Created on:2021-09-02 08:48

Port equipment_ Maintenance of tire gantry crane -- improvement scheme of steering hydraulic system

Port equipment_ Maintenance of tire gantry crane -- improvement scheme of steering hydraulic system

(1) Improvement scheme

The crux has been found, and the next step is to "suit the remedy to the case". After in-depth analysis and Research on the causes of the fault, we consulted the relevant technical data, and finally formed an improvement scheme on the steering hydraulic circuit on the basis of retaining the original hydraulic mechanism (see figure s). The purpose is to improve the positioning accuracy of the steering hydraulic cylinder by using the characteristic that the hydraulic control check valve can reliably lock the actuator in any position. Why not directly use a 0-type directional valve that can provide higher positioning accuracy to replace the original Y-type directional valve? It is also the reason for the above analysis. The reverse torque generated during transfer may still cause small gap leakage between the valve body and valve core of the o-directional valve, resulting in inaccurate positioning, and the hydraulic control check valve can provide a good oil circuit sealing effect. Generally, the sealing effect of O-type directional valve can be achieved: if the influence of external load is not considered, in the process of reversing, due to the large impact caused by inertial force, the repeated position of reversing point is more accurate; If considering the leakage of valve core caused by external load, its positioning accuracy will be reduced. The sealing effect of one-way hydraulic control lock can be achieved: when there are pressure holding requirements, the good tightness of cone valve closing can be used to keep the pressure of oil circuit for a long time, and has high positioning accuracy. Therefore, it is decided to connect a hydraulic control check valve in series at the two oil ports of the hydraulic cylinder in the crane steering hydraulic circuit of the tire gantry crane. The two hydraulic control check valves are installed in the same valve body, so it is also called two-way hydraulic lock. When the hydraulic cylinder stays at a certain position, the two interfaces of the hydraulic cylinder are locked by the hydraulic control check valve, the oil in the hydraulic cylinder will not flow out of the cylinder under the action of external load, and the external oil cannot enter the hydraulic cylinder, so as to effectively prevent the movement of the piston rod and produce better positioning effect. This is the function of two-way hydraulic lock here. Since a hydraulic control check valve is installed between the reversing valve and the hydraulic cylinder, the problem of internal leakage of the reversing valve under the action of external force is eliminated, and the piston rod will not retract, so the hydraulic cylinder can be reliably "locked" in the required working position to meet the transfer requirements.

S.jpg

(2) Component selection

The remaining problem is to select the appropriate hydraulic control check valve according to the working pressure required by the steering hydraulic mechanism of the gantry crane (see Figure T). Because the oil of the hydraulic control check valve can pass freely from port a to port B, but it is cut off from port B to Port A. When the oil needs to flow from port B to port a, the control pressure PC needs to be applied to control port C; The control pressure PC generates a thrust on the control piston and opens the check valve. At this time, the oil can flow from port B to Port A. Because the pressure P1 acts on the right side of the check valve core, the control pressure PC must be large enough to overcome the force of P1 and open the valve.

T.jpg

① Through the stress analysis of the control piston and valve core

pc =(A1/A2)p1+c (9-1)

Where P1 -- pressure of oil port B, PA;

A1 -- Conical cross-sectional area of main valve, RN2;

A2 -- sectional area of control piston, 1112;

C -- constant (take 0.5MPa).

② Analysis of balance circuit of hydraulic oil circuit (see Figure U)

p1=(A3/A4)p+F/A4 (9-2)

Where P -- upper chamber pressure of hydraulic cylinder, PA;

A3 - area of rod cavity of hydraulic cylinder, m;

A4 - area of rodless cavity of hydraulic cylinder, m;

F - all loads acting on the hydraulic cylinder.

From equation (9-1) and equation (9-2):

PC = (A1 / A2) [(A3 / A4) P + F / A4] + C, because PC = P

So there are:

PC = (a1f + a2a4c) / (a2a4-a1a3) (9-3)

The control pressure of hydraulic control check valve depends not only on its own structural parameters, but also on the structural parameters of hydraulic cylinder and external load. The actual control pressure of the hydraulic control check valve must be greater than the determined value. In addition, in order to improve the positioning accuracy of the hydraulic control check valve, the correct model selected for the matching directional valve should be Y-type or H-type. Because Y-type or H-type directional valve is adopted, when the valve core is in the middle position, the hydraulic cylinder is in the floating state, and both load ports are connected to the oil tank. At this time, the hydraulic control check valve can be effectively closed, and the piston rod and load of the hydraulic cylinder stop moving quickly, so as to improve the positioning accuracy of the circuit. The crane steering hydraulic mechanism of Ederer tire gantry crane originally used Y-type three position four-way directional valve, which is consistent with the form of directional valve required by our technical transformation. Therefore, the original directional valve can be used and continue to be used. The model z2s6-1-6x of hydraulic control check valve meeting the requirements is determined by searching the data.

Many tests have proved that the transformation has achieved the expected goal, the transfer function of the two tire gantry cranes has been fully restored, and the steering failure rate of the crane has been reduced from 95% to less than 5%, which provides a strong guarantee for the normal and orderly production of the company.

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