|
Bulletin: SVB-106
Date Issued: May 28, 2004
Category: Inspection
Subject: Block Push Assembly Drive Shaft Failure
Machine Models: ASC Block-Push Bottom Feeders with serial number
JN10301 and later
Back to Index
Problem:
An operator of an ASC Block-Push Bottom Feeder
recently reported that the block-pusher drive mechanism came off its
track during normal operation and fell onto the lift assembly. The
protective guarding on the operator side was heavily damaged as the
mechanism fell, however, no operators were near this area at the
time. There was no warning or indications of an impending failure
with this assembly. This prefeeder had been in regular service for
approximately 6 years.
Inspection of the block-pusher drive shaft
found the solid shaft had completely fractured inside of the
electric motor gearbox that turns this shaft. The fracture location
could not have been visually detected in advance of this failure due
to the design and assembly of these parts. The operator replaced the
drive shaft.
Alliance is aware of other similar reports on
the ASC series of block-push prefeeders involving breakage of the
block-pusher drive shaft in this area and/or excessive wear in the
two rack & pinion drive gears on the ends of this shaft. These
conditions result in an unexpected failure of the block-pusher drive
mechanism that renders the prefeeder inoperative until it is
repaired.
Back to top
Recommended Action:
Alliance recommends that you perform an initial
inspection as described below within 90 days after receipt of this
service bulletin.
If the initial inspection is satisfactory and
the original drive shaft is not replaced with a new unit, Alliance
recommends that you perform a repeat inspection within 2-3 years.
Back to top
Procedure:
-
De-energize and lock-out the machine as
described in the Operators Manual.
-
Remove the block pusher drive assembly
from the prefeeder. Remove the pinion gears from the drive
shaft, and remove the drive shaft from the bearing supports and
motor gearbox. The drive shaft must be completely separated from
the motor gearbox in order to perform an adequate inspection.
Remove keys and inspect all keyway slots for signs of fatigue
and wear.
If any parts require
replacement contact the Alliance Spare Parts Desk at (509) 535-0356
for assistance with parts identification and ordering.
-
Using magnetic particle or dye-penetrate
methods inspect the reduced-diameter portion of the drive shaft
for the presence of cracks. This area is approximately 15” long
and includes the keyway slots. If cracks are confirmed, replace
the drive shaft.
-
The overall condition of the rack and
pinion gears should be checked and parts replaced if excessive
wear is found. The following diagram shows the condition of
both new and worn gear parts.
-
Reinstall the keys in the drive shaft, and
reinstall the drive shaft to the motor gearbox and into the
block pusher assembly. Reinstall the pinion gears making sure
that the taperlock bushings are tight (if installed). Ensure
that the block-push drive assembly is correctly timed with
respect to the engagement of the pinion gears with the rack,
i.e., that one side is not ahead of the other.
-
The rack gear engagement should be checked
for proper mesh. The following diagram shows the proper gear
mesh. This can be adjusted by rotating the main drive shaft
bearings up or down to obtain the proper gear mesh.
-
The brake on the electric drive motor
should be checked for the proper air gap of 0.010” – 0.012”.
This will help the block pusher assembly stop in a constant
position and reduce over-travel, preventing the assembly hitting
the hard stops.
-
Limit switches for the block-pusher
assembly should be checked for proper operation and location.
This will help prevent the possibility of the assembly
contacting the hard stops.
-
Alliance has developed a “Secondary
Restraint Safety Cable Retrofit Kit” to provide a mechanical
backup method to physically prevent the block pusher assembly
from falling off its track. Alliance highly recommends that
operators obtain and install this retrofit kit as a part of
performing this service bulletin inspection. Contact the
Alliance Spare Parts Desk at (509) 535-0356 for further
information and assistance with kit ordering.
-
Remove lockouts, energize the prefeeder,
and check for proper block-pusher operation in accordance with
the Operator Manual.
Please advise Alliance of any significant
findings resulting from your inspections. Comments may be forwarded
to Mr. Mike Thayer, Customer Service Manager, at
mthayer@alliancellc.net.
Back to top
Back to Index |
