Repair of hydraulic cylinder: Once the hydraulic cylinder leaks, under normal circumstances, it should be disassembled and decomposed to check if there are damaged and aging seals that should be replaced or repaired.
Since the piston frequently repeats the reciprocating movement in the hydraulic cylinder, the piston and the inner wall of the cylinder are most easily to wear and strain. Judging from the actual disassembly situation,after being worn out, the piston often takes the shape of a truncated cone or an ellipse. Therefore, checking and measuring carefully before repairing is necessary.
For pistons that are in direct contact with the cylinder and rely on O-ring seal, if the surface and groove of the piston are worn or scratched above 0.2～0.3mm, you can simply use sandpaper, files, oilstone, etc. If it is not enough, use a mold repair machine to repair. For pistons that are not in direct contact with the cylinder, to such pistons relying on U-shaped or Y-shaped seals, you need to replace the sealing ring to restore the sealing between the piston and the cylinder.
The relative movement of the piston bar and the guide sleeve is the main factor causing external leakage. When the chromium-plated layer on the piston rod surface falls off due to wear or longitudinal pull marks, it will directly cause the failure of the seals and then cause leakage. Therefore, when repairing hydraulic cylinders, it's important to check whether the surface roughness and geometric tolerance of the piston bar meet the technical requirements.
In general, it should be ensured that the surface roughness of the piston bar is no more than 0.4um, and the geometric tolerance of the roundness and cylindricity tolerances are no more than half of the diameter tolerance. When the surface of the piston bar is plated by chrome, the thickness of the chrome-plated layer is about 0.03-0.05mm, and it is polished or grounded. The hardness is usually among the range of HRC50 to 60. If the piston bar is bent, it should be straightened to meet the requirements. The guide sleeve is often installed in the hydraulic cylinder head at one end of the hydraulic cylinder. Its function is to maintain the coaxiality of the piston bar and the hydraulic cylinder barrel and to bear the lateral force of the piston rod, so as to achieve the purpose of reducing leakage and planing the surface of the cylinder barrel to roughen.
In addition, attention should be paid to the fit between the piston bar and the guide sleeve, which is supposed to be very particular: if the fit is too large to perform the proper function of the guide sleeve, and it is easy to cause jamming and unilateral wear; If it is too small, it will easily cause the friction between the piston bar and the guide sleeve to increase, causing wear and strain.
The inner surface of the hydraulic cylinder and the piston seal are important causes of hydraulic cylinder diarrhea. Because the inner wall of the cylinder is often subjected to friction from the reciprocating movement of the piston, uneven wear, pull marks or corrosion will occur. The disassembled cylinder should pay attention to check whether its inner surface dimensional tolerance and shape tolerance meet the technical requirements, whether there are longitudinal draw marks, and also whether the depth of the longitudinal draw marks affects the normal operation of the hydraulic cylinder.
After the hyd cylinder is worn, which increases the gap, causing internal diarrhea to increase, and even the pressure cannot be built up. If the inner surface of the cylinder is only partially worn or pitted, it can be eliminated by polishing it evenly by fine sandpaper or whetstone. If there are deep pull marks or wear in the longitudinal direction, the cylinder can be sent to machining for boring and grinding to eliminate those pull marks. When the grinding method is used to eliminate the abrasion of the inner wall of the cylinder, the processing quality of the grinding must be ensured. The roundness and cylindricity error after grinding should be no more than half of the inner wall diameter tolerance. And the roughness of the inner wall of the cylinder should be between 0.4～0.2um. If the surface roughness is too high, the sealing effect will not be good; if it is too low, it will cause it completely sealed and an oil film on the inner surface of the cylinder tube cannot be formed and lead to dry friction, which will intensify the wear of the piston and the cylinder tube.
In addition, if the inner wall of the cylinder is severely worn and there are deep longitudinal pull marks, a professional manufacturer should conduct physical surveying and re-produce a new hydraulic cylinder for replacement.
In conclusion, the repair of hydraulic cylinders needs to adopt a principle of "specific circumstances, specific analysis" and use the easiest method to meet the needs of the work of which the repair cost is low, the time is short, and also the service life is long.