A mixed lubrication model of a rotary lip seal using flow factors

A mixed lubrication model of a rotary lip seal using flow factors has been developed. The model consists of coupled fluid mechanics, contact mechanics and deformation mechanics analyses. The fluid mechanics analysis is described by a Reynolds equation that takes into account the surface roughness effect using flow factors. The contact mechanics analysis uses the Greenwood and Williamson model to compute contact pressure. The deformation mechanics analysis utilizes the influence coefficient approach to compute deformation of the seal. Results for a typical seal show how the operation parameters and the surface roughness affect seal behavior.     

表面纹理对旋转轴唇形密封性能的影响

在唇形密封圈唇端两侧设置整齐排列的圆形、正方形和等边三角形3种凹坑纹理形式,建立具有表面纹理的旋转轴唇形密封圈的有限元模型,并分析获得密封面静态接触压力和变形系数矩阵;建立综合考虑混合润滑和空化及表面纹理形状影响、耦合流体场和弹性变形场的唇形密封圈接触区域密封数值计算模型,并建立集有限元分析与数值计算于一体的唇形密封圈接触区域泵吸率计算流程。计算结果表明:表面纹理结构使得密封唇与轴的接触压力相对下降,且有效地增大唇形密封圈的膜厚并改善泵吸效果;相较于圆形和正方形纹理,三角形纹理对唇形密封圈的改善效果最佳。但表面纹理结构在改善密封区域润滑状态的同时,也造成密封动态压力的波动,且三角形纹理的影响更显著。     

混合润滑状态下旋转唇形密封的失效机制模型

为探究旋转唇形密封的失效机制,综合考虑流体、微凸体、弹性变形和温度对旋转唇形密封的影响,构建旋转唇形密封多场耦合模型,并基于多场耦合模型与关键点更新策略提出混合润滑状态下旋转唇形密封的磨损退化模型仿真方法。通过设计故障模拟试验,将试验结果与仿真结果进行对比,验证了仿真方法的有效性。结果表明：唇形密封件在初期磨损速率较大,之后趋于平缓;唇尖处接触压力最大,磨损速率最大。     

高温超高压金属弹性环密封技术研究

针对氟橡胶O型圈只能使用在210℃、210 MPa的难题,设计了一种新型弹性环密封结构。该新型弹性环密封结构能使氟橡胶O型圈在250℃、250 MPa工况下安装简便、可靠密封。通过有限元分析方法,针对弹性环密封结构中的弹性环,分析各结构参数对弹性环的应力和变形的影响,快速、准确确定弹性密封结构尺寸。该密封结构在一定程度上可替代金属密封结构。     

双唇型油封的密封性能及其结构优化

利用有限元分析软件模拟分析双唇油封主唇区域的静态接触压力分布,并与单唇油封的静态接触压力进行比较;同时分析双唇油封安装后副唇的位移和变形。结果表明:油封的腰部结构不同导致双唇油封主唇区域密封效果低于单唇油封;副唇的位移和变形导致在实际运行中副唇与旋转轴存在空隙,影响防尘效果。为改善双唇油封的性能,提出采用渐进式腰部结构代替原弓形腰部结构和采用较长的防尘唇的双唇型油封结构优化方案。结果表明:采用渐进式腰部结构的双唇油封的主唇口接触压力曲线更接近单唇油封,密封效果优于普通双唇油封;采用较长的防尘唇,且安装时使防尘唇与旋转轴之间具有一定的过盈量,可以使防尘唇在油封装配变形后仍保持与旋转轴接触,减少了防尘唇唇尖与旋转轴之间的空隙,能够有效地提升防尘效果。     

Simulation and experimentation on the contact width and pressure distribution of lip seals

