| Underground hydraulic impact hammer is a powerful and efficient tools for trenchlessconstruction. It has the advantages of cabinet structure, low cost, long life and easyprotected. Compare with pneumatic impact spear, it has greater impact energy and higherefficiency.This article is founded on the structure of hydraulic impact hammer with sleeve valvemodel. By means of virtual machine technology, we can explore the dynamic mechanismand make the structural parameters optimization viable. At the same time, a set of drawingsfor hydraulic impact hammer also be supported which can be use to realize the productionin the future.The hydraulic hammer is mainly assembled with piston, housing, sleeve valve,valveseat. There is the extruding bit in front of it and positioner at the back. Hydraulic hammer isa type of impact equipment working with the media of hydraulic oil. The circulation of oilinside the close loop brings energy to drive the piston moving to and fro. By means of thecollision between piston and extruding bit the wallop can doing work to processingextruding drilling.The hydraulic hammer of this article adopted the sleeve valve model with the frontcavity being common pressure. It is a representative three way sleeve valve controlhydraulic vibration device. The main function of the valve is to changing the connectingstate of the back cylinder. When the sleeve valve kept it's back position, oil with highpressure comes into the back cylinder. Because there is a area discrepancy between theforehead and the back. Efficient force can be generated to push the piston forward. Thus aclash procession is formed. Dual apertures were designed inside the middle housing totransfer the feedback oil that can push the valve forward. When the flange of piston gettingacross the pushing-valve apertures, high pressure oil will push the sleeve valve forward,then the back cavity will connect to the regurgitation. While the collection between pistonand extruding bit finished, the valve kept it's position just got then the back moving ofpiston can be proceeded. During the course of withdrawal, the pushing-valve apertures willno longer connected to the high pressure. Once the piston strike onto the sleeve valve, thepushing-valve apertures switch on the regurgitation. Both the piston and the sleeve valverun backwards together. The high pressure port will opened antecedently. But the piston isstill running back at considerable velocity. Under the effecting of high pressure in the backcavity, the slower process started. During the relaxation, the velocity of the piston will beslowed down, the backwards energy can be collected by the accumulator. Until the sleevevalve get its original position, the piston reach the end of withdrawal. Subsequently anotherworking cycle will begin. Energy of single strike and frequency is the most important performance parameters ofhydraulic hammer. Because the oil pressure can be 20MPa supported by the power station,the piston can reach very high velocity in a short distance. Hence the high energy can begenerated during a single circulation. But the maximize velocity is limited by the intensityof the material and the manufacture structure. So the rated pressure of the hydraulic systemis set to 16MPa, the range of maximize velocity is controlled from 8 m/s to 10 m/s.Additionally such important parameters like the backwards velocity reach almost zero whilestriking the positioner and the efficiency of the hydraulic loop greater than 60% is anotheraspect must be discussed among the simulation. To realize the objective confirmed above, the exact digital model must be establishedaccording to the principle of the hydraulic hammer in advance. The following simulationcourse can explore the reciprocal relation between various parameters. According the resultgenerated during the process of simulation, optimization for both structure and performancecan be proceeded. Simulation based on virtual machine is just like to do the experiment inside thecomputer. The pivotal contact is to make sure that the digital model is suitable with theactual part, the load added is fit with the real working condition. Dynamics equation will befounded by the software and solved inside the program. The whole digital template includesthree-dimensional entity model of underground hydraulic impact hammer, dynamic loadadded by working condition analysis and the measure being taken to solve the problem .Such three-dimensional entity model can be made by CAD technology, the dynamic force 6applying to the moveable parts must be investigated distinguishably to the various phasebelongs an integrated circulation. There are seven parts compartmentalized as follows:1.Single piston runs forward. 2.The piston and sleeve valve runs forward together. 3. Thestriking end instance of stroke. 4. Single piston backhaul. 5. The sleeve valve go with thepiston. 6.Piston relaxative withdrawal. 7. The striking end of withdrawal. In order to describe the working condition conveniently, the dynamic equation listed isa all-purpose expression. The wave of pressure caused by collision at stroke end andwithdrawal end must be treated especially. For example the coupling form of the dynamicequation about piston is such like the below: ??M ?? x(t) + B x(t) + K { } .. [ ]{ } . [ ]{x(t)} ={F(t)} (1) p Usually the mass of the piston, the viscidity of the oil and the volume flexibility can beconsidered constant. Using centric difference can solve the equation directly. Think the stepof time is Δt, the equation can be dispersed, and the respond of displacement at thedispersed nod can be worked out. By means of centric difference, the velocity andacceleration listed as follows: { } . xn = 1 (2) 2?t ?{xn+1 ? xn?1} { } .. xn = 1 (3) 2?t2 ?{xn+1 ? 2xn + xn?1} During the course of numerical integral, the external force is fetched with the average force of the contiguous three nods. So the original equation can be changed to the form just like expression4. Because the pressure acting on the piston is associated with the character of the power station also the performance of the liquid, we have no means to solve the complex non-linear equation now. Thus we suppose that: 1. The runoff of the pump is considered constant and the dynamic respond of pressurevalve has been ignored. 2.The viscidity of the oil is considered constant also the temperature. 3.Water-hammer causes the pressure mutation, but doesn't influence the movement.
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