Experimental and numerical study of O/W emulsion lubricated strip rolling in mixed film regime

An experimental and numerical study of cold rolling lubricated by O/W emulsion has been carried out. The strip rolling experiment was carried out on a Hille experimental rolling mill with a view to study the performance of emulsion lubrication in terms of practical rolling parameters. Accordingly, rolling parameters such as rolling force and torque were measured. The experimental measurements compare favourably with the computed results from a numerical scheme developed by the authors. The scheme, based on a two-phase lubricant model, is capable of calculating the oil concentration at any point within the inlet zone and work zone, rolling pressure, film thickness, and fractional contact area ratio associated with strip rolling under mixed film lubrication at different rolling speeds. Using this scheme, the intertwined effects of an emulsion’s parameters such as: oil concentration, mean oil droplet size, and rolling speed on strip rolling were investigated. The numerical study encompassed the mixed film regime for speed, S ranges from 10⁻⁴ to 10⁻², supply oil concentration level λ_ds from 1 to 10%, and oil droplet size D _S from 5 to 10. Experimentally, the differences between water, oil and emulsion-lubricated rolling are not discernible except for film thickness. At a low speed of 10 RPM, force and torque of water-lubricated rolling are marginally higher than oil- or emulsion-lubricated ones. However, the difference between emulsion and neat oil is not apparent. The numerical results show the occurrence of a moderate oil concentration increase in the inlet zone followed by a sharp one at the beginning of the work zone. The effect of the concentration process is predominantly seen in the film thickness and the lubricant pressure whilst its effect on the total pressure is less pronounced. The analysis of the results suggests that it is possible to lower the emulsion oil concentration without any adverse effect on the rolling process. This principle can be used to control the outlet lubricant film thickness and hence the surface quality of the rolled strip.     

电动汽车涡旋压缩机内油气分离器的研究

通过数值模拟的方法研究了电动汽车涡旋压缩机在不同转速工况下,进口结构对油气分离器的流场和性能的影响.采用RSM模型对油气分离器内的气相流场进行模拟计算,同时利用DPM模型对4种分离器的油滴轨迹进行追踪.研究结果表明:进口结构变窄将促使油气分离器内部流场具有良好的对称性,并随着转速的提高,不同进口结构分离器的压降都呈抛物...     

Nanosys-1000机床静压止推轴承流场分布规律及承载特性

为了提高Nanosys-1000非球面曲面光学零件超精密加工机床加工精度,研究了机床核心部件静压止推轴承内流场分布规律,进而揭示其承载特性。利用ANSYS/Fluent软件建立对称结构静压止推轴承扇形油垫的仿真模型,采用层流模式对进油压力为1.3~1.9 MPa、油膜厚度为20~36 μm的油垫流场分布规律与承载特性进行分析。研究结果表明：油垫内压力在油腔区域比较均匀,沿封油边呈线性下降;油膜承载力随油腔压力线性增长,且在同一进油压力下,油膜厚度越小,油膜承载力越大,进油压力为1.5 MPa时,油膜厚度从36 μm减小到20 μm,油腔压力从3.05×10⁵ Pa增加到8.02×10⁵ Pa,油膜承载力相应地从880 N增加到2 109 N;同一负载即油膜承载力下,进油压力越高,油膜厚度越大,油膜承载力为1 320 N时,进油压力从1.3 MPa增加到1.9 MPa,油膜厚度从26 μm增加到30 μm;同一油膜厚度下,进油压力越高,润滑油流量越大,油膜厚度为28 μm时,进油压力从1.3 MPa增加到1.9 MPa,润滑油流量从0.179 L/min增加到0.231 L/min。相关研究结果在研制的Nanosys-1000非球面曲面超精密加工机床静压止推轴承上得到了验证。     

Isoviscous flow past a rigid sphere partially immersed in a thin oil film

Numerical solutions to steady state circular contact elastohydrodynamic lubrication problems normally employ Reynolds equation, forcing the assumption that the flow through the conjunction is two‐dimensional and single‐phase. In this paper, the full Navier–Stokes equations are used on a simpler rigid isoviscous sliding point contact. The aim of the study was to compute the lubricant flow patterns through and around the conjunction of a point contact when the oil inlet is a free surface that has a similar wavy shape to the wake. This model is like some seen experimentally in a ball and plate machine or industrially in a radial ball bearing with insufficient lubricant supply. There is first a discussion on the alteration with time of the oil wake geometry after it has left the conjunction. Then, the computed results mapped the areas of varying concentration between oil and air. They showed an accumulation of oil and vapour forming a reservoir at the inlet to the conjunction. Within it was a vortex attached to the stationary surface, just downstream of which, the main pressure distribution commences. The computed flow patterns were compared with experimental pictures wherever possible. Copyright © 2007 John Wiley & Sons, Ltd.     

