室内球墨铸铁管丝扣法兰连接的密封性能分析

本文主要结合武汉恒隆广场二期购物中心及地下室工程的施工现场实际情况,通过车床对室内球墨铸铁管丝扣法兰连接进行加工,其管螺纹可选择直螺纹组合或者锥螺纹组合.进而分析了圆柱管螺纹组合、圆柱内螺纹及圆锥外螺纹组合、圆锥内螺纹及圆锥外螺纹组合的密封性能,并根据工程实际最终选择了"柱/柱"组合形式,满足项目使用要求.球墨铸铁管丝扣法兰连接的密封性能分析,可提高丝扣法兰连接的施工效率和可靠性.     

浅谈薄壁螺纹零件的滚压加工工艺

薄壁螺纹零件由于工件壁较薄,在夹紧力的作用下容易产生变形,在切削力的作用下,也容易产生振动和变形,影响工件的尺寸精度、表面粗糙度、形状精度和位置精度,利用常规的车削加工非常困难。本文主要讲述了薄壁螺纹零件的滚压加工的原理,通过案例具体阐述加工工艺和方法,提出相关建议,对薄壁螺纹零件的滚压加工具有指导意义。     

Ti-6Al-4V合金表面超声振动滚压强化研究

采用超声振动滚压加工技术对Ti-6Al-4V合金表面进行处理,探究该项技术对Ti-6Al-4V合金表面质量的影响。通过对该工艺加工前后的Ti-6Al-4V合金进行表面粗糙度参数、XRD图谱、截面微观形貌、表层残余应力及显微硬度的对比分析,结果表明:经该工艺处理后的合金表面各项粗糙度参数皆有明显降低;加工后的合金表面XRD图谱的衍射峰减弱且宽化,衍射角向高角度方向偏移;加工后的合金表层β相组织相较加工前明显细化,且随着深度增加β相组织逐渐增大;在距离表面约50μm位置的残余应力值最大可达到-967 MPa;加工后的合金表面显微硬度可达到421HV,且在0~140μm的深度范围内,显微硬度随着深度的增加逐渐减小至与基体硬度一致。经超声振动滚压加工后的Ti-6Al-4V合金表面质量显著提高,有利于提高其零部件的使用性能。     

奥氏体不锈钢管母材和焊缝的显微组织对超声检测的影响

采用金相试验手段研究了在不同焊接方法下同种奥氏体不锈钢管母材及焊缝的显微组织特性,以及在相同焊接方法下奥氏体钢管和碳钢钢管母材及焊缝的显微组织特性。用超声检测方法对试样焊缝中的人工刻槽缺陷和边缘端角进行灵敏度和信噪比的定量检测,研究了超声波在奥氏体不锈钢管和碳钢钢管中的传播特性差异。结果表明:在两种不同的焊接方法下,奥氏体不锈钢管母材及焊缝的显微组织状态基本相同,对超声检测的影响差异不大;在相同的焊接方法下,304奥氏体不锈钢管和20碳钢钢管的焊缝显微组织明显不同,超声波在奥氏体不锈钢管焊缝内的传播效果较差,检测存在一定困难;临界纵波双晶探头的灵敏度和信噪比均很高,在检测表面缺陷时能获得较好的效果。     

火焰矫正温度对SA-213TP347H不锈钢管组织和性能的影响

通过改变火焰矫正温度,从火焰矫正后钢管的硬度、显微组织以及析出相三个方面研究了火焰矫正温度对SA-213TP347H不锈钢管组织和性能的影响。结果表明:火焰矫正温度愈高,矫正后钢管的硬度则愈低;不锈钢管在火焰矫正过程中没有发生相变,始终是单相奥氏体,但矫正温度过高容易产生晶粒长大、过热甚至过烧。     

国标气瓶圆锥外螺纹基面中径的测量方法

气瓶螺纹的PZ系列和R系列,虽然均为气瓶圆锥螺纹,但是其螺纹基本牙型和参数定义不同,因此测量圆锥外螺纹基面中径的测针直径计算公式不同,且基面中径的计算公式也不同.文章依据给定的测量方法推导出相应的测针直径和基面中径的计算公式,并编制了测量软件,可以快速准确地测量气瓶圆锥外螺纹的基面中径.     

