Leakage Prediction Method for Contacting Mechanical Seals with Parallel Faces

Since the beginning of the 20th century, many researches on the sealing characteristic of mechanical seals were carried out broadly and in depth by various methods and some leakage models were built. But due to the lack of the way to characterize the main factors of influence on the leakage, most of the early researches were based on the assumptions that the seal faces topography and the frictional conditions were invariant. In the early built models, the effect of the surface topography change of the seal face on the leakage rate was neglected. Based on the fractal theory, the contact of end faces of the rotary and stationary rings was simplified to be the contact of a rough surface and an ideal rigid smooth surface, and the contact interface＇s cavity size-distribution function as well as the fractal characteristic of the cavity profile curve was discussed. By analyzing the influence of abrasion on the seal face topography and the leakage channel, the time-correlation leakage prediction model of mechanical seals based on the fractal theory was established and the method for predicting the leakage rate of mechanical seals with parallel plane was proposed. The values of the leakage rate predicted theoretically are similar to the measured values of the leakage rate in the model test and in situ test. The experimental results indicate that the leakage rate of mechanical seals is a transient value. The surface topography of the end faces of the seal tings and its change during the frictional wear of mechanical seals can be accurately characterized by the fractal parameters. Under the work conditions of changeless frictional mechanism, the fractal parameters measured or calculated based on the accelerated testing equation can be used to predict the leakage rate of mechanical seal in service. The proposed research provides the basis for determining the leakage state and predicting working life of mechanical seal.

Friction Characteristics of Mechanical Seals with Laser-textured Seal Faces

Heat generated by friction between faces of mechanica l seals is a major factor that causes deterioration of the seals and shortens th eir service life. Excessive temperature rise can greatly alter the seal geometry and vaporize the sealing fluid, resulting in friction of boundary lubrication. These effects on face seals usually lead to excessive leakage and ultimately ren der the seal inoperable. In order to maintain the reliability of seals, high fri ction and unwanted wear must be avoided. Using the laser-texturing process to produce regular micro-surface structures is a fast and convenient technique compared to some more conventional etching or erosion technique currently used by the seal industry for various grooved face seals. Indeed, by using a pulse laser, better control is obtained on the geometr y, size and pore ratio of seal rings made of metallic or ceramic materials. In t his study, seal rings are made of silicon carbide and carbon. Mating faces of th e rings are polished and only silicon carbide rings are laser-textured. The las er texturing can be controlled to produce spherical pores at selected diameters, depths and pore ratio. The textured rings are then super-polished to remove th e bulges formed on the pores rims. After this process the average pore diameter, pore depth and pore ratio reach the predetermined parameter. Some untextured ri ngs are also treated to the same surface roughness and served as a reference for comparison of the textured rings. A special test rig is used to simulate a mech anical seal system and to measure the effect of the laser texturing on friction and seal performance. Tests are performed at various rotational speeds and vario us axial loads. Compared with the conventional mechanical seals, temperature rise, friction torq ue and friction coefficient of mechanical seals with laser-textured seal faces are much lower. These preliminary results show the potential of improving fricti on performance and increasing seal life with laser-textured seal faces.

Thermal Fluid-Solid Interaction Model and Experimental Validation for Hydrostatic Mechanical Face Seals

Hydrostatic mechanical face seals for reactor coolant pumps are very important for the safety and reliability of pressurized-water reactor power plants.More accurate models on the operating mechanism of the seals are needed to help improve their performance.The thermal fluid–solid interaction（TFSI）mechanism of the hydrostatic seal is investigated in this study.Numerical models of the flow field and seal assembly are developed.Based on the mechanism for the continuity condition of the physical quantities at the fluid–solid interface,an on-line numerical TFSI model for the hydrostatic mechanical seal is proposed using an iterative coupling method.Dynamic mesh technology is adopted to adapt to the changing boundary shape.Experiments were performed on a test rig using a full-size test seal to obtain the leakage rate as a function of the differential pressure.The effectiveness and accuracy of the TFSI model were verified by comparing the simulation results and experimental data.Using the TFSI model,the behavior of the seal is presented,including mechanical and thermal deformation,and the temperature field.The influences of the rotating speed and differential pressure of the sealing device on the temperature field,which occur widely in the actual use of the seal,are studied.This research proposes an on-line and assembly-based TFSI model for hydrostatic mechanical face seals,and the model is validated by full-sized experiments.

