用双重曲柄滑块机构范成加工高速凸轮的研究

通过对高速凸轮的设计加工问题进行研究,提出了一种新型的由双重曲柄滑块机构组成轮轮廓范成装置。对该范成凸轮的运动动力学进行了分析,并对加工刀具的误差补偿及其它主要的加工工艺进行了简要讨论。     

高速瓦楞辊啮合与纸板成型理论

通过建立移动式和摆动式统一形式下的瓦楞辊啮合运动坐标系 ,得出了统一的两辊啮合方程组与纸板成型的关系 ,应用计算机编程求解得出了齿廓全部啮合点的通解 ,并得到了运动学性能图谱     

细间距SMD焊接强度试验研究

通过对细间距SMD焊接强度试验 ,分析了影响焊接强度的诸多因素 ,找到适合SMT要求的焊膏、模板、焊膏量、温度曲线等系列工艺材料参数。     

Process simulation using finite element method — prediction of cutting forces, tool stresses and temperatures in high-speed flat end milling

End milling of die/mold steels is a highly demanding operation because of the temperatures and stresses generated on the cutting tool due to high workpiece hardness. Modeling and simulation of cutting processes have the potential for improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. The main objective of this study was to develop a methodology for simulating the cutting process in flat end milling operation and predicting chip flow, cutting forces, tool stresses and temperatures using finite element analysis (FEA). As an application, machining of P-20 mold steel at 30 HRC hardness using uncoated carbide tooling was investigated. Using the commercially available software DEFORM-2D™, previously developed flow stress data of the workpiece material and friction at the chip–tool contact at high deformation rates and temperatures were used. A modular representation of undeformed chip geometry was used by utilizing plane strain and axisymmetric workpiece deformation models in order to predict chip formation at the primary and secondary cutting edges of the flat end milling insert. Dry machining experiments for slot milling were conducted using single insert flat end mills with a straight cutting edge (i.e. null helix angle). Comparisons of predicted cutting forces with the measured forces showed reasonable agreement and indicate that the tool stresses and temperatures are also predicted with acceptable accuracy. The highest tool temperatures were predicted at the primary cutting edge of the flat end mill insert regardless of cutting conditions. These temperatures increase wear development at the primary cutting edge. However, the highest tool stresses were predicted at the secondary (around corner radius) cutting edge.     

某细粒贫硫金矿石选矿工艺研究

陕西某金矿石中主要为微粒和超微粒自然金，主要为粒间金和部分包裹金，为合理开发利用该金矿资源，针对该矿石性质进行了重浮联合流程选别试验，重选利用尼尔森选矿机进行试验。试验最终获得的金精矿1金品位5 250 g/t，对重选尾矿进行浮选，获得的金精矿2金品位41.17 g/t，金总回收率达95.45%，尾矿金品位0.09 g/t。相较于单一流程，联合工艺的应用有助于获得更好的选冶指标，使矿产资源得到合理的开发利用。     

Bubble growth obtained from pressure fluctuation in vibration separation fluidized bed using wavelet analysis

The dynamics of pressure induced bubble in vibration separation fluidized bed was identified and investigated by calculating the correlation of the approximate signals at different levels. Effects of gas velocity, vibration frequency, vibration amplitude and static bed height on the correlation coefficients of pressure signals at levels A₇ and A₈ were studied. It was shown that the correlation coefficients of A₇ and A₈ scale signals first increase and thereafter decrease with the increase in gas velocity, vibration frequency, amplitude, and static bed height parameters. Meanwhile, the formation and aggregation of bubbles can be effectively suppressed by vibration within the height range of 90–140 mm under the condition of A = 2 mm, f = 20 Hz, and v = 14 cm/s. In addition, the E values of the separation accuracy of 1–3 mm raw coal reaches the minimum, which indicate that fine coal has achieved the criteria of ash reduction and quality improvement after sorting.     

构建精细化工教学新模式,培养创新型综合型人才

论述了民族院校开设精细化工课程的重要意义,并探讨了精细化工课程在教学中如何根据民族院校的特点,选择有关的教学内容及实验教学内容,同时对精细化工课程及精细化工实验的教学方法的改革进行了探讨。     

Evaluating the rollover propensity of trucks—A roundabout example

The rollover propensity of SUVs and trucks has long been recognized as a potential safety issue. The propensity may increase with the growing number of roundabouts that are being built on high-speed roadways designed for 50 mi/h or higher. This paper presents a research methodology developed to evaluate the rollover propensity of trucks on existing roundabouts and other roads with tight curves and high-speed traffic. The research objective was accomplished by developing an advanced 3D model of rollover that is applicable to field observations of the undisturbed behavior of multiple vehicles. This model was supplemented with a nonintrusive method of data collection based on recording video from a remote location and a novel method of extracting the data from the video material and processing it to generate the input required by the rollover model. The method is demonstrated in this paper on an example roundabout by evaluating the rollover propensity of semi-trailers in daytime and nighttime conditions. The results indicate that the drivers observed in nighttime conditions compensated well for the challenging conditions by driving more cautiously, which led to their rollover propensity at night being lower than during the day. The method was found useful for timely detection of the potential rollover problem without waiting for crashes.     

Cooking‐related PM2.5 and acrolein measured in grocery stores and comparison with other retail types

We measured particulate matter (PM), acrolein, and other indoor air contaminants in eight visits to grocery stores in California. Retail stores of other types (hardware, furniture, and apparel) were also sampled on additional visits. Based on tracer gas decay data, most stores had adequate ventilation according to minimum ventilation rate standards. Grocery stores had significantly higher concentrations of acrolein, fine and ultrafine PM, compared to other retail stores, likely attributable to cooking. Indoor concentrations of PM_2.5 and acrolein exceeded health guidelines in all tested grocery stores. Acrolein emission rates to indoors in grocery stores had a mean estimate about 30 times higher than in other retail store types. About 80% of the indoor PM_2.5 measured in grocery stores was emitted indoors, compared to only 20% for the other retail store types. Calculations suggest a substantial increase in outdoor air ventilation rate by a factor of three from current level is needed to reduce indoor acrolein concentrations. Alternatively, acrolein emission to indoors needs to be reduced 70% by better capturing of cooking exhaust. To maintain indoor PM_2.5 below the California annual ambient standard of 12 μg/m³, grocery stores need to use air filters with an efficiency rating higher than the MERV 8 air filters commonly used today.     

高耸烟囱不同爆破切口位置破坏过程摄像观测分析

为了解高大钢筋混凝土烟囱在倾倒过程中不同爆破切口位置处预留支撑体及切口上、下部筒体的破坏过程,采用高速摄影技术对其进行了观测。通过对比分析,得到了它们在倾倒过程中的破坏规律,为类似爆破工程的设计和参数选择提供参考。