Note: Descriptions are shown in the official language in which they were submitted.
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GROUND-ENGAGING TOOL FOR AN EXCAVATION BUCKET
BACKGROUND OF THE INVENTION
THIS invention relates to a ground-engaging tool, and more specifically to a
ground-engaging tooth for an excavation bucket.
Conventional ground-engaging teeth for excavation buckets generally are
designed to be replaced when wom. In some of the known anangements,
the teeth comprise one-piece tips which are wetded to a lip on the bucket and
which have to be cut off the lip when replaced. In other arrangements, each
tooth includes an adaptor which is either releasably attachable to a
nosepiece on a bucket lip or is welded directly to the bucket lip, and a tip
which is releasably attachable to the adaptor, typically with a locking pin.
This
type of tooth is replaced by removing the locking pin and sliding the tip off
the
adaptor.
In certain applications, for example dragline operations, the tips are exposed
to excessive abrasion and tend to wear down relatively quickly so that it is
necessary to replaoe these tips fairly often. Since replacement of the ground-
engaging teeth interrupts the dragline operation, it is desirable to have
relatively durable teeth which do not require frequent replacement.
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For the purpose of this specification, the term "excavate"
includes the operation of a dragline, and accordingly
reference to an "excavation bucket" should be understood to
include a dragline bucket.
SUMMARY OF THE INVENTION
According to a broad aspect of the present invention there is
provided a ground-engaging tool for an excavation bucket. The
ground-engaging tool includes an outer wear element in the
form of a tool body formed from a material having a hardness
greater than or equal to 35 Rockwell C hardness. The tool
body defines a contact surface at one end for receiving
impacts. A longitudinal axis extends rearwardly from the
contact surface, and at least one operatively upper surface.
An inner wear element, in the form of a hardened, wear-
retarding core, extends rearwardly from the contact surface or
a region approximate the contact surface for transferring
impacts through the tool body. The hardened core is formed
from a material having a hardness which is at least 20%
greater than the hardness of the material of the tool body and
defines a longitudinal axis which extends substantially
parallel to the longitudinal axis of the tool body and which
lies between the at least one operatively upper surface and
the longitudinal axis of the tool body.
Typically, the contact surface is sized so as to present a
blunt edge at one end of the tool body.
In a preferred embodiment of the invention, the hardened core
is in the form of a cylinder and the longitudinal axis of the
core is offset relative to the longitudinal axis of the tool
body.
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ln a particularly prefemed embodiment, the tool body Is formed from a steel
which has a yield strength of approximately 700 MPa and which is heat
treated to a hardness of approximately 40 Rockwell C hardness, and the
hardened core is formed from a Tungsten Carbide having a hardness of
approximately 83,5 Rockwell A hardness.
The tool body may be machined and the core may be press frtted into a pre-
formed hole in the tool body. In this case, an adhesive may be applied to the
core prior to insertion into the tool body.
Altematively, the ground-engaging tool may be formed in a casting process-
!n one arrangement, the tool body is designed to be welded to the lip of the
excavation bucket.
In another arrangement, the tool body includes a formation which is
releasably connectable to an adaptor on the lip of the excavation bucket.
Typically, the tool body tapers inwardly towards the contact surface.
RIEF DESCRIP'17ON OF THE DRAWINGS
The invention will now be described in more detail, by way of example only,
with reference to the accompanying drawings in which;
Figure 1 shows a perspective view of a ground-engag[ng tool
according to the present invention;
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Figure 2 shows a front view of the ground-engaging tool illustrated in
Figure 1;
Figure 3 shows a top view of the ground-engaging tool illustrated in
Figure 1;
Figure 4 shows a cross-sectional view along the line 4-4 In Figure 3;
and
Figure 5 shows a perspective view of the ground-engaging tool of the
invention welded to a lip on a dragline bucket.
DESCRIPTION OF AN EMBODIMENT
A ground-engaging tool according to the present invention is illustrated in
various views in Figures 1 to 4 of the accompanying drawings. The tool is
designated generaily with the reference numeral 10 and indudes a tool body
12 and a hardened core 14 which extends through a substantial portion of
the tool body.
As can be seen, the tool body 12 defines a contact surPaoe 16 at one end 18
thereof for engaging material to be excavated In use. The contact surface Is
sized to present a blunt edge at the end 18, as shown, and the tool body 12
is seen to taper inwardly towards this blunt edge: At an opposite end 20 of
the tool body there Is a formation 22 which facilitate.$the welding of the
tool
to a lip (not shown) on a dragline bucket (also not shown).
In this embodiment of the invention, the core 14 is in the form of a cylinder
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which extends from the contact surface 16 towards the formation 22. The
core 14 is positioned so that the exposed tip of this core is located at a
region
on the contact surface 16 at which the highest impact loads occur In use. In
tests conducted by the applicant, it has been found that the region of highest
impact loading is oNset relative to the longitudinal axis of the tool body 12
and accordingly the core 14 is arranged so that its longitudinal axis is
suitably
offset relative to the longitudinal axis of the tool body.
In practice, the tool body 12 is machined from a steel having a yield strength
of 700 MPa, typically WELDOXTM 700 steel, and Is subsequently heat treated
to a hardness of approximately 40 Rockwell C hardness. The core 14 Is
formed from a Tungsten Carbide having a hardness of approximately 83,5
Rockwell A hardness and is press fitted into a pre-fomned hole in the tool
body 12. If desired, an adhesive may be applied to the outer surface of the
core 14 immediately prior to inserting the core into the tool body.
With reference now to Figure 5 of the accompanying drawings, the ground-
engaging tool 10 is welded to a lip 24 on a dragline bucket 25 with butt welds
26. A protector plate 28 is then welded to the lip 24 with welds (not shown)
and to the tool 10 with a but weld 30. Typically, eight ground-engaging tools
are welded to the lip 24 at spaced-apart locations along the length of the
lip to form a plurality of ground-engaging teeth on the bucket 25.
In use, as the dragline bucket Is dragged through material to be excavated,
the contact surface 16 of each tooth receives impact loads which are
transferred to the lip of the bucket through the tool body,12. Since the core
14 has a higher hardness than the rest of the tool 10, the portions of the
tool
body 12 around the core initially wear down at a faster rate than the core,
and this results in the sharpening of the free end of the tooth. However, as
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the tool body 12 around the core 14 wears away and the tip of the core =
becomes more and more exposed, the core receives a greater proportion of
the impact loads and thereby retards the wear on the tool body. The increase
in the impact loading of the core 14 eventually results in the breaking away
of
the exposed tip of the core and the wear pattem is then repeated. When the
tool 10 is fully wom, it is cut off the lip and replaced.
It has been found that the presence of the core 14 which results in the wear
pattern described above serves to increase the wear life of the tool 10
substantially.
In another, non-iiiustrated embodiment of the invention, the ground-engaging
tool includes a formation which Is releasably connectable to an adaptor on a
lip of a dragline bucket.
Although the invention has been described above with reference to a
machined tool body, it should be appreciated that the ground-engaging tool
could also be formed in a casting process_
