Note: Descriptions are shown in the official language in which they were submitted.
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LATCH SYSTEM FOR A POWER SHOVEL DIPPER DOOR
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application
No. 61/605,550,
filed March 1, 2012, the entire contents of which are hereby incorporated by
reference.
BACKGROUND
[0002] In heavy earth moving equipment or excavators, such as power shovels
for mining, it
is typical to employ a large dipper or bucket for shoveling the materials from
the work site. The
dipper is normally provided with teeth on the front to provide a digging
action against the surface
being worked and further includes a hollow dipper body for collecting the
material so removed.
On the rear of the dipper, a door is pivotally mounted. A latch mechanism
secures the door in its
closed position and, when released, allows the door to open. Conventional
latch mechanisms
typically include a moveable latch lever generally beneath the dipper door.
The latch lever is
typically coupled to a slidable latch bar that selectively engages a latch
keeper. To open the
dipper door, the latch lever is moved, which causes the latch bar to slide
away from the latch
keeper and thereby disengage from the latch keeper. The dipper can be suitably
tilted so as to
open the dipper door under its own weight plus the weight of any material
contained within the
dipper body. The door is thereafter closed by swinging the dipper in such a
direction so as to
cause the dipper door to move by inertia towards its closed position until the
latch bar reengages
the latch keeper.
SUMMARY
[0003] In some embodiments, a power shovel dipper door includes a hollow
dipper body
defining a first end and a second end opposite the first end, a plurality of
dipper teeth coupled to
the first end, a dipper door pivotally mounted at the second end, and a latch
system for releasably
securing the dipper door in a closed position. The latch system includes a
latch bar and a latch
keeper. At least one of the latch bar and latch keeper is movable between a
first position and a
second position. The latch keeper is engaged by the latch bar when at least
one of the latch bar
and latch keeper is in the first position. The latch system further includes
removable inserts
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positioned proximate an interface where the latch bar and latch keeper are
capable of engaging
each other. One or more of the removable inserts includes a tool steel.
[0004] In other embodiments, a latch system for a power shovel dipper door
includes a latch
bar movable between a first position and a second position, a latch keeper
that is engaged by the
latch bar when the latch bar is in the first position, and removable inserts
positioned proximate
an interface where the latch bar and latch keeper are capable of engaging each
other. One or
more of the removable inserts include a tool steel.
[0005] Other aspects of the invention will become apparent by consideration
of the detailed
description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a perspective view of a shovel with a dipper.
[0007] FIG. 2 is an enlarged perspective view of the dipper of the shovel
of FIG. 1.
[0008] FIG. 3 is a cross-sectional view of the dipper taken along line 3-3
of FIG. 2,
illustrating a latch system according to one embodiment of the invention.
[0009] FIG. 4 is an enlarged partial perspective view of the latch system
of FIG. 3
illustrating latch bar and keeper inserts.
[0010] It should be understood that the invention is not limited in its
application to the details
of construction and the arrangements of the components set forth in the
following description or
illustrated in the above-described drawings. The invention is capable of other
embodiments and
of being practiced or being carried out in various ways. Also, it is to be
understood that the
phraseology and terminology used herein is for the purpose of description and
should not be
regarded as limiting.
DETAILED DESCRIPTION
[0011] FIG. 1 is a perspective view of a shovel. Generally, the illustrated
shovel 10 includes
a base 25, which is supported on drive tracks 20, and a boom 45 extending
upwardly from the
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base 25. A pulling mechanism 58 (e.g., pulley or boom sheave) is mounted on
one end of the
boom 45 remote from the base 25. A dipper 55 is suspended by a flexible hoist
rope or cable 62
from the pulling mechanism 58. The flexible hoist rope 62 extends from the
base 25, upwardly
along the boom 45 and over the pulling mechanism 58, and downwardly to an
attachment point
on the dipper 55.
