Failure analysis of the tipping bucket cylinder of

Failure analysis of the tipping cylinder of loaders for many times

a lw420f loader delivered by a company broke three piston rods of the tipping cylinder continuously within three months, and each time it broke the tipping cylinder on the same side. The broken parts are as follows:

II. Cause analysis

the company has never received such a major failure before. The service personnel of the company immediately went to replace a new cylinder for the user at the first feedback, Less than a month after the replacement, the user said that the replaced oil cylinder broke again. The service personnel did not carefully analyze it, but immediately went to replace a new oil cylinder for the user. As a result, the fracture occurred again within a month. Obviously, it was not the quality problem of the oil cylinder, but the interference of the mechanism in motion. After the RP0 observation calculated by the field observation, the interference inspection of the moving elements was carried out, and the following problems were found:

1. The unloading limit block on the right rocker arm seat beam was in unilateral contact with the rocker arm during unloading, that is, the right rocker arm was in contact with the limit block by using PET aerogel coated with flame retardant as the lining material, and the outer side plate was in contact with the limit block, while the inner side plate was not in contact with the limit block

2. There is no adjusting gasket at the rocker arm seat beam, and the nylon sleeve in the center of the rocker arm is also seriously worn, with a large gap. The rocker arm can be swayed left and right by hand, which is invaded by money everywhere

3. There is no adjusting pad at the articulated part between the bucket and the boom. During full load operation, it is found that the bucket moves left and right on the boom, with a large amount of movement

the above three reasons can cause the tipper cylinder to be subjected to lateral force. We believe that the important factor causing the piston rod fracture is problem 1, because there are several lw420f of the company in this area, with the same working conditions, problems 2 and 3 also exist. The working time is longer than that of this vehicle, and there is no piston rod fracture

the technician readjusted the limit block of the car, ensuring that after bilateral contact, the user no longer fed back the problem

III. improvement measures:

since the unloading block is the field welding of the bucket under the highest unloading condition, if the welding workers are not skilled, it is likely to have the phenomenon of false sticking of the limit block. Therefore, it is suggested to cancel the limit block and limit it only by the limit block at the lower part of the bucket, but the facts have proved that it is not feasible. During the industrial assessment test, it was found that the contact surface between the limit block on the bucket and the boom was seriously damaged, and a pit appeared in the boom plate and the limit block. The unloading angle of the bucket was far greater than 45 degrees. The limit block had no effect, but was limited by the minimum installation distance of the tipping cylinder. Therefore, the tipping cylinder piston rod 3 and the force sensor of the testing machine collided with the cylinder block and damaged the cylinder, Even there is interference between the tipper cylinder and the boom beam, causing the piston rod of the hydraulic cylinder to bend near its head

in order to prevent such accidents from happening again, we have developed a detailed welding process