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AppTip_Shocks0 pages
APPLICATION TIP
Product category: Pneumatic Actuators
Industry: Paper and Plastics
Problem:
Inoperable cushion seals and damaged
sealing bands on band-type cylinder
Cause:
Inertia spikes and final velocity speeds
exceeding actuator cushion capacities
Solution:
Application of external shock absorbers
Actuator internal cushions vs. external shock absorbers: Knowing when
and how to use them is crucial for maximum actuator life.
Exceeding the capacity of the
actuator’s internal cushions
can cause irreparable damage
to the cushion seals and
sealing bands.
www.tolomatic.com
Tolomatic pneumatic band-type
cylinders have been proven industry
workhorses since they were first
introduced back in 1985. It is an
unusual circumstance to find an
actuator that fails prematurely,
particularly after an initial installation.
Tolomatic went to the customer’s facility
to find out why.
A plastics container manufacturer was
using a Tolomatic internal bearing style
band cylinder to move a flying knife
assembly across a piece of plastic
film as rolls were released from the
extruding machinery. The 10-pound
flying knife assembly moves the full
101-inch stroke in 1.5 seconds every
45 minutes. Flow controls were being
used with an air pressure rating of
40 psi. Most of the cylinders they
employed failed during the first 100
strokes or less while others would
run up to 6 months before needing to
be replaced. The particular cylinder
being analyzed had been running for
two weeks when erratic behavior was
noticeable. After inspecting the cylinder,
it was determined that the actuator’s
internal cushions were rendered
inoperable due to damaged seals.
Removing the head from the actuator
also revealed that the sealing band
was bent and “cupped”, a sign that an
inertia spike was causing the damage.
The actuator’s sealing band experienced
cupping damage caused from inertia spikes.
To explain why this was happening
we need to define how the actuator’s
internal cushions work.
The cushion’s function is to slow the
actuator’s load at the end-of-stroke