[0012] Referring also to FIG. 2, the dipper 55 includes dipper teeth 56
along a front edge of a
dipper body 57. As used herein, the terms "top," "bottom," "front," "rear,"
"side," and other
directional terms are not intended to require any particular orientation, but
are instead used for
purposes of description only. The dipper teeth 56 are used to excavate a
desired work area. The
hollow dipper body 57 is provided for collecting the excavated material. As
shown in FIGS. 1
and 3, a door 70 is pivotally mounted to a rear of the dipper body 57. A latch
mechanism 100
(described below) secures the door in a closed position and, when released,
allows the door 70 to
open, e.g., to transfer the collected material to a desired location.
[0013] FIGS. 3 and 4 illustrate the dipper 55 including the latch system
100 according to one
embodiment of the invention. The latch system 100 includes a slidable latch
bar 110 and a latch
keeper 120 that is selectively engagable by the latch bar 110. In the
illustrated embodiment, the
latch bar 110 is coupled to a latch lever 130, which in turn is coupled to the
dipper door 70 on an
underside thereof. The latch keeper 120 is coupled to the dipper body 57. The
dipper door 70 is
held closed when the latch bar 110 is in engagement with the latch keeper 120.
To open the
dipper door 70, the latch lever 130 is moved, which causes the latch bar 110
to slide away from
the latch keeper 120 and thereby disengage from the latch keeper 120. Movement
of the latch
lever 130 may be accomplished by means of mechanical, hydraulic, pneumatic, or
electric
systems depending upon the capabilities and configuration of the latch lever
130. The dipper 55
may also be tilted toward direction 140 so as to open the dipper door 70 under
its own weight
plus the weight of any material contained within the dipper body 57. The door
70 is thereafter
closed by swinging the dipper 55 in the direction 150 so as to cause the
dipper door 70 to move
by inertia towards its closed position, and until the latch bar 110 reengages
the latch keeper 120.
[0014] Proximate an interface where the latch bar 110 and the latch keeper
120 are capable
of engaging each other, the latch system 100 includes removable inserts 160,
170. In the
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illustrated embodiment, the inserts 160 and 170 are coupled to the latch bar
110 and the latch
keeper 120, respectively. The latch bar insert 160 is received in a recess
formed on the latch
bar 110. An outer surface of the latch bar insert 160 is flush with an outer
surface of the latch
bar 110, so that the assembly of the latch bar 110 and the latch bar insert
160 gives a smooth
linear appearance. Likewise, the latch keeper insert 170 is received in a
recess formed on the
latch keeper 120, and an outer surface of the latch keeper insert 170 is flush
with an outer surface
of the latch keeper 120 so that the assembly of the keeper 120 and the insert
170 gives a smooth
linear appearance.
[0015] In the illustrated embodiment, the latch bar insert 160 and the
latch keeper insert 170
are arranged so as to define a gap 180 therebetween when the dipper door 70 is
closed. When
the dipper door 70 is swinging toward a closed position, the latch bar insert
160 may contact the
latch keeper insert 170 intermittently or occasionally, e.g., via inertia.
Through these contacts,
the removable inserts 160, 170 may become gradually worn; however, as
explained below, the
wear life or service life of the removable inserts 160, 170 disclosed herein
can be enhanced by
using tool steel. Although FIG. 4 illustrates the latch bar insert 160 and the
latch keeper insert
170 as being separated when the dipper door 70 is in the closed position, in
some embodiments,
the latch bar insert 160 and the latch keeper insert 170 may occasionally
contact or slide against
each other when the dipper door 70 is closed. In other embodiments, the latch
bar insert 160 and
the latch keeper insert 170 may be in constant contact with each other when
the dipper door 70 is
closed.
[0016] For at least the past twenty years, certain carburized steel alloys
have been used as the
latch keeper insert, with or without a latch bar insert. Where a latch bar
insert is used, certain
through-hardened steel alloys have been used as a suitable material. The
service life of such
latch bar and keeper inserts, however, have been typically limited to
approximately 10-15 days.
