Note: Descriptions are shown in the official language in which they were submitted.
CA 02277254 1999-07-09
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DOG BONE CHAIN LINK
Field of the Invention
The present invention pertains to chains and chain links in general, and
dragline
chains in particular.
Background of the Invention
Draglines are commonly used for removing large volumes of material, such as
dirt,
loosened ore, etc., and are particularly well-suited for removing overburden
in large strip
mining operations where tens of millions of yards of material must be removed
in an e~cient
manner. A typical dragline is shown in FIG. 1. Draglines work by dragging a
large bucket
along the surface to scoop up material, hence the name. Draglines provide
several
advantageous features over other earthmoving equipment, including a long reach
for both
digging and dumping, the ability to dig below their tracks (or base), and a
high cycle speed.
Draglines are available in a variety of different sizes, with the largest
draglines being
among the most massive mobile equipment ever produced. For example, the
dragline shown
in FIG. 1 is a Marion 8750 series dragline that has a 360 foot boom, and is
equipped with a
135 cubic yard bucket. The largest dragline ever built has a bucket capacity
of 220 cubic
yards and weighs nearly 14,000 tons.
Referring to FIG. 1, the major components of a dragline include a powerplant
100, a
boom 102, a hoist cable 104, a bucket 106, hoist chains 108, drag chains 110,
dump cables
112, and drag cables 114. The machine powerplant 100 is mounted on a rotary
base 115,
allowing the boom to swing in the horizontal plane. Smaller draglines
typically employ sets
of tracks for moving the machine, while larger draglines use a "walking"
mechanism. These
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larger machines are referred to as walking draglines. The hoist cable 104 can
be retracted or
extended by means of a hoist drum (not shown) that is located in the
powerplant. Likewise,
the drag cable 114 can be retracted and extended by means of a drag drum (not
shown)
located in the powerplant.
As shown in FIG. 2, the drag cable 114 is connected to pair of drag sockets
116. The
drag sockets 116 are connected through drag clevises 118 to the drag chains
110. The drag
chains 110 are connected to the bucket 106 at hitch clevises 120. The drag
sockets 116 are
also respectively connected to a pair of dump sockets 122 at dump clevises
124. A second
pair of dump sockets 126 is connected to the front of the bucket 106 at anchor
links 128. The
dump sockets 122 and 126 are commonly connected to a respective pair of dump
cables 112
which ride on dump sheaves 130. A pair of upper hoist cables 132 are commonly
connected
to the bottom pickup link 134 at their top ends, and opposing sides of a
spreader 136 at their
bottom ends. A pair of lower hoist cables 138 are connected to the spreader
136 at their top
ends, and are connected at their bottom ends to the bucket 106 at trunnions
139. The pickup
1 5 link 134 is connected to a hoist equalizer 140, which in turn is connected
to hoist sockets 142.
The hoist sockets 142 are connected to the hoist cables 104. The hoist
equalizer 140 is also
connected to a pickup link 144, which is connected to a dump sheave shackle
assembly 146
that holds the dump sheaves 130.
The loads on the hoist and drag chain links are massive. It is common for the
largest
draglines to employ hoist and drag cables that are 5 inches in diameter. These
cables are
made out of very high strength steels, and support suspended loads of upwards
of 750,000
lbs. The loads placed on the hoist chains and drag chains are equally
impressive. These
loads dictate the use of specialized chain links made from ultra-high-strength
alloyed steels.
In addition, these chains and chain links must be designed to endure a
tremendous amount of
wear, as discussed below.
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A typical dragline digging cycle is shown in FIGS. 3A-3F. As shown in FIG. 3A,
the
digging cycle begins by lowering the bucket into the mine pit with both the
hoist cable and
the drag cable nearly taut until the bucket contacts the pit surface. At this
point the hoist
cable is slightly slackened and the drag cable is pulled toward the powerplant
(FIGS. 3B-3E).
This results in the bucket teeth digging in and cutting a slice of material
that piles inside the
bucket. The depth and angle of the cut may be controlled by varying the hoist
cable length as
the drag cable is pulled.
