Analysis of the technical optimization of bolts based on original skills

S is the equivalent stiffness of the test piece (mainly bolt), m0 is the equivalent motion quality of the test piece, Fp is the pre-tightening force of the test piece (bolt nut pair), and fg is the rolling friction force related to the lateral vibration of the test piece. . Unlike the usual hydraulic servo system, the force of the test piece is quite special. Before the test piece is not loose, when the loading force generated by the power mechanism is less than the friction force generated by Fp on m0, the test piece only exhibits elastic deformation (ie, no movement occurs), and when the loading force of the power mechanism and Fp are generated. When the friction is balanced, the test piece will move with m and no further elastic deformation will occur. When the power mechanism outputs an alternating load, the two stress states of the test piece alternately appear as shown. The design of the hydraulic power mechanism is mainly to determine the rated flow of the servo valve, that is, the no-load flow rate of the valve Qom and the effective working area of ​​the hydraulic cylinder. Although the optimized design of the hydraulic servo system is very mature, the system Has its characteristics. First of all, the load is more complicated. Even at the same amplitude, the specimen exhibits an elastic load when Ks is small, and the specimen is similar to the friction load when Ks is large. Secondly, the power source used in the test bench is also limited, and only a flow rate of about 75 L/min can be provided when the Ps is 21 MPa. Power mechanism output characteristics; load trajectory 3 conclusions The guiding ideology of the hydraulic power mechanism design of the lateral vibration test bench of the fastener under the condition of limited oil source power and complex system dynamics is to ensure that the system has enough towing Under the premise of dynamic capacity, the maximum load flow of the valve is minimized, thereby reducing the system's requirements on the power of the oil source, and the double valve is used in parallel to solve the problem that the no-load flow of the valve is large and affects the system bandwidth. A useful attempt has been made to design the hydraulic power mechanism of such systems.

The minimum outlet flow rate of the pump is set to be slightly greater than the sum of the total system leakage, which only solves the requirements for meeting the process oil supply. In fact, the set minimum pump outlet flow is not sufficient to take away the heat generated by the mechanical efficiency and volumetric efficiency of the pump. In order to solve this problem, two measures were taken: forced cooling of the oil supply to the pump casing using a low pressure. The forced flow rate is taken as half of the maximum flow rate of the constant pressure variable pump. Because this flow is too large, the shaft seal of the pump will be destroyed due to excessive oil return resistance of the cooling oil, and unnecessary flow consumption is also increased. A low-resistance suction line design is used. The specific method is that the maximum flow velocity of the oil suction pipe is controlled within 0.2 m/s, and the reducer joint and the rubber hose with approximate parabola are adopted at the suction port of the pump, so that the total resistance of the oil suction pipe is small, and the suction pipe is effectively controlled. The negative pressure of the road limits the separation of air in the oil. Because the free air in the oil will reduce the bulk modulus of the oil, affecting both the variable mechanism damping ratio and the natural frequency of the variable mechanism.

Since the oil source unit was put into production in October 1999, the coarse adjustment and fine adjustment can be carried out simultaneously, and the speed of each movement meets the process requirements; the working pressure point set by the hydraulic pump has not changed; the system oil temperature is not In the case of changing the original cooling conditions, it has not exceeded 55 °C; the annual average equivalent electric power is less than that of the original system.

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