GB2258876A

GB2258876A - Tools

Info

Publication number: GB2258876A
Application number: GB9216537A
Authority: GB
Inventors: Alexander Brian Graham
Original assignee: Sandvik Rock Tools Ltd
Current assignee: Sandvik Rock Tools Ltd
Priority date: 1991-08-20
Filing date: 1992-08-04
Publication date: 1993-02-24
Anticipated expiration: 2012-08-04
Also published as: AU661005B2; JPH06212875A; DE4226976A1; GB2258876B; CA2076437A1; GB9117993D0; ZA925913B; AU2078192A; GB9216537D0

Description

1 TOOLS This invention relates to tools for breaking or excavating, such

as for mineral cutting, which comprise a working insert of a harder material projecting from a hole at the tapered front end of a body of the tool, typically of steel.

Such tools with working inserts of hard metal have been produced in configurations (EP 122893) which have a lower energy consumption for a given operating capability.

Although the front tip of the insert is intended to provide the cutting or breaking action in these low energy tools, any of the softer material of the body exposed to impact or abrasion during operation of the tool can suffer wear and damage, one result of which is to weaken the attachment of the insert. The tool then fails prematurely because the insert has been dislodged.

As regards the forms of tool illustrated in EP 122893, this kind of problem is more likely to be encountered when the insert is a simple cylinder with a conical tip. Other forms shown have inserts with conical portions much larger than the hole into which the insert fits, so that the outer regions of these conical portions provide protection for the forward end of the body.

However, these alternative hard metal inserts are more difficult to produce, because their complex shapes are not well adapted to the pressure sintering method that must be 2 used. They also require substantially more hard metal.

In SU 899916 it has been proposed to form the hard metal insert with a large disc-like skirt intermediate its length so that when the cylindrical rear end of the insert is placed in a fitting bore in the front of the tool body the skirt covers the front face around the bore. This requires less material than the large conical portions of the inserts shown in EP 122893, but the shape cannot be formed satisfactorily by sintering, because the very high sintering pressures demanded cannot be applied evenly and the insert will have weaknesses that will give premature failure.

DE 2442146 and 3005685 show examples of tool in which the front portion of the tool body is composed of a is matrix containing hard metal. This does not overcome the problem of wear because the softer mass of steel in which the hard metal is held is exposed and although the hard metal particles may not wear they will be dislodged as the steel wears. A greater concentration of hard metal in the matrix to avoid this disadvantage would lead to increased material costs without simplifying the manufacture of the tool.

The tool disclosed in GB 2004315 has, on the outer circumference of the leading end of its body, a cylindrical ring of hard metal as reinforcement of the body, but the metal body between the ring and the insert is still exposed to wear. Furthermore, to the extent that the outer ring functions to protect the tool against 3 abrasion in use it is not possible to use this solution to manufacture a so-called low-energy tool because the ring will only have this effect if the entire front end of the tool participates in the cutting or breaking action.

Finally, there may be mentioned examples of tools which can be considered analogous to that in GB 2004315 in that, instead of the outer ring of hard metal, there is a layer of hard metal extending as a complete sheath over at least the forward portion of the shank.

One example is to be found in US 4682987 in which the hard metal is applied as a fused coating to the shank, clearly a rather complicated and expensive solution. US 3627387 shows another example in which a considerably thicker sheath of hard metal is provided, adding to the cost of the tool.

According to the present invention, there is provided a tool comprising a working insert having a body portion held in an aperture in the forward end of a body of the tool and a tapered forward tip projecting from said aperture, a separately formed ring surrounding said body portion of the insert and covering a front face of the tool body, said insert and ring both being secured in position on the tool body and-being formed from a harder material than the tool body.

Preferably there is some radial clearance between the ring and the insert. One function of such a clearance would be to simplify not only the assembly but also the securing of the ring and insert in place. Thus 4 if they are secured by brazing, it is possible to place the brazing alloy in the tool body aperture the clearance allowing passage of the brazing material from the aperture holding the insert to flow into contact with the ring and simultaneously secure both parts in place.

