Schweißen im Behälter- und Apparatebau

Welding in Tank and Plant Construction Since a relatively limited number of plastics types are used, the welding tasks involved in chemical apparatus engineering can be accomplished with just a few welding techniques are well-known and welding can be carried out efficiently, reliably and economically by this means. In this respect, however, a number of important principles have to be observed. The DVS guidelines provide vital information on questions relating to calculation, design, personnel, equipment, material and testing. Extrusion welding enjoys prime importance as regards quality and economic aspects.     

Der Einfluß von Temperatur und Zeit beim Schweißen von Baustählen mit Strahlen hoher Intensität

Temperature and Time Dependent Fusion Welding with Beams of High Intensity By a special set-up very high local and time-dependent temperature gradients were measured in the weld zone of beam affected areas. Under certain weld conditions a leading preheat wave does not exist. As to the resulting microstructure in the beam, the characteristic steep temperature curves do not allow any prediction. Zones of enlarged hardness were reduced by different heat-treatments.     

Einfluß von Schweißen und Kaltumformung auf das Kurzzeitschwingfestigkeitsverhalten von austenitischem Stahl

Influence of Welding and Cold Forming on the Low-Cycle-Fatigue Behaviour of Austenitic Steel The low-cycle-fatigue behaviour of the austenitic steel X 10 CrNiTi 189, as received and welded, was investigated after cold forming up to 10 per cent by strain controlled tests. The fatigue life to crack initiation of the unwelded material is 10 times higher than the fatigue life of the butt-welded and unfinished material. The grinding of the butt-welds however leads to an increase of the fatigue life by a factor of 4 in comparison to the unfinished state. In comparison to these results obtained under 1 Hz the reduction of the frequency to 0.1 Hz causes a significant cyclic hardening and decrease of the fatigue life. The cold forming remains in all cases without influence. This hardening is a result of the diffusionless transformation of the austenitic microstructure into ferromagnetic α′-martensite under the lower frequency. The increase of the hardness caused also by the cold forming makes the stainless material more sensitive to corrosion.     

Untersuchungen zum Schweißen der aushärtbaren Aluminiumlegierungen AlMgSi 1 und AlCuMg 1 mit einem gepulsten Festkörperlaser

Investigations on the Welding of the Age Hardenable Aluminium Alloys AlMgSi 1 and AlCuMg 1 Using a Pulsed Solid State Laser The age hardenable aluminium alloys AlMgSi 1 and AlCuMg 1 were laser welded using a pulsed 1.2 kW Nd: YAG-laser. Butt welds of 1mm thick plates were produced. With a gap width of 50 μm good welds good be produced even without filler. The small beam diameter (approximately 0.2mm in the focal point) leads to small welds and heat affected zones. The grain size within the weld is small and the amount of grain boundary liquation in the mushy zone is low due to the high temperature gradient in the melt pool. In samples which were welded in the age hardened condition the hardness in the weld drops down to the level of the homogenized condition. However, no significant evaporation or oxidation of alloying elements happens and the maximum hardness can be regained by a complete age hardening treatment. The tensile strength is higher than that of conventional welded sheets but the fatigue strength is reduced significantly.     

Neue Entwicklungen auf dem Gebiet der Schweißtechnik

Recent Development in the Field of Welding Technique. Because of important advantages as soundness of gap, no overlapping and possibility of mechanization the welding procedure takes a considerable plave in the wide field of joint techniques. Often the mechanical properties of the weld metal exceed the values of the base metal. The following report describes recent welding techniques: welding with cored-wire electrodes, the narrow-gap-welding and electron-beam welding at atmosphere. This procedures are often used for the welding of new grades of materials.     

Erfahrungen beim Schweißen gasempfindlicher hochreiner Werkstoffe

Experiences in Welding Highly Pure, Gas-Sensitive Materials Highly pure steels and non-ferrous react during processing, particularly welding, with atmospheric gases and change their service properties. Hence special measures are often necessary in forming and inert gas welding. Taking the specific example of a high pure chromium steel (superferritic), welding properties, processing data and selection of suitable inert gas torches are described. The possibility of applying this information to other materials such as titanium is discussed.     

Schwingfestigkeit schubbeanspruchter Schweißverbindungen nach dem örtlichen Konzept

Fatique strength of shear loaded welded joints according to the local concept In the present work local stress values for fatigue loaded welded joints under shear stresses are derived according to the concept of local elastic stresses by means of test data of the relevant literature re‐analysed in a uniform matter and of numerically obtained notch stress concentration factors. Together with the derived statistically based scatter band of the particular S‐N‐curves and of the local characteristic stress values the obtained results form a reliable basis for codes designing shear stress fatigue loaded welded joints. Further fatigue tests may be desirable howewer under observing usual standards in arranging, carrying out and evaluating fatigue investigations.     