Removing and replacing the inserts from the dipper door after the useful
service life can be
costly and time consuming. First, the dipper door needs to be hauled or
hoisted to an open
position (e.g., approximately 100 to approximately 20 ). This can be
accomplished either by
temporarily welding a steel support (not shown) between the dipper door 70 and
the rest of the
dipper 55, or by adjusting the latch lever 130 relative to a corresponding
latch lever retainer (not
shown) on the door 70 using shims. Once the door is opened, the latch keeper
insert can be
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removed and replaced. In large dippers, the dipper door can weigh on the order
of 15-20 metric
tons and the latch bar itself can weigh on the order of one metric ton.
Removing and replacing
the worn latch inserts is therefore be time-consuming and cumbersome. Thus,
there has
developed a need for removable inserts with a longer service life. Others in
the industry,
however, have failed to meet this need for at least the past twenty years.
[0017] In the illustrated embodiment, to decrease wear on the latch bar 110
and keeper 120,
the removable inserts 160, 170 are each made of a tool steel, such as D2 and
S7. The nominal
composition of the D2 tool steel includes, by weight, approximately 10% to
approximately 18%
chromium, approximately 1.5% carbon, approximately 1.0% vanadium,
approximately 0.7%
molybdenum, approximately 0.45% manganese, approximately 0.30% silicon,
approximately
0.030% phosphorus, approximately 0.030% sulfur, and the balance iron and
incidental elements
and impurities. Use of the word "approximately" to describe a particular
recited amount or range
of amounts is meant to indicate that values near to the recited amount are
included in that amount
such as, but not limited to, values that could or naturally would be accounted
for due to
instrument and/or human error in forming measurements. The D2 tool steel can
be through-
hardened to a Rockwell C-scale hardness of approximately 57 to approximately
59 by placing
the steel in a furnace, tempering at a suitable temperature, and subsequently
cooling in air.
[0018] The nominal composition of the S7 tool steel includes, by weight,
approximately
3.25% chromium, approximately 1.40% molybdenum, approximately 0.70% manganese,
approximately 0.50% carbon, approximately 0.30% silicon, and the balance iron
and incidental
elements and impurities. The S7 tool steel can be hardened to a Rockwell C-
scale hardness of
approximately 54 to approximately 56 by placing the steel in a furnace,
tempering at a suitable
temperature, and subsequently cooling in air.
[0019] Tool steels such as D2 and S7 have been used in the machining world
(e.g., for dies
and shear blades) for approximately 40-50 years. These steels can attain a
high hardness.
Generally, the hardness of an alloy is inversely proportional to its
toughness. Therefore, the high
hardness of the tool steel would indicate that the toughness may be unsuitably
low (i.e., brittle)
for applications that are exposed to a high impact. The toughness of the tool
steel may be further
reduced at low temperatures due to a ductile-to-brittle transition, and in
light of the fact that a
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power shovel may be exposed to temperatures lower than approximately ¨40 C.
Therefore, latch
inserts for a power shovel dipper door are expected to require high toughness
at such low
temperatures. For this reason, tool steels were hitherto not used as latch
inserts, although they
have been used in the machining world.
[0020] In the illustrated embodiment, the latch bar insert 160 and the
latch keeper insert 170
have different hardnesses, and are of different tool steels. In one particular
embodiment, the
latch bar insert 160 is made of the D2 tool steel a Rockwell C-scale hardness
of
approximately 57 to approximately 59, and the latch keeper insert 170 is made
of the S7 tool
steel with a Rockwell C-scale hardness of approximately 54 to approximately
56. Moreover, a
ratio of wear life of the latch bar insert 160 to wear life of the latch
keeper insert 170 is
approximately two to one. In other embodiments, however, the ratio of the wear
life of the latch
bar insert 160 to the wear life of the latch keeper insert 170 is different.
Moreover, the latch bar
insert 160 and the latch keeper insert 170 can be made of tool steels other
than D2 or S7, and the
latch bar insert 160 and the latch keeper insert 170 may or may not be made of
the same tool
steel. In yet other embodiments, the latch bar insert 160 and the latch keeper
insert 170 have the
same hardness.
