Takeaways

1. Takeaways • Key Concepts to Remember

2. 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

3. Key Principles • Variable effective area - ∆Ae – Bellows side wall geometry • Gas laws - ∆P ~ ∆V • Lateral spring rate – Bellows side wall geometry • Damping

4. Variable Effective Area

5. Gas Laws 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

6. 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

7. 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 Lateral Stability

8. 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 Damping (Not Dampening!)

9. Applications that Demonstrate Key Principles

10. Air Springs Used as Springs

11. 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

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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

18. 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

19. Gas Laws 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

20. 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.

21. Kinetic energy stored in the spring as potential energy and returned to the object

22. Air springs used as vibration isolators

23. 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).

24. 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.

25. Vibrating conveyors Vibrating hoppers Food Processing Equipment 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

26. 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

27. Effective Area

28. Gas Laws 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

29. Air Springs Used as Actuators

30. Air Spring Actuators This is the concept that is the most familiar to fluid power distributors.

31. 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.

32. 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

33. Effective Area

34. The End (Really, this is the end!)