Analysis and Countermeasures of creeping of QT60 t

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Analysis and Countermeasures of "creeping" of QT60 tower crane

QT60 tower crane used in the construction site often has a so-called creeping phenomenon: when the tower body is adjusted, the hydraulic cylinder and the parts it bears appear fast and slow, and the vibration occurs alternately when the speed is reduced and stopped. This situation will cause the impact fatigue damage of the tower crane, and even fracture accidents in serious cases. 1. Cause inspection of "creeping" phenomenon "creeping" phenomenon is mainly caused by improper design of hydraulic system, but it is often difficult to find this problem at first, but it is found through the detection of a series of hydraulic components and the principle of "gradually approaching failure". The diagnosis results show that the intermittent vibration of the hydraulic cylinder on the tower surface and when the load drops is not caused by the characteristics of hydraulic friction and the reduction of the stiffness of the hydraulic system, but also has nothing to do with the air in the pipeline in the pressure adjustment of the system. The "creep" fault may be related to a circuit in the hydraulic system. After testing, the rated working pressure of hydraulic pump 3 is 25MPa, the output oil volume and pressure of the pump are normal, and the maximum pressure of overflow valve 5 control system is normal after testing. There is no abnormal condition when the manual reversing valve 6 reverses, and the two-way hydraulic lock 7 forms the balance locking circuit of the system. From this point of view, the key to the problem lies in the two-way hydraulic lock 71. 2. Safety protection measures: the analysis of the balance circuit of the two-way hydraulic lock system is shown in Figure 1. Due to the function of the two-way hydraulic lock 7, when the hand operated reversing valve 6 is in the middle position, the hydraulic lock is in the unloading state, and the hydraulic cylinder is only locked in any position. When the reversing valve 6 is in the right position, the two-way hydraulic lock 7 is opened and enters the lifting condition. At this time, due to the jacking load, there is resistance to the pressure of the rodless oil chamber, There will be no "negative pressure" phenomenon in the left liquid chamber check valve B, so there will be no vibration. When the manual reversing valve 6 is in the left position lowering condition, the hydraulic oil from the oil tank opens the hydraulic lock and enters the rod chamber of the hydraulic cylinder, and the hydraulic rod piston drops rapidly under the hydraulic pressure and load weight, followed by vibration. 1. Oil tank 2 Oil filter 3 Hydraulic pump 4 Pressure gauge 5 Overflow valve 6 Hydraulic manual change-over valve 7 Hydraulic control one-way speed regulating valve 8 As shown in Table 4, when the hydraulic cylinder 8 vibrates, the pressure also vibrates, and its change law is very similar to the opening and closing law of the hydraulic check valve B through which the original oil return is executed by the intermittent vibration law. Therefore, it can be concluded that the vibration generated by the expensive catalyst currently used when the hydraulic cylinder 8 descends is closely related to the opening and closing pressure of the check valve B. When the piston and load drop rapidly, because the speed is too fast, the oil supply of hydraulic pump 3 is fast, and the oil supply of hydraulic pump is too late to supplement the short-term "negative pressure effect" caused by the rod rush. At Kunshi, the hydraulic pressure relief of check valve B of two-way hydraulic lock 7 also drops, and the hydraulic check valve B is controlled and closed. As a result, the oil circuit is blocked, and the hydraulic cylinder 8 suddenly stops falling. After the hydraulic control check valve B is closed, as the quantitative hydraulic pump continues to supply oil, the oil pressure rises again, the hydraulic check valve B is reopened, the oil return is unblocked, and the piston and load drop rapidly. Such a cycle until the end of the stroke, the check valve is opened and closed, causing the hydraulic cylinder to vibrate, resulting in the "crawling" phenomenon. 3. Improve the balance locking circuit of two-way hydraulic lock. The function of two-way hydraulic lock is to lock when there is no oil inlet and limit the speed when descending. The improvement method is: retain the one-way liquid chamber shown in Figure 1 to provide customized integrated material solutions - its excellent lightweight, easy molding characteristics and durability. Valve a remains unchanged. It is only used in the descent circuit, and the control rise is not too fast. This rarely happens: change the hydraulic control one-way valve B to an overflow valve as a back pressure valve. At the same time, in order to make the hydraulic cylinder rise without Lee flow loss, a one-way valve can be connected in parallel at the same time, In fact, if a hydraulic balance valve (speed limit valve) is formed, the balance circuit of the hydraulic system will maintain a good development trend, which can well prevent "crawling", ensure the steady decline of the whole mechanism at a constant speed, and also make the mechanism pause or jog according to the working conditions. The hydraulic schematic diagram after specific changes is shown in Figure 2. 1. Oil tank 2 Oil filter 3 Hydraulic pump 4 Pressure gauge 5 Overflow valve 6 Hydraulic manual directional valve 7 Hydraulic control single extraction flow valve 8 Hydraulic cylinder extraction 9 Hydraulic balance (speed limit) valve 4 conclusion the elimination of the "crawling" phenomenon of QT60 tower crane and the improvement of its structure have introduced the advanced technology in the "structural design of new hydraulic balance valve of construction machinery", which greatly improves its stability and safety under the working conditions of lifting and luffing, and effectively prevents the occurrence of hidden dangers and accidents

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