Spannungsberechnungen in Schweißnahtmodellen mit Hilfe neuer Werkstoffgesetze

Stress Calculation in a Weld Model with the Help of New Material Laws Based on the incremental formulations of the material theory from Mises for two dimensional problems a subroutine has been developed for using new material laws in finite element programs. Using this subroutine a phenomenological material law has been used to consider the influence of the strain in finite element calculation of inhomogeneous weldments.     

Schweißverhalten von Aluminium und seinen Legierungen

Weldability of Aluminium and Al Alloys Aluminium is behind steel the most used metal. Advantages of Al-materials are the low weight, the favourable strength and deformation properties, the good corrosion resistance and the good electrical and thermal conductivity. Welding of aluminium encounters difficulties due to high melting oxide layer at the surface, the strong heat dissipation from the welding region, the tendency to form craters or pores and the high heat extension. This contribution describes the basic facts and special features of arc welding and weld properties of aluminium and Al-alloys during welding.     

Lebensdauer von Schweißverbindungen unter mehrachsigen Belastungen mit variablen Amplituden – Schadensakkumulation und Hypothese der wirksamen Vergleichsspannung

Fatigue Life of Welded Joints under Multiaxial Variable Amplitude Loading – Damage Accumulation and the Effective Equivalent Stress Hypothesis Flange‐tube joints from fine grained steel FeE 460 with different notch factors were investigated under biaxial constant and Gaussian variable amplitude loading (bending and torsion) in the range of 10⁴ to 5 · 10⁶ cycles to crack initiation and break‐through, respectively. In order not to interfere with residual stresses they were stress relieved by a heat treatment. Damage accumulation under a Gaussian spectrum can be assessed for in‐ and out of phase combined bending and torsion using an allowable damage sum of 0.35 for weldments in the as‐welded state and 0.16 for joints with machined weldments with a lower notch factor of the critical area. For the evaluation of multiaxial in‐ and out‐of‐phase stresses the introduced hypothesis of the effective equivalent stress leads to good results. For this, the knowledge of local strains or stresses is necessary. This hypothesis considers the fatigue‐life reducing influence of out‐of‐phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from the weld geometry and loading mode were included.     

Charakterisierung des Ermüdungszustandes in zyklisch beanspruchten Schweißverbindungen durch röntgenographische und mikromagnetische Kenngrößen

Characterization of the Fatigue of Cyclically Loaded Welded Joints by X-Ray Diffraction and Micromagnetic Testing The fatigue behaviour of welded Joints is influenced by the state of the material, its microstructure and residual stresses. By means of the micromagnetic Barkhausen-noise testing method in connection with x-ray diffraction the behaviour of cyclically loaded welded joints of the steel S355 is investigated. Proved by the results of the present investigations, the macro-and micro-residual stresses, micromagnetic and strain characteristic values are strongly connected with each other. Plastic deformations in the HAZ and base material during cyclic loading were identifies by a significant relaxation of the micro-residual stresses and a characteristic change in the micro-residual stresses determined by X-ray profile analysis. Analogous to the growing plastic strain amplitude an advancing damage process in the material is accompained by a significant change in the micromagnetic parameters. As a conclusion the micromagnetic testing method can be suited for the identification of fatigue processes in the material before a final damager of the specimen.     

Abscheidung optisch,elektrisch und akustisch wirksamer Schichten mit dem Doppel‐Ring‐Magnetron

Numerous applications in optics, electronics and sensor technology require thin dielectric films. Conventionally they are deposited by evaporation, activated evaporation, rf‐sputtering or CVD‐techniques. This paper describes the deposition of such films using reactive Pulse Magnetron Sputtering. This technology not only enables a tenfold deposition rate compared to the conventional techniques but also offers new possibilities for influencing film growth. For example it is possible to alter film composition during deposition and hence to deposit complete optical systems without interruption of the plasma process. Furthermore the energetic bombardment of the growing film can be controlled in a wide range by the pulse mode and the pulse parameters. This can be used to either deposit very dense films by strong energetic bombardment or to deposit films at low thermal load onto temperature sensitive substrates. Examples of film deposition for laser optics, electrical insulation applications and surface acoustic wave devices show how these new technological possibilities advantageously can be used for creating innovative layer systems. Film deposition is carried out in stationary mode using a Double Ring Magnetron. This type of magnetron ensures film thickness uniformity better than ± 1 % on 8” substrates by the superposition of the thickness distributions of two concentric discharges.     

