Repair of the center slewing joint of the QY8E type truck crane

After being idle for two years, the center slewing joint of the QY8E truck crane experienced external leakage. During the repair process, it was found that the groove depth of the O-ring exceeded the maximum allowable depth by 0.1mm, resulting in insufficient initial compression of the O-ring. In addition, the coaxiality of the installation between the housing and the core exceeded the tolerance, and the O-ring aged and could no longer perform the sealing function, thus causing low-pressure leakage.

Solution:

When choosing O-rings, intentionally select products with larger inner diameters and cross-sectional diameters in the same specification. Before assembly, carefully grind the orifice of the joint shell and the bevel of the core, remove burrs and apply grease to ensure that the O-ring is not damaged during assembly. After the repair, the central rotary joint has not experienced any external leakage since its use.

It is suggested that manufacturers take the following measures when designing and processing:

(1) Strictly control the dimensional tolerance and roughness of the groove part to ensure that the O-ring has sufficient pre-compression, so that there is sufficient clamping force between the O-ring and the mating surface.

(2) Strictly control the fit clearance between the shell and the core to prevent the O-ring from being squeezed out and damaged.

(3) Strictly control the coaxiality of the sealing groove and the core to prevent one part of the O-ring from being compressed too much while the other part is compressed too little or not compressed at all, which may cause sealing failure.

(4) Carefully grind the orifice of the joint shell and the bevel of the core, remove burrs, and prevent the O-ring from being scratched during assembly.

(5) In the design, it is preferred to use O-rings with larger cross-sections or adopt other oil seals.

(6) Install a stop valve at the tank outlet below the liquid level to facilitate maintenance.