Improvement of butt-welding characteristics of double wall polyethylene pipes

In this study, a new heat plate with a groove for butt-welding was developed to investigate the misalignment effects on the joining strengths of polyethylene double walled pipes. Thermal analyses of the material determined the temperature profile of the welding. After the welding, the joining characteristics of the pipes were compared with those welded by the conventional heat plate. The results of the stiffness and flattening tests showed that there were no big differences between the joints made from these two plates. In the leakage test, however, the pipes welded with the conventional heat plate leaked below the required test conditions, while the pipes welded with the grooved heat plate did not show any leakage, even in a range higher than the required conditions. The tensile and bending strength were also improved. The results demonstrated that the grooved heat plate accomplished more complete fusion at the pipe joints and induced high quality joints.     

Phase change flattening process for axial grooved heat pipe

A novel processing technique named phase change flattening process has been developed to fabricate the flattened grooved heat pipes, which are in high demand for electronics cooling. The phase change vapor pressure in the flattened heat pipe is analyzed on the basis of its operating principle. An elasto-plastic FEM simulation is proposed to analyze stress and strain distribution for the flattening process. An experiment is also set up to verify this elasto-plastic deformation of axial grooved heat pipe (AGHP). Results show that the vapor pressure is determined by the saturated vapor pressure equation of heat pipe. Punch load of the upper plate greatly increases due to its higher vapor pressure and the buckling phenomenon can be well eliminated when the vapor pressure reaches 1.002 MPa at vapor temperature 453 K. The maximum equivalent plastic stress and strain distribute on the maximum bend points at the bending wall of heat pipe when the punch stroke is over 3 mm. The width, vapor area and grooves of flattened heat pipe change greatly as the flattening proceeds.     

锆合金薄壁管三点弯校直中的截面扁化

锆合金薄壁管类零件是核电站中重要零件,校直中会出现截面扁化现象。应用弹塑性原理研究锆合金薄壁管校直变形中的应力和应变,在设定平面位移函数为三角级数条件下,建立了锆合金薄壁管类零件扁化率计算公式,对直径72mm、壁厚2mm、支点距离600mm的锆合金管进行校直实验,在11000N载荷下截面发生扁化变形,结果表明,截面扁化率计算公式对锆合金管校直有一定指导意义。     

扁平沟槽烧结吸液芯热管的设计与制造

随着电子芯片热流密度的急剧增加及有效散热空间的日益狭小,具有高热导率、高可靠性、快热响应、无需额外动力等特点的扁平热管已成为电子领域使用的理想导热元件。提出了沟槽烧结吸液芯扁平热管的加热相变压扁制造方法;理论分析了加热相变压扁制造过程中热管几何形状变化和热管弹塑性大变形的成形过程,并进行了实验测试。结果发现：相变压扁过程作用机制为热管内部的饱和蒸汽压方程;相变压扁过程中,热管几何形状变化很大,最大等效塑性应变主要发生在扁平段吸液芯/蒸汽界面上;当压扁温度为480 K时,压扁热管的屈曲率微小,可忽略不计;相变压扁力随着压扁温度的升高和压扁位移的增大而增大。     

EIZ80空分机壳铸造工艺

针对EIZ80机壳铸造工艺特点,采用组芯造型、抽芯式模型结构,运用均衡凝固理论设计浇注系统.采用分散3层阶梯式浇注系统,用陶管分别从铸件的底层、中间和最上层引入等工艺措施,成功浇注出铸件内在质量好,表面光洁,加工过程中无铸造缺陷的EIZ80机壳铸件,实现了国产化铸造.     

