Cutting edge

Details Cutting edge Cutting edge

2000-12-22

2003-06-03

Batson, Victor (Department: 3671)

Excavating

Digging edge

Specific material

C172S747000, C172S701300

Reexamination Certificate

active

06571493

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a cutting edge well suited for use in the blade of a construction machine or track particularly used for snow removal.
BACKGROUND ART
Snow removal conventionally carried out by a motor grader or the like involves operation for removing snow cover and sherbet-like snow and operation for scraping snow which has been compressed into a frozen path (hereinafter called “compressed snow”). Snowremoving cars usually travel at a speed of about 30 km/h for removing snow cover and sherbet-like snow, and in the event of collision with projecting obstacles such as a manhole lid or a joint of a bridge during snow cover removal, a big shock occurs at the cutting edge end of the blade and causes chipping or cracking unless the cutting edge of the blade is made of a material having high toughness. For easy compressed snow removal, snowremoving cars travel with the blade being tilted (to change the angle of the blade edge), thereby grinding the tip of the cutting edge to be sharpened. However, in cases where the material of the blade cutting edge is low in toughness, the cutting edge would be chipped when its angle is changed with its tip portion in a sharpened condition.
For solving the chipping problem of blade cutting edges, there have been proposed, up to now, various means for increasing the durability of a blade cutting edge. Examples of them are as follows.
(1) The most popular one is the cutting edge such as disclosed in Japanese Patent Publication (KOKAI) Gazette No. 9-158144 (1997), which is made from steel for machine construction use (e.g., SCM435) which underwent thermal treatment to have a hardness of H
RC
45 to 55. The cutting edge
100
disclosed in this publication is designed as shown in FIG.
21
. Specifically, the tip portion
102
of an edge member
101
made from a steel plate of a specified size is sharpened and partially cut to form indents
103
at a specified pitch, thereby forming ground contacting teeth
104
at spaced intervals in the form of saw teeth. Reference numeral
105
is a mounting hole.
(2) The cutting edge
106
disclosed in Japanese Patent Publication (KOKAI) Gazette No. 8-302757 (1996) is designed, as shown in
FIG. 22
, such that a plurality of teeth
108
made from a hard metal (tungsten carbide) are attached to a main body
107
having high impact resistance. More specifically, a stepped portion
109
is formed at the leading end of the surface of the main body
107
and the plurality of divided teeth
108
arranged in a widthwise direction are brazed to the stepped portion
109
.
(3) There are known cutting edges which use, in their leading edges, a hard material in which a hard substance such as crushed hard metal grains is dispersed in a low-melting metal, and examples of such cutting edges are as follows.
{circle around (1)} Japanese Utility Model Publication (KOKAI) Gazette No. 55-85155 (see
FIG. 23
) according to which a hard material
110
is formed by enclosing a core material
111
by a plate
113
made of an appropriate metal (e.g., soft steel), the core material
111
being formed by integral solidification of crushed grains
112
of a hard alloy such as tungsten carbide in a solution of a base metal such as copper alloy.
{circle around (2)} Japanese Patent Publication (KOKAI) Gazette No. 56-13465 (see
FIG. 24
) according to which a hard material
115
is formed by dispersing crushed hard metal grains
117
in a low-melting alloy
118
within a flat box the three side of which are formed from a metal plate (steel plate)
116
which is easy to weld.
{circle around (3)} Japanese Patent Publication (KOKAI) Gazette No. 53-78602 (see
FIG. 25
) according to which a cutting edge
120
is formed by inserting a wear resistant plate-like piece
121
(hard material) made from a synthetic material containing wear resistant grains
122
so as to be held between two partially thinned steel plates
123
,
123
and then integrated with the latter by welds
124
,
124
′ (plug welds).
(4) A cutting edge made of a casting in which the leading end of the edge is provided with hard metal grains as an insert (produced by Pacal (U.S.A.)).
(5) The cutting edge such as disclosed in Japanese Patent Publication (KOKOKU) Gazette No. 5-54543 (see FIG.
26
). The cutting edge
125
has an edge body
126
and two kinds of hard metals
127
,
127
′ are brazed to the leading end of the edge body
126
in the form of layers, thereby achieving both wear resistance and impact resistance.
(6) The cutting edge having a bit mounted on its leading end (produced by Kennametal Inc. (USA)).
(7) The cutting edge such as disclosed in PCT Publication WO97/44994 (see FIG.
27
). In the cutting edge
130
, holes
133
are made at the leading end
132
of an edge body
131
at a specified pitch in a widthwise direction and pins
134
made from a hard metal are inserted into these holes
133
so as to project from the leading end
132
of the edge body
131
by an appropriate length t.
(8) The cutting edge disclosed in Japanese Patent Publication (KOKAI) Gazette No. 11-166249 (see FIG.
28
). In the cutting edge
135
, a hard material layer
137
is formed on the leading end of an edge body
136
by overlaying of a hard material.
The above known techniques have, however, revealed the following disadvantages. The cutting edge (
1
) is inexpensive and less dangerous, but has short service life, requiring frequent edge replacement. Service life can be improved by increasing the thickness of the edge, but this disadvantageously increases ground contact area and therefore decreases ground contact pressure, entailed by decreased compressed snow removal performance. With intent to increase compressed snow removal performance, the ground contact teeth
104
are arranged at spaced intervals in the form of comb teeth as shown in FIG.
21
. However, increased ground contact pressure causes significant wear, resulting in extremely short life.
The cutting edge (
2
) shown in
FIG. 22
uses teeth
108
made of a hard metal without processing/treatment, so that the cutting edge (
2
) costs high and has a high risk of breakage due to big cracks if the very brittle hard metal teeth directly collides with projecting obstacles such as rocks.
The following problem is presented by the cutting edges (
3
) which use a hard material of a structure in which a hard substance such as crushed hard metal grains is dispersed within a low-melting metal. Since wear due to scratching mainly occurs in snow removal, if the hard metal grains (hard grains) are small in size, the supporting base metal part is scooped away and looses its supporting force so that the hard metal grains drop off before they exert their intrinsic wear resistance. As a result, high wear resistance cannot be achieved.
The cutting edge (
3
)-
{circle around (1)}
shown in
FIG. 23
is formed by cladding the core material
111
with the plate
113
made of soft steel such that the plate
113
encloses the entire periphery of the core material
111
in its longitudinal section, and therefore the hard grains (crushed grains
112
) to be contained in the hard material cannot be introduced from other areas than the longitudinal end face. This cutting edge, therefore, suffers from the problem that where the entire length of the hard material is long, large-sized hard grains are difficult to introduce and likely to be nonuniformly dispersed.
The cutting edge of (
3
)-
{circle around (2)}
shown in
FIG. 24
has the disadvantage that where the hard material is welded to a blade or the like at the retaining back face which is formed by the metal plate (steel plate)
116
and located opposite to the surface in which the hard grains (crushed grains
117
) are dispersed, the surface having the hard grains (crushed grains
117
) are easily chipped or broken as it is susceptible to impact force due to direct collision with soil and rocks. The cutting edge (
3
)-
{circle around (3)}
shown in
FIG. 25
is complicated in structure and costly.
The cutting edge (
4
) has a disadvantage attributable to i

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