某发动机复杂油路流场分析及优化设计

以某航空发动机附件齿轮箱“连通折弯式”的复杂油路为研究对象，对油路内部的三维流场进行仿真分析并建立压力-流量模型。基于流场的计算结果，分析齿轮箱进口润滑油流量不足的原因并提出优化方案。结果表明：该发动机因喷嘴结构设计不当，导致齿轮箱油路中局部流通面积较小，局部阻力损失较大，使得油路进口处的润滑油流量偏小。通过对喷嘴结构局部优化，提高了油路中局部流通面积，有效增加了进口的润滑油流量，满足了设计要求。优化后的齿轮箱油路中，压力损失最大的区域在每个喷嘴的喷孔段，但各个管流段压力变化不大，整个油路的压力分布更加合理。建立齿轮箱工作压力范围内的压力-流量的数学模型，为不同进口压力下的润滑油体积流量选择提供了数据支撑     

Lubrication of Strip Rolling in the Low-Speed Mixed Regime

An analytical model for strip rolling in the low-speed mixed lubrication regime is developed. An average Reynolds equation for longitudinal saw-tooth surfaces under conditions of high fractional contact area, is combined with an analysis for asperity flattening under conditions of bulk plastic flow, to treat lubrication in the mixed regime. Analyses for the inlet zone and work zone and the influence of pressure on viscosity are included in the model. The model indicates that hydrodynamic lubrication effects are important at much lower speeds than previously considered possible. The film thickness predicted by the model is somewhat smaller than that measured using the oil drop method in rolling aluminum alloy with a mineral oil.     

旋转压缩机吸油管特性数值研究

在不考虑润滑油可压缩性的条件下,采用标准k-ε湍流模型,对旋转压缩机供油系统进行了数值模拟,分析了吸油管入口大小对供油量的影响,并揭示了吸油管内压力分布及影响供油量的机理.计算结果表明:当吸油管入口太小时,由于节流效应,供油系统供油量明显不足;当吸油管入口太大时,虽然节流效应已不明显,但是吸油管内壁面无法形成高压区,供油量反而减小.吸油管入口大小存在一个最优值,此时节流效应不明显,又能在吸油管内壁面形成高压区,从而使供油系统达到最大供油量.     

A mechanism of fluid replenishment in elastohydrodynamic contacts

The use of aerated oil has enabled observation of the direction of flow around an elastohydrodynamic contact formed between a glass plate and steel ball. Replenishment of the inlet region from lubricant side bands was seen to occur within the inlet meniscus. The balance between the rate at which oil is entrained and the rate at which it is lost around the contact edges determines the inlet boundary position. Similar replenishment action has also been observed to occur in line contact using blended rollers.     

Mixed film lubrication of strip rolling using O/W emulsions

A numerical study on the oil concentration effect of O/W emulsion in cold rolling operating in the mixed film lubrication regime has been carried out. The developed scheme is able to calculate oil concentration at any point within the inlet zone (IZ) and work zone (WZ), rolling pressure, film thickness, and contact ratio for various rolling speeds. Hence the intertwined effects of oil concentration of the supplied emulsion and rolling speed on strip rolling are discussed. The study encompasses mixed film regime with speeds S range from 10⁻⁵ to 10⁻³ and supplied emulsion's oil concentration levels λ_ds range from 5% to 90%. The result shows that a moderate rise in oil concentration occurs in the IZ followed by a rapid one at the beginning of the workzone. In most cases, the oil in the emulsion would have been transformed from disperse phase to continuous phase throughout the WZ. Notwithstanding further concentration, which depends on the oil concentration of the supplied emulsion, could still occur in the WZ. The effect of the concentration process is predominantly seen in the development of the lubricant pressure whilst its effect on the total pressure is less pronounced. The analysis of the results suggests that it is possible to lower the emulsion oil concentration without detrimental effects on the rolling process; and from the analysis of the outlet film thickness, it is shown that the variation of emulsions’ oil concentration could control the exit lubricant film thickness and consequently the strip surface quality.     

Elastohydrodynamic Film Thickness and Tractions for Oil-in-Water Emulsions

Emulsions, consisting of a small volume of oil dispersed in water in the form of small particles, are popular lubricants for metal rolling and some machine design applications. A number of mechanisms have been suggested for the lubricating behavior of emulsions, among which plate-out, starvation, and dynamic concentration are of particular interest here. At low speeds, the emulsion provides essentially the same lubricating ability as neat oil for a point contact, consistent with plate-out. At some critical speed, the emulsion behavior departs from the neat oil, associated with starvation of the inlet zone. At a second critical speed, dynamic concentration becomes the important mechanism. This article measures the film thickness and traction coefficients of oil-in-water emulsions in the different regimes of behavior and compares the results to existing theoretical understanding. The effect of droplet size is isolated as a causative element in fluid film formation.     