电站锅炉用TP304H不锈钢管显微组织的老化特征

应用金相、扫描电镜、透射电镜和X射线衍射等分析技术,研究了电站锅炉用TP304H不锈钢管显微组织老化的主要特征,明确了σ析出相含量与管子寿命的定量关系。结果表明：一定的压力条件下,TP304H钢管的显微组织变化与运行温度和时间相关,在设计温度下,随着运行时间的延长,TP304H钢管晶界开始析出呈链状分布的碳化物,继续运行σ相开始沿晶界（特别是三角晶界处）析出;当口相含量达到15％时,爆管几乎不可避免,因此,可以采用定量分析方法通过测定σ相含量来监测TP304H钢管的寿命。     

超超临界锅炉用E911钢管的高温性能

对德国Vallourec＆Mannesmann公司生产的159mm×27mm的E911钢管进行了力学性能、显微组织、抗氧化性能和持久强度的试验,并对供货状态的E911钢管进行了时效试验和时效后的显微组织测定。试验结果表明,在650℃下E911钢管基本不氧化,其常温性能、高温性能和持久强度都优于T91钢,完全可代替TP304H,TP321H和TP347H不锈钢管,解决了异种钢焊接问题,并可降低锅炉的制造成本。     

螺纹花键同轴零件高效同步滚压成形研究动态

螺纹花键同步滚压在一次滚压成形中可同时成形零件上不同部位的螺纹和花键齿形,克服了先后不同时间分别成形螺纹和花键生产螺纹花键同轴零件的高成本、低效率、成形质量不稳定等缺点。重点介绍了螺纹花键同步滚压成形工艺原理和特点,分别从模具和工件运动特征、滚压塑性变形行为、成形过程建模仿真等方面评述螺纹和花键滚压成形工艺的国内外研究现状,指出了螺纹花键同步滚压成形工艺应用发展所需要解决的关键技术问题。     

超声滚压对高速激光熔覆GH5188高温合金涂层组织和力学性能的影响

目的 为了提高GH5188高速激光熔覆涂层的摩擦磨损性能和耐腐蚀性能,采用超声滚压(UR)技术在GH5188涂层表面制备纳米晶层。方法 利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、能谱分析仪(EDS)、维氏硬度计、高温摩擦磨损试验机和电化学工作站研究超声滚压作用下GH5188涂层的微观形貌、相组成、显微硬度、高温摩擦磨损性能和耐腐蚀性能。结果 超声滚压后,GH5188涂层表面达到镜面效果,与未滚压相比,粗糙度下降58%;制备出厚度为18 μm的纳米晶层;与H13基体相比,未滚压的涂层表面显微硬度提高21%,超声滚压后的涂层表面显微硬度提高70%;与H13基体相比,未滚压的涂层耐磨性提高69%,超声滚压后的涂层耐磨性提高81%;电化学测试结果表明,与H13基体相比,未滚压的涂层耐腐蚀性提高12%,超声滚压后的涂层耐腐蚀性提高17%。结论 超声滚压后的涂层表层组织位错密度和晶界增加,获得了纳米晶层,有效改善了GH5188涂层的显微硬度、耐磨性和耐腐蚀性等力学性能。     

TP304不锈钢薄壁管的表面残余应力

利用X射线应力测试仪分别测定了TP304不锈钢无缝薄壁管管身的表面轴向和切向残余应力,并分析了表面残余应力的形成原因。结果表明:该不锈钢管表面存在较大的残余应力,且分布极不均匀;另管表面的切向残余应力大于轴向残余应力,前者为后者的1.5~2.5倍;该不锈钢管生产过程中的冷拔、冷矫直等工艺、固溶保温时间不足以及钢管表面存在局部缺陷等都是导致其表面残余应力较大的原因。     

