GB2196669A

GB2196669A - Improvements in cutter-bit assemblies

Info

Publication number: GB2196669A
Application number: GB08724088A
Authority: GB
Inventors: Wilhelm Stoltefuss
Original assignee: Gewerkschaft Eisenhutte Westfalia GmbH
Current assignee: Gewerkschaft Eisenhutte Westfalia GmbH
Priority date: 1986-10-21
Filing date: 1987-10-14
Publication date: 1988-05-05
Anticipated expiration: 2007-10-14
Also published as: DE3635706A1; GB2196669B; SE465326B; SE8703399L; GB8724088D0; SE8703399D0

Abstract

A cutter-bit (1) has a cylindrical shank (6) journalled for rotation in a bearing bushing (4) of a tool carrier (2). The bushing has a flange (10) adjacent a head (5) of the cutter bit (1). The flange (10) and the head (5) are shaped with mating curvilinear bearing surfaces (12,13). <IMAGE>

Description

SPECIFICATION Improvements in cutter-bit assemblies The present invention relates to a cutter-bit assembly as used for cutting or milling work in mineral mining or tunnel driving, for example.

Cutter-bit assemblies take a variety of forms but the invention is primarily concerned with an assembly consisting of a cutter bit with a cylindrical shank which is detachably and rotatably journalled within a bearing bushing of a carrier or holder. Such assemblies are well known for a cutting drum or roller where the bushings are fitted into the drum which thence forms the carrier. The cutter bits themselves are often subjected to very high loading forces transverse to their longitudinal axes. These forces, and especially impact forces, can fracture the shanks of the cutter bits or cause the shanks to work loose from the bushings.

Where the cutter bits are working with abrasive rock, dust can easily penetrate into the bushings and as the cutter bits rotate these particles grind away the mating cylindrical surfaces of the bushings and the cutter bit shanks. Any canting or tilting of the shanks in the bushings aggravates the situation and the working life of the assembly is drastically reduced. The cost of refitting and of consequential shut-downs is thus significant.

In an attempt to overcome these problems it has been proposed in DE-OS 3408209 to provide a hard metal insert above the bushing on which the head of the cutter bit bears. The insert takes the form of a ring with a Vshaped or frusto-conical surface which forms a seating for a similar surface of the cutter bit head. Another analogous assembly described in DE-OS 3439491 has an annular collar on the cylindrical shank of the cutter bit and this collar bears on an end face of the carrier. DE PS 2915510 describes an assembly where the bushing is keyed into a bore of the carrier and projects axially from the bore towards the cutter bit head to engage in a groove in the head. These known constructions attempt to provide a seal between the bushing and the cutter bit to resist the penetration of fine particles between the rotary surfaces of the shank and the bushing and to mitigate wear.

There is however still a need for an improved design.

A general object of the present invention is to provide such an improved cutter bit assembly. A more specific object of the invention is to improve the sealing action and preclude the ingress of dust and dirt into the bearing bushing and to resist impact and load forces more efficiently.

A cutter-bit assembly constructed in accordance with the invention comprises, as is known per se, a cutter bit with a head and a cylindrical shank, and a bushing which receives the shank for rotation. In accordance with the invention, the bushing has a convex surface which mates with a complementing annular concave surface on the head of the cutter bit. The bushing may have a part spherical surface which seats in a bearing cup surface in the head of the cutter bit to provide a self-centering or self-aligning action in the manner of a ball joint to hold the longitudinal axis of the shank of the cutter bit aligned with the bushing axis. The radii of curvature of these mating surfaces preferably have a common centre on these coincident axes of the bushing and the shank.

Despite the location of the head in the manner of a ball joint on the bushing, the shank is still freely rotatably in the bushing. The mating curvilinear surfaces also copes well with transverse forces and provides an enhanced sealing action. Even if the shank is forced to tilt slightly in the bushing no fine material can easily penetrate into the bushing and the working life of the assembly is thus prolonged. The mating curved surfaces preferably merge over rounded zones onto the main internal cylindrical surface of the bushing and the cutter bit shank. The cup shaped surface on the underside of the head of the cutter bit inherently provides an undercut and the radius of curvature of the mating surfaces is best made between one and two times the diameter of the shank.

The convex surface of the bushing is preferably provided on a flange integral with the bushing with rests in a recess in the carrier.

The recess can have a comparatively wide shoulder surface to support the flange over as large an area as possible. The flange of the bushing preferably has a wall thickness at least twice that of the wall thickness of its main cylindrical portion.

The shank of the cutter bit can be detachably locked in the bushing by locking means such as a circlip, or clamping device fitted to the lower end of the shank remote from the head of the cutter bit. To avoid undue wear on the lower end of the bushing a wear resistant ring is preferably fixed to the bushing or to the bore of the carrier.

