无铅波峰焊设备的特点

相对于传统的Sn-Pb焊料,无铅焊料需要较高的焊接温度,而且润湿性差,另外免清洗助焊剂和水溶性助焊剂的固体含量低,活性温度高和活性区间窄。无铅焊料和助焊剂的特性决定了无铅波峰焊设备在结构和材料选用上有很大不同。通过对无铅波峰焊设备的各个部分的特点进行分析,为传统的旧波峰焊设备的改造提供参考。     

汽油喷雾撞壁雾化的数值模拟

撞壁雾化是现代直喷式中小缸径发动机中普遍存在的现象,研究撞壁雾化的特性对改善发动机的燃烧具有重要的意义。根据Mundo等人提出的飞溅喷雾撞壁模型,对定容室中的汽油喷雾撞壁现象进行了模拟计算与分析。通过改变壁面温度、壁面粗糙度、喷雾速度及网格数,对比分析了不同条件下喷雾撞壁过程发生的变化,为进一步进行喷雾撞壁试验、完善喷雾撞壁模型提供了参考。     

海洋非成岩天然气水合物原位快速制备实验及评价

我国的海洋天然气水合物（以下简称水合物）资源主要分布在沿海大陆架水深介于300～3 000 m的深水区，具有弱胶结、非成岩的特征，为了测试和研究该类型水合物必须原位、大量、快速制备样品，而目前常用的搅拌法、喷淋法、鼓泡法等制备技术却存在着生成速度慢、储气密度低等问题。为此，自主设计、研制了1 062 L非成岩水合物快速制备釜，针对我国南海非成岩水合物的物性特征，开展了搅拌法、鼓泡法、喷淋法单一制备方法及“三合一”法（上述3种方法相结合）水合物制备实验，测试了实验过程中温度、压力、电阻率及反应时间等数据，分析比较了几种不同制备方法的水合物生成情况与制备效率。实验结果表明：①搅拌法、鼓泡法、喷淋法制备水合物过程中，生成的水合物均缓慢增加并逐渐铺满整个液面；②搅拌法制备过程中可以观测到明显的诱导期，而喷淋法、鼓泡法及“三合一”法却无明显的诱导期；③单一制备方法及“三合一”法制备水合物过程中，电阻率均随反应时间的增加而增加，其变化趋势亦与水合物制备速率基本一致；④“三合一”法的制备周期明显短于单一制备方法（搅拌法、喷淋法、鼓泡法单一方法的制备时间分别约为“三合一”法的5.14倍、3.59倍、3.16倍）。结论认为，所研制的1 062 L水合物快速制备釜能够实现海洋非成岩水合物样品的原位、快速制备；较之于单一制备方法，“三合一”法大大提高了水合物的制备效率。     

Homogeneous polymer/filler composite membrane by spraying method for enhanced direct methanol fuel cell performance

In this work, composite membranes for a direct methanol fuel cell (DMFC) were prepared using a spraying method to improve cell performance especially at a high methanol concentration. Nafion polymer and mordenite as a filler were used for the composite membrane preparation using a spraying method and a conventional solution casting method and the membranes from the two methods were compared. SEM images showed that a more homogeneous composite membrane could be obtained using the spraying method. The effect of mordenite content was also studied. The membranes were consequently characterized and tested in DMFC operation. The results were compared to those prepared using the solution casting method at 30, 50, and 70 °C with methanol concentrations of 2, 4, and 8 M. It was found that the membrane with 5 wt.% mordenite from the spraying method showed a vast improvement in DMFC performance. When the cell was operated at 70 °C, the maximum power density of 5 wt.% mordenite from the spraying method was higher than that of commercial membrane and 5 wt.% from the solution casting method. Power densities from the 5 wt.% sprayed membrane were higher by around 29%, 40%, and 60% at 2, 4, and 8 M methanol concentration, respectively.     

