GB2517958A - Self-sharpening tooth - Google Patents

Abstract

A tooth for an excavator bucket comprise a ductile support material 25 , and a hard material 26 aligned with the projection of the tooth 23. The hard material may be an insert, or may be integrally formed or attached to the ductile material. In use, as the ductile material wears away, the hard material maintains a cutting edge 27 of substantially constant sharpness. The hard layer 26 may also consists of a form locking profile where it locks with the softer ductile layer 25.

Description

Self-sharpening tooth

Technical Field

This invention rdates to a self-sharpening tooth, particularly for the shovel or bucket of a digging or loading machine.

Background to the Invention

Digging or loading machines, such as self-propelled excavators, generally include a shovel or bucket having a toothed edge for initial engagement with the material or substrate to be moved. Typically a row of teeth will be provided to assist in breaking through a hard material or to penetrate a dense material, so that the material will pass easily into the body of the shovel or bucket.

In use, such teeth wear away, and it is known to provide individual teeth as attachments so that replacements can be fitted as required. It is also known to harden the outer surface teeth in order to providc a wear rcsistant layer, and to build-up worn teeth by the application of a new hardened layer -for example by weld hardfacing of e.g. a carbide a'loy matrix.

A characteristic of hard materials is that they tend to be brittle as compared with less hard materials. A ductile material is prefelTed, but such materials have a comparatively high rate of wear.

Ideally it would be desirable for such teeth to remain sharp as they wear away, but existing tooth designs tend to become blunt with use, notwithstanding that hard teeth become blunt more slowly than ductile teeth.

A further problem with hard faced teeth is that weaknesses may be introduced by the hardfacing, which may result in tooth breakage.

I

It has also been proposed to provide ridged teeth whereby a new point is created as each successive ridge is worn away in use. Such teeth also demonstrate weaknesses, and moreover the sharpness of a tooth is not optirnised throughout the fife thereof.

What is required is a self-sharpening tooth that remains sharp throughout the life of the tooth, such that the sharpness remains substantially constant notwithstanding that the tooth wears away.

In this specification the term "excavator" is used to encompass all such digging and loading machines and the term "bucket" is used to encompass all kinds of bucket, shovel, digging and loading apparatus used on such machines. The invention is described in relation to buckets of excavators, but could also be applied to single tooth machines such as pneumatic road drills, rock drills and the like.

Summary of the Invention

According to the invention there is provided a bi-component tooth for the bucket of an excavator, said tooth comprising a hard material and a relatively soft material in side by side relationship, said materials being aligned with the projection of said tooth.

In such a tooth, the relatively soft material wears away preferentially leaving the hard material as a projection at the tooth apex. Typically the rate of wear of the soft material reduces as the projection of the hard material is increased so that, depending on the abrasive qualities of material being excavated, the average projection of hard matenal may be relatively constant.

It will be understood that the hard material will also wear, but at a lesser rate than the relatively soft material; however during the service life of the tooth the hard material will provide a generally consistent sharp tip of substantially unchanging effectiveness.

It will be understood that the terms "hard" and "soft" are rdative. In practice the soft material may be a strong ductile steel, and the hard material may be a hard less ductile steel or another hard material such as ceramic, or a resin bonded material containing hard material such as industrial diamond.

The nature of the hard and soft materials will be determined by the skilled man according to the quality of the material to be excavated and the required service fife of the tooth. Additionally the shape of the tooth may be determined according to the materials and required service life.

The position of the hard material with respect to the soft material may be selected according to the intended duty. For example the hard material may comprise an outer surface of the tooth, or alternatively the hard material may be encased within the relatively soft material.

The hard material may extend substantially from the tip to the root of the tooth. In one embodiment the hard material may not extend to the extreme tip of a new tooth, so that the soft material can protect the hard material during transit and assembly to an excavator bucket. In use the soft material will wear relatively quickly. thus exposing the hard material at the tooth tip.

The hard material may not extend to the rear of the tooth, which may in practice comprise a tooth mounting feature wholly of softer material, such as a flange andJor attachment aperture to permit fitting of the tooth to an excavator bucket or the like.

The hard and soft materials may be integrated at the junction thereof so as to be inseparable, in the manner of a welded join. Alternatively, the hard material may be contained within the soft material by a form-locking profile, such as a mortise and tenon, or be surrounded by the soft material.

A tooth according to the invention may have several regions of hard material, so as to provide a saw-like profile to the leading edge, in use.

The hard material may have a substantially constant cross-section from root to tip, and may comprise a trapezoidal or a rhomboid section whereby one or more sharp side edges is presented as the soft material wears away. Such sharp edges can also contribute part of a form-locking profile.

In another aspect the invention may be characterised as a cutting or digging tooth comprising a base material of a first hardness, and a working material of a second hardness, the working material extending through the base material substantially from the tooth root to the tooth tip, wherein the second hardness is greater than the first hardness.

As noted above such a tooth may comprise a working material of substantially constant cross-section which is exposed for use as the base material is worn away in use.

In one embodiment the tooth of the invention is created by forming a tooth of a first material, and treating the tooth, for example heat treating to form the second material.

Accordingly in another aspect the invention provides a method of making a tooth for the bucket of an excavator, and comprising forming a tooth and treating the tooth to give a hi-component structure whereby a hard component adjoins a relatively soft component along the tooth substantially from root to tip. The hard and soft components may be considered as respective layers of homogeneous hard and relatively soft materials.

