Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates generally to heavy lift cranes
and more particularly concerns an arrangement for increasing the
capacity of a heavy lift crane.
Modern heavy lift cranes embody many desicn trade-offs.
While high lifting capacity is obviously desirable, that requires
increased crane size and weight, and that affects cost and manue-
verability. Since a crane is seldom called upon to work at or
near capacity, there is a degree of inefficiency in a design
scaled for high capacities but working well beneath capacity.
It would be highly desirable to have a crane scaled for
the bulk of the work to be done on a given job, and then have
available some means of increasing the capacity of that crane --
when increased capacity is called for. Although it was not
sound procedure, this objective was often sought in practice by ~-
crane users through such expedience as simply hanging additional
counterweight, such as a bulldozer, on the rear of a crane. Under
modern safety regulations, the addition of a meaningful amount of
counterweight above that for which the crane is designed cannot
be done because it would change the rearward tipping equations.
That is, when the crane is not under load, the extra counter-
weight would tend to tip the crane rearwardly.
According to the present invention an arrangement is
provided for increasing the capacity of a crane having a carbody
supported by a pair of crawler as~emblies which permit movement
of the crane under both heavily loaded and unloaded conditions
and an upper deck on the carbody supports a boom at one end and
a normal counterweight at the other end, with an additional item
of counterweight secured to and becoming part of the normal
counterweight, and a pair of auxiliary carbody weights in sub--
stantially box-like form attached to the front and rear of the
, carbody between the ends of the crawler assemblies so as to con-
stitute weighted extensions of the carbody to supplement the
additional counterweight and prevent forward tipping of the crane
during heavy lifting and to counteract rearward tipping due to
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the additional counterweight when a load is not being lifted by
the crane, wherein at least one of the carbody weights includes
walking treads on the upper surface thereof and a plurality of
open steps are fixed between spaced risers attached to the outer
side of the carbody weights to permit easy access to the upper
deck.
Other objects and advantages of the invention will become
apparent upon reading the following detailed description and upon
reference to the drawings, in which:
Figure 1 is a frasmentary perspective of a crane embodying
the present invention;
Fig. 2 is an enlarged plan of the lower works portion of
the crane shown in Fig. l;
Fig. 3 is a fragmentary section taken approximately along
the line 3-3 in Fig. 2;
Fig. 4 is a fragmentary plan of a portion of the structure
shown in Fig. 3; and
Fig. 5 is a fragmentary elevation taken approximately
along the line 5-5 in Fig. 3.
Turning now to the drawings, there is shown in Fig. 1
a conventional crawler crane 10 modified in accordance with the
arrangement of the invention. The crane 10 includes a carbody
11, supported by a pair of crawler assemblies 12 and 13, and an
upper deck 14 on the carbody mounting a boom 15, a gantry or
mast 16, and a normal counterweight 17 at the end of the deck
14 opposite the mast 15.
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Pursuant to the invention, an additional item of
counterweight 21 is secured to, so as to become part of, the
normal counterweight 17 and a pair of auxiliary carbody weights 22
and 23 in substantially box-like form are attached to the front
and rear of the carbody so as to constitute weighted extensions
of the carbody 11. In the illustrated embodiment, the
counterweight 21 consists of a plurality of mPtal slabs tacked
together and mounted on the normal counterweight 17 (see Fig.l).
Preferably, the auxiliary carbody weights 22, 23 are plates welded
into boxes containing, as weight, sand, concrete or scrap metal.
For ease of handling, the carbody weights 22, 23 are
formed with pairs of arms 25 carrying lugs 26 adapted to mate with
lugs 27 formed on brackets 28 welded to the carbody 11. Blocks 29
on the weights 22, 23, abut the ends of the carbody 11 when the
lugs 26, 27 are mated. The arms 25 are also drilled to form
holes 31 above the center of gravity line so that an auxiliary
crane can be conveniently attached at the holes 31 to the
counterweights 22, 23, allowing the weights to be simply lowered
into mounted position. The brackets 28 are formed with cam
surfaces 32 to guide the lugs 26 directly into engagement with
the lugs 27.
In order to reliably lock the carbody weights 22, 23 in
position, the arms 25 and the brackets 28 are formed with holes
which are alined when the weights are in position, and locking
pins 33 are fitted into the holes preventing inadvertent
dislodgement of the carbody weights.
In the illustrated embodiment, non-skid walking treads 34
are mounted on the tops of the weights 22, 23 and a plurality of
steps 35 are fixed on the outer sides of the weights, thus
providing convenient access to the upper deck 14. Preferably~
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each of the carbody weights 22, 23 is slightly heavier than the
added counterweight 21. This insures that the stabilizing effect
of the carbody weights more than offsets the added tipping load
imposed by the added counterweight.
The effect of the arrangement can now be readily
appreciated. The added counterweight 21 becomes part of the basic
crane counterweight, thus increasing the capacity of the crane.
The carbody weights 22, 23 stabilize the crane and, at maximum
capacity ranges, also tend to increase the crane counterbalancing
mass. Less obviously, the carbody weights 22, 23 have the effect
of lowering the center of gravity of the entire crane, thus
increasing the arc that the center of gravity must traverse if
the crane is overloaded and starts to tilt. The increased arc
means increased time in such a situation, and this gives the crane
operator more opportunity to sense the condition and correct it.
Those skilled in the art will also readily appreciate
that the increase in crane capacity has been achieved at little
cost and, primarily because of the positioning of the carbody
weights, there is no interference with otherwise normal operation
of the crane.