INVESTIGATION INTO EFFECT OF SPRING PRESSURE ON PERFORMANCE OF BALANCED MECHANICAL SEALS

The loads acting on the sealing elements of balanced mechanical seals are analyzed. When the balance factor approaches the back pressure factor, the spring pressure will become main part of the face pressure. The leakage model of balanced mechanical seals is established on the base of M-B model for rough surface. Several GY-70 type balanced mechanical seals are tested. The influences of the spring pressure both on the leakage rate and on the friction characteristic of balanced mechanical seals are investigated. The research results indicate that as spring pressure increases, both the clear-ance between two end faces and the leakage rate will decrease, and the friction will be more serious because lubrication medium between the rotating ring and the stationary ring reduces, though the increase of the spring pressure may not be enough to change the face friction state of mechanical seals. There exists an optimum spring pressure for mechanical seal operation. Under this spring pres-sure, not only leakage rate is small, but also the seal end surfaces have a fine friction characteristic. Under different operating conditions, identical type mechanical seals may possess different spring pressure. Appropriate selection of spring pressure is valuable to realize long-period and small leakage rate operating of balanced mechanical seals.

An Improved Design of Spiral Groove Mechanical Seal

The coupling effect among the flow of fluid film, the frictional heat of fluid film and the thermal deformation of sealing rings is inherent in mechanical seals. The frictional heat transfer analysis was carded out to optimize the geometrical parameters of the sealing rings, such as the length, the inner radius and the outer radius. The geometrical parameters of spiral grooves, such as the spiral angle, the end radius, the groove depth, the ratio of the groove width to the weir width and the number of the grooves, were optimized by regarding the maximum bearing force of fluid film as the optimization objective with the coupling effect considered. The depth of spiral groove was designed to gradually increase from the end radius of spiral groove to the outer radius of end face in order to decrease the weakening effect of thermal deformation on the hydrodynamic effect of spiral grooves. The end faces of sealing rings were machined to form a divergent gap at inner radius, and a parallel gap will form to reduce the leakage rate when the thermal deformation takes place. The improved spiral groove mechanical seal possesses good heat transfer performance and sealing ability.

Influencing factors on hydrodynamic lubrication failure of upstream pumping mechanical seal

Considering the effect of viscosity-temperature relationship and cavitation of micro-scale film,the influencing factors on hydrodynamic lubrication performance of upstream pumping mechanical seal were investigated based on the theory of hydrodynamic lubrication.N-S equation,energy equation,viscosity-temperature equation and vapor transport equation were solved with the finite volume method by using Fluent software,which was performed to analyze the influence of the viscosity-temperature and cavitation effect on hydrodynamic lubrication failure of the film.The research demonstrates that it will lead to the significant difference of the temperature field by considering the coupling of temperature and viscosity.When the film thickness decreases and the rotating speed rises,cavitation regions and viscous friction heat increases,the opening force of the film is also enhanced.However,the growth rate is restricted to the cavitation regions and viscous friction heat,and the opening force begins to decline to a certain extent,and thereby being insufficient to open the surfaces of the seals and leading to the failure of automatic adjustment function and severe wear,lubrication failure occurrs.Through comprehensive research on the influences of viscosity-temperature and cavitation effect on hydrodynamic lubrication performance,the theories of failure and design of upstream pumping mechanical seal are further developed.