The invention may be understood more readily, and various other aspects and features of the invention may become apparent, from consideration of the foliowing description.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing which is a part sectional side view of a cutter-bit assembly constructed in accordance with the invention.

As shown in the drawing, a cutter-bit assembly is composed of a carrier 2 and a cutter bit 1 with a cylindrical shank 8 rotatably fitted into a bushing 4 mounted in the carrier 2. The carrier 2 itself can take a variety of forms, for example, it can be, at least a part of, a cutting or milling roller or drum of a machine such as a tunnel-driving machine. The cutter bit 1 has a head 5 provided with a hard metal tip 8. The bushing 4, which can be made from steel, is fitted into a bore 3 in the carrier 2 and is secured against rotation. The shank 6 received in the bushing 4 is reduced in diameter in relation to the head 5 of the cutter bit 1. To releasably secure the cutter bit 1 to the carrier 2 a locking device 7 such as a circlip, clamping sleeve, or screw is provided on the lower end of the shank 6 to overlap the bushing 4.To protect the bushing 4 from premature wear due to contact with the device 7 a replaceable ring 15 is provided at the lower end of the bushing 4. The ring 1 5 can be replaced after it suffers wear. The wear ring 15 is fitted to the bushing 4 or to the carrier bore 3 with the use of pins, screws or the like.

The bore 3 has an enlarged counter-bored region 9 which forms a shoulder for supporting a flange 10 of the bushing 4 with mating surfaces 11. The flange 10 has a thickness, measured perpendicularly to the coincident longitudinal axes M of the shank 8 and the bushing 4 which is at least twice the thickness of the main cylindrical wall of the bushing 4. The flange 10 has an annular convex face 1 2 nearest the head 5 with a radius of curvature centred at 0 on the axes M. The radius of curvature is preferably from about one to two times the diameter of the shank 6. The curved face 12 is defined by a portion of the flange 10 which projects out from the bore 3. The bit 1 has a region between the head 5 and the shank 6 which has an an annular concave lower face 13 complementary to the face 12 and mating therewith. The surfaces 12,13 merge over rounded zones 14 with the inner peripheral surface of the bushing 4 and the outer surface of the shank 6 respectively.

The bit 1 bears with its curved support face 13 on the bearing face 12 of the bushing 4 in the manner of a ball joint and this permits slight articulation movements in all directions.

The relatively large area of contact precludes large pressures and transfers transverse forces from the head 5 to the carrier 2. Even if the longitudinal axis of the shank 6 should incline slightly relative to the longitudinal axis of the bushing 4 no fine material can penetrate between the head 5 and the flange 10 and find its way into the bushing 4.

Claims

1. A cutter-bit assembly comprising a cutter bit with a cylindrical shank and a head and a bushing mounted on a carrier which rotatably receives the shank; wherein the head and the bushing have mating curvilinear surfaces.

2. A cutter-bit assembly comprising a cutter bit with a cylindrical shank and a head and a bushing mounted on a carrier which rotatably receives the shank; wherein the head is provided with a concave undersurface and the bushing is provided with a convex end surface which engages with the concave surface in the manner of a ball joint.

3. A cutter-bit assembly according to claim 2, wherein the bushing has an integral flange adjacent the head of the cutter bit and the convex surface is provided on the flange.

4. A cutter-bit assembly according to claim 3, wherein the flange has a thickness at least twice the wall thickness of a main cylindrical portion of the bushing.

5. A cutter-bit assembly according to claim 3 or 4 wherein the carrier has a bore receiving the bushing and a recess adjoins the bore and forms a shoulder surface for supporting the flange of the bushing.

6. A cutter-bit assembly according to claim 5, wherein the convex surface of the bushing is formed on a portion of the bushing which projects outwardly from said bore.

7. A cutter-bit assembly according to any one of claims 2 to 6, wherein the radii of curvature of the concave and convex surfaces have a common centre on the aligned longitudinal axes of the bushing and the shank.

8. A cutter-bit assembly according to any one of claims 2 to 7, wherein the radii of curvature of the concave and convex surfaces are each between one and two times the diameter of the shank.

9. A cutter-bit assembly according to any one of claims 2 to 8, wherein the convex and concave surfaces merge smoothly with an internal cylindrical surface of the bushing and an external cylindrical surface of the shank, respectively.

10. A cutter-bit assembly according to any one of claims 2 to 9, wherein there is further provided a wear resistant ring at the end of the bushing remote from the head of the cutter bit and detachable locking means for retaining the shank in the bushing which engages with said ring.

11. A cutter-bit assembly substantially as described with reference to, and as illustrated in, the accompanying drawing.