[0021] An illustrative embodiment of the removable inserts is described in
greater detail
below. Additionally, counterexamples (Examples 1, 2, 3, and 5) were also
prepared and tested
for comparison. In the examples and counterexamples, removable inserts 160,
170 were applied
on a latch system 100 of a dipper door 70 in a power shovel 10. The shovel 10
was used to move
material, and the wear on the latch keeper insert 170 was measured as a
function of time and
material moved. Initially, the latch keeper insert 170 was a generally
rectangular box with faces
joined at right angles to each other. As the test progressed, however, an edge
of the latch keeper
insert 170 that contacts the latch bar insert 160 gradually receded and became
rounded. The
receded length to the latch keeper insert 170 edge was measured vertically and
horizontally, as a
function of time and material moved.
EXAMPLE 1
[0022] A latch bar insert was made of a manganese steel bar and a latch
keeper insert was
made of a carburized steel alloy. Example 1 is a counterexample. The service
life of the latch
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bar and keeper inserts was exhausted after 15 days of moving material. The
following Table 1
summarizes the measurements.
TABLE 1
Number of days from Cumulative material Vertical length to the Horizontal
length to the
start of test moved (ton) receded edge (inch) receded edge
(inch)
1 28,364 Not measured Not measured
2 37,916 0.0625 0.0625
8 409,994 0.6250 0.1250
13 806,020 0.6250 0.5000
15 878,108 1.1250 0.5000
EXAMPLE 2
[0023] A latch bar insert was made of a manganese steel bar and a latch
keeper insert was
made of a weld overlay. Example 2 is a counterexample. The service life of the
latch bar and
keeper inserts was exhausted after 13 days of moving material. The following
Table 2
summarizes the measurements.
TABLE 2
Number of days from Cumulative material Vertical length to the Horizontal
length to the
start of test moved (ton) receded edge (inch) receded edge
(inch)
1 71,568 Not measured Not measured
13 735,518 1.1875 0.7500
EXAMPLE 3
[0024] A latch bar insert was made of a stainless steel and a latch keeper
insert was made of
TOUGHMET . TOUGHMET is a copper-based alloy with a nominal composition, by
weight,
of approximately 15% nickel, approximately 8% tin, and the balance copper and
incidental
elements and impurities. Example 3 is a counterexample. The service life of
the latch bar and
keeper inserts was exhausted after 3 days of moving material. The following
Table 3
summarizes the measurements.
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TABLE 3
Number of days from Cumulative material Vertical length to the Horizontal
length to the
start of test moved (ton)
receded edge (inch) receded edge (inch)
1 33,206 Not measured Not measured
3 139,984 1.0000 1.0000
EXAMPLE 4
[0025] A latch bar insert was made of the D2 tool steel and a latch keeper
insert was made of
the S7 tool steel. The service life of the latch bar and keeper inserts was
exhausted after 54 days
of moving material. This represents an approximately fivefold increase in
service life of the
removable inserts. The following Table 4 summarizes the measurements.
TABLE 4
Number of days from Cumulative material Vertical length to the Horizontal
length to the
start of test moved ton
receded edte inch receded edte inch
1 22,678 Not measured Not measured
4 261,108 Not measured Not measured
12 926,532 0.5625 0.4375
15 1,190,040 Not measured Not measured
28 2,234,246 0.8125 0.6250
37 3,136,680 Not measured Not measured
54 5,036,272 Not measured Not measured
EXAMPLE 5
[0026] Both the latch bar insert and the latch keeper insert were made of
Nano Steel.
Example 5 is a counterexample. The service life of the latch bar and keeper
inserts was
exhausted after 9 days of moving material. To keep the latch system running in
place, a welding
was required on the latch keeper insert. The following Table 5 summarizes the
measurements.
TABLE 5
Number of days from Cumulative material Vertical length to the Horizontal
length to the
start of test moved (ton)
receded edge (inch) receded edge (inch)
1 116,498 Not measured Not measured
9 752,928 Not measured Not measured
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[0027] Although the invention has been described in detail with reference
to certain preferred
embodiments, variations and modifications exist within the scope and spirit of
one or more
independent aspects of the invention as described.
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