Firestone Applications

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Takeaways
Key Concepts to Remember
Firestone Contacts

Applications Engineer
 Facundo Lay

Global Industrial Channel Manager
 Don Foulke

Regional Manager
 Greg McNamar

Marketing Specialist
 Jacek Okonski

Customer Service Representatives
 Ahmet Uzun
 Shelley Ooi Lay Shin
 Rose DaSilva
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Key Principles

Variable effective area - ∆Ae – Bellows side wall geometry

Gas laws - ∆P ~ ∆V

Lateral spring rate – Bellows side wall geometry

Damping
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Variable Effective Area
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Gas Laws
Pa 1V1  Pa 2V 2
n
n
n=1 for isothermal compression
n=1.4 for adiabatic compression
Firestone has determined an exponent of 1.38 is the most
practical number for most air spring dynamic applications

 V1
k  Pg  14 . 7  A c 

 Vc






1 . 38
 V1
 A c 
 Ve

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1 . 38
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  14 . 7  A c  A e
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
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Lateral Restoring Force (spring rate)

When you deflect the
bellows laterally at a
low height it causes
the tension vectors on
the side wall to shift as
in figure F = instable

When you deflect the
bellows laterally at a
high height it causes
the tension vectors on
the side wall to shift as
in figure G = stable
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Lateral Stability
Always use Airmounts at the Recommended Design Height
Triple Convoluted and 1T Style parts are less laterally
stable than Single and Double Convoluted parts - please
contact Firestone
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Damping (Not Dampening!)
NOT THE SAME AS ISOLATION
Damping is what SLOWS an oscillating system over time until it
comes to rest
ISOLATOR: like the springs on your car to reduce amount of vibration
energy transmitted to passengers
DAMPER: like the shock absorbers on your car to keep it from
bouncing after a bump
Air springs are great isolators, but lousy dampers
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Applications that
Demonstrate Key Principles
Air Springs Used as Springs
Aluminum Can-Making Machinery
Counterbalance for a
Cupping Press
The air springs act as a very
low rate adjustable spring.
They keep a constant
upward force on the upper
platen of the press. This
keeps the drive system
always working in tension
instead of cycling between
tension and compression.
The result is much better
bearing life and reduced
stress on all of the drive line
components.
Press equipment manufactured by Standun
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Missile Modal Vibration Testing
In this case the air springs again act as low rate springs. They are really not intended to
“isolate” the vibrations induced into the vehicle, although they do accomplish that. The
intent is to allow the vehicle to vibrate and move freely as if it were floating in space.
This allows for the testing of the effects of the vibration on the vehicle.
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Spring Type Applications
•The purpose of the air springs in the two above applications is
to support a mass and to allow it to move with as little effect
as possible from the supports (they act as a balancer)
•In the three following applications the purpose is to support a
mass and transfer as little of the impact force as possible
through to the supporting structure.
•In both cases, the air springs are acting like “springs”, and in
these cases they are special springs that have as little spring
rate as possible.
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Die Cushion
In this application the air springs create
a more gradual build up of the forming
pressure in the press, reducing shock
impact on the tooling and drive system.
It can also be used to eject the finished
part out of the forming die.
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Lumber Machinery
Log Carriage Shock
Bumper
In this case the application is pretty clear.
The bumper is meant to stop the log
carriage from impacting the stop at the end
of the carriage way. By reducing the
impact force you reduce maintenance and
repair costs.
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Shock Testing Machine
In the case of impact
test equipment, the
impact force is a
necessary part of the
performance of the
machine. However, you
don’t want that impact
force to be transmitted
into the floor causing
both structural damage
and noise transmission.
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Counterbalance
•The purpose of a “counterbalance” type of application is to
offset the force of gravity, not to “isolate” anything
•You want as little spring rate as possible so that the load can
be moved with minimal change in the force
•Spring rates in air springs have two basic causes
• ∆Ae
• ∆P~∆V
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Shock Impact
Calculate the potential or kinetic energy of the system:
PE = Mass * Gravity * height
KE = ½ * Mass * Velocity^2
Determine the amount of energy the air spring can
absorb.
Technigram # 112
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Gas Laws
Pa 1V1  Pa 2V 2
n
n
n=1 for isothermal compression
n=1.4 for adiabatic compression
Firestone has determined an exponent of 1.38 is the most
practical number for most air spring dynamic applications

 V1
k  Pg  14 . 7  A c 

 Vc






1 . 38
 V1
 A c 
 Ve




1 . 38

  14 . 7  A c  A e


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Results

As the moving object compresses the air spring the pressure
inside goes up according to the change in volume

The force on the object and the mounting surface goes up
because of both the increased pressure and the change in the
effective area.

The energy stored in the air spring also the net effect of the
pressure increase and the force increase.

Once the movement is stopped, the energy is returned to the
object as bounce back.
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Kinetic energy stored in the spring as
potential energy and returned to the object
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Air springs used as
vibration isolators
Vibration Isolation Applications
In a vibration isolation application the air spring’s purpose is to
support a load and prevent the motion of either the load, or the
supporting structure, from disturbing the other object.
In this case the important factor is to insure the minimal amount
of transmission of the energy of vibration between the two
objects. This is done by achieving the maximum separation
between the forcing frequency and the natural frequency of the
supporting structure (air springs).
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Optical Table
These tables are used for laser holography, electron microscopes, micro chip inspection
equipment, etc. In this case you are trying to reduce the energy of floor vibrations from
disturbing the equipment mounted on the table. Air springs are the lowest frequency
passive isolators available and, therefore, reduce the transmitted vibration energy of lower
frequency structural vibrations better than other passive devices. Remember, Ferraris.
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Food Processing Equipment
Vibrating conveyors
Vibrating hoppers
In the case of these devices,
vibration energy is a necessary part
of the performance of the machine.
The air springs allow the equipment
to vibrate, but transmit the lowest
amount of energy through to the
supporting structure.
Conveyor equipment manufactured by Key Technology
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Results

In these cases the motion of the isolated object is cyclic

The purpose of the isolator is to allow the motion of the moving
object without transmitting that energy into the isolated object

Again the movement causes the air spring to compress and
extend with the results being governed again by the change in
effective area and the gas laws

The lower the spring rate, the less force is generated at the
mounting surface of the isolated object, reducing the effect of
the motion
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Effective Area
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Gas Laws
Pa 1V1  Pa 2V 2
n
n
n=1 for isothermal compression
n=1.4 for adiabatic compression
Firestone has determined an exponent of 1.38 is the most
practical number for most air spring dynamic applications

 V1
k  Pg  14 . 7  A c 

 Vc






1 . 38
 V1
 A c 
 Ve




1 . 38

  14 . 7  A c  A e


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Air Springs Used as Actuators
Air Spring Actuators
This is the concept that is the most familiar to fluid power distributors.
F  PA
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Lockheed Plane Dolly
Here, of course, the air spring is not
acting as a spring at all. The air
spring is acting as a high force, short
stroke pneumatic actuator.
We currently have air springs up to
950 mm maximum diameter that can
produce up to 45 tons of force over
short strokes.
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Results

Although the concept of fluid pressure working on an area is
well known to fluid power specialists, the air spring has a bit of
a different wrinkle

Because convoluted air springs have a variable area, the force
is not constant

You need to evaluate the total travel of the actuator and the
effective area at the end of the travel to determine which size
part will give you the required force
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Effective Area
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The End
(Really, this is the end!)
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