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Basics for selecting pneumatic cylinders
Pneumatic cylinders are important components in pneumatic systems that generate mechanical movements using compressed air. They are used in a variety of applications, such as in the manufacturing industry, in plant construction or in custom machine construction.
What is a pneumatic cylinder?
A pneumatic cylinder, or compressed air cylinder, is an actuator that uses compressed air to convert a force into linear motion. In pneumatic systems, compressed air is supplied through pipelines from the compressor to consumers. There, it is converted into mechanical movements by actuating elements, such as cylinders. These cylinders generally perform linear movements, but can also perform pivoting movements using transmission components. They usually consist of a cylindrical housing, a piston and a piston rod and are used in various applications to transfer forces or to lift and move objects. The selection of the correct pneumatic cylinder depends on the requirements of the respective application. Important factors are, for example, stroke length, force, operating pressure and temperature.
Construction of pneumatic cylinders
Pneumatic cylinders generally consist of the following main components:
- Cylindrical housing: The cylindrical housing is similar in shape to a tube or a “drum” and is usually made of steel. It contains other components such as the piston, piston rod and sealing elements.
- Connections: Connections are located at the ends of the pneumatic cylinder. Compressed air can enter or exit through it.
- Piston: The piston is located inside the cylinder and is moved by compressed air.
- Piston rod: The piston rod is located in the cylinder tube and is connected to the drive piston. The linear movement of the piston is transferred to other machine parts with the piston rod.
- Sealing elements: Sealing elements ensure that the pressure in the cylinder is maintained or compensated.
(1) Piston rod (2) Cylindrical housing (3) Connections (4) Piston (5) Sealing elements
Differentiation of pneumatic cylinders according to operating principle
The function principle of pneumatic cylinders is based on the principle of pressure and volume change. The compressed air directed into the cylinder moves the piston. Depending on the operating principle and application of force, a distinction is made between single-action pneumatic cylinders and double-action pneumatic cylinders.
A single action pneumatic cylinder has a single connection. Compressed air enters through this connection, extending the piston rod. Due to the operating principle of single-action pneumatic cylinders, the force can only be exerted in one direction. If the compressed air is released via the same connection, the rod is returned to its original position. Rod retraction can be controlled by using a return spring or external force.
A double-action pneumatic cylinder works in both directions. It has two compressed air connections, which alternately pressurize the pneumatic cylinder from both sides. In this way, the piston rod is moved forwards and backwards. Depending on which side is supplied with compressed air, the pneumatic cylinder controls the direction of movement and unfolds its full force in both directions.
Different versions of pneumatic cylinders
There are different versions of pneumatic cylinders. The explanations listed below are among the most common and/or well-known variants to serve as examples. In addition to these, there are other variants for various special applications.
Pneumatic cylinder with end position damping
Compressed air cylinders with end-position damping are equipped with elastic buffers or adjustable throttles to slightly decelerate the movement of the piston rod before it reaches its end position. This damping protects against shock and increases the service life of the system by preventing the piston from impacting the cylinder bottom at excessive speeds.
Rodless cylinder
Rodless compressed air cylinders are a special form of pneumatic cylinders that are different from conventional cylinders due to the absence of a projecting piston rod. The piston moves within the cylinder and transmits its force either through an external guide, a belt or through the lateral attachment of a linear actuator. This type of construction allows longer stroke lengths in a more compact form, making them particularly suitable for precise applications and spatial restrictions.
Synchronous pneumatic cylinder
In a synchronous compressed air cylinder, the cylinders are designed to work synchronously with one another. This allows all cylinders to move at the same time and at the same speed. This allows machining processes to be optimized because synchronous motion allows for movements beyond the intensity of a single cylinder. Synchronous pneumatic cylinders are often used in applications where precise and uniform movements are required, such as in assembly technology or packaging technology.
Multi-position cylinders
This type of cylinder also consists of several dual-action compressed air cylinders that are directly connected to each other. Depending on the application of compressed air, the individual cylinder pistons extend in different directions. For example, when two cylinders of different stroke lengths are connected, the actuation and stroke division results in four positions that the cylinder can assume. Multi-position cylinders are generally used when several target positions are required, such as in packaging technology or assembly technology.
Membrane cylinders
Membrane cylinders also belong to the pneumatic cylinder class and, in contrast to the compressed air cylinder, have a flexible membrane or a bellows instead of a piston. The membrane expands in response to the compressed air supply, creating motion and force. One advantage of membrane cylinders is the ability to work in environments where leakage or contamination risks must be avoided by eliminating the need for piston rods or seals that project from the cylinder. They are therefore ideal for clean or sterile applications.
Selecting pneumatic cylinders
When selecting a pneumatic cylinder, the force required to move the load at a certain speed plays a key role. The force of the cylinder should be slightly higher than the force required to move the load. How much force is generated depends on various factors, including the operating pressure and the effective diameter of the piston. The basic formula for calculating the force F of the pneumatic cylinder is:
F = p \times a
Where p is the pressure exerted on the piston and a is the effective surface area that comes into contact with the air. The diameter of the piston d is used to calculate the effective surface area a:
a = {\frac{\pi}{4}} \times D^2
Using the operating pressure p and the determined surface area a, the potential maximum force can now be determined and thus the maximum output of the cylinder. However, the force generated in reality can be somewhat lower due to aspects such as friction or pressure drop in lines and valves. It should also be mentioned that the above-mentioned formulas and the calculation of the force relate to single-action pneumatic cylinders. For double-action pneumatic cylinders, the calculation must also take into account the return stroke in addition to the deployment stroke.
Advantages and disadvantages of pneumatic cylinders
Pneumatic cylinders are characterized by a variety of advantages. An important factor is their robust construction. They can withstand various environmental influences and mechanical stresses. Due to their simple design, compressed air cylinders are firstly cheaper because they do not require complex electronics or controls, and secondly, their maintenance and repair is also easier than, for example, compared to electronic or hydraulic systems. In addition, it should be mentioned that pneumatic cylinders work very cleanly, as they only work with compressed air. Even if air escapes through a leak, there is no contamination. In addition, assembly is very easy, as the exhaust air can exit directly into the environment and thus no complex return lines are required.
One of the disadvantages is that pneumatic cylinders require clean and dry air to function optimally. Contamination or moisture in the air can cause premature wear or condensation in the system, which in turn would impair the efficiency and service life of the cylinders. Another aspect to consider is the so-called stick-slip effect.. This effect refers to the gliding of moving solid bodies against each other and occurs when the static friction is significantly greater than the sliding friction. Since the forces of static friction in pneumatic cylinders are approximately twice as great as those of sliding friction, the stick-slip effect can sometimes occur very quickly.
Application areas of pneumatic cylinders
Pneumatic cylinders are used in a variety of industries and applications. They are often used in mechanical engineering and plant engineering to perform repetitive movements, such as automated production lines. Compressed air cylinders are used there to perform tasks such as clamping, turning or lifting. However, pneumatic cylinders are also used in conveyor systems to open or close sliders, for example, or to move materials from one belt to another.
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MISUMI offers a variety of high-quality pneumatic cylinders in different versions. Select the appropriate pneumatic cylinder for your application. You can also find numerous pneumatic accessories such as valves, adapters, sensors or compressors in the MISUMI online shop.
