Hitachi Excavator Repair
Correct grounding method for welding operations and failure cases caused by improper grounding
保护周围液压油缸免受电焊火花的飞溅。 确认 Before welding, confirm whether there are flammable materials around; protect the surrounding wires from the splash of welding sparks; repair the excavator to protect the surrounding hydraulic cylinders from the splash of welding sparks. Grind all weld beads with a grinder to make them flat and smooth; take care not to cause undercuts and other welding defects during welding; pay attention to safety and maintain ventilation during welding. When welding the front-end working devices of the hydraulic excavator, such as the boom, stick, bucket, and lower traveling body, the upper platform of the machine, the ground wire should be placed on the part to be welded; On the side teeth on the other side of the bucket. If the welding bucket or stick connects the ground wire on the lower traveling body or the upper platform, the welding part will form a circuit with the ground part, and this circuit passes through the cylinders of the front-end working device, and the strong current generated during welding will Damage the rubber seal of the hydraulic cylinder and the internal components of the cylinder. Therefore, the position of the ground wire should be at the same welding position as far as possible to prevent the current generated by the circuit from flowing through the hydraulic cylinder or electrical components during welding.
An excavator worked until 2890 hours when the stick cylinder had leaked oil. The piston rod of the stick cylinder had a straight pull mark. Based on past experience, service personnel replaced the cylinder head oil seal and piston rod. However, after repairing for a period of time, the same failure occurred. The service staff did not completely solve the problem after repeatedly replacing the cylinder head oil seal several times, but had no choice but to replace the entire stick cylinder assembly. During the disassembly inspection, it was found that the inner bushing of the cylinder head of the oil cylinder was damaged, which caused the piston rod to have pull marks during the reciprocating motion. After investigating the repair history of the machine, it was learned that the user had welded and repaired the bucket before the oil leakage of the cylinder, and put the ground wire on the track shoe. It can be known that the damage to the inner liner of the cylinder head of the stick cylinder is caused by the current generated by welding. Please take a look at the photo on the right! The front-end working device of the machine, especially when the bucket has to be welded and repaired, must be grounded in the bucket area. The "closest principle" should be considered when grounding, and it should never be taken elsewhere. Otherwise, the current circuit will flow through the oil cylinder and the electric shock of the oil cylinder parts will be damaged.