Common faults and solutions of 2500LB S235JR Agitator rollaway nest and supporting wheel (Ⅲ)
Shanxi Haokun flange Group Co., Ltd. specializes in the production of 2500LB S235JR Agitator rollaway nest.
The concrete mixer truck is a special equipment for mixing and transporting concrete. The front end of the mixing drum is connected with the reducer. The rear cone of the mixing drum is welded with a raceway, which is supported by two supporting wheels in rolling contact with the raceway, and the raceway is in contact with the supporting wheel to form a "moving pair". Its structure is shown in Figure 1. Through the investigation of the use of concrete mixer truck, it is found that the frequency of "moving pair" fault between the mixing drum raceway and the supporting wheel is high, and there are three kinds of common faults: one is the cracking of raceway weld, the other is the abnormal sound of supporting wheel rotation, and the third is the surface scratch .
3 surface scratch of 2500LB S235JR Agitator rollaway nest
After the concrete mixer truck is put into use, the ideal state of the 2500LB S235JR Agitator rollaway nest and supporting wheel is that after 5 ~ 7 days of use, after cold work hardening, the friction surface between the raceway and supporting wheel forms a bright surface. However, due to the user's non-standard use and operation of the mixer and the defects in the manufacturing process, the moving pair of raceway and supporting wheel can not reach the ideal state in the use process, and the surface will be skinned, scratched, grooved and so on. The possible reasons are as follows:
(1) Design factors. If the design of mixing truck raceway and supporting wheel is unreasonable, abnormal wear will occur on the raceway surface. Therefore, it is necessary to recheck the contact stress between raceway and supporting wheel. In addition, if the hardness of the raceway and the supporting wheel is not matched properly, no matter which one is worn first, it will cause damage to the moving pair, and it is also easy to have problems such as surface scratch during work.
Solution: calculate the contact stress between the raceway and the supporting wheel. Taking a concrete mixing truck as an example, when it is fully loaded, the self weight of the concrete and mixing drum is about 21t, and the installation angle of the mixing drum is 13.5 °. According to the stress analysis of the mixing drum (see Figure 3), the calculation shows that the acting force at the raceway is about 9.68t, that is, the total stress at the raceway is p = 95kn. It can be seen from Figure 1 that the force acting on the supporting wheel f = 58kn. According to the elasticity, when two cylinders with parallel axes contact each other and are compressed, the contact surface is a long and narrow rectangle, and the maximum contact stress occurs on the center line of the contact area, and its value is:
σ max=0.418[FE/b × (R1+R2)/(R1 R2)]1/2=522(MPa)
Where: σ Max -- maximum contact stress, kn;
B - raceway width, B = 0.08m;
F -- force at the supporting wheel, f = 58kn;
R1 - raceway radius, R1 = 0.87m;
R2 - radius of supporting roller, R2 = 0.108m;
E -- elastic modulus, e = 2.06 × 108kn / m2 (the raceway is made of forged steel and the supporting wheel is made of 45 steel).
According to the mechanical design manual, the allowable contact stress of steel parts with dry and wet friction[ σ]= 570MPa。
At the same time, the hardness of raceway and supporting wheel shall be reasonably selected and the hardness inspection shall be strengthened to ensure that the hardness of raceway and supporting wheel is reasonably matched.
(2) Manufacturing factors of 2500LB S235JR Agitator rollaway nest. If the axis of the mixing drum raceway is not parallel to the axis of the supporting wheel, axial swing will occur when rotating on the supporting wheel, resulting in strain of the friction surface.
Solution: improve the welding process between mixing drum and subframe to reduce the cumulative assembly deviation. The axis of the mixing drum raceway is determined by the tooling accuracy of the mixing drum and the roundness of the drum, and the supporting wheel axis is determined by the angle of the upper cover plate of the subframe. Before the mixing drum is assembled with the raceway, the tooling of the mixing drum shall be corrected to ensure the assembly accuracy of the raceway; The control of cylinder rounding process shall be strengthened to avoid cylinder out of round. Before welding the subframe, the welding tooling shall be corrected and the welding deformation shall be controlled. During welding, the current and voltage shall be controlled to reduce welding deformation, so as to ensure the parallelism between the axis of the 2500LB S235JR Agitator rollaway nest and the axis of the supporting wheel.