Beschichten,Reparieren und Generieren durch Präzisions‐Auftragschweißen mit Laserstrahlen

Laser beam build‐up welding belongs to the technical group of thermal coating. With a coating thickness between 0.1 and 3 mm it is positioned close to PTA and TIG cladding. The special features consist in the excellent controllability of the cladding process, high precision of the material deposition, low thermal influence on the workpiece and low base material mixing, the absence of mechanical effects on the melt pool as well as the large number of coating and substrate materials available for the manufacturing process. Currently, the most important application is the repair of complex shaped and expensive components and tools. Examples are wear damaged moulds, metal forming dies, or aircraft engine components, which original properties can be completely restored by accurate and local replacement of the lost material. In the field of surface protection, laser technology offers advanced solutions for the surface modification of light alloys. Components of Ti, Al or Mg alloys can be protected effectively against wear and corrosion by laser cladding, alloying, and hard particle dispersing. Generating of metal Prototypes by CNC controlled Direct Metal Deposition is a further application of the laser technique. Using this method, mould inserts, active parts of tools, or engine components can be generated directly from the 3D CAD data.     

Vergleichende Untersuchungen zur Anrisslebensdauervorhersage gekerbter Proben mit dem Örtlichen Konzept und dem Nennspannungskonzept am Beispiel des Stahls Cm15

Comparative Investigations on Service Life Assessment of Notched Specimens Based on the Local Strain and the Nominal Stress Approach to Fatigue for a Steel SAE 1017 It is still unclear whether the strain based approach to fatigue or the stress based approach to fatigue should be preferred for service life assessment of notched components. In order to clarify the similarities and differences between these concepts stress and strain controlled fatigue experiments have been performed with notched specimens. It has been found, that stress and strain controlled fatigue testing results in the same number of cycles until failure. Essential for this correlation is that the cyclic stable strain amplitude at the notch root is taken for the entry into the strain‐life diagram in both cases. Starting from an elastic‐plastic analysis of the material behaviour at the notch root it is shown, how the strain‐life curve can be converted into a stress‐life curve. Based on that result service‐life is calculated from both approaches mentioned above. The calculation gives nearly the same service‐lives for both cases, but overestimates the measured data. It becomes obvious, that a S‐N curve determined under one‐level loading doesn’t provide a proper basis for service life assessment. While strain or stress‐life curves always contain crack initiation phase as well as crack propagation phase, the fatigue process under irregular loads is mainly governed by crack propagation. As a consequence, the damage per cycle is underestimated for loads near the fatigue limit, if Miner’s rule is used.     

Ermittlung mechanischer Kenndaten von Kohlenstoffaserverstärktem Kohlenstoff (CFC) mit dem Biege- und Zugversuch

Research on Mechanical Data of Carbon Reinforced Carbon (CC) in Bending and Tensile Mode CC is a ultra high temperature material used until 2200°C in inert atmospheres. The testing geometries of reinforced carbon (CC) are not standardized in West Germany today. Therefore the SIGRI GmbH has defined material specific geoand tensile mode. It is shown, that the tensile strength has a higher level than the bending strength when the laminate orientation is (0/90°). When the laminate has a (0/± 45/90°)-orientation, the relation is inverted. If the laminate orientation is known, the fracture mode can be predicted.     

Festigkeitsverhalten von Schweißverbindungen unter kombinierten phasengleichen und phasenverschobenen mehrachsigen Beanspruchungen

Fatigue Behaviour of Welded Joints under Combined In-and Out-of-Phase Multiaxial Loading Welded crucifix-type specimens from fine grained steel StE 290 and flange-tube as well as tube-tube joints from fine grained steel StE 460 with unmachined and machined welds were investigated under biaxial constant amplitude loading in the range of 10³ to 5 · 10⁶ cycles to crack initiation and break-through, respectively. In order not to interfere with residual stresses they were relieved by a heat treatment. Inphase loading can be treated fairly well using the conventional hypotheses (von Mises or Tresca) on basis of nominal, structural or local strains or stresses. But the influence of out-of-phase loading on fatigue life is severely overestimated if conventional hypotheses are used. However, the introduced hypothesis of the effective equivalent stress leads to fairly well predictions. Herefore, the knowledge of local strains or stresses is necessary. They are determined by boundary-elemente analyses in dependency of weld geometry. This hypothesis considers the influence of out-of-phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from weld geometry and loading mode were included.