内外施焊接管焊接接头应力的有限元分析

应用Ansys有限元应力分析软件,根据钢制化工容器结构设计规定(HG20583-1998),分别建立了内部施焊和外部施焊的内伸入式接管与壳体间焊接接头的模型,分析了焊接接头处应力分布情况,并对焊接接头处的应力进行了对比。结果表明,内部施焊的整个焊缝X方向的应力平均值大于外部施焊焊缝;外部施焊的整个焊缝Y方向应力水平略大于内部施焊焊缝;内部施焊焊缝等效应力的应力值小,但其高应力区域范围较大。     

New results on the spin welding of plastics

Short welding times make spin welding particularly suitable for mass production. This paper presents an analysis of the friction phase, which makes it possible to estimate the influence of the welding parameters and the material being welded on the temperature in the welded zone, the melt rate, and the torque in the spin welding of semicrystalline thermoplastics. A comparison of experimental and calculated results shows an acceptable correlation. In addition, the influence of speed, axial pressure, and braking on the weld seam quality of different amorphous and semicrystalline thermoplastics is discussed.     

Long‐Term Properties of Butt‐Welded Poly(propylene)

It is still not clear why the long‐term properties of plastic weld seams can only be differentiated by the very expensive medium tensile creep tests. One hypothesis for justifying this is based on the change in the structure of the weld seam surroundings, another cites the consumption of antioxidants and the following ageing in the weld seam area to be responsible for this. Butt‐welded weld seams made of poly(propylene) were systematically produced under different process parameters. Corresponding to the particular hypothesis, these weld seams were then analyzed in various ways to find correlations or to prove one of the hypotheses. Regarding their short‐term weld seam quality, the analyzed weld seams could not be differentiated through short‐term tensile or short‐term bend test. However, the medium tensile creep tests showed significant differences in both time until failure and long‐term weld seam quality. Under long‐term loading, the start of the brittle crack could be detected in most weld seams in the fine spherulite‐zone or between this zone and the area of the flow lines. This demonstrated again that only long‐term tests are suitable for examining different weld seam qualities. Depending on the welding parameters, times until failure decline with increasing heated‐tool temperature and heating time. Though these parameters lead to a higher consumption of antioxidants in the weld seam, a degradation was not detected in the breaking area. In fact, increasing heated‐tool temperatures and heating times, as well as higher joining pressures lead to a change in the internal structure of the material. This can be seen in morphological structure analyses in the larger bend of the entire weld seam area. A larger bend, however, correlates with higher residual stresses in the weld seam. In the medium tensile creep tests, these residual stresses as well as the tensile stress in the border region and the compressive stress in the middle are superimposed by the tensile stress resulting from the test stress. Thus a greater bend of the weld seam area and higher residual stresses in the weld seam itself lead to shorter times until failure in medium tensile creep tests.

Schematic representation of the formation of residual stresses in a weld seam and residual stresses in the different bended weld seam areas.     

Ultrasonic welding of all-polypropylene composites

In this study, the mechanical properties of ultrasonic welded lap joints of all-polypropylene composite (APPC) were investigated and compared to the interlaminar properties of the composite sheet itself. The process control parameter was welding time: welded samples were prepared with an ultrasonic welding machine in the 0.1–1.0 second time range. In most cases, the shear strength of the welded samples exceeded that of the unwelded APPC. Although it was found that during the ultrasonic welding process, the reinforcing tapes partially melted in the welding zone (WZ), the seam remained strong enough because the heat released and the pressure applied during the welding process further improved the consolidation of the APPC layers. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48799.     

Parameters influencing wood-dowel welding by high-speed rotation

Oven-dry dowels, insertion of hot dowels, cross-cut dowels, substrate holes of step-decreasing diameter as a function of depth, use of ethylene glycol or other compounds able to decrease the glass transition temperature of wood components have all been shown to contribute to improving weld joint strengths in a variety of less drastic conditions than the 10 mm/8 mm dowel/substrate hole diameter difference. The results show that once the depth of the dowel is much greater than 15 mm, then almost all the conditions used improve the weld strength. This means that the proportion of area welded in relation to the tensile strength of the dowel itself is a determining factor. The greater this area the higher the strength, irrespective of the application conditions used. Thus, over a certain welded area the dowel breaks when tested in tensile, i.e., the joint is stronger than the dowel. Temperatures > 180°C are reached during the quick welding step with the temperature decreasing in less than 1 min to 60–70°C. The same chemical reactions as occurring in vibrational welding have been shown by solid-state ¹³C-NMR analysis to also occur in dowel rotation welding. In dowel rotation welding the production of carbohydrate-derived furanic aldehydes is higher (a) from the wood material of the substrate in which the hole is pre-drilled rather than from the material of the wood dowel itself, (b) when the weld joint strength is good, and (c) when the rate of dowel insertion is higher.     

