I. Types of pneumatic cylinders
In pneumatic transmission, the pressure energy of compressed gas is converted into mechanical energy by pneumatic actuators. Pneumatic cylinders can be classified into two types: those that perform reciprocating linear motion and those that perform reciprocating oscillating motion. The pneumatic cylinders that perform reciprocating linear motion can be further divided into single-acting, double-acting, diaphragm type, and impact pneumatic cylinders.
① Single-acting pneumatic cylinder: Only one end has a piston rod. Gas is supplied from one side to accumulate pressure, which then pushes the piston to extend and returns by a spring or self-weight.
② Double-acting pneumatic cylinder: Gas is supplied alternately from both sides. Force is output in one or both directions.
③ Diaphragm type pneumatic cylinder: A diaphragm replaces the piston, and force is output in only one direction. It uses a spring for repositioning. It has good sealing performance but a short stroke.
④ Impact pneumatic cylinder: This is a new type of component. It converts the pressure energy of compressed gas into the kinetic energy of the piston's high-speed (10-20 meters/second) movement to perform work. The impact pneumatic cylinder has a middle cover with a nozzle and a discharge port. The middle cover and the piston divide the pneumatic cylinder into three chambers: the air storage chamber, the head chamber, and the tail chamber. It is widely used in various operations such as cutting, punching, crushing, and forming. Pneumatic cylinders that perform reciprocating or oscillating motion are called oscillating pneumatic cylinders. The blades divide the inner chamber into two, and gas is supplied alternately to the two chambers, causing the output shaft to perform an oscillating motion. The oscillation angle is less than 280°. In addition, there are rotary pneumatic cylinders, hydraulic damping pneumatic cylinders, and stepping pneumatic cylinders, etc.
II. Function of the pneumatic cylinder: It converts the pressure energy of compressed air into mechanical energy, driving the mechanism to perform linear reciprocating motion, oscillation, and rotational motion.
III. Classification of pneumatic cylinders: Linear motion reciprocating pneumatic cylinders, oscillating pneumatic cylinders for swinging motion, pneumatic claws, etc.
IV. Structure of the pneumatic cylinder: The pneumatic cylinder is composed of the pneumatic cylinder barrel, end cover, piston, piston rod and sealing components. Its internal structure is shown in the following figure.
V. pneumatic cylinder Structure Principles
1. pneumatic cylinder barrel: The inner diameter of the pneumatic cylinder barrel determines the output force of the pneumatic cylinder. The piston must move smoothly in the pneumatic cylinder barrel. The surface roughness of the inner surface of the pneumatic cylinder barrel should reach Ra0.8um. For steel pneumatic cylinder barrels, the inner surface should also be plated with hard chromium to reduce friction resistance and wear, and to prevent rust. The material of the pneumatic cylinder barrel can be high-carbon steel, high-strength aluminum alloy, or brass. For small pneumatic cylinders, stainless steel tubes can be used. Pneumatic cylinders with magnetic switches or those used in corrosive environments should use materials such as stainless steel, aluminum alloy, or brass. SMC CM2 pneumatic cylinder pistons use combined sealing rings to achieve bidirectional sealing. The piston and piston rod are linked by press-fitting without nuts.
2. End cover: The end cover has inlet and exhaust ports, and some also have a buffer mechanism inside. The end cover on the rod side has sealing rings and dust-proof rings to prevent air leakage from the piston rod and prevent external dust from entering the pneumatic cylinder. The end cover on the rod side has a guide sleeve to improve the guiding accuracy of the pneumatic cylinder, withstand a small amount of lateral load on the piston rod, reduce the deflection when the piston rod extends, and extend the service life of the pneumatic cylinder. The guide sleeve usually uses sintered oil-containing alloys or inclined copper castings. The end cover used to be made of cast iron, but now to reduce weight and prevent rust, it is often made of aluminum alloy by die-casting. Micro pneumatic cylinders use brass materials.
3. Piston: The piston is the pressure-receiving part of the pneumatic cylinder. To prevent the two chambers of the piston from communicating with each other, a piston seal ring is provided. The wear-resistant ring on the piston can improve the guiding performance of the pneumatic cylinder, reduce the wear of the piston seal ring, and reduce friction resistance. The wear-resistant ring is usually made of materials such as polyurethane, polytetrafluoroethylene, or fabric-reinforced synthetic resin. The width of the piston is determined by the size of the sealing ring and the necessary sliding part length. If the sliding part is too short, it is prone to early wear and jamming. The material of the piston is usually aluminum alloy or cast iron. The pistons of small pneumatic cylinders are made of brass.
4. Piston rod: The piston rod is the most important load-bearing part of the pneumatic cylinder. It is usually made of high-carbon steel, and is treated with hard chromium plating or stainless steel to prevent corrosion and improve the wear resistance of the piston seal ring.
5. Sealing ring: Components at rotating or reciprocating motion locations are called moving seals, while the sealing of stationary parts is called static seals. The connection methods between the pneumatic cylinder barrel and the end cover mainly include the following types: integrated type, riveting type, threaded connection type, flange type, and pull rod type.
6. When the pneumatic cylinder is working, it relies on the oil mist in the compressed air to lubricate the piston. There are also a small number of non-lubricated pneumatic cylinders.
VI. Working Principle of Pneumatic Cylinder
The thrust and pull forces on the piston rod are determined based on the required force for operation. When selecting a pneumatic cylinder, it is necessary to ensure that the output force of the pneumatic cylinder has a slight margin. If the pneumatic cylinder diameter is too small, the output force will be insufficient, and the pneumatic cylinder will not operate normally; however, if the pneumatic cylinder diameter is too large, it will not only make the equipment heavy and costly, but also increase the air consumption, resulting in energy waste. In fixture design, it is advisable to use force amplification mechanisms as much as possible to reduce the size of the pneumatic cylinder.
Above is the structural principle and basic functions of the pneumatic cylinder. To learn more related information, visit https://www.joosungauto.com/.