Fracture Surface Analysis in HDPE Pipe Material Fatigued at Different Temperatures and Loading Frequencies

Effect of temperature and loading frequency on the fatigue fracture process in high-density polyethylene (HDPE) pipe material has been investigated in this study via optical and scanning electron microscopy. Fatigue tests were performed using rectangular coupons obtained by slitting and flattening 50-mm-wide ring sections from 4-inch schedule 80 HDPE pipes. The flattening was carried out in a specially designed compression fixture at a temperature of 105?°C. Fatigue tests were conducted at temperatures of 0, 23, and 40?°C and loading frequencies of 0.1, 1, and 50?Hz. Fracture surface examinations reveal that the fatigue crack-growth process at all the test temperatures and loading frequencies involved mechanisms of shear yielding and crazing. Crack growth via crazing was found to be the dominant mechanism at higher temperature of 40?°C, while at 0?°C, a small amount of initial shear yielding precede the crazing process. Filler material particles contained in the HDPE pipe material play an important role of stress concentrators and help in micro-void nucleation, which promotes crack growth via crazing. The fatigue resistance of HDPE may thus be improved by addressing the stress concentration effect of filler particles.     

模具结构及参数对厚饼类锻件内部质量影响

为了提高厚饼类锻件内部质量,减少探伤密集性缺陷,对锥板镦粗+展平工艺及平板镦粗工艺进行了数值模拟分析。对比了两种成形方式对锻件内部金属运动轨迹、最终位置及等效应变分布的影响,同时对锥板镦粗+展平工艺中锥板夹角α及锥顶平台长度h对锻件内部质量的影响进行研究,从而为确定正确的锥板镦粗+展平工艺方案提供依据。     

中厚板纵向边裂产生原因与控制方法

针对中厚板纵向边裂问题,研究了其形成机理,对轧钢工序中加热制度,上、下工作辊辊径,辊速配比对钢板上、下表面边部变形均匀性的影响进行了工业试验研究。结果表明,通过调整加热制度及上、下工作辊辊速可改善钢板上、下表面变形均匀性,将钢板下表面边裂控制在距边部30mm内,钢板切边后可以完全消除纵向边裂,使钢板合格率达90%以上。     

Optical and Electrical Properties of Heterogeneous Coatings Produced by Aluminum Powder and Boehmite Suspension Plasma Spraying

Spectral selective materials have attracted an increasing interest because of Concentration Solar Power Plant. Those materials are expected to exhibit specific optical properties at temperatures higher than 450?°C. Plasma-spraying process is commonly used to manufacture high-temperature coatings. In this study, heterogeneous coatings made of aluminum and alumina were produced by spraying both powder and suspension of boehmite clusters. Both optical and electrical properties were measured because, according to the Hagen-Ruben??s law, the higher the resistivity the lower the reflectivity. The reflectivity was assessed by spectrometry at 10???m and the resistivity by the four-points technique. The results were combined with the diameter of flattened lamellae and the volume fraction of alumina in the coatings. Then the highest reflectivity is achieved with a metallic coating exhibiting high flattening degree, while the coatings containing a large amount of alumina exhibit the lowest reflectivity and the highest resistivity.     

On the processing,microstructure, mechanical and wear properties of cermet/stainless steel layer composites

This study deals with layer composites of carbide reinforcements and stainless steel prepared successfully by powder technology. The layer material consisted of two layers. The top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as the binder material for the carbides. The bottom layer was entirely of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the top layer (TiC–NbC/465 stainless steel) showed the typical core–rim microstructure of conventional steel bonded cermets and the bottom layer showed the structure of sintered steel. An intermediate layer was found with a gradient microstructure, having a higher carbide content towards the cermet layer and lower carbide content towards the stainless steel layer. The bending strength of the layered material measured in the direction perpendicular to the layer alignment was remarkably high. The variation of strength as a function of the thickness of the bottom layer revealed that the character of the material changed from the cermet, to a layer composite and then towards metallic materials. The wear resistance of the top layer was studied against high speed steel. The wear mechanisms were discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microploughing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microploughing and rapid removal of material from the wear surface was observed at high wear load. The fracture morphologies of the top, bottom and intermediate layers are reported.