基于盲孔法的ABS热焊板件残余应力测量

采用盲孔法对4种丙烯腈–丁二烯–苯乙烯塑料(ABS)热焊板进行了残余应力的测量,获得了这4种热焊板焊趾区的残余应力数据,结果发现,ABS经过热焊成型后容易在焊趾区形成较高的残余应力,随着测量时间的延长,热焊板焊趾区的残余应力逐渐增大,在测量7 min后释放完全。为了验证盲孔法应用于塑料热焊板残余应力检测的可行性,对ABS热焊板母材区和焊趾区以及热处理前后焊趾区的残余应力进行了测量,同时测试了4种热焊板的焊接强度,发现母材区的残余应力低于焊趾区,80℃热处理后焊趾区的残余应力比热处理前的低,残余应力较低的热焊板具有较高的焊接强度,这些结果均表明盲孔法对塑料热焊板件残余应力测量结果具有一定的参考价值。     

Predicting the Thermal Behaviour of Wood During Linear Welding Using the Finite Element Method

A numerical model to simulate the temperature behaviour of wood welding samples during the welding process was developed to understand the influence of material parameters on the welding temperature. A finite element method and the CAST3M software were used to simulate and model the temperature changes during welding of beech wood. This model takes into account the different properties of the wood welded bondline, the geometry of the sample and the external conditions. The energy produced by the friction welding of the wood samples was determined from infrared thermography measurements for the welding process and inputted into the model. The comparison between the predicted and experimental results shows that the model is reliable. The applied pressure, the vibration, the extrusion of material and the chemical reactions, particularly exothermic reactions, are not taken into account in this model and thus probably explain the differences existing between actual and simulated values. However, this numerical simulation gives information on the distribution of the temperature in the sample. The model predicted that the temperature difference between the centre and the side of the sample is not higher than 4°C. This means that the border effects are negligible. The model was tested for different welding times. According to the model a heat flow about 70 kW/m² is necessary at the welding line to ensure a satisfactory bonding for the chosen sample geometry. Welding of large wood pieces has also been simulated in this study.     

钢制工业管道材料基本许用应力的确定

要对管道元件进行强度计算,首先就要确定管道材料的许用应力。而管道许用应力是在确定了管道材料的基本许用应力后,乘以质量系数所得的值。这里的质量系数是指材料(焊管、焊接管件)的纵向焊接接头质量系数或是铸件质量系数。本文表述的是《工业金属管道安全技术规范》对钢制管道材料的基本许用应力的确定方法。     

Werkstoff- und Schweißfragen bei der Herstellung von dickwandigen Druckbehältern für höhere Betriebstemperaturen aus Stählen mit 2 bis 3% Chrom und ca. 1% Molybdän

Materials and welding in the production of thick-walled pressure vessels for elevated operating temperature made of steels containing 2 to 3% of chromium and ca. 1% of molybdenum . High-temperature steels containing 2 to 3% of chromium and ca. 1% of molybdenum are resistant to hydrogen under pressure at temperatures up to about 500°C. Being readily weldable, they are excellently suited for high pressure equipment in chemical plant construction. Their tendency to embrittlement at operating temperatures of 400 to 500°C is a drawback. However, specific metallurgical measures adopted during the production of the semifinished material and the welding materials, and use of optimized welding techniques and heat treatment keep this embrittlement within limits. The article reports recent experiences gained in producing pressure vessels with welding seam thicknesses of up to 230 mm at the authors company.     

钛制压力容器的焊缝应力研究

通过试验证明钛容器的破坏都是从焊缝开始的，其焊缝应力以离焊根５～１０ｍｍ处最大，达到了筒体按双向强化计算值２．２８～３．５１倍，并在此基础上提出了加强钛容器焊缝强度研究和如何降低焊缝应力峰值研究的新课题     

Joining laser-sintered with injection-molded parts made of PA12 using infrared welding

