As one of the main components of pneumatic drive, the role of the Pneumatic cylinder in industrial development is self-evident. But after using so many Pneumatic cylinders, do you really understand them?
The basic structure of a Pneumatic cylinder
The so-called pneumatic actuator is a component that uses compressed air as power to drive the mechanism to perform linear, oscillating and rotational movements. Take the most commonly used basic type cylinder as an example to see what the internal structure is exactly.
1. 3- Buffer Plunger 2- Piston 4- Cylinder Barrel 5- Guide sleeve 6- Dust Ring 7- Front End Cover 8- Air Port 9- Sensor 10- Piston Rod 11- Wear-resistant Ring 12- Sealing Ring 13- Rear End Cover 14- Buffer Throttle Valve
1) Cylinder barrel
One key parameter of the cylinder barrel is its inner diameter. The size of the barrel diameter determines the output force of the cylinder. The surface roughness of the inner wall of the cylinder barrel should be at least Ra0.8um to ensure that the piston can slide back and forth smoothly inside the cylinder barrel. In addition to using high-carbon steel tubes, the cylinder barrel material will also be made of high-strength aluminum alloy and brass.
2) End cover
Both ends of the cylinder barrel are equipped with end covers, on which intake and exhaust ports are set. Some also have buffer mechanisms. To prevent the piston rod from leaking air outward or external dust from entering the cylinder body, sealing rings and dust-proof rings are installed on the end cover. To enhance the guiding accuracy of the cylinder, a guiding sleeve is also installed on the side end cover of the rod.
3) Piston
As a directly moving component, the piston is undoubtedly a part that is under pressure. To prevent gas leakage in the piston, a piston sealing ring is usually installed. Wear-resistant rings are installed on the piston, which can improve the guiding performance of the cylinder.
4) Piston rod
The piston rod is the direct actuator and also the most important force-bearing component. Therefore, the material requirements for it are also relatively high. Usually, high-carbon steel or stainless steel that has undergone hard chromium plating treatment is used to enhance corrosion resistance and improve the wear resistance of the sealing ring.
5) Buffer plunger, buffer throttle valve
The buffer device is an important component that ensures the service life of the cylinder. We will discuss its specific function later.
Classification of cylinders
Cylinders can be classified into single-acting cylinders and double-acting cylinders.
As the name suggests, a single-acting cylinder supplies air only to one side. The air pressure pushes the piston, causing the piston rod to extend and return to its original position by the spring or its own weight.
There is a very good metaphor. It's like you are a single dog, but you can also play to your heart's content in a squash court, thinking that the squash ball will bounce back to you through the wall.
Double-acting cylinder: A double-acting cylinder supplies air to both sides of the piston, and the forward and backward movement on both sides is achieved through air pressure.
And this is our metaphor that needs to be changed. You have beautifully found a girlfriend, and finally someone can play badminton with you.
Buffer of the cylinder
We also mentioned the buffering issue of the cylinder earlier. If there is no buffer device, when the piston moves to the terminal, it will strike the end cover with great kinetic energy. It won't be long before the parts are damaged, which greatly shortens the service life of the cylinder.
In addition, the noise caused by the impact is also very loud. The noise of a single cylinder may not be loud, but the noise of a factory's cylinders can even reach a level that humans cannot tolerate, just like being beside a jet aircraft that is starting up.
For this reason, the smart designer made a buffer device for the cylinder. Hydraulic buffering is the simplest buffering method. The hydraulic buffer is installed at the front end of the cylinder.
1. The hydraulic buffer device uses mineral oil as the medium and, through a unique damping design, can achieve a smooth transition from high-speed light load to low-speed heavy load.
2. Rubber buffers: Rubber buffers are installed more compactly, but their buffering capacity remains constant and is relatively small. Therefore, it is mostly used in small cylinders.
3. Air buffering. Air buffering is achieved through buffer valves. From the following figure, we can see that the gas inside the wall can only be discharged through the buffer valve. The opening degree of the buffer valve is very small. When the piston moves, the pressure inside the cavity rises rapidly, exerting a counteraction on the piston and causing it to decelerate until it stops.
The limit of the cylinder
The magnetic switch is a component that determines whether the cylinder is in place. It can control the corresponding solenoid valve to achieve the switching action. When the piston moves, the magnetic ring on top will approach or leave the switch, and the current in the switch will be magnetized, attracting each other or disconnecting, thereby generating an electrical signal.
Lubrication of the cylinder
There are usually two ways to lubricate cylinders. One is oil lubrication, which involves mixing lubricating oil with compressed air and delivering it to the cylinder. This method of lubrication requires continuous use. Once it is stopped, its lifespan will drop sharply. Another approach is to use grease for lubrication. Currently, most manufacturers have fully implemented non-oil-gas cylinders.
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