SCUFFING MODEL CONSIDERING INFLUEN OF HYDRODYNAMIC LUBRICATION

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Effects of lubrication and humidity on the abrasiveness of a thin boron carbide coating

Studies using thin boron carbide (B₄C) coatings have previously been performed in order to investigate their potential use as finite-life run-in coatings. Such coatings have been shown to polish the mating surface in a relatively short time. The inherent ability of these coatings to polish can potentially allow them to function as finite-life run-in coatings. Employing such coatings requires a thorough understanding of the parameters which directly influence the changes that occur in the coating abrasiveness throughout the duration of the polishing process. In past studies, changes in the coating abrasiveness during dry sliding wear under ambient conditions have been investigated. However, both lubrication and humidity can strongly influence the abrasive wear process. In this study, the influences of the operating environment, namely humidity and lubrication, on the coating abrasiveness are directly investigated. The coating abrasiveness decreases at a slower rate when a lubricant is added and when the humidity decreases.     

复合织构化压裂泵柱塞密封副动压润滑性能仿真研究

为改善压裂泵柱塞密封副的摩擦磨损性能,在压裂泵柱塞密封副表面建立不同的复合表面织构(不同复合织构类型、不同分布方式、不同截面形状等),并在结合柱塞密封副几何结构特征、压力边界条件及雷诺方程的基础上,建立织构化柱塞密封副动压润滑理论模型,采用有限差分对雷诺方程进行求解,仿真分析复合织构对柱塞密封副动压润滑性能的影响规律。数值仿真研究结果表明:复合织构对动压润滑性能的影响与外织构深度有密切关系;内织构为凹坑或凸起,以及内织构为不同截面形状的复合织构,主要是通过影响织构平均深度与摩擦副间隙的大小关系,而对复合织构的动压润滑性能造成不同的影响规律;内织构分布于外织构右侧(润滑介质入口一侧)对复合织构动压润滑性能的提升最大。     

Effects of Load Direction on Performance of Tiliting Pad Journal Bearings

At the previous works for tilting journal pad bearings （TPJBs）, most TPJBs are designed to operate with the load either directly on-pad（LOP） or directly between-pad（LBP）. However, in practice, in some cases, the load direction can change dramatically in operation. With the current requirements for the analysis of dynamic characteristics of the rotor-bearing systems, the effects of the load direction on the bearing performance must be known. So, in this paper, the effects of load direction on the static and dynamic characteristics of TPJBs are obtained with theoretical analysis based on the hydrodynamic lubrication theory, and the influence of load direction on the performance of TPJBs in different structure and operating parameters is also analysed. The results show that the load direction has considerable effects on the static and dynamic characteristics of the TPJBs, especially for the TPJBs that are operating under heavy load and high rotor speed. And for the operating condition that load direction changed rapidly, TPJBs with more pads, smaller length to diameter ratio, larger clearance ratio and smaller perload ratio can reduce the performance fluctuation with the variation of load direction.     

Performance of supercritical carbon dioxide sprays as coolants and lubricants in representative metalworking operations

This paper investigates the cooling and lubrication properties of supercritical carbon dioxide (scCO₂) sprays as potential substitutes for aqueous emulsions and straight oils used in the metalworking industry today. Sprays of rapidly expanding scCO₂ act to cool and lubricate machining and forming processes by delivering a mixture of dry ice and lubricant deep into the cutting/forming zone. In this work, experiments with turning, milling, drilling, thread cutting, and thread forming were performed with scCO₂ and other metalworking fluids (MWFs) to evaluate their relative performance with respect to tool wear and machining torque. Observations reveal that scCO₂–MWFs are more effective in removing heat from the tool-workpiece interface than conventionally delivered (flood) aqueous MWFs as well as other gas-based MWF sprays. In addition, scCO₂–MWFs delivered in lubricant-expanded phase, where scCO₂ is used to increase volume of lubricant in the spray field, are shown to provide better lubricity than straight oils and oil-in-air minimum quantity lubrication (MQL) sprays. As a result, scCO₂–MWFs can reduce tool wear and improve machining productivity in a wide range of manufacturing operations leading to appreciable improvements in the economics of manufacturing. Also given that CO₂ is a recovered waste gas that is non-toxic, scCO₂–MWFs can improve the environmental and worker health performance of manufacturing operations.     