The relative motion between two mated parts of machinery always generates heat from friction. The lubricant serves as a medium not only to reduce the friction but also to enhance heat dissipation. In order to contain the lubrication oil, lip seal is a most frequent sealing part used in these applications. This paper aims to study the contact width and contact pressure of the seal lip under the various interference fits between the shaft and seal. The contact force associated with the pressure was used to estimate the generated heat due to friction. Thereby, this frictional heat flux was employed to analyze the temperature distribution within the rubber seal. According to the temperature distribution, the thermal deformation of the seal and the concern of material ageing can be examined. Since the use of a seal with a shaft under allowable dimension tolerance is foreseeable, the fit with different degree of interference was investigated. On the other hand, a simple apparatus to measure the width and pressure on the contact lip zone under different diameters of shaft was designed and fabricated. The contact width and contact pressure were distilled from the press mark of a pressure-sensitive film. The measurements were used to demonstrate the feasibility and accuracy of the proposed set up.     

Shaft roughness effect on elasto-hydrodynamic lubrication of rotary lip seals: Experimentation and numerical simulation

Numerical analyses of the isothermal elasto-hydrodynamic lubrication (EHL) have made considerable advances in order to identify the most important features in the successful operation of rotary lip seal, and the results have shown a good agreement with experiments.Most of the models previously published are capable of predicting the combined effects of thin film through deformed lip and rotating shaft, but they assume a smooth surface of the shaft. Although this assumption is only verified for shaft roughness much smaller than that of the seal lip, it is the best solution to avoid a transient model.First, the present study describes an experimental work that provides a basis upon which a numerical EHL model of rotary lip seal is constructed by taking into account both the shaft and lip roughness. After confirming the validity of the current model by comparing experimental with numerical results, simulations have been performed and have underlined the effect of shaft roughness amplitude and profile on the rotary lip seal performance. It is shown that for shaft roughness beyond half of the lip roughness, the seal may leak.     

Analysis of flow field around a ribbed helix lip seal

In this study, a direct numerical simulation model has been developed to elucidate the pumping mechanism of a radial lip seal with helical ribs. The flow field around the contact region between the seal lip and the shaft surface in the environment of a pumping-rate test rig, where both air and oil sides are filled with oil initially, was simulated. The streamline pattern and pressure field around the seal lip were examined. Complicate three-dimensional streamline topology was depicted. On the air side, high pressures built up on the windward faces of ribbed helices next to the lip helping to pump oil back to the sump. The vortex generated next to the lip on the oil side rotates such to create an inward pumping effect too. The pumping rates were calculated at shaft speeds, ranging from 2000 to 6000 rpm, and compared to the measured values from the test rig. Good agreement was observed. Both calculated and measured pumping rates increase as the shaft speed increases. The current results demonstrate the promising application of CFD in the design of radial lip seals.     

An unsteady mixed soft EHL model, with application to a rotary lip seal

A rotary lip seal usually operates with full-film lubrication. However at low speeds, such as those encountered during startup and shutdown, mixed lubrication occurs and asperities on the lip contact the shaft. To simulate this condition, a mixed soft EHL model has been constructed. The fluid mechanics of the lubricating film is described by a Reynolds equation that can handle interasperity cavitation. The bulk deformation of the lip is computed using influence coefficients, while the junctions between the asperities and the shaft are modeled as Hertzian contacts. Since the shaft is rough, the flow is unsteady and an unsteady analysis is required. The model shows how the shaft roughness affects such seal characteristics as load support, contact load ratio, contact area ratio, cavitation area ratio, reverse pumping rate and average film thickness.     

The contact forces of lip seals for a ball bearing

Simplified equations are derived for the evaluation of the axial contact forces for a special design of lip seal for bearings. The contact forces of the lip seals for a ball bearing are analysed as a function of the ratio of real contact length, the thickness of the seal lip, the inclined angle of the seal lip, and the deflected interference between the edge of the seal lip and the rotating inner ring. An experimental apparatus is developed for testing the seal lip contact forces. Using a non-linear FEM program, the contact force of the seal lip was analysed for various values of the deflected interference. The calculated results show that the deflected interference and the circumferential stress cause considerable change of contact forces for the low sealed lubricant pressure. The results of contact forces obtained from the derived equation for the contact force are in good agreement with experimental and numerical results.     