Research on mine dust suppression by spraying: Development of an air-assisted PM10 control device based on CFD technology

In order to solve the serious pollution problem of PM10 in a fully mechanized mining face, focusing on the drum cutting process which produces the most dust, a new type of shearer sprayer is developed in the paper. At present, it is difficult for a single spray device to meet the dust control demands of a mine. Therefore, in combination with the airflow-carrying-droplet mechanism, a fan is added to the shearer’s spray device to develop an air-assisted PM10 control device. A No. III nozzle is optimally chosen following the spray experiments, and CFD software is used for a numerical simulation of the 4307 fully mechanized mining face of the Bailu Coal Mine. According to the airflow and spraying field distribution, it is observed that when the spray device’s pressure is 8 MPa, the spraying field’s microscopic parameters are more conducive to the settling of PM10 by the mist droplets. The PM10 data measured at 1^#-3^# measuring points of the 4307 fully mechanized mining face of the Bailu Coal Mine have shown that the best PM10 settling effect is at a spraying pressure of 8 MPa. The PM10 concentrations at 1#-3# measure points were reduced to 0.987 mg/m³, 0.405 mg/m³ and 0.262 mg/m³ respectively, with the dust control rate being above 90%. Thus the serious PM10 pollution problem in a fully mechanized mining face has been solved effectively.     

Rolling contact fatigue of alumina ceramics sprayed on steel roller under pure rolling contact condition

The rolling contact fatigue of sprayed alumina ceramics with a nominal composition of Al₂O₃–2.3 mass% TiO₂ was studied with a two-roller test machine under a pure rolling contact condition with oil lubricant. The influence of undercoating of sprayed Ni-based alloy on the rolling contact fatigue was investigated. The failure mode of all sprayed rollers was spalling caused by subsurface cracking. The undercoating did not contribute to the improvement of the rolling contact fatigue life. The elastic modulus of the alumina sprayed layer evaluated with the nano-indentation method was around 85 GPa. The depths of the observed subsurface cracks corresponded approximately to the depths where the orthogonal shear stress or the maximum shear stress calculated with two-dimensional FEM became maximum.     

用Fick第二定律描述混凝土中氯离子浓度分布的适用性

结合室内试验及现场试验所测得的氯离子浓度分布，与Fick第二定律给出的氯离子浓度分布曲线进行比较．分析了不同侵蚀环境下氯离子浓度分布的特点并计算了其与Fick分布两者间的相关性。结果表明，Fick第二定律适用于室内试验环境、现场盐雾作用环境和海水浸泡环境，经适当修正后，还可适用于有碳化或硫酸根影响的环境，但不适用于海水反复淋溅作用下的环境。     

超音速火焰喷涂Cr_3C_2-25%NiCr涂层的滑动摩擦磨损性能研究

采用超音速火焰喷涂工艺制备了Cr_3C_2-25%NiCr陶瓷,对涂层的组织结构、显微硬度及在滑动摩擦条件下的失重进行了分析,得出了涂层摩擦因数与时间的关系,对涂层的滑动摩擦磨损机理进行了分析。结果表明Cr_3C_2-25%NiCr涂层致密,孔隙率为0.96%,涂层截面的显微硬度平均值HV_(0.3)为867。涂层稳定的摩擦因数为0.1。初始阶段涂层的磨损主要是磨屑对涂层的磨粒磨损作用,摩擦稳定后涂层的磨损主要是由于相对运动面的磨削作用。     

陶瓷粉末等离子喷涂技术的应用

通过实例,阐述了等离子喷涂陶瓷粉末技术应用中应注意的技术问题。     

等离子喷涂工艺参数对B4C涂层性能的影响

本文研究了喷涂距离对大气等离子喷涂Ｂ４Ｃ涂层的沉积效率、气孔率、显微硬度和抗热震性能的影响,发现喷涂距离会严重影响Ｂ４Ｃ粉末在等离子体射流中的熔融状态,从而对这些性能产生显著影响。实验结果表明,通过优化工艺参数,尤其是选择适当的喷涂距离,可以在大气呀涂条件下制得同高压等离子喷涂相近所孔率和显微硬度的Ｂ４Ｃ涂层。