激光选区熔化成形工艺对304L不锈钢冲击韧性的影响

目的 了解激光选区熔化(SLM)成形工艺参数对304L不锈钢冲击韧性的影响,从而得到304L不锈钢的最佳成形工艺参数。方法 对激光功率300~340 W,激光扫描速度800~1 500 mm.s^?1条件下的激光选区熔化成形304L不锈钢开展冲击试验,通过表面硬度、微观组织及断口形貌观察对冲击韧性的影响规律进行分析。结果 SLM成形304L不锈钢微观组织为跨越熔池生长形成的不规则柱状晶粒,成形工艺参数对试样表面硬度影响不显著;随着激光功率的增大和激光扫描速度的降低,304L不锈钢断面致密程度提高,孔洞类缺陷尺寸减少且数量减少,冲击韧性增大,冲击功最大值为141.9 J。结论 基于冲击试验结果,在激光体能量密度为100~140 J/mm³的条件下,304L冲击韧性稳定在138 J左右,为SLM成形304L材料的最佳成形参数区间。     

Investigation of the effects of plasma arc parameters on the structure variation of AISI 304 and St 52 steels

In this study, AISI 304 stainless steel and St 52 carbon steel have been cut by plasma arc and the variations of structural specifications occurred after cutting has been investigated. According to the experimental results, it has been seen that burning of particulars and distribution amount were increased when the cutting was performed using the speeds which are upper or lower limits of the ideal cutting speeds proposed by the manufacturer of the machine tool. Moreover, it was determined that the hardness from the outer surface to the core decreased, while the hardness near to the outer surface which affected by the high temperature occurred during cutting increased.     

The investigation on electrochemical denatured layer of 304 stainless steel

Electrochemical grinding (ECG) is one of nontraditional manufacturing methods that are widely used on various chromium alloys like 304 stainless steel and GCr15, etc. It has been considered that a thin passive film is formed on alloys during the electrochemical process and much research has been done on it. However, it is found that a kind of denatured layer (which is much thicker than passive film) is formed on 304 stainless steel surface during the process while the characteristics and influence factors of the denatured layer have been rarely focused. In this paper, an experimental study as well as a computational method were implemented to investigate characteristics of denatured layer on 304 stainless steel and influential mechanisms of electrochemical parameters on thickness of denatured layer. We found that the hardness of denatured layer was decreased by 70%, and third-order equations for predicting layer thickness under different electrochemical parameters were proposed. The obviously reduced hardness and controllable thickness of the denatured layer are expected to be of great significance in machining of chromium alloy.     

Economical and ecological cryogenic machining of AISI 304 austenitic stainless steel

 While it is a clean alternative to conventional machining using environmentally polluting cutting oils and emulsions, cryogenic machining using liquid nitrogen has been reported to increase cutting forces and shorten tool life when cutting AISI 304 austenitic stainless steel. This paper presents improved results by using an economical cryogenic cooling approach designed after studying the cryogenic properties of the stainless steel material. By injecting a small amount of liquid nitrogen to the chip–tool interface, but not to the workpiece, this approach yielded a 67% tool-life improvement at 3.82 m/s and a 43% improvement at the medium speed of 3.40 m/s when compared with conventional emulsion cooling. It improved machining productivity and reduced production cost. In this study, different cryogenic machining approaches were compared in the machining test using commercial carbide inserts. The results show the cooling approach is crucial in attaining the benefits of cryogenic machining in cutting stainless steel. Received: 7 February 2000 / Accepted: 30 April 2000     

