Why do our bearing blocks have such a short life
on our Model 150?
Problem: After about a
year, our Model 150 started to wear out bearing blocks at approximately one
every four weeks. The first block lasted well over a year and now we can’t
figure out why they wear out so fast.
Analysis: This application’s
press runs in single stroke mode at about 50 spm.
Our customer built a heavier tray and some heavy-duty tray clamps to handle a
tray slip problem caused by the single stroke cycle. The constant starting
and stopping of the press and the extra weight caused a greater-than-normal
torque moment (twist) between the block and rail. This unloader has only one
block and rail so tray weight and tray location can have a great impact on
the bearing’s life. There was also a hidden problem; the rail was pitted
caused by the excessive torque and rapid acceleration where the ball bearings
in the bearing block go from a stop to full speed in a fraction of a second.
The rail grooves that were most damaged were under the top surface of the
rail and were hidden from the operator’s view. An inspection of the rail with
a fingernail was all that was needed to identify the pitted condition.
Finding: A combination of the unloader’s use
in single stroke mode and the additional weight added to the carriage and
block were the majority of the problem. Lightening the load and minimizing
the twist in the bearing should solve the problem. The root cause however,
was the tray slippage in single stroke mode. Better gripping tray clamps will
be needed to keep the tray were it belongs while
keeping the carriage assembly’s weight to a minimum.
Solution: The bearing
replacement problem was resolved by adding a second bearing block to the rail
with a special carriage; a two rail unloader also makes the carriage assembly
more rigid. The modified carriage was machined thinner to allow for a taller
aluminum t-bar. Standard serrated grippers were added to the tray clamp
increasing its grip while not increasing its weight. The combined weight
saving of 10 pounds and the increased rigidity eliminated the short life of
the bearing block. Periodic inspection of the rail will also help prevent
premature replacement of the block.
Tray clamp with gripper insert added
Detail: The following are the part numbers
and descriptions for the above parts.
Carriage Double Bearing
M8-1.25 x 20 Flat Head Bolts
T-bar Aluminum; specify length
Tray Clamp With Gripper
5/16-18-f Handle Quick Release
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