XM-250/20A密炼机减速机箱体裂纹的焊接修复

针对XM-250/20A密炼机减速机箱体出现的裂纹,决定采用焊接修复.详细介绍了焊接修复前的准备工作、焊接操作工艺及规范、焊道长度及温度,去内应力措施等.最后还介绍了焊后处理方案.     

钢／PVC-U复合管制造的新技术

介绍一种最新的钢塑复合管连续生产技术,它的特点是:在钢带焊接成管时,通入惰性气体进行冷却,将焊道温度降低到PVC分解温度以下,从而保证与之粘连的PVC树脂不受分解.由于冷却,焊接部位与两管结合部位之距离可以缩短,减少了挤出压力,提高了挤出速度;距离缩短,芯棒和口模可以缩短,二者易于调节同心,挤出管材壁厚均匀.由于冷却惰性气体中不含氧,焊接管不会产生粗糙易脱落的氧化膜,两管复合时不会因此处的薄弱环节而分层溃烂.     

浅谈学习GB150—89《钢制压力容器》（第十章）之体会（下）

四、焊接焊接是压力容器制造非常重妥的工作。焊接质量决定了容器的质量。因此,本标准对焊接部份提出的内容和要求比原JD741更全面。 1.A,B类焊缝余高焊缝余高对压力容器多道焊焊接的焊缝是不可避免的,而且还有上面焊道对下面焊道起保温和缓冷作用,并对消除最后一层强度焊缝应力和改善组织有好处。但焊缝余高     

一种新的钢塑复合管制造技术

介绍了一种新的钢塑复合管连续制造技术,其特点是：在钢带焊接成管时通人惰性气体进行冷却,将焊道温度降低到PVC分解温度以下,从而避免与之粘连的PVC树脂分解。由于采用了冷却的方式,焊接部位与两管结合部位的距离可以缩短,减少了挤出压力,提高了挤出速度;可以缩短芯棒和口模的距离,使二者易于调节同心,挤出的管材的壁厚均匀。由于冷却的惰性气体中不含氧,焊接管不会产生粗糙易脱落的氧化膜,两管复合时不会因此处的薄弱环节而分层。     

09MnNiDR钢埋弧焊缝低温韧性的控制研究

在焊接材料确定后,09MnNiDR钢焊接接头的焊缝组织状态是影响低温韧性的关键因素,焊缝组织状态又决定于焊缝冷却过程,特别是从800℃冷却至500℃的时间t8/5。而t8/5又决定于焊接线能量、板厚、层间温度、焊道布置等的多种因素。经过资料查照、计算、归纳,找出相关数据,并做了大量试验引证,掌握了09MnNiDR钢的埋弧焊焊接接头低温韧性变化规律,使低温韧性得到有效的控制。采用埋弧焊焊接方法运用于09MnNiDR钢的最小厚度,比ASME范围和我国某些企业经验范围更小,从而提高了焊接生产率。     

国际工程管道焊接质量过程管理初探

本文从质量管理程序建立、组织机构及人员配置、焊接工艺评定、焊工考试及管理、焊接检验、奖罚培训制度、焊接信息系统等方面的分析,论述了在国际工程项目建设中通过加强过程管理可以有效地控制管道焊接质量,最大限度地降低焊道返修率。     

油气管道自动焊接焊缝检测实验研究

油气用钢管的强度等级较高,管径和壁厚较大,油气管线施工多以自动焊和半自动焊为主,手工焊为辅。油气输送管线的焊接质量要求很高,既要控制缺陷的产生,又要焊道内表面光滑,因此如何提高焊接效率和焊接质量成为首要问题。为了研究分析管道自动焊接质量差等问题,以X70钢级管线钢为对象进行自动焊接实验,针对焊接后形成的焊缝分别进行焊缝外观实验、X射线无损探伤实验、焊缝成型特征实验、低温冲击韧性实验,对提高管道自动焊接质量具有重要意义。     

高寒地带长输管道冬季焊接施工

兰州—银川输气管道工程第2A单元所处位置海拔2450m,管道施工期间,环境最低温度达到-25℃,管道钢管材质为X70钢。工程施工过程中,施工人员和技术质量管理人员通过摸索、总结和对比,从控制焊接施工的小环境温度、加强环境参数检测、落实焊道焊后保温缓冷等几方面着手,制定了一套行之有效的冬季施工措施和操作程序,很好地解决了高寒地带冬季施工如何保证焊接质量的技术难题。     

联箱式外取热器管束焊接工艺

联箱式外取热器管束制造的关键工序是焊接和对焊道的检验。只有控制好焊接过程,采取必要的操作方法,合理选用检验项目,才能真正反映并保证产品质量。     

水泥机械设备制造中的焊接变形及处理

１．前言 在焊接的过程中，由于焊接热源于母体上进行局部且不均匀的急速加热与冷却，使得焊道附近的熔填金属与母材产生热应变，由于热应变再产生热应力，此不均匀的热应力便是焊接变形的主要原因。由此可知，焊接变形是由于在焊接的过程中，不均匀的温度分布所产生热胀与冷缩之结果而造成的。焊接变形的存在，将会影响焊接结构的组装。精度、性质（如强度）、及性能（如可靠性与稳定性）等。水泥机械设备属于大型机械设备，在采用焊接时，如机座、盘、筒体之类的构件、焊后会产生较大的焊接变形。为此本文对有关焊接变形问题进行系统探讨…     

