratio between hard metal and steel in the front surface of the bit is more suitably distributed between the peripheral parts of said bit and its central parts. In the majority of known bits, the width of the inserts is the same at the periphery as at the center, which means that the ratio of hard metal to steel in the front surface of the bit is much higher at the center than out at the periphery. By designing an insert in accordance with the invention, it is also possible to reduce the solder stresses occurring in the bit and also to decrease the amount of hard metal, particularly when the inserts are such that they also converge towards the neck of the bit. The invention also permits the user of harder types of hardmetal which are more resistant to wear.

The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 is an end view of one embodiment of a bit according to the invention, and Fig. 2 is a sectional view taken on the line Il-Il in Fig. 1.

The bit illustrated in Figs. 1 and 2 may be different types of bits or may be bits arranged in a so-called integral drill rod. The bit illustrated in the drawing has on its front surface 1 two mutually similar inserts 2, one insert 3 which is longer than the inserts 2 and one insert 4 which is shorter than the inserts 2.

Each of the inserts has chisel-like cutting surfaces with an edge 5. The inserts are arranged in end-milled recesses in the bit. The cutting surfaces of the inserts in said bit are of sector shape, i.e. tapered in a direction towards the flushing bore 6 of the bit, which bore extends from a centrally arranged flushing-bore chamber 7 and discharges in said front surface. The flushing bore extends obliquely in relation to the axis of the bit, i.e.

forms -an angle with said axis. Since the insert 4 is shorter than the radially opposite insert 3, the flushing bore 6 is eccentrically positioned in the front surface. The inserts are also so positioned in the bit that the main planes of said inserts form an angle of 90 with each other, although it will readily be understood that the inserts may be arranged in another way, for example in an arbitrary X-form. It will also be understood that the inserts may be arranged in any desired configuration in the front surface and extend, for example, in a cordal direction.In a conventional bit, the ratio of hardmetal to steel in the front surface 1 of the bit decreases radially outwardly from the center of said bit, since the front surface of the insert has the same width over the whole of its extension, i.e. the inserts are not of sector configuration, The ratio does not noticeably decrease in a case of the bit according to the invention, and the inserts may also be constructed in a manner such that the ratio of hardmetal to steel remains constant in the radial direction.

As will be seen from Fig. 1, the recesses, or insert seats, are provided with inwardly projecting lips 8 at the periphery of the bit. The purpose of these lips is to hold the inserts in position when the inserts are handled before being-soldered to the bit. The inserts can be dropped in the recesses from the front side of the bit.

The bit is provided with sludge grooves 9 between the insert seats.

Claims (3)

1. A rock drilling tool having a bit with a so-called solid center and comprising at least two inserts having chisel-like cutting edges, and a flushing bore which extends from a flushing bore chamber and opens into the front side of the bit, the inserts being arranged in recesses in the bit, said recesses extending inwardly from the periphery of said bit and being open outwardly towards the periphery thereof and towards its front but closed towards the center of said bit, characterized in that said inserts taper in a direction towards the center of the bit, and in that the chisel-like cutting edges of at least two mutually radially opposing inserts are of mutually different lengths, and in that the flushing bore opens out at a location eccentrically of the center of the front surface of the bit between said two inserts.

2. A tool according to claim 1, characterized in that the flushing bore extends obliquely in relation to-the axis of the bit, i.e.

forms an angle with said axis.

3. A rock drilling tool substantially as hereinbefore described with reference to the accompanying drawings.