Two Hitachi excavators of a company are used machinery that was purchased, mainly used for the clearance of bulk cargo such as chemical fertilizers. When they first arrived, the car conditions were not good. The track will fall off more than 10 times, seriously affecting normal production. At present, the crawler tensioning hydraulic cylinder of one of the excavators has been bent and deformed, and cracks have appeared in the parts shown in Figure 1-12 and the oil has leaked. After research, it was decided to improve the crawler tensioning hydraulic cylinder.
1. Current status of crawler tensioning hydraulic cylinder
As can be seen from Figures 1-12, the hydraulic cylinder is fixed on the chassis frame of the vehicle by the clamping table 7, the butter is injected from the oil injection nozzle, and enters the cylinder body through the internal oil passage. The plunger head has three oil seals), and the outer end of the plunger is pressed against the front wheel bracket 1, and the bracket drives the front wheel to extend, increasing the distance between the front and rear wheels, so as to achieve the purpose of tensioning the track. If the track is too tight, the large nut at the oil drain can be rotated to release part of the butter. The spring outside the cylinder is used to cushion the impact load.
Because the machine is a used machine, the technical information is incomplete. At the same time, the track tension hydraulic cylinder that has been damaged on the machine is improved and processed after the track tension hydraulic cylinder on the original vehicle is damaged. The original buffer spring in the cylinder A part has been broken, so the current spring is shorter than the original one. From the structural point of view, the inner hole of the hydraulic cylinder is slender and difficult to process: the total length of the hydraulic cylinder is 627mm, the outer diameter is small and the inside is hollow, the cylinder wall is thin, and the overall rigidity is poor: the horizontal impact force suffered by the hydraulic cylinder is large.
2. Improvement plan and effect
From the above analysis, it can be seen that the design of the crawler tensioning hydraulic cylinder is unreasonable, and the length should be reduced or the shaft diameter increased as much as possible. Think of another way.
(1) Design the hydraulic cylinder into separate parts (see Figure 1-12), process part A and part B separately, then put part B into A, and add three oil seals at the junction to prevent the leakage of butter. In order to ensure the coaxiality, the length of the joint is determined to be 70mm and the material is 40Cr.
(2) Install a 30mm thick backing plate 6 on the right side of the clamping table 7 to shorten the distance between the flange of the hydraulic cylinder and the clamping table, so that the spring can fully play a buffering role.
After changing to a split structure, the length of the joint is 70mm. If there is any radial component, it will only act on the 70mm long section, and the force is balanced. At the same time, the cushioning capacity of the spring is enhanced by the addition of the shim plate. Even when the impact load that the spring cannot cushion is encountered, the parts A and B can move relatively without causing the hydraulic cylinder to bend and deform.
The improved excavator has unloaded two ships of chemical fertilizer continuously, and its crawler tensioning hydraulic cylinder has good performance, which ensures the normal work of the crawler, and has achieved a good port loading and unloading performance of 56,000 tons of chemical fertilizer unloaded in 10 days.