Structure and mechanical properties of optimized extrusion welds

A knowledge of how welding parameters affect the mechanical properties of welds is important. However, the mechanical properties of welds cannot be characterized by nondestructive testing methods. Because of its sensitivity to process conditions, extrusion welding of polypropylene-homopolymer (PP-H) was used to investigate the effects of welding parameters on the resulting mechanical properties of welds. Overall optimization of the welding process to obtain stable conditions during welding, which required a redesign of the welding shoe and the welding geometry, resulted in improved weld properties through better build-up of critical weld areas and suppression of void formation. Investigation of material heating characteristics led to a new air nozzle design. The effect of air temperature and welding velocity on the temperature and thickness of the molten layer was determined. The effects of individual process parameters on the structure and mechanical behavior of welds were established, thereby making it possible to specify narrow limits on the values of the weld parameters for producing high-quality welds. The quality of these joints cannot be determined by short-time tests because, even with severe testing conditions, cracks occur in the bulk material. Polarized optical microscopy was used to correlate crack behavior with the build-up of a specific multilayer structure in the weld area. Long-term tests demonstrated that, in both the time-to-crack and crack behavior, the joining area is not the weakest link in an extrusion weld when the welding parameters are chosen correctly.     

Characterization of fusion welded ceramics in the SiC-ZrB2-ZrC system

Various SiC-ZrB₂-ZrC ceramics were joined by fusion welding to determine the maximum silicon carbide content that could be joined. Commercial powders were hot pressed, machined, and preheated to 1450 °C before joining with a tungsten inert gas welding torch at 160–200 A. Resulting welds were cross-sectioned and analyzed to determine which compositions were weldable and to characterize microstructural evolution in welded samples. As compositions approached the ternary eutectic, the welds had smaller SiC grains and exhibited better weldability. Penetration depth of welds was controlled by a combination of current input and welding speed. The ternary eutectic in the system was found at 36.9 ± 1.3 vol% SiC, 42.7 ± 1.5 vol% ZrB₂, and 20.4 ± 1.9 vol% ZrC and its melting temperature was 2330 ± 23 °C. A ternary phase diagram for the SiC-ZrB₂-ZrC was constructed and proposed via microstructural analysis of arc melted pellets on binary joins between each binary eutectic and the ternary eutectic in the system.     

Cross-thickness vibration welding of polycarbonate,polyetherimide, poly(butylene terephthalate), and modified polyphenylene oxide

In vibration welding of thermoplastics, frictional heat generated by vibrating two parts under pressure, along their common interface, is used to effect welds. In the normal, well-understood mode, the vibratory motion is along the weld seam, which is at right angles to the thickness direction for straight boundaries. But in many applications, such as in the welding of closed seams of box-like parts, this vibratory motion occurs in the part-thickness direction, so that a portion of the molten layer along the seam is exposed to the ambient air during each vibratory cycle. The resulting reduction in temperature can affect weld quality. The process phenomenology and the weld strengths of such cross-thickness vibration-welded butt joints are investigated for four neat resins. Weld amplitudes and weld pressures are shown to affect the strengths of 120-Hz welds differently. It is shown that strengths on the order of the strengths of the neat resins can be achieved in 250-Hz butt welds.     

The impact strength of butt welded vibration welds related to microstructure and welding history

A study has been made of vibration butt welds between plaques of polypropylene. The quality of the welds, as determined by impact tests, has been examined as a function of the welding variables: pressure and vibration amplitude. In addition, the microstructure of the welds has also been examined, classified, and correlated with the welding variables and weld quality. Penetration as a function of time shows three distinct regimes and It is shown that the impact strength of the welds is independent of time once the third regime is reached. The time required to reach the third regime decreases as pressure or amplitude increases and is more sensitive to amplitude of vibration than to pressure. The highest quality welds were produced at low pressure and low amplitude with corresponding long times to reach regime three and exhibited a unique, readily identifiable microstructure.     

Failure characterization of polypropylene block copolymer welded joints

The failure behavior of polypropylene block copolymer double-V welded joints was investigated. Joints were prepared using the hot-gas welding technique at varying gas temperatures in the range of 230–260°C. Uniaxial tensile tests, fracture mechanics experiments, several microscopy techniques, and complementary FEM analysis were carried out to assess the quality of filler rods and welding interfaces. The developed interfaces were weaker than the parent material as a consequence of polymer chains segregation during the welding process. The hot-gas temperature had a marked effect on the failure behavior of the welds. The highest interface toughness was attained at the highest gas welding temperature used at which, polymer chains were able to quickly diffuse into the parent material enlarging the distance of penetration and hence the micro-deformation capability of the joint. POLYM. ENG. SCI., 47:1062–1069, 2007. © 2007 Society of Plastics Engineers     

