The mixing drum is the key component of the concrete mixer truck for loading, mixing and transporting concrete. A flange is welded at the head of the mixing drum, and a raceway is welded at the rear cone. The mixing drum is driven by the reducer, and is supported by the rollers in rolling contact with the raceway to rotate, so as to realize the loading and unloading and mixing functions of concrete. Due to the eccentric load generated by the concrete mixer truck during mixing and the starting and braking of the vehicle on complex roads, the force on the mixing drum is extremely complex, and the design or welding process defects may lead to cracking of the raceway welds. The concrete mixer truck manufacturer analyzes the cause of the cracking of the raceway weld and proposes a repair plan.

Cause Analysis of Weld Cracking

When the mixing drum is working, in addition to the bending moment caused by the self-weight of the drum and the weight of the concrete, it also bears the torque action caused by the rotary motion of the mixing drum and the force of the concrete in the circumferential and axial directions in the mixing drum. force is more complicated. Under the action of cyclic alternating load, initial micro-cracks may form in areas of high stress, and then develop into macro-cracks, and then the macro-cracks will continue to expand, eventually leading to cracking of the weld bead or base metal.

The main reasons for the initial microcracks affecting the raceway are as follows:


(1) Stress concentration at the raceway weld

Reason: When the raceway and the cylinder are welded, stress concentration often occurs at the weld. In addition, during the use of the mixing drum, the concentrated load at the raceway and the supporting roller and the overall deformation of the raceway section will also cause stress concentration at the weld.

Countermeasures: Grind the stress concentration weld and re-weld. For the weld or base metal with macro cracks, punch holes to cut off the source of the crack and re-weld.

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