The most important chain links in the hoist chains are the links that are in
close
proximity to the uppermost portion of the bucket sidewalk. It is common for
these links to
get damaged or worn when the spreader bar does not adequately prevent these
links from
hitting the sidewall of the bucket. Such a situation is shown by FIGS. 4A and
4B. In FIG. 4A
the spreader 136 is shown in the ideal position, being centered above the
bucket 106 so as to
prevent contact between any of the chain links and the sidewalk 146 of the
bucket. FIG. 4B
shows the position of the spreader and hoist chains when the boom is swung
before the
1 5 bucket has been lifted clear of the surrounding material, a common
occurrence during
operation. In this case the chain link 147 adjacent the upper edge of the left-
hand side of the
side wall 146 contacts the left-hand upper sidewall 146 of the bucket at area
148. The links
that so contact the bucket sidewall become so worn that they fail prior to the
failure of the
remainder of the links of the chain, and must be replaced, which is very
costly in terms of
material and downtime.
A similar contact between one of the chain links and the bucket sidewall can
occur if
the bucket does not track straight when it is being dragged, or if the bucket
encounters a large
boulder on one side, causing the bucket to rotate. As shown in FIGS 3A-3F the
chain link
150 moves back and forth adjacent to wear area 152. The chain link 150 wears
against the
wear area when the bucket is dragged while askew. To compensate for the wear,
wear shoes
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(shrouds) are sometimes added to the upper sidewalk. However, this generally
increases 'the
contact between the chain links and bucket (at the shoes (in comparison to a
bucket without
shoes)), shortening the life of the chain links even further.
FIGS. SA and SB show a conventional scheme for compensating for the contact
between the lower hoist chain links and the bucket sidewall. This scheme
employs the use of
two large barrel-shaped links 154, each of which provides a large surface area
to wear against
the bucket sidewalls. While these links provide an improved life over
conventional links,
they have the drawback of being significantly heavier than the links they
replace. They also
increase the bucket sidewall wear due to their larger diameter and barrel
shape which results
in instances of contact that would not occur with a conventional link.
In addition to the foregoing sidewall wear problems, conventional hoist chains
are
heavier than desired. This extra weight reduces the payload (the amount of
material removed
with each bucket load) the dragline can carry, and also increases the stress
loading placed on
the boom. The payload for a given machine is generally limited by the size of
its bucket and
1 5 the type of material the dragline is working in. The size of the bucket is
limited by the
maximum allowable suspended load rating of the. machine, the suspended load
including the
weight of a loaded bucket and the weight of the various other components that
are supported
by the hoist cable (the hoist chains, drag chains, sockets, clevises, etc. -
hereinafter the
bucket support components). The suspended load rating is primarily a function
of the
strength of the boom, the torque capacity of the hoist drum and drag drum, and
the overall
horsepower of the machine.
The maximum suspended load rating for a machine is determined by performing an
engineering analysis of the boom structure, using a safety factor that in part
is determined by
prior experience. It is generally desired to maximize the payload for a given
machine, and
this usually leads to using the machine at near its maximum suspended load
rating. However,
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operating at near the maximum rating usually can only be performed on newer
machines,
because the strength of boom is reduced over the lifetime of the dragline.
This is due to the
constant fatigue loading that is applied to the boom during machine operation.
The fatigue
loading of the boom can be reduced by reducing the suspended load.
Unfortunately, a
reduction in the suspended load usually means a reduction in payload.
It would therefore be advantageous to be able to (1) maximize the payload
without
reducing the suspended load and/or (2) reduce the suspended load without
reducing the
payload capacity. The first object can be accomplished by increasing the size
of the bucket in
conjunction with a decrease the weight of the bucket support components. The
second object
can be accomplished by simply reducing the weight of the bucket support
components while
maintaining the bucket size.
Both of these objects can be achieved by reducing the weight of the hoist
chains.
Conventional hoist chain links are sized so that they will be able to support
their loads after
significant wear. The most common failure point of a hoist chain link is at
its ends, which
1 5 continuously wear on the ends of connecting links as the hoist chains are
flexed during
dragline operations. Thus, the dragline chain links are sized so that they
will support their
required load after significant wear of the end portions of the link. The
nominal size of the
chain links (generally a cross-section thickness) is primarily a function of
the strength of the
chain link material, the load that must be carried, and empirical wear data.
As a result of the
wear considerations, conventional hoist chain links are sized to be much
larger (and heavier)
than would be necessary to carry their nominal loads.
Although a reduction in the weight of the hoist chains is desired, such weight
reduction has previously been limited because of the foregoing wear
considerations. It is
therefore desired to produce reduced-weight hoist chains that have similar
performance (wear
and strength) characteristics when compared with heavier conventional chains.