滚滑轴承滑块的油-气两相流润滑分析

为改善滚滑轴承的润滑,运用两相流理论对其滑块进行油气润滑设计,建立滑块的油-气两相流CFD模型,分析不同入口角度、进气速度、进油速度和润滑油黏度对流场油相分布的影响。结果表明:油-气混合润滑方式能在内外滚道接触区形成有效的润滑油膜;油气管道夹角影响油滴分布,角度过大时大量油滴会在滑块侧面上附着,角度过小时油滴会在外滚道入口处堆积,造成供油连续性不好,油膜稳定性下降;进气速度过大会降低油滴附着率,无法形成有效油膜,而进油速度过大会造成润滑油累积,出现搅油现象,因此选择合适的进气和进油速度,才能控制油滴的大小和保持润滑过程的连续性;润滑油黏度会影响油滴在滑块上的附着效果,合理地选择润滑油黏度,才能保证流场油相分布均匀。     

Measurement of high-water-content oil-water two-phase flow by electromagnetic flowmeter and differential pressure based on phase-isolation

When the oil field has been exploited by long-term water-flooding, it will be in high water-content stage of production. However, it is a great challenge for high-water-content measurement due to oil droplets extremely dispersed in the water. In this paper, we developed a phase-isolation based method for high-water-content oil-water two-phase flow measurement. Phase-isolation was realized by axial-flow swirler to concentrate scattered and random oil droplets into the pipe center and change the inlet flow pattern into a particular annular flow before measuring. Owing to the axisymmetric velocity and phase distribution, the electromagnetic flow meter avoided the effect of random distribution of insulating phase, and then had a good measurement performance for total volume flow rate. Furthermore, we respectively studied using axial pressure drop, radial pressure drop and the ratio of the two pressure drops to measure water content. The results showed that the ratio of the two pressure drops not only improves the resolution of oil and water, but also effectively reduces the impact of error transfer. In the dual-parameter measurement experiment, the relative errors of total volume flow rate and water content were almost within ±5%.     

基于CFD方法的冷轧过程乳化液特性研究

应用CFD工具FLUENT建立冷轧过程乳化液内部压强及轧板所受压力求解分析模型,计算分析冷轧过程乳化液进口速度对乳化液内部压强及轧板所受压力的影响。模拟结果表明,乳化液内部压强随着乳化液进口速度的加大而增加,轧板所受压力也随之增加。通过对比生产现场的轧制力数据,得到乳化液的最优进口速度。通过分析不同油水混合比例乳化液的离水展着性,得到最优的油水混合比例,使得冷轧润滑效果最好,进而实现最优的板面质量。     

Experimental Support for the Dynamic Concentration Theory of Forming an Oil Reservoir at the Inlet of the Roll Bite by Measuring the Onset Speed of Starvation as a Function of Oil Concentration and Droplet Size

The dynamic concentration theory describes a mechanism of how an oil reservoir forms at the inlet of the roll bite when an emulsion is used as the lubricant. This theory assumes that oil droplets larger than the thickness of the lubricant film in the deformation zone become trapped when they come into contact by both the surface of the sheet and the surface of the work roll. As the droplets move toward the deformation zone, water is left behind or squeezed out by the flattening of the oil droplets. At some point, the surfaces of the trapped oil droplets come into contact with each other, resulting in an inversion where oil becomes the continuous phase. The dynamic concentration theory predicts that the height of the meniscus where this inversion occurs is a function of the percent oil concentration and the diameter of the oil droplets. To test the dynamic concentration theory, the onset speed of starvation on a laboratory rolling mill was determined by measuring the speed in which load increases relative to the load measured for the same process but where the lubricant film is fully flooded. Both the concentration of oil and the size of the monodisperse oil droplets were varied to change the height of the meniscus and consequently the onset speed of starvation. Solid support for the dynamic concentration theory was obtained when starvation occurred at the same speed for emulsions with different oil droplet sizes in which their concentrations were specifically adjusted so that their meniscus heights theoretically were the same. Finally, an unexpected consequence of the dynamic concentration theory was that the thickness of a starved lubricant film is independent of rolling speed, but this is only true at high speeds.     

