The simplicity, long life, cost-efficiency, and ease of installation and maintenance of pneumatic cylinders contribute to their popularity. It produces a great deal of force across a broad spectrum of speeds, maintains high-speed operation for a long period of time without overheating, and suffers no damage if it stalls. Furthermore, pneumatic cylinders are rugged enough to handle dirty and dusty environments, high-pressure washdowns, high humidity, and explosive environments.
However, this versatility can make it difficult to determine exactly which type of actuator is the best fit for your particular application; a few important factors are consider.
Rodless or piston rod actuation is the first distinction to be made when choosing a pneumatic cylinder design. The piston rod of a single-action rod type is moved by compressed air entering through an exhaust port at one end of the cylinder. Each stroke moves the load and exhausts the air. The speed at which the rod moves depends on how fast the air is exhausted. Double-acting cylinders also drive the rod back again, allowing a push-pull load motion, while single-acting cylinders use a return spring.
Rod-style cylinders can break down yet further into different types:
- Compact design for small spaces and short stroke operation. Mostly single-action.
- Durable and repairable.
- Disposable and not repairable.
- Directed, for controlled, precise linear motion and high side loads.
- Rack-and-pinion, to convert linear motion to angular rotation.
Rodless cylinders can either be bellows-type, with an inflatable elastomer tube that creates a high force and bends in any direction; or linear sliders, with a carriage-mounted or cable-and-pulley load. Magnetically coupled actuators and guided linear slides are also available. Pneumatic cylinders without rods are ideal for high moment loads or applications requiring a long stroke and can save space since the stroke action is contained within the overall cylinder
Identifying the stroke length will also help narrow down the type of cylinder required. The length of strokes varies with the job, and overlaps may occur, but there are general classifications:
- The stroke can be as short as 1/16″ for compact cylinders.
- For light automation, the stroke can be up to 3 feet.
- For automatic doors (e.g.), 40-99″ long stroke
- Cable-and-clamp pulling a piston up to 25 feet, with a special stroke
As the cable can be any length that meets the application and mounting requirements, cable cylinders can be located remotely.
Another factor to consider when choosing a pneumatic cylinder is how much force it must generate to run your application. To calculate push force, you must know the internal diameter or bore size of the cylinder, as well as the air pressure. Pull force calculates by reducing the bore size by the cross-section of the piston rod.
Therefore, theoretical push force is an equation:
- (Air Pressure) x (Bore Size) = Force
- (Power Factor = Force * Available Pressure)
- To calculate the necessary cylinder bore for a safety factor of 50%, multiply the cylinder power factor by 1.5.
- If (Bore Size) x 1.5, then (Bore)2 ÷ 4.
Generally, the force requires for high-friction and vertical applications will be twice the load, but sometimes additional force will require to compensate for excessive friction. Spring returns can also complicate calculations, but manufacturers’ catalogs provide tables for easy reference. Use our cylinder sizing calculator.
Alternatively, you can consult the force tables provided by manufacturers in their catalogs. Airmax pneumatics lists these values in the product data fields for convenience.
The speed of your cylinder affects how well it can control its load, as well as how long it will last and how productive it will be. The stroke speed of a pneumatic cylinder can be calculate using the following formula:
Where s= 28.8q/A
- Inches per second = speed
- In cubic feet per minute
- Piston area measures in square inches
Speed can also affect by other factors, such as the size of the ports, hoses, and tubing, and the rate of inlet and exhaust flow. Sometimes there can be a bottleneck in the flow of air into or out of the cylinder, reducing air pressure and slowing the cylinder down.
Also Read: Mechanism and Importance Plug Valve
In fast-cycling applications, it is often necessary to calculate the cylinder’s air consumption carefully to ensure that enough air is available. As air starvation at a crucial moment will adversely affect performance, you should ensure that the compressor has the capacity to supply your pneumatic equipment even in the worst-case scenario.
A mounting configuration describes how a cylinder connects to the equipment. Many mountings, both rigid and articulate, produce as standard, making it easier to meet your application’s movement requirements. It is possible to modify the style of cylinder you want if the hardware cannot match your desired mounting position, but commissioning unique hardware will cause delays and increase costs.
Most pneumatic cylinders are made from brass, steel, stainless steel, aluminum, engineered polymers, or a combination of several materials. The material you choose depends on the operating environment. The same is true for seal materials, but alternative materials can be specified for use in hazardous environments.
Standard components can’t always do the job and a custom design is necessary. By designing a new configuration for standard and/or modified components, or by creating a whole new unit. Using this option is feasible if you require a high level of efficiency, complex motion control, or components that do not currently fit standard combinations. Nowadays, intelligent design is much more capable of incorporating special configurations and will create custom products that are tailor exactly to your needs.
There are clearly many factors that can influence your decision. There is an additional factor involve, such as load position, sensor, temperature requirement, and any special movements that may require cylinder modifications. Magnetic cylinders have positioning feedback controls, and cushions or shock absorbers reduce impact and noise. To control the pneumatic cylinders, there is a directional control valve came into action.
You should choose your pneumatic cylinder carefully because it will account for a significant part of your installation budget. It’s always best to discuss your specific needs with the manufacturer or a technical sales engineer.
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