A Mixed Flow Model for Lubrication with Emulsions

An oil-in-water emulsion in the inlet zone of a concentrated contact is modeled by treating the oil particles as flattened cylinders surrounded by water. In an independent flow model, the oil and water flows are coupled only through the pressure gradient. However, the model leads to anomalous behavior with regard to the flow of water. To overcome this problem, corrections to the pressure gradients due to interactions between the oil and water were derived. Both models showed that the emulsion became concentrated because the higher viscosity oil was preferentially drawn into the conjunction. The net effect was similar to an inlet starved of oil. The inlet film thickness predicted by the interactive theory was in good agreement with Dow's experimental measurements for an EHL contact.     

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.     

The Effectiveness of Boundary and Hydrodynamic Lubrication when Cold Rolling Aluminum Metal

How hydrodynamic and boundary lubrication affect a lubricant's film strength when cold rolling aluminum was studied using a laboratory mill. The film strength of the lubricant was determined by increasing the amount of reduction until a rapid rise in load and temperature produced a herringbone pattern on the surface of the metal. The hydrodynamic lubrication was changed by increasing the viscosity of the base oil or by increasing the rolling speed. The boundary lubrication was changed by increasing the concentration of the additives or by changing the type of additives. The results of the test showed that either increasing the amount of the hydrodynamic lubrication or increasing the amount of the boundary lubrication were effective ways to increase the film strength of the lubricant; however, the effectiveness of each decreased as the calculated film thickness of the lubricant increased. It is proposed that this can be explained by the decrease in contact area between the work roll asperities and the surface of the sheet as the thickness of the lubricant film increases.     

A Two-Wavelength Model of Surface Flattening in Cold Metal Rolling with Mixed Lubrication

A new model of surface flattening is developed for cold metal rolling in the mixed regime. Longitudinal surface roughness is modeled by two separate wavelengths. The new model follows the asperity crushing analysis of Sutcliffe (1999) for unlubricated rolling but additionally includes a hydrodynamic model to account for the effect of the lubricant. The effect of various parameters including speed, reduction in strip thickness, roughness wavelength and lubricant properties is examined. The results show similar behavior to previous models of mixed lubrication, with a speed parameter A_s having the most influence, and confirm the results for unlubricated rolling that the short wavelength components of the surface roughness persist more than the long wavelength components. The predicted changes in roughness are in good agreement with experiments.     

The Influence of Bulk Plastic Flow on Lubricant Permeation from Micro Oil Pits in Metal Forming

An analysis of the oil permeation from micro oil pits under the influence of bulk plastic flow has been developed. A series of rolling experiments was conducted and the experimental results were analyzed. It is found that the bulk strain rate can reduce the resistance of asperity to permeation and change the surface finish significantly. The influence of strain rate on the nondimensional specific permeation flux, which is defined as the permeation flux per unit relative sliding velocity and width of oil pit, is also studied. The average nondimensional specific permeation flux increases rapidly with increasing strain rate. For small reduction where the interfacial pressure is small, it is easy for the lubricant to seep into the contact area. The nondimensional specific permeation flux is therefore higher for smaller reduction and is saturated when the strain rate becomes sufficiently high.     

Numerical Analyses of Hydrodynamic Lubrication and Dynamics of the Rolling Piston and Crankshaft in a Rotary Compressor

In this article, numerical analyses of hydrodynamic lubrication and dynamics of the crank, rolling piston, and vane were carried out to study the tribological performance of a rotary compressor. Dimensionless Reynolds equations of journal and thrust bearings in dynamic load condition were derived and solved numerically. To deal with the lubrication of the rolling piston, the effect of the nonuniformity of tangential velocity over the bearing surface on the Reynolds equation was taken into account. In addition, combined with the analyses of dynamics and kinematics of the crank, piston, and vane, the angular velocities of the crank and piston as well as the motion mode between the piston and vane were studied. Analysis results illustrate characteristic oil film pressure distributions of the crank and piston bearings, which are different from that of common journal bearings. Under the influences of dynamic load and eccentricity of the cam, the wedge effect as well as the stretch and squeeze effect contribute greatly to hydrodynamic pressure. The relative motion mode between the piston and vane tip is not always pure sliding but accompanies rolling in some cases, which depends on the magnitude of the friction coefficient between the piston and vane tip. The analysis results are helpful for the improvement of rotary compressor design.     

