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Tackle Block
Information Continued:
| Crosby's
Bearing Calculator |
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Tackle Block and Sheave Maintenance |
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Tackle
Blocks and Sheaves
must be regularly inspected, lubricated, and maintained for peak efficiency
and extended usefulness.
Their proper use and maintenance
is equal in importance
to other mechanical equipment. The frequency of inspection
and lubrication is dependent upon frequency and periods of use, environmental conditions,
and the user’s
good judgment.
Inspection: As a minimum, the
following points should be considered:
1. Wear
on pins or axles, rope grooves, side plates, bushing or bearings,
and fittings (See Fitting Maintenance). Excessive wear
may be a cause to replace parts or remove block from service.
2. Deformation in side plates, pins and axles,
fitting attachment points, trunnions, etc. Deformation
can be caused by abusive service and / or overload and may be
a cause to remove block from service.
3. Misalignment or wobble in sheaves.
4. Security of nuts, bolts, and other locking methods,
especially after reassembly following a tear
down inspection. Original securing method should
be used; e.g., staking, set screw, cotter pin, cap screw.
5. Pins retained by snap rings should be checked
for missing or loose rings.
6. Sheave pin nuts should be checked for proper
positioning. Pins for tapered roller bearings should be
tightened to remove all end play during sheave rotation.
Pins for bronze bushings and straight roller bearings should
have a running clearance of .031 inch per sheave of end play
and should be adjusted accordingly.
7. Hook or shackle to swivel case clearance is
set at .031 to .062 at the factory. Increased clearance
can result from component wear. Clearance exceeding .12
to .18 should necessitate disassembly and
further inspection.
8. Deformation or corrosion of hook and nut threads.
9. Surface condition and deformation of hook (See
Fitting Maintenance and ANSI B30.10.)
10. Welded side plates for weld corrosion or weld
cracking.
11. Hook latch for deformation, proper fit and
operation.
12.
Remove
from service any bushings with cracks on inside diameter or
bushing end. Bushings that are cracked and /or extended beyond
sheave hub are indications of bushing overload.
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Lubrication: The
frequency of lubrication depends upon frequency and period of product use as well as
environmental conditions, which are contingent upon the user’s good judgment.
Assuming normal product use, the following schedule is suggested when using lithium-base
grease of a medium consistency. |
Sheave
Bearings
Tapered
Roller Bearings — Every 40 hours of continuous operation
or every 30 days of intermittent operation.
Roller Bearings — Every 24 hours of continuous
operation or every 14 days of intermittent operation.
Bronze Bushings — (Not Self Lubricated) —
Every 8 hours of continuous operation or every 14 days of intermittent
operation.
Self Lubricating
Bronze Bushing —
are for slow
line speeds and infrequent use (moderate bearing friction). Frequent
inspection is required to determine the condition of bushing.
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| Hook Bearings |
Anti Friction —
Every 14 days for frequent swiveling; every 45 days for infrequent swiveling.
Bronze Thrust Bushing or No Bearing — Every 16 hours for frequent swiveling;
every 21 days for infrequent swiveling. |
Tackle Block Maintenance also depends upon
proper block selection (see “Loads on Blocks”), proper reeving (see “The
Reeving of Tackle Blocks”), consideration of shock loads, side loading, and other
adverse conditions.
Sheave Bearing Application
Information |
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Sheave in a 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. Refer to Page 296 "How to Figure
Line Parts" for assistance in determining lead line loads used
for bushing or bearing selection.
BRONZE BUSHINGS—
Bronze Bushings are used primarily for sheave applications using slow
line speed, moderate load, and moderate use. The performance capability
of a bearing is related to the bearing pressure and the bearing surface
velocity by a relationship known as true PV (Maximum Pressure - Velocity
Factor). The material properties of the Bronze Bushings furnished
as standard in Crosby catalog sheaves are:
(BP) Maximum Bearing
Pressure: 4500 PSI
(BV) Maximum Velocity at Bearing: 1200 FPM
(PV) Maximum Pressure Velocity Factor: 55000 |
(It should be noted that due to material
property relations, the maximum BP times the maximum BV is NOT equal to the maximum PV.)
Formula for Calculating Bearing
Pressure:
| BP = |
Line Pull x
Angle Factor
Shaft Size x Hub Width |
Note: Angle Factor
Multipliers listed on page 293.
Formula for Calculating Bearing Velocity:
Formula for Calculating Line Speed:
| Line Speed = |
BV
(Tread Diameter + Rope Diameter
Shaft Diameter |
Calculations can be made to find the
maximum allowable line speed for a given total sheave load. If the required line
speed is greater than the maximum allowable line speed calculated, then increase the shaft
size and/or the hub width and recalculate. Continue the process until the maximum
allowable line speed is equal to or exceeds the required line speed. |
