The braze-welding technology allows joining of steel sheet with preventive zinc-aluminium coatings in a productive and efficient manner. Low temperature of the process and small quantity of introduced heat limit the width of the zinc-evaporating surface. In spite of small damage to the zinc covering on 1+2 mm width from the weld-parent metal boundary, effective protection from the harmful action of air contained in it moisture and impurities. Very low current-voltage parameters of the process permit to carry it out without the spatter and excessive deformation, which positively affects aesthetics of the finished product, and permits bonding of thin elements. The possibility of utilisation of many standard welding sources of current makes it easier to introduce this technology into production line without any costly investment in special equipment. In turn, the higher than in the welding cost of fillers is compensated by the efficiency of the process, and quality of obtained joints. The braze-welding technology makes it possible to bond materials regarded as not weldable, e.g. constructional steel (C45) - cast iron, (ZL-250) systems. The use of additional heat treatment for this system (preheat) does not ensure the required quality of joints in which cracks often occur. The correct method of dealing with the problem is to lower the temperature of the process, and thus to moderate the thermal cycle of welding, and the generated stresses. This is provided by braze-welding in which the temperature does not exceed 1050 deg C. Additionally, this avoids partial melting in steel and limits its effect in cast iron, including its harmful passage into the filler. Further, the use of braze-welding for the bonding of this material system does not involve any heat treatment prior to and after welding. High strength properties characterise the joint, in spite of a zone of high hardness in the area of diffusion, and mutual solubility on the side of the cast iron. The economics of the process follows from the elimination of additional heat treatment, low cost of the filler in comparison with welding, and high efficiency. The braze-welding also offers the opportunity to regenerate systems by overlaying elements made in steels regarded as unweldeable or difficult, e.g. 42CrMoNi. The success of overlaying is conditioned by correct thermal runs prior to and after processing. An alternative to those costly regenerative technologies is overlaying with layers of bronze. In this case, no heat treatment at any stage is required.
MIG/MAG braze-welding of galvanised steel sheets and examples of difficult to weld systems
Welding International ; 22 , 4 ; 239-244
2008
6 Seiten, 8 Bilder, 2 Tabellen, 11 Quellen
Article (Journal)
English
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