Sliding-wear resistance of pure near fully-dense B4C under lubrication with water,diesel fuel,and paraffin oil

The sliding-wear resistance of pure near fully-dense B₄C is investigated, and the wear mode/mechanisms identified, under lubrication with water, diesel fuel, and paraffin oil. It is found that the wear is mild in the three cases, with specific wear rates (SWRs) of 10^?16–10^?17 m³/N m. Nonetheless, the wear resistance of the B₄C ceramic is one order of magnitude greater under oil lubrication (10¹⁶ N m/m³) than under water lubrication (10¹⁵ N m/m³), and twice as great for the specific case of paraffin oil than diesel fuel, attributable to the lubricant’s viscosity. It is also found that the wear mode is always abrasion, and that the wear mechanisms are plastic deformation and localized fracture with grain pullout. However, in agreement with the macro-wear data, the severity of the wear damage is lower under lubrication with paraffin oil, followed by diesel fuel, and lastly water. Finally, microstructural considerations are discussed with a view to enhancing the sliding-wear resistance of B₄C triboceramics.     

Assessment of spray quality from an external mix nozzle and its impact on SQL grinding performance

Spray quality is the critical factor which decides the efficacy of Small Quantity Lubrication (SQL) technology in a high specific energy involved machining process like grinding. Yet, the understanding about spray quality, the actual process mechanics and its effect on machining performance is inadequate. The present work is an attempt to establish a correlation between the spray input variables, quality of the spray and machining performance of SQL grinding through modelling and experiments. Using computational fluid dynamic techniques, the variation of droplet size, droplet velocity, number of droplets and heat transfer coefficient have been analysed at different input parameters and the computed trends have been verified and validated. CFD modelling of spray indicates that it is possible to produce aerosol medium with high heat dissipation ability at moderately high air pressure and low flow rate. It also shows that any increase in atomising air pressure favourably leads to notable increase in wetting area and also results in substantial enhancement in heat dissipation ability. Reduction of residual stress is thus remarkably good. On the other hand, grinding fluid flow rate, if increased, offers significantly better lubricity and reduces the grinding force which also reduces tensile residual stress. Short spell grinding test results are found to be in good agreement with CFD results.     

可监控性油气混合分配器的供油动态特性分析

基于单线卸压式油气润滑系统中油气混合分配器对给油动作的不可监控这一缺陷,设计了一新的给油结构,其不但结构简单、满足系统工作要求,而且能够通过阀芯动作指示杆观察到给油动作,减少了电气系统的监测,节约了成本。应用AMESim软件HCD液压元件库对供油结构进行仿真分析,重点研究了输入压力变化、阻尼孔直径和锥阀弹簧刚度对出口喷油流速的影响。在AMEsim仿真结果基础上,设定气相速度,利用Fluent UDFs改变混合器入口油液喷油速度变化规律,进一步仿真研究油气两相环状流的发展过程。为其结构设计及系统工作压力的选择提供依据。     

水润滑扇形瓦推力轴承润滑性能的边界元分析

用边界元法分析水润滑扇形瓦推力轴承的润滑性能,将雷诺方程转化为类似泊松方程的形式,采用边界元法求解该方程,研制了一套C++计算程序,得到多组轴瓦参数下的水膜厚度、压力分布和相关润滑性能,可以显著降低代数方程组的阶数,从而减少计算所需时间,并可提高计算精度。研究表明瓦块张角和瓦块倾角对最小水膜厚度、最大水膜压力、摩擦功耗、压力中心位置和进水口流量有不同程度的影响,该研究将有助于合理的设计水润滑扇形瓦推力轴承的轴瓦参数。     

基于层次分析法的典型切削润滑冷却技术探究

为提高机床加过过程中的能效,降低切削液对环境的影响,本文从机床加工能耗、润滑、冷却、废物排放、成本等方面对三种典型切削润滑冷却技术(浇注式切屑、MQL切削、干切屑)进行分析探究。再利用模糊层次分析法进行综合性的分析,确定各指标的权重,判断三种切削润滑冷却技术对能耗、废物排放、切削效果以及加工成本方面的影响,构建指标体系,科学的选出最优方案。     

Application of fullerene C60 nano-oil for performance enhancement of domestic refrigerator compressors

