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Crosby's
Overhaul
Weight Calculator |
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How to
Determine Overhauling
Weights |
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| To determine the
weight of the block or overhaul ball that is required to free
fall the block, the following information is needed: size
of wire rope, number of line parts, type of sheave bearing, length
of crane boom, and drum friction (use 50 pounds, unless other
information is available). |
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Sheaves
in system of blocks rotate at different rates of speed, and
have different loads. When raising and lowering the line tension
is not equal throughout the system. To help figure the number
of parts of line to be used for a given load, or the line
pull required for a given load, (for example, use Reeving
Diagram, on page 294. Only numbered
lines shall be used in a calculation). The following ration
table is provided with examples of how to use it. The ratios
are applicable for blocks as shown on page 295
and also indpendent sheave systems that line is reeved through.
| Crosby's
Parts of Line
Calculator |
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Wire Rope
Size
(in.) |
Factor A
- Wire Rope Weight |
Lbs. Per
Ft., 6 x 19 IWRC |
3/8 |
.26 |
7/16 |
.35 |
1/2 |
.46 |
9/16 |
.59 |
5/8 |
.72 |
3/4 |
1.04 |
7/8 |
1.42 |
1 |
1.85 |
1-1/8 |
2.34 |
1-1/4 |
2.89 |
Number
of Line
Parts |
Factor B
- Overhaul Factors |
Roller Bearing
Sheaves |
Bronze Bushed
Sheaves |
1 |
1.03 |
1.05 |
2 |
2.07 |
2.14 |
3 |
3.15 |
3.28 |
4 |
4.25 |
4.48 |
5 |
5.38 |
5.72 |
6 |
6.54 |
7.03 |
7 |
7.73 |
8.39 |
8 |
8.94 |
9.80 |
9 |
10.20 |
11.30 |
10 |
11.50 |
12.80 |
The
Formula is:
Required
Block Weight = [(Boom Length x Factor A) + Drum Friction] x Factor
B
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Example
To determine the required block or overhaul weight using 5 parts
of 7/8" diameter wire rope, a 50 ft. boom and roller bearing
sheaves:
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Ratio A
Bronze Bushed
Sheaves |
Ratio B
Anti-Friction
Bearing Sheaves |
Number
of
Line Parts |
.96 |
.98 |
1 |
1.87 |
1.94 |
2 |
2.75 |
2.88 |
3 |
3.59 |
3.81 |
4 |
4.39 |
4.71 |
5 |
5.16 |
5.60 |
6 |
5.90 |
6.47 |
7 |
6.60 |
7.32 |
8 |
7.27 |
8.16 |
9 |
7.91 |
8.98 |
10 |
8.52 |
9.79 |
11 |
9.11 |
10.60 |
12 |
9.68 |
11.40 |
13 |
10.20 |
12.10 |
14 |
10.70 |
12.90 |
15 |
11.20 |
13.60 |
16 |
11.70 |
14.30 |
17 |
12.20 |
15.00 |
18 |
12.60 |
15.70 |
19 |
13.00 |
16.40 |
20 |
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Total
Load to be Lifted |
| Ratio
A or B = |
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Single
Line Pull (lbs.)
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After calculating
Ratio A or B, consult table to determine number of parts of line.
Examples
- To find the
number of parts of line needed when weight of load and single
line pull are known, and using Bronze Bushed Sheaves.
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72,180
lbs. (load to be lifted) |
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Ratio
A = |
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=
9.02 |
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8,000
lbs. (single line pull) |
(Ratio
A) |
In table above, refer to ratio 9.02 or next highest number, then
check column under heading “Number of Line Parts” =
12 parts of line to be used for this load.
- To find the
single line pull needed when weight of load and number of
parts of line are known, and using anti-friction bearing sheaves.
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68,000
lbs. (load to be lifted) |
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| Single
Line Pull = |
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=
9,290 lbs. |
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7.32
(Ratio B of 8 part line) |
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9,290 lbs. single line pull required to lift this load on
8 parts of line.
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