The Firestone Airstroke™ and Airmount™ Engineering Manual and Design guide is one of the most comprehensive engineering guides available globally for the ubiquitous air springs used in machinery including conveyors, hoppers, vibrating screens, lifters, metal stampers, tensioning webs, belt takeup, shock absorbers, clamps, couplings and suspensions.
According to National Sales and Marketing Manager, James Maslin, there are differences between air springs and conventional pneumatic cylinders. Whereas conventional cylinders contain their air in a rigid metal jacket, air springs contain theirs in a flexible but immensely strong rubber and fabric-reinforced bellows.
Key advantages of air springs
- Ends of the air springs are sealed by bead plates
- Available in a variety of styles
- Contain no pistons, rods or static or dynamic seals, making them less to operate than air cylinders
- Friction is reduced and there are no internal moving parts to break or wear
- Suitable for high repetition tasks such as actuating change gates on conveyor lines, or powering stamping presses
- Ability to arc without a clevis; bend and tolerate uneven and fluctuating loads
Hinged conveyor drive tables
Conveyor lines are one of the most common materials handling applications of air spring actuators (Airstrokes). Because air springs are engineered by Firestone to be robust enough to function for hundreds of thousands of kilometres in heavy truck and bus suspensions, they are sufficiently flexible and robust to survive millions of cycles in conveyor tasks such as gravity transfer sections, actuated diverters, belt take-up, roller friction brakes, end stops and two-way switches. Air springs provide a number of advantages, including:
- space and cost savings
- simplicity of engineering
- durability because of lack of complexity and flexibility
- Actuated hinged drive tables are used where gravity transfer stations cannot provide the speed and precision required
Conveyors, or rolls of paper or fabric, moving across a number of rollers at high speed require constant tension to prevent slack, breakage, or damage. Conventional cylinders may suffer from seal and bearing “sticktion” and therefore do not operate as smoothly, providing inconsistent tension.
- the friction-free actuators provide consistent tension over their entire stroke
- air springs are far more tolerant of shock loads then conventional pneumatic cylinders
- shock to the web or roll can damage the cylinder or, as a result of the cylinder’s ability to absorb chock, damage the web
Frequently in materials handling operations scissors-lift tables move loads from one height to another, while maintaining a specific attitude, regardless of load centre. Because of static friction, conventional cylinders to not provide smooth motion, particularly at low pressures. A certain weight is required to overcome static friction, so the table lowers in jerky increments instead of a smooth stroke.
- air springs are not affected by static friction and provide smooth operation at any pressure
- air spring pressures can be adjusted to accommodate a variety of package weights within specified limits
Unlike conventional cylinders, air springs may be used not only as actuators, but also as long-life isolators. In applications such as suspending vibrating screens or motors, they isolate the offending source of vibration from the surrounding relative tranquility.
Alternatively, they may be used to isolate delicate computers of electronic materials handling componentry from ambient vibration.
Because they can reliably achieve isolation efficiencies high enough to be used beneath surgical operating tables, they offer outstanding potential for industrial applications such as vibrating screens, vibrating packers and vibrating bins. They are also utilised beneath motors or machinery that could disrupt surrounding workplaces or automation machinery
As Australian states move toward more stringent workplace and environmental guidelines, this isolation capability is becoming a major factor in machinery design.
A common materials handling isolation application is isolation of bin vibration. This type of vibration is typically used to maintain a homogeneous mix or flow of material inside a hopper. It must be isolated from bin supports so as to prevent structural fatigue.
Solid rubber isolators or steel springs can be used, but they must be tuned to one specific load and a single height.
Air springs provide a high degree of isolation compared with other methods, where they are used down to disturbing frequencies of 3-4 Hz. Isolator inflation can be changed to compensate for different loads or heights without compromising isolation efficiency.
Air Spring isolators (Airmounts) are generally used where weights exceed 100kg per mounting point.