In this work, the fullerene C₆₀ nano-oil is proposed as a promising lubricant to enhance the performance of domestic refrigerator compressors. The stability of fullerene C₆₀ nanoparticles dispersed in a mineral oil and the lubrication properties of the nano-oil were investigated experimentally. It was confirmed that the nanoparticles steadily suspend in the mineral oil at stationary conditions for a long period of time. The friction coefficients of the nano-oil significantly decrease with increasing the concentration of nanoparticles in the mineral oil, especially at the lower applied loads. The friction coefficients of the nano-oil with the concentration of 1–3 g L⁻¹ are 12.9–19.6% lower than that of pure mineral oil. The applications of the nano-oil with the specific concentration of 3 g L⁻¹ to two domestic refrigerator compressors were examined by compressor calorimeter experiments. The results shows the COPs of two compressors were improved by 5.6% and 5.3%, respectively, when the nano-oil was used instead of pure mineral oil.     

Investigation of long-term engine oil performance using lab-based artificial ageing illustrated by the impact of ethanol as fuel component

The effect of ethanol and its combustion products on the lubrication system is not very well understood. In this paper, a novel lab-based artificial ageing method for the evaluation of engine oils for bio-fuelled automotives and the results thereof are presented. Artificial ageing of three fully formulated engine oils with addition of ethanol, acetaldehyde, and acetic acid was carried out. The oil formulations chosen represent a consequent series of optimisation steps based on the engine oil performance in terms of preservation of typical oil parameters, e.g. base reserve and oxidation, observed during the artificial ageing procedure. It was shown that ethanol as well as acetaldehyde has almost no effect on the oil degradation especially in the case that advanced additive technology was used. On the contrary, acetic acid significantly affected the formulated oil showing influence on the detergent chemistry and even caused sludge formation. The use of the novel artificial ageing method proved to clearly differentiate the impact of the respective compounds added with the possibility to simulate enhanced stress conditions without the need of time-consuming and expensive engine bench tests. Hence, the novel setup offers valuable input for the formulation and the pre-selection of future engine oils suitable for bio-fuel.     

Role of thermal,mechanical and oxidising treatment on structure and chemistry of carbon black and its impact on wear and friction Part I: Extreme pressure condition

Carbon black was blended in different oil formulations that included base oil with ZDDP and dispersant as well as fully formulated oils. The blended formulations were then subjected to various thermal, oxidative and mechanical treatments to force interaction between the carbon black and different constituents of the oil and thermo-oxidative decomposition products of oil. Wear studies conducted on the treated compositions were compared with formulations that were blended with extracted diesel soot. XANES analysis of extracted diesel soot and treated carbon black were compared to elucidate similarities between the two in terms of their chemical constituents. Tribological and XANES results indicate that it is possible to simulate wear conditions similar to those seen with diesel soot when appropriate thermo-oxidative conditions were used.     

Optimization of cutting conditions for minimum residual stress,cutting force and surface roughness in end milling of S50C medium carbon steel

Residual stresses are usually imposed on a machined component due to thermal and mechanical loading. Tensile residual stresses are detrimental as it could shorten the fatigue life of the component; meanwhile, compressive residual stresses are beneficial as it could prolong the fatigue life. Thermal and mechanical loading significantly affect the behavior of residual stress. Therefore, this research focused on the effects of lubricant and milling mode during end milling of S50C medium carbon steel. Numerical factors, namely, spindle speed, feed rate and depth of cut and categorical factors, namely, lubrication and milling mode is optimized using D-optimal experimentation. Mathematical model is developed for the prediction of residual stress, cutting force and surface roughness based on response surface methodology (RSM). Results show that minimum residual stress and cutting force can be achieved during up milling, by adopting the MQL-SiO₂ nanolubrication system. Meanwhile, during down milling minimum residual stress and cutting force can be achieved with flood cutting. Moreover, minimum surface roughness can be attained during flood cutting in both up and down milling. The response surface plots indicate that the effect of spindle speed and feed rate is less significant at low depth of cut but this effect significantly increases the residual stress, cutting force and surface roughness as the depth of cut increases.     

双向润滑系统在混凝土输送泵及泵车中的应用

以流体动力学为基础,基于混凝土泵送设备两个输送缸交替送料的特点,提出一种新型的双向润滑系统,对该系统进行数学建模及分析,通过求解得到砼活塞唇口处润滑点的油膜厚度曲线,并在实际中得到验证.双向润滑系统不仅可以改善泵送设备结构运动副的润滑效果,延长泵送系统的使用寿命,而且能够减少润滑剂使用量约33%,降低成本,减少对环境的...