回转圆盘刀具横向振动流体控制建模与分析

在对圆盘刀具进行正方化扇形网格划分及建立单元型函数的基础上,针对回转圆盘薄片刀具实际工作时存在的横向振动问题,应用拉格朗日方程和流体动压润滑理论建立含流体动压膜的回转圆盘薄片刀具的动力学方程。通过对该动力学方程的分析,利用专门设计、制造的试验装置,对圆盘薄片刀具系统的动态特性进行测量,将测量数据与理论分析的结果进行对比。结果表明:建立的圆盘薄片刀具系统的动力学方程是正确的,流体动压膜可有效地减少刀具横向振动的幅值。     

Lubrication,emissions, and performance analyses of LPG and petrol in a motorbike engine: a comparative study

ABSTRACT

The increased level of air pollution has caused the automobile industry to investigate alternate greener fuels to make vehicles more environmentally friendly. This study focuses on the performance, emission, and lubrication oil deterioration of 125cc motorbike engines, operated using petrol and LPG. Performance tests were conducted for a constant load using a water brake absorber using both fuels with fresh ((L.O.)_F) and deteriorated lubrication oil ((L.O.)_Det). Lubrication oil was deteriorated by running motorbike for both fuels. Emission testing was performed by applying three different loads and five different representative speeds. Moreover, NO_x, HC, CO, and CO₂ emissions levels were obtained using exhaust gas analyzer. For both fuels with (L.O.)_F and (L.O.)_Det, emission data was fitted to Weibull distribution and ascertained for 95% confidence interval for means. Flash point, ash, water content, total acid number (TAN), kinematic viscosity, and viscosity index tests were performed for analyzing both (L.O.)_F and (L.O.)_Det. Brake power, torque, and maximum speed of LPG fueled motorbike lowered by 17.4%, 10%, and 6.9% as compared to petrol using (L.O.)_F, and 21%, 10.6%, and 7.7% using (L.O.)_Det respectively. The average specific NO_x decreased by 11.5% for LPG. The lubrication oil TAN increased by 65.2% and 21.7% for petrol and LPG respectively.     

水润滑条件下制动材料摩擦学性能研究进展

汽车刹车片摩擦因数在雨天或湿润的环境里衰退到非常低的水平是一个很严重的问题,直接威胁到交通安全。但目前国内外关于摩擦材料的试验规范并没有涉及到水润滑条件,相关的研究应越来越受到人们的重视。介绍摩擦材料在水润滑条件下的摩擦性能及相关研究的现状,对比干、湿2种条件下的摩擦机制,表明水作为一种冷却介质和润滑介质,对摩擦材料性能产生了复杂的影响。提出水润滑条件下摩擦材料的研究方向。     

热连轧精轧机连接轴润滑系统回油管路改造

针对武钢热轧总厂三分厂现有润滑系统回油管路缺陷,在流量校核满足现场需要的理论基础上,将现有上下主轴集中回油模式改为单独回油模式,并通过管路合理布置避免回油管被下阶梯垫油缸撞坏,从而避免事故发生,节约生产成本。     

Numerical modeling and experimental measurement of MQL impingement over an insert in a milling tool with inner channels

This paper compares experimental and numerical simulations of liquid film formation for different rotating velocities of a milling tool. The numerical model used was based on an unsteady Reynolds–Average Navier–Stokes (RANS) formulation and multiphase Lagrangian model for liquid film formation by the droplet impingement model on a solid surface. The details of spray–wall interaction are presented and the model was used to simulate the liquid film formation in the Micro-Quantity Lubrication (MQL) coolant process for different milling tool velocities. The shape and the size of the liquid film obtained by the calculation and the experiments were compared to improve understanding of the MQL cooling process. Overall, good agreement was observed between the numerical and the experimental measurements of liquid film size from an estimated numerical film thickness border. This study provided greater understanding of oil mist behavior. The impingement analyses predicted better lubrication when highly oriented channels and high inlet pressure were used, especially in High Speed Machining.     