核电管道用316LN不锈钢等离子切割工艺参数优化研究

为解决AP1000核电挤压成形厚壁管道等离子切割表面和切口成形质量差、裂纹多、后续加工量大等问题,本文搭建了大功率等离子切割试验平台,并针对20～100 mm厚核电管道用316LN不锈钢板材,采用控制变量法研究了等离子切割过程中主要工艺参数对切割质量的影响规律。研究结果表明：切割电流175～210 A,切割速度770～830 mm/min,气体压力0.56～0.64 MPa,喷嘴高度7.1～7.8 mm为20 mm厚316LN不锈钢等离子切割质量较好的工艺窗口;在等离子切割过程中,4个主要工艺参数对切割质量的影响规律曲线均为凹型;切割电流和切割速度之间的相互匹配显著影响切割的表面质量,切割速度对后拖量影响较大,喷嘴高度对切缝宽度及切口成形影响较大。将本文实验方法及工艺参数对切割质量的影响规律应用于60～100 mm厚316LN不锈钢切割工艺参数的优化研究,获得了中厚板等离子高质量切割的工艺窗口,实验验证表明,切割表面质量和切口成形质量均有明显提升,满足后续加工工艺要求,且去除量较小,可为核电厚壁不锈钢管道的高质量切割提供工艺参考。     

Comparative study of the effect of surface texturing on cutting tool in dry cutting

Recent researches in the field of dry machining have indicated that surface texture has the potential to influence tribological conditions. Researchers have studied the application of controlled surface microtextures on cutting tool surfaces to improve machining performance by changing the tribological conditions at the interfaces of tool–chip and tool–work piece. An experiment to study the performance of the microtextured high-speed steel cutting implement within the machining of steel and aluminum samples was performed. Surface textures were introduced using Rockwell hardness tester, Vickers hardness tester, and by scratching with diamond dresser on the face of single point cutting tool. Machining in dry conditions was applied on mild steel (EN3B) and aluminum (AA 6351) samples using lathe machine with microtextured and traditional cutting tool for the constant range of feed, depth of cut, and for varying range of cutting speeds. Measurement of cutting force, cutting temperature, and surface roughness of the work surfaces after machining were made. The results showed reduction in cutting forces and cutting temperature with textured tools in comparison with those of the untextured tool. Chips collected from different samples were studied under a microscope and the results showed that textures created on the tool surface by various methods exhibited variations in chip formation. Cutting tools without texture and with texture were comparatively studied and the outcomes of the experimental study are presented in this paper.     

Investigations on surface quality of WEDM-manufactured meso bevel and helical gears

This article presents investigations on and analysis of surface finish of meso bevel and helical gears made of stainless steel (SS 304) manufactured by wire electric discharge machining (WEDM) process using thin soft plain brass wire of 0.25?mm diameter. Effects of eight WEDM process parameters, namely, peak current, pulse-on time, pulse-off time, wire feed rate, wire tension, servo-gap voltage, dielectric pressure, and cutting speed on average and maximum surface roughness of the meso bevel and helical gears have been studied by conducting 31 experiments using one-factor-at-a-time approach to identify their optimum ranges/values for further experiments. Tooth profile, microstructure, microhardness, and topography of tooth flank surface have been studied for the best quality meso gears. Average and maximum surface roughness of tooth flank surfaces of meso bevel and helical gears increase with increase in peak current, servo-gap voltage, pulse-on time, wire feed rate, wire tension and cutting speed, and decrease with increase in pulse-off time while dielectric pressure does not significantly influence surface roughness. This work establishes that WEDM process can be an economic and sustainable manufacturing alternative for net-shaped meso-sized bevel and helical gears having better surface finish which will eliminate need of any subsequent finishing processes.     

屈服准则对不锈钢弯管变形预测精度影响

通过XRD衍射及不同方向单向拉伸试验验证,经过多道次拉拔生产出的304奥氏体不锈钢管材存在有明显的各向异性现象.采用Mises各向同性、Hill1948和Barlat1991各向异性屈服准则对不锈钢弯管过程进行有限元模拟,分析弯曲后管材内外侧壁厚分布、弯曲角度及管坯截面椭圆度的变化规律,通过模拟与实验结果对比发现,当实验数据较少时,采用Hill1948各向异性屈服准则,能够很好预测304奥氏体不锈钢管材弯曲成形过程,而Barlat1991各向异性屈服准则中的一些参数经过近似后,对成形行为的预测精度明显降低.