Sealing Performance and Optimization of a Subsea Pipeline Mechanical Connector

Researchers seldom study the optimum design of a mechanical connector for subsea oil-gas pipeline based upon the sealing performance. An optimal design method of a novel subsea pipeline mechanical connector is presented. By analyzing the static metal sealing mechanism, the critical condition of the sealing performance is established for this connector and the formulation method of the contact pressure on the sealing surface is created. By the method the minimum mean contact pressure of the 8.625 inch connector is calculated as 361 MPa, which is the constraint condition in the optimum design of connector.The finite element model is created in ANSYS Parametric Design Language(APDL) and the structure is optimized by the zero-order method, with variance of contact pressure as the objective function, and mean contact pressures and plastic strains as constraint variables. The optimization shows that variances of contact pressure on two sealing surfaces decrease by 72.41% and 89.33%, respectively, and mean contact pressures increase by 31.18% and 52.84%, respectively. The comparison of the optimal connectors and non-optimal connectors in the water pressure experiments and bending experiments shows that the sealing ability of optimized connectors is much higher than the rated pressure of 4.5 MPa, and the optimal connectors don’t leak under the bending moment of 52.2 kN·m.This research provides the formulation to solve contact pressure on the sealing surface and a structure optimization method to design the connectors with various dimensions.

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relation- ship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.

A Hydrodynamic Model for Dimpled Mechanical Gas Seal Considering Interaction Effect

The mechanical gas seal of aero engine has to face the problems of high wear rate and short lifetime.Surface texture has shown beneficial effects over the tribological characteristics.Here,a hydrodynamic model for dimpled annular area of mechanical gas seal considering the″interaction effect″between adjacent dimples is developed based on the Reynolds equation.Different multi-row columns are chosen and the dimensionless pressure in radial and circumferential directions is calculated.The results indicate that the″interaction effect″is more obvious in the circumferential direction than in the radial direction,even when the area and depth of the dimples are same.Moreover,for the 5×5column,the dimensionless average pressure considering the″interaction effect″increases by45.41% compared with the 1×5column.Further analysis demonstrates that the model with the 5×5column can be more reasonable with the consideration of reducing the calculation error caused by boundary conditions to investigate the hydrodynamic effect for dimpled mechanical gas seal.

Preparation and property of seal coating for gas turbine compressor

Double-layer structure of seal coating which consisted of a Ni5Al bond coating and a Ni25 graphite top coating were prepared on steel substrate of gas turbine compressor cylinder block.Bond coating was prepared by atmospheric plasma spraying and top coating was prepared by flame spraying.The microstructure,mechanical properties and abradability of the coating were characterized by scanning elec-tron microscope(SEM),hardness tester,universal testing machine,thermal shock testing machine and abradability testing machine.The res-ults show that the overall spraying structure of the seal coating is uniform,the nickel metal phase is the skeleton supporting the entire coat-ing,and the coating is well bonded without separation.The seal coating has a bonding strength of not less than 7.7 MPa,excellent thermal stability,and thermal shock resistance cycle numbers at 500℃more than 50;the scratch length,deepest invasion depth and wear amount of the coating increase with rise of test temperature,with almost no coating adhesion,indicating that the seal coating has excellent abradability.

Tribological properties of low-temperature time-dependent pretreated graphite for mechanical seal pairs in high-speed turbopump

The friction coefficient and wear rate of pretreated graphite with liquid nitrogen were obtained by using a ball-on-disk tester,and the wear of GCr15–graphite seal pairs with the low-temperature time-dependent pretreatment was discussed by comparing the wear morphology.The results show that liquid nitrogen pretreatment can affect the hardness and interlayer spacing of graphite.The range of the friction coefficients of pretreated graphite changes from 0.17 to 0.22.With the increase of liquid nitrogen pretreatment time,the wear mechanism of graphite would change from dominated three-body wear to adhesion wear.The experimental results of the mechanical seal with liquid nitrogen pretreatment show that the wear rate of stator is less than 0.00165 mm^(3)·N^(−1)·m^(−1),and the graphite shows a good low-temperature compatibility.

Mechanical property design method of cement sheath in a horizontal shale oil well under fracturing conditions

Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing.This method takes the failure types of the cement sheath,such as tensile failure,plastic yield,interface crack propagation along interface and zigzag propagation into account.Meanwhile,the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method,and the safety and risk areas of wellbores are defined,which quantify the yield strength and tensile strength indexes of cement sheath.The results show that decreasing elasticity modulus,increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath;increasing the tensile strength of cement sheath can prevent its tensile failure;increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack,but will increase the risk of interface cracks zigzagging into cement sheath.The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.

