Bad Consequences of Scratches on the Inner Hole Surface of Hydraulic Cylinder Block and Quick Repair Methods

① The material particles extruded from the scratch groove will be embedded into the seal, which may cause new scratch area marks while damaging the working part of the seal during operation.
② Deteriorates the surface roughness of the inner wall of the cylinder barrel, increases the friction, and is prone to creep.
③ The internal leakage of the hydraulic cylinder is aggravated, and the working efficiency of the hydraulic cylinder is reduced. The main causes of the scratch on the surface of the inner hole of the cylinder block are as follows.
(1) Scars caused when assembling hydraulic cylinders
① During assembly, foreign matters are mixed to cause scars. Before assembly, all parts of the hydraulic cylinder must be fully deburred and cleaned. When the parts are installed with burrs or dirt, foreign matters are easily embedded into the surface of the cylinder wall due to "no strength" and the weight of the parts, resulting in scars.
② When installing the hydraulic cylinder, the piston, cylinder head and other parts have large mass, large size and large inertia. Even with the auxiliary installation of lifting equipment, due to the small specified fit clearance, they will not be put in any way. Therefore, when the end of the piston or cylinder head boss collides with the inner surface of the cylinder wall, it is very easy to cause scars. The method to solve this problem: for small products with large quantities and large batches, use special assembly guide tools during installation; Only careful and careful operation can avoid heavy, thick, large and medium hydraulic cylinders.
③ The scars caused by the contact of the measuring instrument are usually measured by the internal diameter dial indicator. When measuring the internal diameter of the cylinder block, the measuring contact is inserted into the hole wall of the cylinder body while rubbing. The measuring contact is mostly made of wear-resistant hard alloy with high hardness. Generally speaking, the slender scratches with small depth caused by the measurement are slight, which will not affect the operation accuracy. However, if the size of the measuring rod head is adjusted improperly, the measuring contact will be hard embedded, which will cause relatively serious scratches. To solve this problem, first of all, measure the length of the adjusted measuring head. In addition, stick a piece of paper tape with holes only in the measuring position on the inner surface of the cylinder wall, that is, the above shape scratches will not be generated. The slight scratches caused by measurement can generally be wiped off with the back of old abrasive cloth or toilet paper.
(2) Minor running wear traces
① The scars on the sliding surface of the piston are transferred. Before the piston is installed, the sliding surface of the piston has scars, which are not treated, and it is installed intact. These scars will in turn scratch the inner surface of the cylinder wall. Therefore, these scars must be fully repaired before installation.
② The sintering phenomenon caused by excessive pressure on the piston sliding surface will cause the piston to tilt due to the dead weight of the piston rod, resulting in uneven force, or the pressure on the piston sliding surface will rise due to the lateral load, which will cause the sintering phenomenon. During the design of hydraulic cylinder, its working conditions must be studied, and full attention must be paid to the length and clearance of piston and bushing.
③ It is generally believed that the hard chromium plating layer on the surface of the cylinder body peels off due to the following reasons.
A. The electroplated coating is not well bonded. The main reasons for the poor adhesion of the electroplated coating are: before electroplating, the oil removal and degreasing treatment of the parts are not sufficient; The surface of the parts is not completely activated and the oxidation film is not removed.
B. Hard layer wear. The wear of the hard chromium plating layer is mostly caused by the abrasive action of the friction iron powder of the piston. When there is water in the middle, the wear is faster. The corrosion caused by the contact potential difference of the metal only occurs at the place where the piston contacts, and the corrosion occurs in the form of dots. The same as above, when there is water in the middle, it will promote the development of corrosion. Compared with castings, the contact potential difference of copper alloy is higher, so the corrosion degree of copper alloy is more serious.
C. Corrosion caused by contact potential difference. Contact potential difference corrosion is not easy to occur for hydraulic cylinders running for a long time; It is a common fault for hydraulic cylinders that have been stopped for a long time.
④ Damage of piston ring The piston ring is damaged during operation, and its fragments are caught in the sliding part of the piston, causing scratches.
⑤ The material of the sliding part of the piston is sintered and cast, which will cause sintering phenomenon when bearing large transverse load. In this case, the sliding part of the piston shall be made of copper alloy or welded with such material.