Furthermore,
CA 02277254 1999-07-09
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it is also desired to have a chain link that is configured so as to lessen the
contact with bucket
sidewalk while maintaining or improving upon the life of the chain link (when
compared to
conventional hoist chain links), without requiring any additional weight.
Summary of the Invention
The invention is a dog-bone-shaped chain link that can be used in hoist chains
and
drag chains to both reduce the chain weight and in the case of the hoist
chains reduce the
wear between the bucket sidewalls and the links located adjacent to the
sidewalls. The chain
link is especially well-suited for high-load application, such as dragline
hoist chains.
The chain link comprises a shank portion connected to a pair of eye portions
at each
end of the shank, thereby forming a dog-bone shape with eyelets at the ends.
The eyelets are
formed by a generally Y-shaped root section that is connected to a hat section
that is shaped
like half of a torus. The illustrated embodiment of the chain link is
preferably flat on its top
and bottom side and the cross-section of the shank portion of the chain link
is substantially
rectangular with radiused corners. According to a second embodiment, the cross-
section of
the shank portion is a radiused broad I-beam profile having overall a
substantially square
shape that has a pair of slots formed on its opposing sides. The slots are
blended outward
toward the ends of the shank portion so as to disappear. The shank portion may
be of circular
or other configuration.
In the illustrated embodiments the cross-section of the outside portion of the
eye hat
sections is half square with radiused corners to match the outside half of the
shank cross-
section at the forks of the Y-shaped roots. The cross-section of the inside
portion of the eye
hat sections comprises an arcuate profile over a substantial portion of the
length of the hat.
The arcuate profile extends slightly above and below the nominal thickness of
the link to
increase the bite area between a pair of links.
CA 02277254 1999-07-09
_7_
The chain link is preferably made of a high-strength cast alloy steel. A chain
can be
fabricated by casting a first set of links and then integrally casting a
second set of links
wherein each second-set link is situated between a pair of first-set links and
the links are
oriented in an alternating fashion. Subsequent to the casting process, the
chain links are
preferably heat-treated to increase the hardness of their outer surfaces and
tensile strength.
Additional surface hardening processes may also be employed to increase the
life of the
chain.
Brief Description of the Drawings
FIG. 1 shows a typical large dragline and its major components;
FIG. 2 shows a detailed view of the bucket area of the FIG. 1 dragline;
FIGS. 3A-3F show the configurations of the bucket and bucket support
components
during a dragline digging cycle;
FIGS. 4A and 4B show end views of the bucket and hoist chains under normal and
askewed conditions;
FIGS. SA and SB show application of a prior art chain link when the bucket and
hoist.
chains are under normal and askewed conditions;
FIGS. 6A and 6B show the chain link of the invention when the bucket and hoist
chains are under normal and askewed conditions;
FIGS. 6C and 6D show hoist chains comprising multiple dog bone chain links
when
the bucket and hoist chains are under normal and askewed conditions;
FIG. 7 is a plan view of a first exemplary chain link of the invention;
FIG. 8 is a cross-sectional view of the chain link of FIG. 7 taken along line
8-8;
FIG. 9 is a cross-sectional view of the chain link of FIG. 7 taken along line
9-9 of
2 5 FIG. 7;
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_8_
FIG. 10 is a cross-sectional view of the chain link of FIG. 7 taken along line
10-10 of
FIG. 7;
FIG. 11 is a plan view of a second exemplary chain link of the invention;
FIG. 12 is a partial cross-sectional view of the chain link of FIG. 11 taken
along line
12-12 of FIG. 11;
FIG. 13 is a cross-sectional view of the shank portion of the chain link of
FIG. 11
taken along line 13-13 of FIG. 11;
FIG. 14 shows an optional configuration of the FIG. 7 chain link that includes
a
shroud;
FIG. 15 is a cross-section view of the shank portion and shroud of FIG. 14
taken
along line 14-14 of FIG. 14.
FIG. 16 is a plan view of the shroud of FIG. 14 when assembled; and
FIG. 17 is a plan view of the base plate of the shroud of FIG. 14.
Detailed Description
Referring first to FIGS. 7-10, the chain link 10 therein shown comprises a
shank
portion 12 connected at opposing ends to a pair of eye portions 14, 16
defining openings 17,
19, respectively. The eye portions 14, 16 are each formed by a Y-shaped root
section 18 that
is connected to a half torus-shaped hat section 20 at the ends 22, 24 of forks
26, 28, at which
ends the section 10-10 is taken. As shown in FIG. 8, the top surface 13 and
bottom surface
I 5 of the chain link 10 preferably are substantially flat and parallel,
except for the areas near
the hat sections 20.