Analysis of contact force and thermal behaviour of lip seals

Using the Mooney-Rivlin model, the contact force and thermal behaviour of a radial lip seal are studied numerically and experimentally as a function of the interference. The numerical and experimental results on the static contact forces show good correspondence with and without the garter spring. The FEM calculated results indicate that increased interference may increase the eracking of seal material due to the maximum contact stresses close to the contacting area of the seal lip and produce local separation between the seal lip and the shaft. Also a coupled thermal-mechanical analysis method will be a useful tool to predict the contact behaviour of rubber lip seals for small values of the interference.     

Elastohydrodynamic Analysis of a Rotary Lip Seal Using Flow Factors

An elastohydrodynamic analysis of a rotary lip seal is performed numerically, incorporating both the fluid mechanics of the lubricating film and the elastic deformation of the lip. Asperities on the lip surface dominate the behavior of the flow field in the lubricating film and are taken into account through the use of flow factors. Because previous analyses treated those asperities deterministically, they required very large computation times. The present approach is much less computationally intensive because the asperities are treated statistically. Because cavitation and asperity orientation play important roles, these are taken into account in the computation of the flow factors. An asperity distortion analysis is introduced to model the complex variations in the asperity distribution on the surface of the lip. Results of the analysis show how the operating parameters of the seal and the characteristics of the asperities affect such seal characteristics as the thickness of the lubricating film, reverse pumping rate, power dissipation, and liftoff speed.     

Parametric study of helix configuration in ribbed lip seal

In this study, the effects of the principal geometric parameters in a helix ribbed lip seal on the pumping performance are systematically investigated, through a combined finite element analysis/computational fluid dynamics simulation approach. It is shown that the sealing performance of the modified seal based on the geometrical parameters suggested by the numerical simulations is significantly better than that of the original seal model. The results presented in this study provide a versatile and cost-effective means to derive a set of basic guidelines for designing the conventional helix parameters in such a way as to maximize the reverse pumping effect.     

Elastohydrodynamics of the rotary lip seal

An elastohydrodynamic model of the non-leaking equilibrium behaviour of the rotary lip seal has been developed. It consists of a fluid mechanics analysis of the lubricating film, a structural analysis of the lip, an analysis of the meniscus on the air side of the seal, and an iterative computation procedure. A uniform distribution of microasperities on the lip surface is assumed. The model predicts the location of the meniscus, the film thickness and pressure distributions, and the locations of cavitation regions. It also predicts the maximum pressure that can be sealed with zero leakage, and the maximum speed above which the meniscus is ingested into the sealing zone.     

Influence of an applied electric field on the torque of rotary lip seals on metal shafts. Part I: Effects of lip seal type

The paper presents some results of experiments on the tribocharging of selected engine oil and on the effect of an auxiliary external DC electric field on the work of machines which contain rotating parts such as shafts, crankshafts, etc. The research was especially aimed at the braking torque of a rotating metal shaft sealed with a lip seal and a possibility of reduction in the torque under external DC electric fields. DC voltage was applied between the stiffening ring of four different lip seals under test and a rotating, earthed shaft in a metal shaft-oil film-lip seal system. The relationships of the torque to the voltage of positive and negative polarities were established on the basis of measurements of the torque under steady-state conditions for a constant oil temperature and given different angular shaft velocities. In general, it was found that positive and negative DC electric fields produce adverse effects on the torque depending on the type of oils and on the material of which the lip seals were made. In only one case, the torque decreased with the increasing absolute value of the negative voltage applied.     