On the compressive heating/cooling mechanism in thermal elastohydrodynamic lubricated contacts

The importance of compressive heating/cooling occurring within lubricating films in thermal elastohydrodynamic lubricated contacts has not been given sufficient attention in the literature. This paper presents a numerical investigation of this mechanism and attempts to quantify its importance as compared to shear heating under pure-rolling and rolling–sliding conditions. It is found that even under pure-rolling, compressive heating/cooling remains in most cases less important than shear heating or at best, of the same order. Under rolling–sliding conditions, as soon as the slightest sliding occurs, heat generation is governed by shear heating. The dependence of compressive heating/cooling on operating conditions is also examined. Finally, the impact of this mechanism on the lubricating performance of these contacts is considered under various operating conditions.     

Effects of molybdenum dithiocarbamate and zinc dialkyl dithiophosphate additives on tribological behaviors of hydrogenated diamond-like carbon coatings

The tribological behaviors of hydrogenated diamond-like carbon (DLC) coatings under varied load conditions lubricated with polyalpha olefin (PAO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyl dithiophosphate (ZDDP) additives were investigated in this paper. Hydrogenated DLC coatings were synthesized through the decomposition of acetylene by the ion source. The tribological performances were measured on a SRV tribometer. The morphologies and chemical structures of the DLC coatings were investigated by the scanning electron microscope (SEM), Raman spectrometer (Raman) and X-ray photoelectron spectroscope (XPS). It was shown that the low friction and high wear were achieved on the hydrogenated DLC coating under MoDTC lubrication, while low wear was found on the hydrogenated DLC coating lubricated by ZDDP. The primary reason was attributed to different tribofilms formed on the contact area and the formation of graphitic layer. Both factors working together leaded to quite different tribological behaviors.     

Hard turning using HiPIMS-coated carbide tools: Wear behavior under dry and minimum quantity lubrication (MQL)

In the present work, experimental investigations carried out to assess the applicability of HiPIMS (High Power Impulse Magnetron Sputtering)-coated carbide tools to hard turning (55 HRC) and to address the widely debated topic about the use of coolants in hard turning are presented. Tool wear progressions and hence, tool life, different tool wear forms and wear mechanisms observed for tools coated with HiPIMS coating technique, namely, nanocomposite AlTiN, nanocomposite multi-layer TiAlN/TiSiN and nanocrystalline AlTiCrN are presented along with the images captured by digital and electron microscope. Characterization results of all the coated tools in terms of their average coating thickness (measured using Calotest and Fractographs), adhesion strength of the coating(s) (determined using Scratch test), composition and microhardness (using EDAX and Vickers microhardness test, respectively) are presented. Experimental observations indicate higher tool life with nanocrystalline AlTiCrN coated carbide tools which shows encouraging potential of these tools to hard turning. Improvement in tool life of almost 20–25% has been observed under minimum quantity lubrication (MQL) due to better cooling and lubricating effects. However, this effect was more prominent at higher cutting speed of 150 m/min.     

Experimental method to analyze the oil mist impingement over an insert used in MQL milling process

This paper proposes an original method to determine the oil mist impingement over an insert based on different machining configurations (rotation velocities) and different inner canalization designs, without material removal, on milling tool. The oil mist spray is determined using different holders as an insert. Glass plate and blotting paper are used and evaluated in this work to get as much information as possible, based on micro–macro scale observations. The imprint size of the oil mist spray distribution, the particle sizes and the fluid film formation have been studied to determine the effects of the different configurations on the oil mist impingement behavior. The droplet impingements and distributions on the glass plate are analyzed under a 3-D profilometer (microscopic scale). On the blotting paper, the distributions are analyzed with pictures of the oil marks (macroscopic scale). This original method gives quite fast particle distributions that can be used in industry. The different experimental results give large information about the oil mist behavior sprayed on the glass plate. Increasing rotation velocities increases the oil mist amount in the cutting area. Increasing the canalization orientation design gives a better focused spray. The rake angle has strictly no influence on the oil mist spray distribution. But sputtering effects have been highlighted and should be avoided to keep MQL efficiency.