铜带轧制变形区摩擦润滑状态研究

观察分析了轧制变形区形貌特征,研究了不同方向粗糙度对轧制润滑的影响。在轧制变形区并存边界润滑和流体动压润滑;轧辊与轧制的塑性挤压边界接触是获得高光亮表面的必要条件。轧后轧件表面粗糙度Ｒａ和丰满度Ｋ趋向于满足一定润滑条件的最佳值。     

Starvation Behavior in Cold Rolling of Aluminum with Oil-in-Water Emulsion

Reich, et al. ( 1 Reich, R., Panseri, N. and Bohaychich, J. 2001. “The Effects of Lubricant Starvation in Cold Rolling of Aluminum Metal When Using on Oil-in-Water Emulsion,”. Lubrication Engineering, 57: 15–18.  [Google Scholar] ) reported that the rolling force for the cold rolling of aluminum increased when starvation occurred in the oil-in-water (O/W) emulsion used as the rolling fluid. They reported that the starvation occurrence was dependent on the emulsion concentration and the size of the oil droplets, but the thickness of a starved lubricant film was independent of the rolling speed. However, from their experimental results, the cause of the increase of the rolling force and the quantitative inlet oil film thickness at the entrance between the roll and the workpiece for the O/W emulsions cannot be understood. In this study, the aluminum rolling experiments using O/W emulsions with different concentrations were carried out in order to reproduce the increase of the rolling force. Experiments were carried out using a laboratory mill with two high rolls. The workpiece material was an aluminum A1050-H. Commercial rolling oil was used as base oil for the aluminum emulsion. The rolling force was measured during the rolling and the appearance of the workpiece after rolling was taken. Moreover, the effect of the surface roughness of the rolls on the increase of the rolling force was investigated. The increase of the rolling force was reproduced in the aluminum rolling with the O/W emulsion using the laboratory rolling mill. It was observed that the increase of the rolling force occurred after the oil starvation, and it depended on the oil starvation, the oil film thickness, the surface roughness of the roll, the rolling speed, and the reduction in thickness.     

Starved Grease Lubrication of Rolling Contacts

Many grease lubricated roller bearings operate in the starved elastohydrodynamic (EHL) regime where there is a limited supply of lubricant to the contact (1). Under these conditions the film thickness drops to a fraction of the fully flooded value (2) and, thus, it is difficult to predict lubrication performance, or bearing life, from conventional EHL models. In this regime film thickness depends on the ability of the grease to replenish the track rather than the usual EHL considerations. The conventional view of grease lubrication is that base oil bleeds from the bulk reservoir close to the track, replenishing the inlet and forming a fluid EHL film (3). Resupply, under starved conditions, will thus depend on both operating conditions and grease parameters. The aim of this paper is to evaluate the influence of these parameters on starved lubrication in a rolling contact. Starved film thickness has been measured for a series of greases and the results have been compared to the fully flooded values. These show that the degree of starvation increases with increasing rolling speed, base oil viscosity and thickener content but decreases at higher temperatures. In many cases an increase in absolute film thickness is obtained when moving from high viscosity base oil to a low one, this result is the reverse of normally accepted EHL rules. Taking the fully flooded film thickness as a guide to lubrication performance is therefore not valid as grease film thickness in the starved regime is determined by local replenishment rather than bulk rheological properties.     

滚锥包络环面蜗杆传动润滑研究

本给出了滚锥包络环面蜗杆传动啮合齿面间诱导法曲率和相对速度计算公式,进而给出蜗轮和蜗杆啮合齿面间弹流油膜厚度计算公式;以此为基础,研究了该种传动蜗轮和蜗杆齿面间弹流油膜厚度分布规律,分析了油膜厚度的影响因素和影响规律。研究工作对于该种传动的设计与制造具有指导意义。     

Lubrication of Aluminum Rolling by Oil-in-Water Emulsions

The dynamic concentration model for lubrication by oil-in-water emulsions proposed by Wilson el al. (1) is applied to strip rolling to derive a relatively simple equation for inlet film thickness. The predictions of the new model are supported by rolling experiments using emulsions as lubricants, where the film thickness is inferred from the surface roughness that is generated on the workpiece during rolling. The experiments also seem to suggest that the efficiency of oil droplet capture increases with increasing rolling speed.     

Predictive Testing of Steel Rolling Oils Using the Elastohydrodynamic Lubrication Rig

Bench testing of steel rolling oils is difficult because there is not a simple laboratory method with good correlation to the field. This work will present a new laboratory method for testing that takes into account the variable slip that occurs in the rolling operation. The method was developed in combination with a field trial of experimental rolling oils. Correlation of the new test data to the field results is markedly improved over traditional test methods.     