Influence of an applied electric field on the torque of rotary lip seals on metal shafts. Part II: Effects of oil type

The experimental results are presented of research on the tribocharging of selected engine oils and on the effect of an auxiliary external DC electric field on the work of rotary machinery. There exists an effect of the type of oil, its temperature, and the electric field on the braking torque of rotating parts such as shafts, crankshafts, etc. sealed with lip seals. The research was especially aimed at the possibility of reduction in the torque under external electric fields for different engine oils. To obtain the auxiliary electric field the DC voltage was applied between the stiffening ring of a fluorocarbon lip seal and the rotating, earthed shaft in the metal shaft–oil film–lip seal system. The measurements of the torque were performed under steady state conditions for given different oil temperatures, angular shaft velocities, and voltages; also three different oils were used. It was found that for the lip seal under test the negative voltage applied produced a beneficial effect on the torque depending on the type of oils.     

Numerical simulation and experimental study of shaft pumping by laser structured shafts with rotary lip seals

A simulation model to predict pumping by shafts with various surface finishes, in combination with a rotary lip seal, has been developed and validated by experiment. The model consists of a fluid mechanics analysis of the flow in the sealing zone coupled with a deformation analysis of the seal. The experimental validation consists of pumping rate measurements with shafts whose surface structures contain laser generated oblique grooves. Plots of pumping rate vs. various parameters show good agreement between the model and experiment. Plots of torque vs. speed, as well, show good agreement between the model and experiment.     

径向金属密封唇部结构接触力学研究*

由于初始过盈量和介质压力的作用,井下流量控制阀径向金属密封唇部的应力和应变梯度变化很大,很容易发生塑性变形。为研究径向金属密封唇部接触力学行为,提出径向金属密封唇部的圆弧结构,基于接触力学建立径向金属密封唇部轴对称结构的圆弧-平面接触模型,得出径向金属密封唇部结构接触力学参数的理论关系式,并基于有限元方法进行验证。径向金属密封唇部接触力学参数的理论解与数值解相符,接触宽度、最大接触应力、初始过盈量和平均接触应力的平均相对误差分别为8.86%、6.96%、8.88%和4.33%,满足工程设计要求。研究表明：径向金属密封唇部的最大接触应力与初始过盈量、径向金属密封唇部径向厚度和轴向厚度成正比,与径向金属密封唇部圆弧半径成反比,因此可通过增加初始过盈量、径向金属密封唇部径向厚度和轴向厚度来增加径向金属密封唇部的最大接触应力。研究结果为井下流量控制阀径向金属密封的设计提供了理论指导。     

Parameter analysis of the radial lip seal by orthogonal array method

This study investigates the effects of structure, material parameters and assembly conditions on the reverse pumping rate and friction torque of the radial lip seal by using a mixed elastohydrodynamic lubrication model. The orthogonal array method is used to make a numerical experiment plan for eight parameters, which are identified as eight control factors. Each factor has five levels. The significance of each parameter on the reverse pumping rate and friction torque of the radial lip seal is evaluated by range analysis and F-test. As a result, optimal values of eight parameters are suggested. The seal with this set of optimal values has a higher reverse pumping rate and lower friction torque than those of a previously-designed seal.     

双唇Y形拉杆密封的密封性能研究*

建立双唇Y形拉杆封的混合润滑模型,并进行流体力学、接触力学、变形力学分析。利用MatLab软件实现对模型的求解,得到密封区域的流量、膜厚和接触压力分布,并分析不同密封件粗糙度对轴向往复双唇Y形密封圈的摩擦力矩、泄漏量的影响。结果表明:在双唇Y形往复密封中,两唇在密封过程中均处于混合润滑状态,且第一内唇处的膜厚大于第二内唇处;第二内唇静态接触压力近似于对称分布,且第二内唇最大接触压力大于第一内唇最大接触压力,表明第二内唇作为密封的第二道防线可以保证良好的密封效果;密封件粗糙度是影响矩形密封性能的重要因素,随表面粗糙度的增加,直线往复密封的摩擦力和泄漏量增大,存在一个临界粗糙度使泄漏方向改变。