Theoretical and experimental study on the rheological properties of WIS grout and the dispersion and sealing mechanism

Recently a new grout material called water inflow sealing(WIS) was invented for sealing water inflow in tunneling and underground constructions. In this study, a special experimental method called intubated counter grouting(ICG) was proposed to investigate the influence of water dispersion on the rheological properties of the grout during the grouting process, and to testify the sealing performance of the grout,such as instant gelling ability(IGA) and anti-dispersion ability(ADA). In the experiment, dispersion was restricted in the downstream of the channel with a high turbulence intensity. The influences of ADA and IGA were therefore decoupled and evaluated separately. Experimental results revealed two distinctive sealing mechanisms of WIS. For a low initial velocity of water, WIS turned the shear flow of water into an overall movement of a plug by absorbing water into the particles. For a high initial velocity and the situation that the particles reached the outlet before sufficiently expanding, WIS modified the rheology of the water in the channel and reduced its velocity till the static state. The distinctive feature of WIS brings a reformation on the sealing mechanism and provides an effective way to control water inflow with high pressure and velocity.

Erosion wear behaviour and mechanism of abradable seal coating

The erosion wear behaviour and mechanism of several middle temperature seal coatings were investigated by a CMS 100 self made vacuum sand erosion machine. The results show that the relationship between the erosion mass loss and the erosion time is linear, the coatings hold a maximum erosion rate at 60° impact angle, and the relationship between the erosion rate and the impact speed is an exponential function. The speed exponent increases with the increase of the impact angle. At 90° impact, indentations and extruded lips were generated on the coating surface subjected to impact. With repetitive impact by the abrasive particles, the extruded lips were work hardened and peeled off, while flattened metal phase grains were impacted repeatedly, loosed and debonded. At 30° impact, the erosion wear of the coating is characterized by micro cutting, plowing and tunneling via pores and non metal phase. The model of the erosion mechanism is advanced on the basis of the above mentioned erosion wear behaviour.

断裂封闭性研究现状及发展趋势

断裂控油气作用主要表现在其对油气运移、聚集过程及分布规律的影响,其实质是断裂封闭性问题。断裂封闭性往往是受多种因素控制的,不同地区不同层系在不同地质时期的断裂封闭机制与封闭性主控因素差异较大。目前,断裂封闭性、封闭机理与评价方法还没有形成完整的研究体系,其评价的精度也有待提高。依据全面系统地调研断裂封闭性方面近年来的研究热点,归纳总结了断裂封闭机理,分析了断裂封闭主控因素,梳理了断裂封闭性评价方法,讨论了断裂封闭性研究中面临的实际问题,并提出了未来研究发展趋势。目前,断裂的封闭机理可以分为垂向和侧向封闭机理,前者包括断裂面封闭机理和断裂带排替压力差封闭机理,后者包括砂泥对接封闭机理、泥岩涂抹形成的侧向封闭机理和断裂带高排替压力封闭机理。断裂发育特征、断裂两盘岩性、应力场环境以及压实、胶结、溶蚀等成岩作用是影响断裂封闭性的主要因素,不同因素对断裂封闭性的作用方式不同,断裂在不同位置、不同时期的封闭性有着明显的差别。断裂封闭性评价研究方法可归结为以下4类:(1)传统地质学方法,包括定性分析和半定量分析;(2)数学地质方法,涵盖逻辑信息法、非线性映射分析法、模糊综合评判法、灰色关联分析法等;(3)构造应力场数值模拟及断裂封闭性相关参数计算法;(4)地球化学方法。碳酸盐岩地层断裂启闭机制与封闭性评价、应力和流体及其耦合作用对断裂封闭性的影响机制、多因素的断裂封闭性综合定量评价、断裂封闭性的时空演化及通源能力评估等是未来断裂封闭性研究的发展方向。

