Cylinder Troubleshooting and Cylinder Repairing

In the last article Hydraulic Cylinder Troubleshooting and Repair, we have introduced a few common malfunction and cylinder repairing methods. This article will continue to describe another type of cylinder troubleshooting and cylinder repairing method.

The adverse consequences of scratches on the cylinder bore surface.

  • The material scraps extruded from the scratched groove will be embedded in the seal. During operation, while damaging the working part of the seal, it may cause new scratches in the scratched area.
  • Deteriorate the surface roughness of the inner wall of the cylinder, increase friction, and easily cause crawling.
  • Increase the internal leakage of the hydraulic cylinder and reduce the working efficiency of the hydraulic cylinder.

The main causes of scratches on the bore surface of the cylinder.

1. Scars caused when assembling hydraulic cylinders.

  • When assembling, foreign matter is mixed to cause scars. Before the general assembly of the hydraulic cylinder, all cylinder parts must be fully deburred and cleaned. When the parts are installed with burrs or dirt, foreign matter is easy to get into the cylinder due to the “unusual strength” and the weight of the cylinder components, causing scars.
  • Scars in the installation cylinder parts When installing hydraulic cylinders, pistons and cylinder heads and other component parts have large masses, sizes, and inertias. Even with the aid of lifting equipment, the clearances are small, so no matter what, you will not put them in hard. Therefore, when the end of the piston or the boss of the cylinder head hits the inner surface of the cylinder bore surface, it is easy to cause scars. The way to solve this problem is that for small products with large quantities and large batches, use special assembly guide tools when installing. For counterweight, thick, large and medium hydraulic cylinders, be more careful in operation to try to avoid them.
  • The scars caused by the contact of the measuring instrument are usually used to measure the inner diameter of the cylinder with an inner dial indicator. The measuring contact is mostly made of high hardness and wear-resistant hard alloy and inserted into the bore surface of the hydraulic cylinder while rubbing. Generally speaking, the thin and elongated scratches caused by the measurement are slight and do not affect the running accuracy. However, if the measuring rod head size is adjusted improperly, the measuring contact is hardly embedded, which will cause more severe scratches. The countermeasure to solve this problem is to first measure the length of the adjusted measuring head. In addition, use a piece of paper tape that only has holes in the measuring position and stick it on the inner surface of the cylinder bore surface, That is, the above-mentioned shape scratches will not be produced. Slight scratches caused by measurement can generally be wiped off with the reverse side of an old emery cloth or horse dung paper.

2. Not serious running wear marks.

  • The scars on the sliding surface of the piston are transferred. Before the piston is installed, there are scars on the sliding surface, and the installation is carried out intact without treatment. These scars will in turn scratch the inner surface of the cylinder wall. Therefore, these scars must be fully repaired before installation.
  • The sintering phenomenon caused by the excessive pressure on the sliding surface of the piston will cause the piston to tilt due to the weight of the piston rod, which will cause unnatural strength, or the pressure on the sliding surface of the piston will increase due to the lateral load, which will cause the sintering phenomenon. When designing a hydraulic cylinder, its working conditions must be studied, and full attention must be paid to the length and clearance of the piston and bushing.
  • The peeling of the hard chromium plating layer on the surface of the cylinder barrel.
  • Damage to the piston ring. The piston ring is damaged during operation, and its fragments are caught in the sliding part of the piston, causing scratches.
  • The material of the sliding part of the piston is sintered to cast the piston, which will cause sintering when subjected to large lateral loads. In this case, the sliding part of the piston should be made of copper alloy or welded with such materials.

3. Foreign matter is mixed in the cylinder.

Among the failures of the hydraulic cylinder, the most problematic is that it is difficult to judge when the foreign matter enters the hydraulic cylinder. After foreign matter enters, if the outer side of the piston sliding surface is equipped with a lip seal, then the lip of the seal can scrape the foreign matter during operation, which is beneficial to avoid scratches. However, the piston with O-shaped sealing ring has sliding surfaces at both ends, and foreign objects are sandwiched between the sliding surfaces, which can easily form scars.

Cylinder Repairing Methods.

The traditional cylinder repairing method is to perform external repair after disassembly of the damaged parts, or perform brush plating or overall surface scraping. The repair cycle of the hydraulic cylinder body is long and the repair cost is high. It is not recommended. The following are the general cylinder repairing processes we are adopting.

  • Bake the scratched parts with an oxygen-acetylene flame (master temperature, avoid surface annealing), and bake the oil that has permeated the metal surface all the year round until there are no sparks.
  • Surface the scratched part with an angle grinder, and grind at a depth of more than 1mm, and grind a groove along the guide rail, preferably a dovetail groove. Drill holes at both ends of the scratch to deepen and change the force.
  • Use absorbent cotton dipped in acetone or absolute ethanol to clean the surface.
  • Apply the metal repair material to the scratched surface. The first layer should be thin, uniform and fully cover the scratched surface to ensure the best bonding between the material and the metal surface, and then apply the material to the entire repaired part and press repeatedly. Make sure that the material is filled and reaches the required thickness so that it is slightly higher than the surface of the guide rail.
  • It takes 24 hours for the material to fully achieve various properties at 24°C. In order to save time, the temperature can be increased by a halogen lamp. Each increase in temperature by 11°C will shorten the curing time by half, and the best curing temperature is 70°C.
  • After the material is solidified, use a fine grindstone or scraper to repair and level the material that is higher than the surface of the guide rail, and the construction is completed.

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