A novel approach to measure slip-length of thin lubricant films under high pressures

Abundant evidence of boundary slip at liquid/solid interfaces has been presented by experiments and theoretical analyses. Recent research reveals that the boundary slip effect of lubricants can be obvious in small confined gaps, even with simple Newtonian fluids. Therefore, it is appropriate to ask if there is boundary slip of thin highly pressurized lubricant films in EHL contacts, and, if so, how to quantify it. This paper proposes a method for measuring the slip-length of lubricant films within a small gap under high pressure. Measurement principles have been addressed in details in the paper. The idea makes use of the phenomenon whereby a tiny quantity of lubricant can be entrapped and forms a dimple film by impacting a steel ball against a lubricated glass plate. The slip-length can be extracted from the relative movement of the dimple against the solid surfaces. Case experiments are also presented to validate the feasibility of the method.     

Causes of chatter in a hot strip mill: Observations, qualitative analyses and mathematical modelling

Severe vibrations, known as chatter, occur often in both hot and cold rolling of steel. A recent chatter outbreak at the second stand of hot strip mill in Hastings, Australia, prompted an investigation into the causes of chatter by a literature review, the development and deployment of mathematical models, and a rigorous analysis of plant observations. The investigation suggests that the frictional conditions in the roll gap are the principal cause of chatter in this mill, though residual chatter marks on work rolls can occasionally cause it. The frictional conditions appear to be associated with the thickness and properties of oxide formed on rolls.     

Astringency sub-qualities of red wines and the influence of wine–saliva aggregates

Astringency is a sensory attribute, related to the quality and mouthfeel of red wines. However, the origin of astringency sub-qualities, such as the typical drying astringency found in immature grapes, is still unknown. Astringency of red wines with similar tannin content but different astringency sub-qualities, from different harvest dates, is studied. Astringency was characterised in terms of friction coefficient, polyphenol content, sensory analysis and tannin/salivary–proteins aggregates characterisation. A different evolution during ripening was found for both Cabernet Sauvignon and Carménère, and tannin–protein aggregates showed differences in size, shape and surface. The velvety sub-quality appears to be related to aggregates with low precipitation, and with specific surface characteristics as roundness and Feret diameter. Results from this work propose an effect of aggregates on sensory perception and opens the possibility to explore their effect on oral lubrication.     

Reduced order finite element model for elastohydrodynamic lubrication: Circular contacts

This paper presents an extension of the reduced order finite element model to the case of circular elastohydrodynamic lubricated (EHL) contacts under isothermal Newtonian considerations. The line contact model was developed and validated in a previous work (Advances in Engineering Software, 2013; 56:51−62). The model is based on a finite element discretization of the EHL equations: Reynolds, linear elasticity and load balance with a reduced order model for the linear elasticity part. All equations are solved simultaneously in a fully-coupled framework using a damped-Newton procedure allowing fast convergence rates for the global solution. This model combines fast convergence rates, reduced memory requirements and negligible model reduction errors compared to the full model which makes it an attractive tool for EHL contact performance prediction.     

Tribological performance of filled PTFE‐based friction material for ultrasonic motor under different temperature and vacuum degrees

In this work, a glass fiber reinforced polytetrafluoroethylene (PTFE)‐based friction material with good properties for ultrasonic motor was fabricated. The effects of temperature and vacuum degree on the tribological behavior of the PTFE‐based friction material were investigated; the evolutions of friction‐wear modes and mechanisms were also discussed as function of temperature and vacuum degree. The results show that the delamination and fatigue wear are predominant under the effects of repeated shearing and dynamic contact under atmospheric environment. While wear mechanisms change from adhesive to abrasive and fatigue wear as it is cooled from 30 to ?60 °C at vacuum environment. Under high vacuum, adhesive wear was prone to taking place at room temperature for high frictional heat which increased the wear rate and extended the running‐in period. Experiment shows that the highest no‐load speed, output power, and holding torque of ultrasonic motor at room temperature under atmospheric environment are 220 rpm, 9.9 W, and 1.21 N m, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45358.