Chain – staple – and horseshoe making – Chains
Reexamination Certificate
1999-05-05
2001-01-09
Jones, David (Department: 3725)
Chain, staple, and horseshoe making
Chains
C059S084000
Reexamination Certificate
active
06170248
ABSTRACT:
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 efficient 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 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 devises
118
to the drag chains
110
. The drag chains
110
are connected to the bucket
106
at hitch devises
120
. The drag sockets
116
are also respectively connected to a pair of dump sockets
122
at dump devises
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 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.
A typical dragline digging cycle is shown in FIGS.
3
A-
3
F. 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.
3
B-
3
E). 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 sidewalls. 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 sidewalls
146
of the bucket.
FIG. 4B
shows the position of the spreader and hoist chains when the boom is swung before the 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.
3
A-
3
F 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 (shrouds) are sometimes added to the upper sidewalls. 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. 5A and 5B
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 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, operating a
Ianello Garrick J.
Johnson Bruce C.
Columbia Steel Casting Co. Inc.
Jones David
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
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