Undetachable joint connections make high demands.
The classification of the joint connections can be done in many ways. For example, according to the type of joint. Are they detachable, conditionally detachable or non-detachable? From a material point of view, the non-detachable joints place special demands on the material and its properties. Therefore, the non-detachable joining connections such as welding, soldering and bonding are examined in more detail against the background of copper materials.
In welding, the components are joined together by heat and/or force with or without filler metal. The creation of the joint can be made possible or even simplified by welding consumables, e.g. shielding gases, welding fluxes or pastes.
Taking into account the special physical and mechanical properties, many copper materials can be welded well. Depending on the material used, the appropriate manufacturing parameters such as welding processes, filler metals and pre- and post-treatments must be selected. Copper can form alloys with many different metals, so that a variety of alloy systems are available in which certain properties such as hardness, tensile strength, yield strength, chemical resistance, wear resistance and others can be specifically influenced. The welding processes used are just as varied as the copper materials. It is therefore not possible to simply conclude from the weldability of pure copper grades to the weldability of alloys such as brass or bronze. Even within the pure copper grades, different degrees of purity lead to different process adjustments during welding.
Copper and copper alloys are well suited for bonded joints. In order to produce high quality bonded joints, great emphasis must be placed on surface preparation. The surfaces of copper materials are best suited for adhesive bonding immediately after machining. In special cases, the application of an intermediate layer as an adhesive primer is also recommended. If lacquered surfaces are to be bonded, the adhesive strength of the lacquer coating should be tested beforehand.
High adhesive strengths can be achieved for bonded joints of copper or copper alloys with aluminium using two-component polyurethane-based adhesives. As copper materials can be easily soft-soldered, the adhesive bonding technique for copper materials was only tested relatively late. The advantage of adhesive bonding is mainly that not only metals can be bonded to each other, but also metals can be bonded to other types of materials, e.g. laminates, wood, plastics, etc. The strengths of adhesive bonding are very good. The strength of bonded joints is of the same order of magnitude as that of soft soldered joints.
Soldering is a process for joining different metallic materials with the help of a molten additional metal (solder). A distinction is made between soft soldering and hard soldering.
The soldering temperature for soft solders is below 450 °C. Due to the low strength of these solders and the corresponding solder joint, they are suitable for low mechanical loads and are mainly used in electrical engineering. Hard solders for soldering copper materials are mostly copper-, silver- or brass-based alloys and are suitable for connections subject to greater mechanical stress. The processing temperatures are between approx. 450 – 1000 °C.
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