基于EWT-KLD的机械密封金刚石涂层磨损声发射降噪

为了准确获得机械密封金刚石涂层在磨损过程的声发射信号,在分析机械密封设备的噪声特性基础上,提出了基于经验小波变换(EWT)和相对熵(KLD)的声发射降噪方法;通过对磨损声发射信号进行经验小波变换得到划分其频带的滤波器组,对磨损声发射信号和背景噪声发射信号用相同的滤波器组划分频带;计算相应频带2种信号的相对熵,用累计和算法在升序排列的相对熵中找到首个大于3σ的值作为阈值,保留相对熵值大于阈值的频带重构信号,完成降噪.研究结果表明:本文所提的EWT-KLD方法可以有效抑制不同工况、不同磨损状态的声发射信号的噪声,有效改善了磨损声发射信号的信噪比,尤其是微弱磨损信号的信噪比,提高了密封端面磨损声发射检测的精度和灵敏度;通过与传统降噪方法的对比发现,本文方法能够对不同工况下的密封磨损声发射信号降噪表现出更强的适应性和稳定性,对于及时检测早期密封磨损和准确监测磨损累积变化过程具有重要意义.

电连接器用聚氨酯胶密封件贮存可靠性统计模型的加速试验验证与评估

针对电连接器用聚氨酯胶密封件在长贮条件下的寿命评估问题,从机理层面分析了聚氨酯胶密封件内聚破坏和边界破坏导致性能下降的原因。依据从机理层面建立的电连接器用聚氨酯胶密封件贮存可靠性统计模型,利用聚氨酯胶密封件温湿度综合应力加速退化试验数据,综合应用粒子群优化算法和回归分析、AD检验及拟合优度等检验方法,从数据统计层面验证了电连接器用聚氨酯胶密封件失效物理方程和退化轨迹模型的合理性。利用扫描电镜和能谱分析验证了失效机理分析的正确性。最后,利用所建模型评估了电连接器用聚氨酯胶密封件在贮存环境下的可靠寿命。

盾构隧道施工期渗漏聚氨酯堵漏作用机制研究

为探明隧道渗漏时聚氨酯的堵漏机制,设计并开展盾构隧道渗漏与聚氨酯注浆堵漏模型试验,通过试验分别对不同地层中隧道渗漏引发的外部地层侵蚀发展规律以及注浆堵漏的作用机制进行研究。研究表明:1)隧道渗漏后砂土与粉土地层周围孔隙水压力迅速下降,水在压力差的作用下以渗流形式向渗漏点补给,造成周边地层侵蚀破坏,但2种地层侵蚀发展规律不同。2)砂土与粉土地层中聚氨酯注浆堵漏机制相似,均可分为3个发展阶段,第1阶段聚氨酯反应释放大量气体,抵抗渗流水压;第2阶段聚氨酯固化,封堵渗漏通道,实现堵漏效果;第3阶段聚氨酯彻底固化,引起隧道结构外部荷载重分布。3)由于砂土与粉土地层渗流侵蚀规律不同,聚氨酯注浆堵漏效果有所差异,粉土地层注浆堵漏效果更好。

基于生产过程的多规格不锈钢管自动封箱装置设计

针对6种不同规格的不锈钢管和企业对产品的包装需求,为实现3~6箱/min的自动包装效率,设计了一种自动封箱装置,该装置由夹箱机构、纸箱拍齐装置、折箱装置、顶升机构和机架5部分组成,通过分析每个机构的结构特点和工作原理,阐述了夹箱机构、纸箱拍齐装置、折箱装置的运动过程,重点分析了折箱机构中针对不同规格的不锈钢管如何设计其短边折箱机构及其主要技术参数的计算方法。实践证明:该封箱装置结构设计合理,整体运行稳定可靠,产品包装速度达到生产要求,减少了单条生产线所需要工人的数量,改变了传统的人工包装方式,提高了生产效率,降低了生产成本,具有较好的推广价值。

基于分形理论的浮环密封端面法向接触刚度仿真研究

浮环密封是现代航空发动机常用的密封形式之一,浮环端面的接触刚度对浮环密封辅助密封面的摩擦磨损性能有重要影响。在分形理论的基础上,基于有限元方法建立了一种新的法向接触刚度计算模型。之后通过该模型计算浮环密封端面法向接触刚度,得到了浮环密封端面法向接触刚度随压力与粗糙度的变化规律。计算结果表明:求得的法向接触刚度与粗糙表面接触试验结果吻合较好,最大相对误差不超过4%;浮环密封端面法向接触刚度随压力的增大而增加,随接触面粗糙度的增大而减小。该方法为浮环密封端面法向接触刚度的计算提供了一种新的思路。