For general backhoe hydraulic excavators, no matter how heavy the machine is and how large the operation size is, they mainly excavate below the ground. Therefore, in order to meet the maximum excavation depth, the boom is usually made into a downward bending shape. The boom is hinged with the slewing platform and stick through the pin shaft. It is one of the main components of the backhoe working device. The integral curved boom of backhoe excavator has the advantages of simple structure, light weight and high stiffness, which can make the excavator have a large excavation depth. It is the most widely used structural form at present. Its disadvantage is that there are few replaceable working devices and poor universality. It is mostly used on excavators with similar long-term operating conditions.
The boom angle of small excavators on the market will be relatively small, which seems to be much more curved than that of medium-sized excavators. This is because small excavators use a single boom hydraulic cylinder, and the position of cylinder hinge point is different from that of medium-sized excavators. In order to increase the excavation depth of the boom, the boom angle is reduced.
According to the data of relevant literature, the value range of boom bending angle is generally 110 ° ~ 140 °. Within the range of these values, a small bending angle is conducive to increasing the excavation depth, but will reduce the maximum excavation height, and is unfavorable to the structural strength, because the stress concentration will be caused at the bending part due to the structure and welding process. The smaller the bending angle is, the more serious the stress concentration is, and the greater the possibility of cracking at the bending part of the boom during the use of the machine.