A Y-shaped root section 18 comprises a base portion 30 that preferably expands
outward from the axial center line 36 along curvilinear paths 32, 34 to the
forks 26, 28. The
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_g_
forks 26, 28 are substantially straight and parallel at their .respective ends
22, 24. The throat
of a root section 18 comprises substantially parallel side walls 38, 40
partially defining the
eye at the respective end that are commonly connected to an end wall 42 by
rounded corners
44. The side walls 38, 40 are preferably parallel to the axial centerline 36,
while the end wall
42 is preferably perpendicular to the side walls 38, 40.
A hat section 20 generally is shaped like a half torus. It comprises an inside
arcuate
surface 46, and an outside arcuate surface 48, having substantially the same
centerpoint. The
hat sections 20 each have a pair of short, parallel extensions 48, 50 that
connect with the fork
ends 22, 24.
The cross-section 52 of the shank portion 12 is preferably substantially
square with
rounded corners 54, as shown in FIG. 9. In a typical link, the cross-section
52 comprises a
thickness T and width W of 3.5 inches, and radius corners 54 having a 5/8 inch
radius.
As shown in FIG. 10, the extensions 48, 50 are also approximately square in
shape
with rounded corners 58 and have a cross-sectional area substantially equal to
that of the
1 5 shank portion 12. As shown in FIG. 8, the outer portion 60 is of a
substantially rectangular
profile that matches the outer half of the hat sections 48, 50. The inner and
outer portions of
62, 60 are blended together by means of curved surfaces 64 and 66. As best
seen in FIG. 8,
the inner portion of the section is reduced in dimension as it approaches the
extension 48, 50
to blend them together.
The inner portion 62 of a hat section 20 is arcuate in profile and of a radius
so as to
extend beyond the top and bottom walls of the portion 60 (as the link is
portrayed in FIG. 8)
as indicated at 68. For example, in a typical link the height H of cross-
section area 60 is 4.0
inches, while the radius of arcuate profile 62 is 2.5 inches, and the nominal
thickness T is 3.5
inches. The purpose of this arcuate profile is to increase the bite (contact)
area between two
connected links, thereby increasing the useable life of the links.
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The second exemplary chain link 70 of the invention shown in FIGS. 11-13 is
substantially similar to the chain link 10, except for the shank portion 72
which comprises a
broad I-beam shaped cross-section as shown in FIG. 13. The shank portion 72
has a width
Wi that typically is larger than the nominal thickness Ti of the shank 70. A
pair of slots 76
are formed in the opposing sides of the shank at a depth of Ds and a width of
Ws. For
example, a typical chain link 70 may have a width Wi of 5 inches, a nominal
thickness Ti of
3.5 inches, a slot depth Ds of 1 inch, and a slot width Ws of 2 inches. The
slots 76
additionally contain inside rounded corners 78 and outside corners 80, which
may have a
radius of about 3/8 inch for a link of the dimensions set forth above.
The slots 76 are adapted to define wells for receiving a hard, wear-resistant
material,
such as Columbia Steel's XTEND~ material, or similar commercially available
hard
surfacing material, positioned in the slots 76 by laying down molten beads of
the material to
fill the slots and preferably extend slightly beyond the corners 80.
The pitch P of the chain links 10 and 70 is preferably at least 8 times
greater than the
1 5 nominal width W (and thickness T) of the shank portions of the links. For
example, the pitch
P of chain link 10 is 42 inches, while the width W is 3.5 inches, leaving a
pitch-to-shank-
width ratio of 42 : 3.5 = 12.
The chain links are preferably formed from a high-strength cast alloy steel
(such as H-
39 or H-55). Such chain links typically have tensile strengths in excess of
175,000 psi. For
example, a chain link of a nominal thickness of 2.5 inches made from H-39
alloy steel may
have a tensile strength of 210,000 psi. Subsequent to the casting process, the
chain links are
heat-treated to increase the surface hardness in high wear areas, such as the
bite area and the
outer surface areas of the link. The chain may also be made using a bi-
metallic composition
process such as Columbia Steel's "XTEND PROCESS" ~ on surfaces that are
subject to high
wear. A chain comprising one or more dogbone chain links can be fabricated by
casting a
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first set of links and then integrally casting a second set of links, wherein
each second-set link
is situated between a pair of first-set links and the links are oriented in an
alternating fashion.