Laser-sintering offers the possibility to produce complex and individualized components cost-effectively. To fully exploit the advantages of laser-sintering in assemblies with mass-produced components, high-performance joining processes like welding are necessary. Thus, a cost-effective customization of products can be enabled, which allows to follow the increasing trend of individualization. Infrared welding, in particular, can also be suitable for complex laser-sintered parts due to the reduced transverse forces during joining, compared to other welding processes. The investigations show that high strength between PA12 laser-sintered and injection-molded components can be achieved by infrared welding. The bond strength is mainly influenced by the welding parameters. Especially a low weld pressure leads to high achievable strengths and failure outside the weld seam. Joints between laser-sintered parts and glass fiber reinforced injection-molded components demonstrate the transferability of the obtained knowledge. The residual melt layer thickness of the joint decreases with increasing weld pressure, as the morphological characterization shows. Besides, the typical morphological seam structure can be seen on the side of the injection-molded component. In the area of the laser-sintered components, a deviating morphological structure can be observed. Distinctive flow lines can be observed, spherulitic structures can only partially be seen as well as deformed spherulites.     

Thickness effects in the vibration welding of polycarbonate

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. Past work on welding characterized the effects of weld parameters such as the weld frequency, the weld pressure, and the weld time, on the welding process and weld strength, and showed that the most important parameter affecting weld strength Is the weld penetration—the decrease in the distance between the parts being welded that is caused by lateral outflow of material in the molten film. However, those weld studies were based on specimens of constant nominal thickness (6.35 mm, 0.25 in). This paper is concerned with the effects of specimen thickness on the weld process and weld strength.     

On the possibility of the electron-beam welding of quartz glasses by a forevacuum plasma electron source

The article demonstrates a principle possibility of the electron-beam welding of high-temperature quartz glasses by a plasma electron source operating in the forevacuum range of pressure of 10–50?Pa. We studied the dependence of the composition of the gas atmosphere in the vacuum chamber on the heating temperature of the weld seam. It is shown that the optimal temperature of the weld seam for melting and minimum mass entrainment from the molten pool is 1300–1400?°C. We determined the welding regime for cylindrical tubes and rods that provides high seam strength, reaching 90–95% of the original strength of quartz glass.     

关于冲击试验的试验温度和冲击吸收功合格指标问题

简要介绍在不同设计温度的钢制压力容器材料、焊接工艺评定和产品焊接试板力学性能检验中,冲击试验的试验温度和冲击吸收功合格指标的确定方法,结合典型问题,用标准规定进行分析、解释。     

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     

Reducing the moisture sensitivity of linear friction welded birch (Betula pendula L.) wood through thermal modification

Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding thermal modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, thermal modification under superheated steam at atmospheric pressure, internal bond (IB) and tensile-shear strength testing and soaking tests. As supposed, the non-modified reference specimens performed poorly after the seven days soaking test (on average 0.33 MPa IB strength), whereas the thermally modified specimens yielded almost the same IB strength in dry and wet condition (on average e.g. 1.15 and 0.93 MPa, respectively). Such a similar load bearing capacity in very different moisture conditions was previously reported only in the case of paduk wood. Similar to the reduction of IB strength occurred during the soaking test, also delamination was observed more clearly in non-modified reference specimens (e.g. 4 vs. 0 total delaminations after seven days soaking). Therefore, the authors suggest that post-welding thermal modification could provide a suitable bond-stabilisation method against moisture, although the process parameters must be optimised in further research, for instance, to ensure scalability.     

谈压力容器焊缝错边的工艺质量控制

论述了压力容器制造中对接焊缝错边量的产生原因 ,在工艺文件和检验中提出了防止焊缝错边的具体控制要求 ,以确保焊缝错边量不超差     

Welding Mechanisms of Plastics: A Review

Strength of welded joints is a function of technological parameters of the production process. The type of function is dependent on the welding mechanism. Different mechanisms were found under various welding conditions. The processes included in the plastic welding mechanism are divided into two groups:

1) Processes which realize the joining of the parts.

2) Processes which create conditions for the first group to proceed. The first series of processes includes:

a) diffusion of macroradicals, molecular segments or molecules of the polymer which can be either in a solid, melted or dissolved state.

b) convective mass transfer.

c) recombination of macroradicals across the contact surface.

d) physical (surface) interaction.

e) any combination of processes described above.

The second group contains:

a) formation of the real contact surface.

b) formation of the macroradicals.

c) destruction and removal of inert layers which prevent real contact of active material.

Each process and the conditions of its proceeding are discussed individually.     

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.     

SAF2507与321管板异种金属焊接接头组织形态和相组织分布

为了解SAF2507和321异种金属管板焊接接头的相比例分布情况,按照ASTM标准对其焊缝截面各重要部位进行了铁素体含量检测。通过金相分析,发现两道焊缝组织形态区别很大,第1道焊缝基本为针片状或羽毛状奥氏体,第2道焊缝却成团块状奥氏体。