The ring may take a variety of forms. A flat annular shape has particular advantages in simplicity of production; prior to sintering the individual rings can be formed simply by cutting them from an extruded tube of the material. It is not necessary that it is a closed ring, however and it may be preferred to make it up from a number of segments, particularly if a form other than the flat annular form is required.

The insert may alsobe given a variety of forms, both as regards the exposed cutting tip and the body portion within the main body of the tool. Generally, the cutting tip will have a rotationally symmetrical form but this may be conical or spherical for example. A generally cylindrical form may be most convenient for the body portion but not necessarily of circular cross-section.

One example of a tool according to the invention is illustrated in the accompanying drawing which shows it in a partly sectioned side view.

The main body 2 of the tool is entirely conventional, being made of steel with a central cylindrical shank 4 which locates the tool rotatably in a bore of a holder (not shown), a shoulder 6 at the forward end of the portion providing an abutment face 8 limiting the insertion of the tool into the bore, and a reduced diameter rear portion 10 on which a locking ring (not shown) can be attached to retain the tool in the bore.

At its forward end the tool body 2 has a tapered front portion 12 in which a central circular bore 14 receives a hard metal cutting insert 20 comprising a main cylindrical portion 22 projecting from the bore and a generally conical tip 24. The tool body has a flat annular face 16 surrounding the bore 14 and that face is covered by a separate hard metal ring 30 of flat rectangular cross- section. The ring outer diameter is chosen such that a line T tangential to the tapered tip and the periphery of the ring lies at a greater angle to the longitudinal axis L of the tool than does the tapered face of the tool body immediately behind the ring so that the body is within the conical envelope defined by the tangential line T. To avoid premature wear of the ring, however, that tangent line T to the tip and ring preferably lies at an angle not substantially greater than about 40' to the tool axis. There is a small radial clearance, eg. not substantially more than 0.5mm, and preferably not substantially more than 0.2mm, between insert 20 and ring 30.

The insert and ring are secured to the tool body by brazing. Brazing material (not shown) placed in the bore 14 before the insert 20 is melted and is able to flow up the sides of the bore and into the interfaces between the insert 20 and ring 30 and the ring 30 and body 2. In r, b this way, both parts 20,30 are brazed simultaneously to the tool body.

In use, the ring serves as a simple and economical shield over the most exposed part of the tool body to reduce the wear around the insert and so prolong the life of the tool. By shielding the metal of the body from direct impact with the surface being worked, eg. in rock cutting, the tool can also reduce the possibility of sparks being generated.

Depending upon the intended use, the ring may be given different forms but it is always made as a separate part to be assembled with the insert on the shank. For particular uses the insert and ring may be made of other materials, such as cubic boron nitride or polycrystalline diamond, including composites of two or more materials, and the two parts can be made of different materials from each other to reflect their different functions.

7

Claims

1. A tool comprising a working insert having a body portion in an aperture in the forward end of a body (2) of the tool and a tapered tip projecting from said aperture, a separately formed ring surrounding the body portion of the insert and covering a front face of the tool body, said insert and ring both being secured in position on the tool body and being formed from a harder material than the tool body.

2. A tool according to claim 1 wherein there is radial clearance between the ring and the insert.

3. A tool according to claim 1 or claim 2 wherein the ring has a flat annular shape.

4. A tool according to any one of claims 1 to 3 wherein a flat annular front face is formed on the tool body to receive the ring.

5. A tool according to any one of the preceding claims wherein a tangent to the tapered tip of the insert and to the ring lies at a greater inclination to a longitudinal axis of the tool than does the tool body periphery immediately rearwards said ring.

6.

A tool constructed and arranged for use and 8 operation substantially as described herein with reference to the accompanying drawings.