Back Matter

Abstract

Droplets of several non-ferrous metals and alloys were solidified on a chill plate and the shape of the bottom after cooling was measured to study the basic deformation behaviour of the initial solid skin. The shape was always parabolic. Deformation of pure metals was positive, i.e. convex towards the chill, and was found to be caused by thermo-elastic deformation after solidification. Deformation of the alloys was positive or negative, depending on the composition. Particularly-large negative deformation was observed near the eutectics of Al-Si and Bi-Sn alloys. The cause is precipitation of secondary phases of large specific volume, such as Si or Bi in supersaturated solid-solution after solidification. The findings are expected to be applicable to the understanding of surface defects in continuously-cast steel and heat transfer phenomena in the mould.     

Back Matter

The inherent difficulties of plating zinc alloy die-castings can only be overcome if care is taken at every stage, beginning with the actual design of the castings. The die-casting technique and the polishing operations are just as important to the plater as the processes directly under his control. From special solutions, nickel may be deposited directly, although usually the deposit obtained is less satisfactory and the plating control more critical than with ordinary nickel solutions. Preliminary deposition of copper is of more general application, and the introduction of the Rochelle-salt solution has removed many of the difficulties previously associated with cyanide-copper plating. This solution requires careful operation, but the results obtainable justify the extra control needed. If a few pre- cautions are taken, chromium, silver, brass and metal colour finishes may be deposited without difficulty.     

Back Matter

Abstract

An investigation has been carried out on the mechanism relating to the nodularisation of eutectic silicon by potassium in as-cast aluminium alloys, under conditions of unidirectional solidification. Potassium is the only modifying element which, until now, appears to nodularise eutectic silicon. Powerful modifying agents, such as potassium, together with endogeneous growth in Al-Si alloys, are prerequisites for the nodularisation of eutectic silicon. The basis of the mechanism depends on the way potassium concentrates at the solid-liquid interface of the silicon and changes the mode of eutectic growth from co-operative to renucleation. The twin angles of silicon are poisoned, making growth impossible by a twinning mechanism. Thus, silicon growth is hindered, the shape of the eutectic silicon changing from a lamellar or fibrous form to a nodular shape.     

Back Matter

Abstract

This paper is concerned with the experimental determination of thermomechanical properties of a cold box sand, which have a strong influence during the solidification in a sand casting process. To this end, the uniaxial behaviour for different temperatures up to the casting temperature of an aluminium alloy is investigated. For the tests at room temperature, the authors use optical measurement equipment, which is ideally suited to measure inhomogeneous deformations and strains within the material specimens. Furthermore, different strain rates are applied to analyse rate dependent behaviour. The storage time of the sand is also varied, since it influences the material characteristic of the binder in the cold box. An effective heating procedure is developed to characterise the mechanical material behaviour due to different isothermal loadings. The pressure dependence of multiaxial stress states is investigated in a pressure cell. The experimental data are intended to develop and identify a material model for sand, taking into account the strength–differential effect (S–D effect), rate and temperature dependence and the effect of hydrostatic stress states.     

浅析前纵梁后部本体反弹的一般整改方法

前纵梁后部本体在整车中对产品的强度要求较高,同时匹配关系比较复杂,精度要求高,因此如何实现整改前纵梁后部本体的反弹,对发舱及整车具有非常重要的意义。     

数控反锪刀具的设计

介绍了一种数控反锪刀具的设计及其工作原理。这种刀具非常适合 Ｎ Ｃ／ Ｃ Ｎ Ｃ 机床,特别是可用于封闭空间的反锪加工     

带包类后桥壳的铸造技术

介绍带包类球墨铸铁后桥壳铸件的生产工艺.通过合理熔炼、造型、制芯及铸造工艺参数,采用冲天炉熔炼,手工造型制芯,实现批量生产优质带包类桥壳球铁件.     

可调向靠背式测速探头测向方法的实验验证及标定系数研究

为解决流场中速度、方向的测量问题，自行设计了一种新型的可调向靠背式测速探头，本文介绍了此测速探头的测向方法，通过实验验证了此方法的可行性，并对标定系数曲线进行了测试。     

某过滤器体上白色多余物分析

某宇航设备上所用气体过滤器在使用过后,发现表面及内壁上都残留有白色物质。采用扫描电镜SEM对其成分进行能谱分析,并对白色物质形貌以及周围基体的形貌进行宏、微观观察。在与正常表面进行了对比的基础上,分析白色物质成分以及出现白色物质的原因。结果表明：此气体过滤套筒内圈存在腐蚀现象;白色物质并非套筒上滤纸所致,其氧含量较高,可能是腐蚀液体与基体作用形成的水合物。     

"起死回生"的拼装汽车

一把焊枪,一柄铁锤,一个简单的龙门吊,几个"野"修理工,兰州市一些小型汽车修理厂就可以把普通的报废卡车"大卸八块",用废弃零件和劣质钢材翻新、改造成"崭新"的自卸车.而这些起死目生的"拼装车"改头换面后冠冕堂皇的流入二手车市场上市交易.     

黄金在医学上的奇特疗效重放异彩的黄金

黄金被称为“金属之王”,自古以来便成为达官贵人显示荣华富贵的象征,而用金子制成的金戒指、金项链、金耳环更是人们喜爱的装饰品。而且由于黄金能耐高温,不易被氧化并具有特殊的杀菌作用,因此还被医学界用来为病人治病,收到了奇特的效果。     

“起死回生”的拼装汽车

一把焊枪,一柄铁锤,一个简单的龙门吊,几个野修理工,兰州市一些小型汽车修理厂就可以把普通的报废卡车大卸八块,用废弃零件和劣质钢材翻新、改造成崭新的自卸车。而这些起死回生的拼装车改头换面后冠冕堂皇的流入二手车市场上市交易。     

后纵臂的断裂原因分析

汽车在试验场行驶21 000 km后发现后纵臂断裂,该类后纵臂曾多次发生断裂故障。后纵臂在使用过程中受拉、压、扭等复杂载荷。通过对后纵臂进行外观观察,对其断口进行宏、微观观察,并对后纵臂进行金相组织检查、硬度检查及有限元模拟,确认后纵臂的失效性质,并分析其断裂原因。结果表明:后纵臂的失效性质为疲劳断裂;后纵臂的断裂过程为:在压应力作用下后纵臂中间安装孔处首先发生失稳变形,当后纵臂再次受拉时最大应力转移到中间安装孔处,在交变载荷的作用下发生疲劳开裂。适当增加后纵臂的厚度以提高其刚度,厚度增加后的后纵臂未再发生过类似的断裂故障。