板带轧机润滑技术分析

分析轧机的润滑方式，介绍各种润滑方式的特点，说明怎样合理地为板带轧机配套相应的润滑系统。     

基于弹性流体动压润滑条件的滚动轴承耐磨损设计

分析了弹性流体动压润滑的理论和条件,阐述了基于弹性流体动压润滑的圆柱滚子轴承耐磨损设计的方法和步骤。     

一种新型热轧带钢轧制润滑系统

分析国内各热轧带钢厂普遍使用的轧制润滑系统存在的问题。针对原轧制润滑系统存在的管路和喷嘴易堵塞,系统设备维护工作量大等问题,提出一种新型的轧制润滑系统,并介绍该系统的技术特点。该新型轧制润滑系统能最大程度发挥轧制润滑系统的功能,以达到提高带钢表面质量和降低生产成本的目标。     

带钢热轧工艺润滑的实验研究

通过不同润滑条件下特殊钢带热轧实验和分析，研究了工艺润滑与带钢热轧过程中的轧制压力、压下率、带钢厚度的关系，并探讨了热轧油特性，油水混合浓度、使用温度等条件对热轧工艺润滑效果的影响。实验结果表明：采用工艺润滑后保证了轧制过程顺利进行，其中，使用高效热轧油轧制Ti-IF钢可以降低轧制压力15％～20％，而在轧制合金钢或轴承钢时压下率明显增加，从而在原有轧机上能够生产出更薄的产品。     

Grease Lubrication of Ultra-High Speed Rolling Contact Bearings

The failure mechanisms of grease lubricated ball bearings operating in the DN range from 1.0 × 10⁶ to 2.0 × 10⁶ was studied. A new rig capable of controlled operation of 20 and 25 mm ball bearings at speeds up to 100,000 rpm is described. Ball separator design seems to be a very important factor and a lightweight single piece machines outer ring controlled ball separator appeared to give the best results. In general, mechanical factors such as vibration, bearing design, bearing fit and tolerances, dynamic balance, load alignment, etc., have more influence on the performance of the bearings studied than gross grease variables. Under ideal conditions it is indicated that adequate lubrication with grease is possible for periods over 100 hours. However, under the test conditions generally in existence in the ultra high speed rigs grease lubrication was only adequate for very short periods.

Grease compositional factors leading to better performance are smooth texture and hard consistency. At the temperature investigated diester type oil was slightly superior to mineral oil and greatly superior to silicone oil.     

冷轧塑性加工中的摩擦性质

根据轧制时轧件金属发生塑性变形特点及摩擦副间的介质实际情况,经理论分析认为冷轧塑性加工中的摩擦性质是混合摩擦或边界摩擦,并得到了实验的验证。     

板材轧制过程中快速有限元在线算法

有限元法(Finite element method,FEM)在轧制过程力能参数、变形参数、温度参数以及组织演变等模拟与预测中发挥了重要作用,但由于有限元求解问题时所需的计算时间较长而无法实现轧制过程参数的在线计算。快速有限元(Fast finite element,FFE)方法具有计算精度高和计算速度快等优点。基于刚塑性有限元(Rigid plasticity finite element method,RPFEM)方法开发了板材轧制过程FFE程序。讨论了单元数目对计算时间和计算精度的影响规律,研究加快计算收敛速度和减少搜索时间的在线算法,包括采用阻尼Newton-Brunt法相结合减少一维搜索时间;采用改进循环中点求积Newton法为Newton-Raphson迭代法寻求比较好的初始值;采用信赖域Newton混合迭代法以及改进的Cholesky分解使Hessian矩阵强迫正定以加快收敛速度;研究计算机操作系统、软硬件条件对计算时间的影响。开发的FFE在线设定模块在某热轧带钢厂取得良好的应用效果。     

CSP热轧工艺润滑效果研究

在理化性能与摩擦学性能测试分析的基础上,对CSP热轧板带钢工艺润滑应用效果进行轧制过程研究。工业应用试验表明:CSP热轧板带钢过程中,并非热轧油体积比越高,工艺润滑效果越好,选择中低黏度、润滑性能良好的热轧油,其体积分数在0.2%时即可平均降低轧制力10%～20%,使连轧过程张力波动控制在20%以内,同时对冷却水的污染也不明显。摩擦学测试和轧制工艺润滑应用试验数据分析表明,控制热轧油体积分数在1%以下即可满足热轧工艺润滑作用效果。可根据具体轧制产品与工艺对热轧油黏度和用量做出相应调整,应以保证CSP热轧生产平稳进行和对冷却水少污染为评价标准,而并非轧制压力的降低值。