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How to diagnose and deal with the failure of the pneumatic cylinder?

                       
Update:10-03-2021
Summary:

Air cylinder malfunction or malfunction The reasons and […]

Air cylinder malfunction or malfunction
The reasons and treatment methods are as follows:  
(1) The valve core is stuck or the valve hole is blocked. When the flow valve or directional valve spool is stuck or the valve hole is blocked, the pneumatic cylinder is prone to malfunction or malfunction. At this time, check the pollution of oil and gas; check whether dirt or colloidal deposits are stuck in the valve core or block the valve hole; check the wear of the valve body.
(2) The piston rod and the cylinder are stuck or the air cylinder is blocked. At this time, no matter how you manipulate it, the air cylinder does not move or moves slightly. At this time, check whether the piston and piston rod seals are too tight, whether dirt and colloidal deposits have entered: whether the axis line of the piston rod and the cylinder barrel is aligned, and whether the wearing parts and seals are invalid.
(3) The control pressure of the pneumatic system is too low. The throttling resistance in the control pipeline may be too large, the flow valve is improperly adjusted, the control pressure is inappropriate, and the pressure source is disturbed. At this time, check the control pressure source to ensure that the pressure is adjusted to the specified value of the system.
(4) Air enters into the air pressure system. Mainly because there are leaks in the system. At this time, check the air level of the pneumatic fuel tank, the seals and pipe joints on the suction side of the pneumatic pump, and the primary suction filter for dirty. If so, add air pressure oil, deal with seals and pipe joints, clean or replace the coarse filter element.
(5) The initial movement of the pneumatic cylinder is slow. In the case of low temperature, the viscosity of the pneumatic oil is high, and the fluidity is poor, resulting in slow movement of the pneumatic cylinder. The improvement method is to replace the air pressure oil with better viscosity and temperature performance. At low temperatures, it can be heated by a heater or the machine itself to increase the oil temperature at startup.

The pneumatic cylinder cannot drive the load when it is working
The main manifestations are inaccurate piston rod parking, insufficient thrust, reduced speed, unstable work, etc. The reasons are
(1) Leakage inside the pneumatic cylinder. The internal leakage of the pneumatic cylinder includes the leakage caused by the sealing of the pneumatic cylinder, the sealing of the piston rod and the sealing cover, and the excessive wear of the piston sealing.
The reason for the leakage of the seal between the piston rod and the seal cover is that the seal is wrinkled, squeezed, torn, worn, aging, deteriorated, deformed, etc. At this time, a new seal should be replaced.
The main reason for excessive wear of the piston seal is improper adjustment of the speed control valve, resulting in excessive back pressure and improper installation of the seal or air pressure oil contamination. The second is that foreign matter enters during assembly and the quality of the sealing material is not good. The consequence is slow movement and weakness. In severe cases, it will cause damage to the piston and cylinder, causing the phenomenon of "cylinder pulling". The treatment method is to adjust the speed control valve, and perform necessary operations and improvements according to the installation instructions; clean the filter or replace the filter element and air pressure oil.
(2) Leakage of the pneumatic circuit. Including leakage of valves and air pressure lines. The maintenance method is to check and eliminate the leakage of the pneumatic connecting pipeline by operating the reversing valve.
(3) The pneumatic oil is bypassed back to the oil tank through the overflow valve. If dirt enters the overflow valve and jams the spool, the overflow valve is normally opened, and the air pressure oil will flow directly back to the oil tank through the overflow valve bypass, causing no oil to enter the air cylinder. If the load is too large, although the regulating pressure of the relief valve has reached the maximum rated value, the pneumatic cylinder still cannot get the thrust required for continuous action and does not move. If the adjustment pressure is low, the vertebral force required for still loading cannot be achieved due to insufficient pressure, which is manifested as insufficient thrust. At this time, check and adjust the overflow valve.

The piston of the pneumatic cylinder slips or crawls
The sliding or crawling of the piston of the pneumatic cylinder will make the operation of the pneumatic cylinder unstable. The main reasons are as follows:
(1) The inside of the pneumatic cylinder is sluggish. The internal parts of the pneumatic cylinder are improperly assembled, the parts are deformed, worn, or the geometric tolerance exceeds the limit, and the action resistance is too large, so that the speed of the pneumatic cylinder piston varies with the stroke position, and slip or crawl occurs. The reason is mostly due to the poor assembly quality of the parts, the surface scars or the iron filings produced by sintering, which increase the resistance and reduce the speed. For example: the piston and the piston rod are not concentric or the piston rod is bent, the installation position of the pneumatic cylinder or the piston rod on the guide rail is offset, the sealing ring is installed too tightly or too loosely, etc. The solution is to repair or adjust, replace damaged parts and remove iron filings.
(2) Poor lubrication or out-of-poor bore diameter machining of the pneumatic cylinder Because the piston and the cylinder, the guide rail and the piston rod all have relative motion, if the lubrication is poor or the cylinder bore is too poor, it will intensify the wear and reduce the linearity of the cylinder center line. In this way, when the piston is working in the pneumatic cylinder, the frictional resistance will sometimes be large and sometimes small, resulting in slippage or crawling. The elimination method is to grind the pneumatic cylinder first, then prepare the piston according to the matching requirements, grind the piston rod, and configure the guide sleeve.
(3) The air pump or cylinder enters the air. Compression or expansion of air can cause the piston to slip or crawl. Elimination measures are to check the air pump, set up a special exhaust device, and quickly operate the full stroke back and forth several times to exhaust.
(4) The quality of the seal is directly related to slippage or crawling. When the O-ring seal is used under low pressure, compared with the U-shaped seal, due to the higher surface pressure and the larger difference between dynamic and static friction resistance, it is easy to slip or crawl; the surface pressure of the U-shaped seal increases with the pressure However, although the sealing effect is correspondingly improved, the difference between dynamic and static friction resistance also becomes larger, and the internal pressure increases, which affects the elasticity of the rubber. As the contact resistance of the lip increases, the sealing ring will tip over and the lip will elongate. It is also easy to cause slippage or crawling. To prevent it from tipping over, a support ring can be used to keep it stable.

 

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