Dragline hoist chains can be formed by linking one or more dog bone chain
links to
conventional chain links. Conventional hoist chains are formed of links that
are substantially
similar to the links used in ship anchor chains which require links of short
pitch so that the
chain is flexible enough to be coiled around windlasses and on reels.
Conversely, the
majority of the length of a hoist chain does not require such flexibility.
Therefore, a hoist
chain that comprises the dog bone chain links will not suffer a performance
penalty due to its
increased chain-link pitch and decreased flexibility. However, it may be
necessary to use one
or more conventional-pitch chain links at the end of the hoist chains,
depending on the
particular characteristics of a given dragline configuration. Chains employing
chain links
made in accordance with the invention will enjoy a reduction in weight of
twenty five percent
or more as compared to chains solely employing conventional links.
An example of the hoist chains that employ the dog bone chain links of the
invention
is shown in FIGS. 6A-6D. FIGs. 6A and 6B and FIGs. 6C and 6D show the same end
views
of a bucket and hoist chains of a dragline that are shown in FIGS. 4A and 4B
and FIGs. SA
and SB. The lower hoist chains 82 include dog bone chain links 84, which are
situated
adjacent to the normal bucket sidewall wear areas 86. The remaining chain
links in the lower
hoist chains 82 and the upper hoist chains 88 in FIGs. 6A and 6B comprise
conventional
links. As an option, additional dog bone chain links 90 can be substituted in
place of
conventional links, as shown by the upper hoist chain 92 and lower hoist chain
94 of FIGS.
6C and 6D. In this instance each dog bone chain link generally replaces two or
more
conventional links, depending on the chain link pitch of the relative links.
The displacement
of the spreader 136 in FIGS. 6B and 6D is identical to the displacement of the
spreader 136 in
FIGS. 4B and SB. However, the left-hand dog bone link 84 does not come into
contact with
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the bucket wear area 86 because of the shape of the link. Furthermore, when
the link 84 does
contact the bucket 106, the contact point will generally be on the outside of
the eye portion of
the link and not on the shank portion. This enhances the life of the chain
link.
A replaceable shroud 202 may optionally be used to prevent wear to the shank
portion. As shown in FIGS. 14 and 15, the shroud 202 may be situated about
midway along
the shank portion 12 of the chain link 10. The shroud 202 comprises a hat
section 204 and a
base plate 206, which are clamped together and onto the shank portion 12 by a
plurality of
bolts 207 and nuts 208.
As shown in FIG. 15, the hat section 204 is designed to fit snuggly to three
sides of
the shank portion 12. The hat section 204 comprises a top plate 210 and a pair
of oppositely
disposed side bars 212, 214, connected to the top plate 210 by four gussets
216. The top
plate 210, side bars 212, 214 and gussets 216 define a rectangular channel in
which the chain
link shank portion 12 is snugly received as shown in FIG. 15.
The base plate 206 includes a center yoke portion 218 which extends between
two
1 5 side bars 220, 222 which are aligned beneath the hat portion side bars
212, 214, the bolts 207
extending through appropriate openings in the opposed side bars, as shown in
FIG. 1 S so that
the hat portion 204 and base plate 206 may be firmly clamped to the shank 12
by tightening
the nuts 208.
The shroud 202 is situated on the shank portion 12 so that when the chain link
10
nears the bucket sidewall the top surface 224 of the shroud engages the
bucket, saving the
shank portion from receiving wear, and reducing the contact of the outside
surfaces of the eye
portions 98, 100 with the bucket, thereby prolonging the life of the link 10.
The shroud 202
may be replaced when it becomes worn.
Having described the principles of the invention with reference to detailed
embodiments, it should be apparent that the invention can be modified in
arrangement and
CA 02277254 1999-07-09
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detail without departing from such principles. For example, larger and smaller
versions bf
the chain link can be made by changing the cross-sectional width of the leg
portions of the
chain with a corresponding change in the pitch length so as to maintain a
pitch-to-cross-
section-width ratio of at least 8:1. The cross-sectional profiles of the shank
portions of the
chain link can also be modified to suit a particular application, such as
increasing the cross
section relative to the cross-sections of the forks and hat sections. Many
other such variations
will be apparent to those skilled in the art.
In view of the many embodiments to which the principles of the invention can
be
applied, it should be understood that the detailed embodiment is exemplary
only and should
not be taken as limiting the scope of the invention. We claim as our invention
all such
embodiments as may fall within the scope and spirit of the following claims,
and equivalents
thereto.
