In addition to the bending moment caused by the self weight of the cylinder and the weight of the concrete, the mixing cylinder also bears the torque caused by the rotary movement of the mixing cylinder and the circumferential and axial force of the concrete in the mixing cylinder, which is complex [5]. Under the action of cyclic alternating load, the initial micro crack may form in the area with large stress, and then develop into macro crack, and then the macro crack will continue to expand, resulting in the cracking of weld bead or base metal. The main reasons affecting the initial microcracks of the raceway are as follows:
（1）滚道焊缝处的应力集中
(1) Stress concentration at raceway weld
原因：滚道与筒体焊接时，焊缝处经常出现应力集中。此外，搅拌筒在使用过程中，滚道与托轮处的集中载荷以及滚道截面的整体变形也都会使焊接处出现应力集中现象。
Cause: when the raceway is welded with the cylinder, stress concentration often occurs at the weld. In addition, during the use of the mixing drum, the concentrated load at the raceway and supporting wheel and the overall deformation of the raceway section will also cause the stress concentration at the welding joint.
对策：打磨应力集中焊缝，重新施焊，对于已经出现宏观裂纹的焊缝或母材，打孔截断裂纹源头，重新焊接。
Countermeasures: polish the weld with concentrated stress and re weld. For the weld or base metal with macro cracks, punch holes to cut off the crack source and re weld.
（2）滚道焊缝处的残余应力
(2) Residual stress at raceway weld
原因：滚道与筒体刚度相差悬殊，一般情况下，搅拌筒筒体厚度为6mm 的钢板，滚道的径向厚度在60mm 左右，筒体和滚道厚度相差很大，在焊接过程中，滚道的热膨胀受到限制，并且在冷却过程中的收缩也受到限制，而筒体受限程度远小于滚道，终影响到焊接应力的大小及分布不均，导致残余应力的产生。
Reason: the stiffness of the raceway is quite different from that of the barrel. Generally, the radial thickness of the raceway is about 60mm for the steel plate with a thickness of 6mm of the mixing barrel. The thickness of the barrel and the raceway is very different. During the welding process, the thermal expansion of the raceway is limited, and the shrinkage during the cooling process is also limited, and the degree of limitation of the barrel is much less than that of the raceway, Finally, it affects the size and uneven distribution of welding stress, resulting in the generation of residual stress.
对策：调整焊接顺序，减少单次热量输入，焊接过程中用紫铜锤敲击构件，采用振动时效方式调整、均化、残余应力。此外，对焊道进行局部打磨，减少焊接缺陷。
Countermeasures: adjust the welding sequence, reduce the single heat input, knock the components with a copper hammer during the welding process, and adjust, homogenize and eliminate the residual stress by means of vibration aging. In addition, the weld bead shall be locally polished to reduce welding defects.
（3）滚道与筒体的刚度变化
(3) Stiffness change of raceway and cylinder
原因：滚道及筒体的刚度随着车辆的使用呈递减趋势，大方量搅拌车尤为明显，刚度的减弱会加速焊道的疲劳失效，导致焊道或母材开裂。
Reason: the stiffness of raceway and cylinder decreases with the use of vehicles, especially for large-scale mixer. The weakening of stiffness will accelerate the fatigue failure of weld bead and lead to the cracking of weld bead or base metal.
对策：在滚道与筒体接触内部增焊加强板，提高该区域的整体刚度，以增强焊接结构的抗疲劳失效能力。
Countermeasures: weld reinforcing plates inside the contact between the raceway and the cylinder to improve the overall stiffness of the area, so as to enhance the fatigue failure resistance of the welded structure.
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