Effects of welding procedures on mechanical and morphological properties of hot gas butt welded PE,PP, and PVC sheets

Mechanical and morphological properties of hot gas butt welds on polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) sheets for four different procedures, which are single and double V‐welds with and without a welding shoe, were investigated. Besides, weldabilities of base materials were evaluated by rheological measurements. These revealed that weldabilities of PE and PP sheets were better than that of PVC. Welding energy (E_w), which is transferred onto weld surfaces, was calculated to evaluate weld quality. The results of tensile, impact, and bending tests indicated that the weld strengths of PVC sheets were lower than those of PE and PP sheets. When the welding shoe was used, weld strength increased significantly for each material because of the presence of sufficient welding pressure and the effective heating on surfaces. The best results were attained for the double V‐welds with the welding shoe. Morphology of welded regions was evaluated by polarized light, stereo, and scanning electron microscopy. Polarized light microscopy studies indicated that the heat‐affected zone (HAZ) consisted of welding rod core, molten zone, and deformed spherulitic zone, and the welding interface was indistinguishable from the base material when the welding pressure was enough. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Semiempirical,squeeze flow,and intermolecular diffusion model. II. Model verification using laser microwelding

This article reviews the application of a coupled squeeze flow and intermolecular diffusion model, which was used to predict the quality and size of microwelds in plastics. Weld widths predictions were compared with previously presented experimental results using moving heat source models and temperature fields. The motivation for this work was to develop and verify a model based on fundamental principles that could accurately predict weld size and strength for conventional plastic welding techniques as well as novel techniques such as laser microwelding. It is envisioned that the resulting model could be used to predict proper welding parameters, including laser power and travel speed, to produce welds of varying size. Although insight into weld quality can be derived from this model, it was not the goal of this work to accurately predict weld strength for laser microwelding because of the difficulty in measuring weld strength on the micron scale. However, as reported in Part 1, weld strength for impulse welds were accurately predicted. In this model it was found that variable temperature histories, rather than a single value of maximum weld temperature, allows more accurate modeling of the welding process. In this work (Part 2), microwelds as small as 11 μm in width were produced with transmission infrared welding. In addition, welds over 150‐μm wide were also generated and the model was able to predict the range of weld widths that were found experimentally. It was found that the predictions were in very good agreement with the experimental results. There was some deviation between the experimental data and the model at the extreme parameters and it is believed that this was due to the temperature‐dependent material properties as well as optical aberrations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Activation energy for diffusion and welding of PLA films

The bonding of polylactic acid (PLA) films was investigated for a broad range of temperatures and contact times above the glass transition temperature in a lap shear joint geometry using an impulse welding system. It was observed that interfacial strength was linearly dependent to the fourth root of welding time until it approached the bulk material strength. Using models based on reptation theories, the interfacial strength of lap shear welds was estimated based on thermal histories. In more detail, the activation energy for interfacial healing and self‐diffusion coefficient was calculated based on shear strength measurements of samples welded with well‐defined thermal histories. The parameters were then used to predict interfacial strength with varying temperature histories. This is the first work to measure the activation of energy for the interfacial welding PLA. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Scale-up laws in heated tool butt welding of HDPE and PP

In order to achieve high fatigue strengths in heated-tool butt welds in plastic pipes used in gas and water supply lines, it is essential that optimum welding parameters be selected. In this paper, the different process phases are described by means of dimensionless characteristic parameters that have been obtained by applying similarity principles to heated-tool butt welding. On the basis of strength studies conducted on welded Joints, it is shown that the best weld quality is attained when the welding parameters are selected such that identical sheaf deformations result in the joint zones of small and large pipes. Laws for scaling data from small-pipe to large-pipe welds are then based on the values of these nondimensional numbers.     

Comparison of vibration and hot‐tool thermoplastic weld morphologies

Because of very different heating rates in hot‐tool and vibration welding, and the higher weld pressures used in vibration welding inducing more squeeze flow, the weld zones in these two processes see very different flows and cooling rates, resulting in different morphologies. The weld morphologies of bisphenol‐A polycarbonate (PC) and poly(butylene terephthalate) (PBT) for these two processes are discussed in relation to these differences. The thickness of the heat‐affected zone (HAZ) in hot‐tool welds increases with the melt time; this zone is thicker than in vibration welds. The HAZ thickness in hot‐tool welds increases from the center toward the edges. The HAZ thickness is more uniform in vibration welds. Hot‐tool welds of PC have large numbers of bubbles around the central plane; the bubble size increases from the center to the edges. PC vibration welds do not have bubbles except near the edges. Both hot‐tool and vibration welds of PBT do not have bubbles. The morphology of the HAZ in PBT is very different in hot‐tool and vibration welds. In hot‐tool welds, the resolidified material consists of a sandwich structure in which two thin layers with very small crystallites surround a thicker central layer in which the spherulites are almost as large as in the original molded material. In vibration welds, the HAZ has large crystallinity gradients across the weld zone as well as squeeze‐flow induced distortion of the small spherulites.