From the perspective of mechanical structure, the excavator arm is mainly composed of a boom, a dipper and a bucket. The boom is connected to the fuselage through a pin and can swing up and down. It is usually made of high-strength steel and has sufficient strength and rigidity to withstand the huge forces during the excavation process. Its up and down swing is achieved by the extension and contraction of the hydraulic cylinder. One end of the hydraulic cylinder is connected to the fuselage and the other end is connected to the boom. Controlling the in and out of the hydraulic oil can lift or lower the boom. The dipper is connected between the boom and the bucket and can be extended and retracted. It is also made of high-strength steel. The length and strength will vary depending on the model and purpose of the excavator. The extension and retraction of the dipper depends on another hydraulic cylinder, which is connected to the boom at one end and the dipper at the other end. The bucket is generally made of wear-resistant steel, with sharp edges and good excavation performance. The opening and closing of the bucket can be controlled by a hydraulic cylinder or a wire rope. A wire rope may be used on a small excavator, while a hydraulic cylinder is usually used on a large excavator.
In terms of hydraulic system, the excavator arm action is mainly realized by hydraulic system. The hydraulic system consists of hydraulic pump, hydraulic valve, hydraulic cylinder and hydraulic pipeline. The hydraulic pump is the power source, which converts the mechanical energy of the engine into hydraulic energy and provides high-pressure oil for the hydraulic system. Common hydraulic pumps include gear pump, vane pump and plunger pump. The hydraulic valve is a control element, which controls the flow direction, pressure and flow of hydraulic oil to realize various action control of the excavator arm, including different types such as reversing valve, overflow valve, throttle valve and pressure reducing valve. The hydraulic cylinder is an actuator, which converts hydraulic energy into mechanical energy to realize various actions of the excavator arm. There are single-acting hydraulic cylinder and double-acting hydraulic cylinder. The hydraulic pipeline is a connecting element, which connects the hydraulic pump, hydraulic valve, hydraulic cylinder, etc. together to form a complete hydraulic system. Its material is usually steel pipe or rubber hose, and the diameter and length depend on the model and purpose of the excavator.
Its working principle is to convert the mechanical energy of the engine into hydraulic energy and then into mechanical energy through the hydraulic system, so as to realize various action control of the excavator arm. During the excavation action, the driver operates the control handle to control the hydraulic oil to enter the boom hydraulic cylinder and the dipper hydraulic cylinder, so that the boom and dipper lower, and the bucket hydraulic cylinder controls the bucket to open. When the bucket touches the ground, continue to operate to extend the dipper and close the bucket for excavation. During the lifting action, operate the control handle to allow the hydraulic oil to enter the boom hydraulic cylinder to raise the boom, and the dipper hydraulic cylinder and the bucket hydraulic cylinder remain stationary. During the unloading action, operate the control handle to allow the hydraulic oil to enter the dipper hydraulic cylinder and the bucket hydraulic cylinder, so that the dipper retracts and the bucket opens.
For second-hand dealers, they also play an important role in the business related to the digging arm of the excavator. When purchasing a second-hand excavator, the second-hand dealer will carefully check the mechanical structure of the digging arm. Check whether the boom, dipper and bucket are damaged, deformed or excessively worn. Check whether the hydraulic cylinder is leaking and whether the pin connection is loose. For the hydraulic system, they will check the working status of the hydraulic pump, hydraulic valve and hydraulic cylinder to ensure that the hydraulic system can operate normally and the various actions of the digging arm can be accurately performed. If problems are found, second-hand dealers will repair or replace the corresponding parts to ensure the quality of the second-hand excavator. When selling second-hand excavators, second-hand dealers will explain the performance and condition of the digging arm to customers in detail, so that customers can understand the actual situation of the equipment and make wise purchasing decisions. At the same time, some second-hand dealers will also provide after-sales service. During the use of second-hand excavators by customers, if there are problems with the digging arm, they will provide technical guidance and maintenance services in time to ensure that the equipment can resume normal operation as soon as possible.
In short, the excavator digging arm completes the tasks of excavation, lifting and unloading through the synergy of mechanical structure and hydraulic system, and the participation of second-hand dealers provides users with more guarantees in the selection and use of second-hand excavators.