| As modern support equipment,hydraulic support has been rapidly popularized and applied in coal mining.In the complex working conditions of the coal mining face,the hydraulic support of the seal is exposed to variety of unfavorable factors,and there may be leakage.The leakage of the sealing medium is harmful to the human body,and even causes the hydraulic support unable to provide effective support for the working face,which increases the potential security risks of the mining work.Bud-shaped composite sealing ring is widely used in the sealing of piston rod of hydraulic support,because of its wear resistance and good sealing performance,and it is of great theoretical significance and practical value to study the sealing characteristics.In this dissertation,the theoretical analysis and finite element simulation of the contact pressure(stress)caused by the sealing of the bud-shaped composite sealing ring of the hydraulic support in the coal mine are carried out.Combined with the contact pressure test of the sealing ring,the influence of the contact stress on the sealing performance is obtained.Front and rear diversion angles and secondary seals are adopted to reduce the amount of leakage and improve the sealing performance.The main research works are as follows:(1)The boundary layer theory is used to analyze the fluid seal interface of reciprocating hydraulic sealing.The Reynolds equation,which is suitable for solving the problem of seal clearance,is deduced and the fluid film height of the piston rod outside and inner stroke is given.Then the leakage formula is obtained.According to the derivation,the stress distribution between the sealing ring and interface has important influence on the sealing performance of the reciprocating hydraulic system,and it is very important to discuss the sealing of the system from the point of view of contact pressure.The calculation results show that the sealing problem studied in this dissertation belongs to the scope of the boundary layer,and the flow state is laminar.After determining the above two conditions,the fluid at the sealing interface is analyzed by using the N-S equation and Reynolds equation,based on the equilibrium of the viscous and inertia force of the flow interface.Then the contact pressure formula of reciprocating hydraulic dynamic is deduced,which shows that the contact pressure of dynamic sealing has relationship with the inner pressure,the fluid viscosity,the velocity of piston rod,the seal clearance length and the square of the length.In these factors,the contact pressure is inversely proportional to the square of the seal clearance height.Usually,this height is micron level,and hence the contact pressure is much higher than the internal pressure of the hydraulic system.That is to say,the sealing ring bears huge stress.At the same time,the contact pressure formula of static sealing and the leakage formula of reciprocating hydraulic system in one cycle are analyzed.In the leakage formula,the leakage is proportional to the stroke and diameter of the piston rod.Therefore,contact pressure,a high pressure gradient on the inside and low on the outside is necessary to maintain a low leakage.When the reciprocating hydraulic system has a low travel speed or high pressure gradient in outside stroke,the leakage is small.And when system has a high speed and pressure gradient in inside stroke,the sealing ring has better pump back capacity,and then the fluid on the piston rod is pumped back into the system.(2)Through the uniaxial tension and compression test of rubber and polyurethane,the Mooney-Rivlin parameters corresponding to the different N values are obtained respectively.The parameters of the 9-parameters model(N=3)are selected by parameter evaluation and curve fitting for the subsequent finite element analysis.The expression of the Mooney-Rivlin parameter is derived from the strain potential function.Based on the comparative analysis and the engineering practice,the uniaxial tension and compression tests are carried out to replace the 6 kinds of pure strain states and obtain the Mooney-Rivlin parameters prepared for the finite element analysis.The uniaxial tensile and compression tests are conducted five sets to obtain the Mooney-Rivlin parameters.After curve fitting,the optimal 9-parameters model is chosen for finite element analysis.(3)The finite element analysis is carried out on bud-shaped composite sealing ring with a radial 10% compression under seven different loads respectively.With the increase of loads,the sealing performance gradually deteriorated,and the seal fails when the load is up to 60 MP.The contact stress distribution is extracted to make a further research on sealing performance.The ring size is measured by a three-dimensional image measuring instrument.According to the finite element analysis based on the ring size and the model parameters obtained by tests,the variation of the sealing performance is summarized by the maximum contact stress analysis and the contact stress curve is obtained.The sealing law of the sealing ring under different loads is concluded by means of the obtained contact stress curve and the influence of the pressure gradient in the leakage formula.Meanwhile,the accuracy of the finite element analysis results is questioned and the experimental method is needed.(4)The contact pressure curve of the sealing ring is obtained by experiment.The influence of the contact pressure change on the sealing performance is analyzed by the fluid theory.The finite element analysis agrees well with the experiment in the trend of sealing performance,while the data is quite different because the contact pressure sensitive paper and surface plastic film involves in the measurement.A test platform for simulating the sealing ring is designed and constructed.The method and principle of measuring the contact stress of the sealing ring by using pressure sensitive paper is introduced.The stability and reliability of the pressure sensitive paper is verified by the calibration system.The operation procedure of the experiment is optimized,which improves the efficiency and reduces the operation intensity.The contact pressure of the sealing ring in the simulation platform is measured,and the contact pressure curves under three different loads are obtained respectively.Compared the experiment and fluid theory,the influence of the pressure curve on the sealing performance is analyzed.The contact stress curve and the finite element contact stress curve are compared,which shows that the contact stress distribution curve obtained by finite element analysis can evaluate the performance of different sealing structures in the trend,but the pressure value obtained has great error.(5)The influence of the front and rear diversion angles on leakage is analyzed,under the condition of the same compression and other characteristics.The leakage raises with the increase of the front diversion angle,when the rear angle is constant,while the leakage reduces as the rear angle decreases,when the front angle is constant.The influence of the secondary seal on the contact stress of the sealing body is analyzed,and the method of selecting and designing the secondary seal is summarized.The reason of the excellent performance of the bud-shaped compound sealing ring is discussed based on the comparison with the rectangular seal,and the feasibility of using the contact stress to evaluate the sealing performance is proved.The influence of the front and rear diversion angles on leakage is analyzed,under the condition of the same compression and other characteristics.At the same time,the change rule of the contact stress with different diversion angles through the stress curve variation under zero and 20 MPa load,and the choice basis of the diversion angle are put forward.The effect of the secondary seal on the contact stress is dissected.The change law of contact stress with the amount of compression alteration is analyzed,under three different compressions with initial and 20 MPa loads. |
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