粉末和纤维多孔材料的技术发展和应用

在粉末冶金工业发展初期的30年代,就开始多孔制品的生产,当时主要制造轴承和过滤器,近20多年来金属粉末多孔零件主要是用10%青铜和315L型不锈钢。但近来随着对耐腐蚀性、耐热性和过滤性能不断提高的要求,发展Hastelloys(耐盐酸镍基合金)、lnconel(铬镍铁合金)或其他镍基材料以及钛、铌、锆等粉末多孔制品。此外,在发展粉末多孔制品的同时,还发展金属纤维烧结多孔制品。     

数控机床热误差测试中的温度传感器研究

热误差是造成数控机床加工精度下降的主要原因之一,对机床温度敏感点的精确测量是进行热误差研究的前提条件。本文介绍了2种自行研制的温度传感器,并对各种传感器性能进行了分析和比较,最后给出了机床温度敏感点测量专用传感器的设计思路。     

洛氏硬度测试误差的原因及防止方法

硬度测试是衡量工件质量优劣的重要标志,而测试是靠硬度计来实现的。由于硬度计、被测件本身存在的问题和环境的影响,以及操作者的经验及熟练程度的限制,在测试中不免要产生一些误差,若误差较大又未被发现致使工件返工给生产造成损失。因此,弄清产生误差的原因及防止方法很有必要。     

机电式预付费电能表的误差分析与测试

讨论机电式预付费电能表的误差计算、测定和调整方法。     

机床主轴回转误差测试系统的研究

针对机床主轴测试方法中存在的测量基准安装偏心的问题,提出了一种有效的解决方法,从测量原理、误差信号的处理等方面来阐述测试方法,最后通过实验对测量结果进行分析,实现了对测试方法的研究.     

基于计算机测试技术的瓷砖误差检测系统研发

本文介绍了一种使用单片机控制的,采用位移传感器作为测量元件的计算机测试系统,在系统的组成、检测原理和数据处理等方面进行了较详细的叙述.应用这种系统对瓷砖误差进行检测,对于提升瓷砖的检测手段,提高检测的准确性和效率具有实际应用价值.     

高速主轴回转误差测试装置研究

主轴回转误差是影响加工精度的关键因素,利用3个电涡流传感器对安装在主轴前端的标准棒进行动态测试,利用设计好的支架,将3个电涡流传感器安装在主轴三维笛卡尔坐标的3个方向上,电涡流采集的3个方向上的位移信号在计算机中显示.通过试验研究,实现了良好的检测结果.     

多孔材料的应用研究与发展前景

针对多孔材料的性能特征、制备方法及应用领域,分析得到多孔材料在未来研究中将面临的主要问题,并对多孔材料的应用研究及发展趋势做出了科学预测及前景展望。     

石墨多孔材料孔隙率测定方法研究

孔隙率是多孔材料的关键指标,是多孔材料若干性能最主要的决定性因素。采用质量体积法、浸泡介质法和压汞法3种实验方法测定多孔石墨材料的孔隙率,并对测定结果进行比较分析。结果表明:浸泡介质法测量的是开口孔隙率,因而数据偏小;质量体积法与压汞法测试结果相差不过5%,表明质量体积法是一种简单可行的孔隙率测定方法。     

机床主轴回转误差测试研究

以LabVIEW为平台,设计了主轴回转误差实验系统。该系统由位移测试单元、采样时钟单元、数据采集卡及通用计算机组成。用于主轴回转精度的实际测量,取得了良好效果。     

Apparent thermal conductivity approach at high-temperature measurements of porous materials

The apparent thermal conductivity approach for high-temperature investigations of porous materials taking into account moisture transport, convective and radiative modes of heat transport, phase-change processes and chemical reactions is presented. Methods for the measurement of apparent thermal conductivity as a material characteristic are analyzed. An example of the practical application of the approach is given, for a hybrid-fiber reinforced cement composite exposed to high temperatures up to 1000 °C. The aspects of the utilization of apparent thermal conductivity as a tool in an assessment of porous materials and their multi-layered systems exposed to high temperatures are discussed.     

Static thermal conductivity methods for solid materials

Various experimental arrangements for the determination of steady-state thermal conductivities, as adopted for different situations, are reviewed. The case where the sample geometry and dimensions are imposed is treated distinctly from that where they may be chosen by the experimenter. In the latter case, it is shown that the set-up adopted may vary significantly according to the magnitude of the conductivity, the temperature range investigated, the geometry, and the dimensions of the samples available. Some devices which were recently developed in the author's laboratory are taken as illustrative examples and briefly discussed.     