Typically heat treatment of a tooth is by heating and quenching to change the material structure used in the desired region(s). Localised heating by any suitable method may be used for example conduction heating, induction heating, laser heating and infra-red heating. Chemical hardening is also envisaged.

Alternatively the method may comprise forming the hard and soft components of the tooth separately, and joining them by welding, bonding, foim-locking or any other suitable method, or a combination of such methods.

In another method, the hard component may be formed by spray deposition of sufficient depth that the hard component is not merely a wear resistant surface coating, but is an integral substantially self-supporting cutting component of the tooth.

It will be appreciated that a tooth according to the invention may be attached to an excavator bucket or shovel in any suitable conventional manner, and that typically a plurality of such teeth are provided at the leading edge in a laterally extending formation.

In another aspect of the invention, the hard and soft materials may have a gradually merging interface whereby, for example. a ductile steel may change gradually to a harder wear resistant steel. This arrangement promotes the formation of a chisel like tooth tip such wear of the tooth is generally inversdy proportional to hardness.

In yet another aspect, the soft material may define a fracture plane whereby, at a threshold wear, the existing tooth tip fractures, leaving behind a new sharp tooth tip.

Brief description of Drawins

One feature of the invention will be apparent from the following description of an embodiment shown by way of example only in the accompany drawings.

Figure 1 is a conventional excavator shovel in side elevation, Figure 2 is a front elevation of the shovel of figure 1, Figures 3 and 4 illustrate wear of a conventional tooth of the shovel of figure i, Figures 5 to 7 illustrated in side elevation a tooth of the invention in several stages of wear, Figure 8 illustrate in cross-section an alternative tooth according to the invention.

Description of Embodiment

With reference to figure 1, an excavator shovel 11 is attached to actuating arms i2, 13 of a backhoe or other digging or loading machine. Such machines are very well known, and need not be further described. The lower leading edge 14 of the shovel includes a lateral array of teeth 15 to assist the shovel in breaking through the surface to be excavated.

Figure 3 illustrates the form of a typical new conventional tooth 15 from the front.

The tip 16a is relatively sharp. However, after a period of use the tip may wear away notwithstanding that it may be provided will a wear resistant coating. Such a tooth is illustrated in figure 4, and it will be observed that the tip 16b is substantially enlarged and is thus less effective in breaking through a suiface.

The invention is illustrated in figures 5 to 7. The front lip 21 of the shovel provides a flange 22 to which a tooth 23 may be attached and locked in place by a fastener passing through a through hole 24. The precise form of attachment of the tooth is not important, and any conventional demountable system maybe used.

The tooth comprises an upper layer 25 consisting of a ductile steel, and a lower layer 26 consisting of a hard, wear resistant material, such as a hard grade of steel. The ductile layer 25 adds strength and toughness to the tooth, but is comparatively soft as compared with the hard layer 26. In contrast the hard layer 26 may be relatively brittle, and unable to function in practice without the support of the ductile layer 25.

A new tooth form according to the invention is illustrated in figure 5. Figure 6 shows the same tooth form after a period of use. Both ductile and hard layer have worn away, but the hard layer protrudes at the leading edge 27. The leading edge 27 may have a chisel like form, as illustrated. The leading edge 27 may also wear on the underside.

Figure 7 illustrates the same tooth after a further period of wear. The ductile layer 25 has worn away still further, but the chisel edge of the hard layer 26 is maintained -in

contrast to the prior art arrangement of figure 4.

Accordingly the tooth of the invention remains substantially at the same sharpness throughout the life thereof, and maintenance and repair costs are reduced.

The hard layer may have a thickness in the range 5-30 mm and a width of 10 mm or more.

Figure 8 illustrates an alternative example in which the hard layer 26 consists of a form locking profile whereby it is mechanically locked into a softer ductile layer 27.

The ducifie layer may surround the hard layer if desired. In such an arrangement the ductile layer 25 wears away around the tooth, but the hard layer always protrudes to define a tooth tip of substantially constant size and sharpness.

Claims (12)

1. Claims I. A bi-component tooth for the bucket of an excavator, said tooth comprising a hard materia' and a relatively soft material in side by side relationship, said materia's being aligned with the projection of said tooth.
2. 2. A tooth according to claim I wherein said hard material extends substantially from the root to the tip of said tooth.
3. 3. A tooth according to claim 1 or claim 2 wherein said hard material is partially encased by said soft material.
4. 4. A tooth according to claim 3 wherein said hard material is wholly encased by said soft material.
5. 5. A tooth according to any prcccding claim whcrcin said hard material comprises a suitace of said tooth.
6. 6. A tooth according to any preceding claim wherein said hard material comprises a strip.
7. 7. A tooth according to claim 6 wherein said strip is retained in said tooth by a longitudinally extending form-locking profile.
8. 8. A tooth according to any preceding claim wherein said hard and soft materials are steel.
9. 9. A tooth according to any preceding claim wherein the hard material has a substantially constant section from root to tip.
10. 10. An excavator bucket having a plurality of teeth according to any of claims I to 9.
11. 11. A loading or digging machine having a bucket comprising a tooth according to any of claims Ito 9.
12. 12. A tooth substantially as described herein with reference to figures 5 to S of the accompanying drawings.