一种液压缸串联式组合密封及流场分析

针对液压缸传统的活塞密封,如接触密封、间隙密封存在的不足,将接触密封与间隙密封沿活塞轴向有机集成,提出一种新型串联式组合密封结构。建立该结构的数值分析模型,通过数值仿真获得流场压力分布、密封圈变形与内泄漏特性,以及结构参数对密封性能的影响规律。结果表明:在进出口压力相同的情况下,相比于接触密封,组合密封的内部结构中压力损失更大,密封圈受到的压力和冲击更小,有利于减少密封件变形;组合密封结构中端部的间隙密封对油液实施了阻滞,使中间的密封圈承受的油液冲击和压力变弱,因而密封圈变形更小;组合密封的多级密封结构能更好地屏蔽泄漏,提升密封性能;组合密封内泄漏受间隙密封长度、密封间隙和油液压力的影响,增大间隙密封长度、减小密封间隙和油液压力,可减少泄漏量。内泄漏物理实验进一步表明,该组合密封能有效减少内泄漏量,提高密封性能,且在密封圈出现损伤故障时,仍能在很大程度上抑制或减少内泄漏,提高密封效果与可靠性。     

偏导射流伺服阀前置级温度特性

利用Fluent软件对偏导射流伺服阀前置级流场进行三维数值模拟,对衔铁组件进行热流固耦合仿真模拟,根据模拟结果分析了入口油温不同时,左右接收腔压力、前置级液动力、黏性热效应以及各组件尺寸的变化情况.通过对比不同入口油温下流场的压力分布,发现温度升高会引起左右接收腔压力升高;左右接收腔压差随温度变化的曲线表明,前置级受到...     

离心脱开型超越离合器弹流润滑分析

离心脱开型超越离合器是航空传动系统中的重要部件,具有低速楔合传动、高速离心脱开的特性,使离合器在不同工作模式下接触载荷与转速呈不同的关系,因此需针对不同工况下离心脱开型超越离合器弹流润滑性能进行分析.建立离心脱开型超越离合器弹流润滑模型,采用多重网格分析方法进行数值求解,分析进油温度与速度对超越离合器弹流润滑性能的影响...     

Non-newtonian thermal analysis of an EHD contact lubricated with MIL-L-23699 oil

A thermal and non-Newtonian fluid model under elastohydrodynamic lubrication conditions is proposed, integrating some particularities, such as the separation between hydrodynamic and dissipative phenomena inside the contact. The concept of apparent viscosity is used to introduce the non-Newtonian behaviour of the lubricant and the thermal behaviour of the contact into the Reynolds equation, acting as a link element between the hydrodynamic and dissipative components of the EHD film, independently of the rheological and thermal models considered. The apparent viscosity enables the application of the rheological model better adapted to each lubricant, without appealing to special formulations of the EHD problem.The Newton–Raphson technique is used to obtain the lubricant film geometry and the pressure distribution inside the EHD contact. The shear stresses developed in the fluid film are evaluated assuming the non-linear Maxwell rheological model. The surfaces and lubricant temperature distributions are determined using the simplified Houpert's method, applied to the inlet contact zone, and the thermal method proposed by Tevaarwerk is applied in the high pressure contact zone.The non-Newtonian thermal EHD model is applied to the analysis of a contact lubricated with MIL-L-23699 oil. Significant results are obtained for the centre and minimum film thickness, for the inlet shear heating and film thickness reduction factor (φ_T), for the temperature rise of the lubricant and of the surfaces and for the friction coefficient inside the contact, considering wide ranges of the operating conditions (maximum Hertzian pressure, inlet oil temperature, rolling speed and slide-to-roll ratio).Finally, the numerical traction curves determined are compared with the corresponding experimental results, showing very good correlation.     

轴入式两级串联旋流器流场分析与性能评估

为解决狭长空间内无法实现油水两相介质高精度分离的问题,结合旋流分离理论,设计了一种可实现轴向进液的两级串联旋流器,针对该装置开展内部流场特性及 分离性能研究。揭示了不同处理量及分流比对旋流器内速度场、压力场、浓度场以及分离效率的影响规律。结果表明：随着处理量的增大,底流口压降最大值逐渐增大且增长速率逐渐增大,旋流腔内切向速度也逐渐增大;增大一级溢流分流比,可减小环式通道及二级旋流器内的切向旋动能,二级溢流分流比对一级旋流器分离性能影响不大;实验及模拟得出研究范围内一级分流比为20%、二级分流比为15%时分离效率最高,最佳处理量为4.8 m3/h,最佳总分流比为32%;装置对不同流量、不同分流比条件具有较强的适应性,分离效率最高可达99.6%。     

超声波喷嘴雾化性能影响因素的研究

为研究新的雾化方式并将其应用于实际的油雾润滑系统中,针对流体动力式超声波喷嘴,设计其雾化性能测试系统。通过测量喷嘴产生的油雾浓度和喷嘴的流量,研究喷嘴在不同进气压力、进出口压差时的雾化性能。研究结果表明:随着喷嘴进气压力的增大,油雾浓度先增大后减小,喷嘴流量先增大后趋于恒定,喷嘴的进口压力最佳值为0.5 MPa;增大喷嘴进出口压差可以明显地提高油雾浓度和喷嘴的流量,喷嘴的雾化性能得到显著提升。