Analysis of thermal conductivity in HI-LEDs lighting materials

The present study devised a measurement system to estimate the thermal conductivity of electronic product materials, especially in HILEDs lighting materials, exhibiting distinct thermal characteristics by conducting thermal performance experiments and theoretical analyses. First, steady-state conduction analysis with thermal resistance method was investigated on three composite material substrates of unknown heat conduction coefficients through a substrate material named Bakelite of low thermal conductivity revealing stable quality. Second, one-dimension semi-infinite transient conduction analysis was utilized to investigate metal materials with high thermal conductivities. Results showed that the Bakelite experimental module was verified for 62.5 % of the original wattages, which closest to the thermal conductivity 0.233 W/m-K of the Bakelite. And these composite materials M1, M2 and M3 composed of polymer and epoxy were 1.311, 0.844 and 2.403 W/m-K, respectively. The thermal performance experiments were investigated and the results have proved the correctness of the theoretical model. According to the experimental results, calculating the temperature value of the metal materials comprising cotton insulation and the transient analysis, this study determined the temperature error to be less 20 %. Consequently, a transient measurement system and method for metal materials with high heat conduction coefficients was established. Finally, the results of this work are the useful thermal conductivity method to facilitate rapid analysis in the future.

     

The measurement of thermal conductivity variation with temperature for solid materials

An apparatus was designed to routinely measure the thermal conductivity variation with temperature for solid materials. The apparatus was calibrated by measuring the thermal conductivity variations with temperature for aluminum, zinc, tin and indium metals. The variations of thermal conductivity with temperature for the Zn-[x] wt.% Sb alloys (x = 10, 20, 30 and 40) were then measured by using the linear heat flow apparatus designed in present work. From experimental results it can be concluded that the linear heat flow apparatus can be used to measure thermal conductivity variation with temperature for multi component metallic alloys as well as pure metallic materials and for any kind of alloys. Variations of electrical conductivity with temperature for the Zn-[x] wt.% Sb alloys were determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity. Dependencies of the thermal and electrical conductivities on composition of Sb in the Zn–Sb alloys were also investigated. According to present experimental results, the thermal conductivity and electrical conductivity for the Zn-[x] wt.% Sb alloys decrease with increasing the temperature and the composition of Sb.     

A unit for measuring the effective thermal conductivity of thin-layer materials

An experimental setup for determination of the absolute values of thermal-conductivity and heattransfer coefficients of thin-layer spacers at room temperature and higher is described. The experimental data processing procedure is given.     

Particle deposition in random fibrous porous materials: effect of acoustic fields,fibres distribution and porosity

Porous filters are widely used to control air pollution and have different industrial applications since they constitute a reliable and low cost solution to separate particulate matter from an air stream.In this study, the particle deposition within 3D porous filters subjected to low-frequency acoustic fields is studied following a numerical approach. Findings demonstrate that the application of acoustic waves enhançes the deposition of particles, which in turn improves filter performance. It is shown that frequencies ranging from 200 to 1000 Hz (intensity 120 dB) increase particle deposition up to 2.5 times. Besides, the manner in which fibres are distributed in the porous material and the filter porosity affect considerably the number of particles deposited, for filters subjected to the same filtration velocity.     

A model for prediction of the effective thermal conductivity of granular materials with liquid binder

A model is developed to predict the effective thermal conductivity of a three-component system containing sand particles bonded with liquid binders. The effective thermal conductivities of the bonded and unbonded sands are measured by the line-heat-source method at room temperature. The parameters of a two-component model are determined from the measurements for unbonded sands. Finally the model for the three-component systems such as bonded sand is developed using the assumption of the coalescence of the liquid binder at the particle contact points. Comparison between the experimental results and the model predictions shows that the model developed in this study predicts well the effective thermal conductivities of fluid-saturated sand or sand bonded with liquid binders. Also, this model can be used to determine the effects of the parameters such as the thermal conductivities and the volume fractions of components and the geometrical characteristics of solid particles on the effective thermal conductivity of granular materials with or without the liquid binder.     

Laser flash method for measuring thermal conductivity of liquids-application to low thermal conductivity liquids

A laser flash method developed for the measurement of thermal conductivity of solids was applied to liquids of low thermal conductivity. The sample liquid was sandwiched in between a small thin metal disk and a sample holder. When the laser beam is absorbed in the front surface of the metal disk, the temperature of the disk quickly rises about 2 K and heat then flows downwards through the sample liquid as one-dimensional heat flow. The thermal conductivity of liquid can be obtained from the temperature fall of the disk without employing any reference materials and also without measuring the thickness of the sample liquid layer. Thermal conductivities of water and toluene near room temperature were measured by this method with a mean deviation of 2.6%. This laser flash method may be applied to the measurement of the thermal conductivity of liquids such as molten salts at elevated temperatures.