Nichrome welding and soldering
Welding
The most widely used argon-arc welding of nickel alloys with a tungsten electrode. Argon-arc welding guarantees high quality of the weld if direct direct current polarity is used. Welding nickel structures requires the use of electrodes (European, domestic or international standard). The electrodes are usually made of tungsten, as refractory metals provide high reliability of welding joints due to high welding temperature. Each electrode is color-coded to avoid confusion.
Electrodes
Tungsten non-consumable electrodes are made according to
Soldering
The use of specific recommended fluxes, gas environments and solders is required. This is necessary because the surface of nickel alloys, covered by a very resistant film of oxides. When nichrome is alloyed with titanium and aluminum, the chemical resistance of the oxide film increases, which causes additional difficulties.
Gas media
When brazing nickel alloys, it is necessary to ensure that the gas environments used have no sulfur compounds, since the interaction of sulfur and nickel forms a fusible eutectic that penetrates deep into the grain boundaries and causes embrittlement of the metal. Brazing of heat-resistant nickel-based alloys in a gas reducing environment requires careful cleaning of the oxygen residue with a dunite or platinum catalyst and additional drying to the dew point (-70 ° C). When brazing such alloys in a vacuum or in neutral gas environments - they should be thoroughly dried with barium peroxide, phosphoric anhydride or zeolite. Before soldering, nichrome is coated with a 15 µm thick copper or nickel layer that ensures that the soldering surfaces are wetted in neutral environments and vacuum without using flux.
Solders
Low-temperature brazing of nichrome requires the use of lead-tin brazing alloys, which contain 40 to 60% Sn, as well as the use of special fluxes. Nickel structures, which operate at temperatures of 350-500°C, require the use of silver solders. Copper brazing alloys are rarely used due to their low corrosion resistance and heat resistance. In addition, nickel dissolves in the solder during the copper soldering process. Therefore, strict control of soldering temperature and precise dosage of solder are required. When brazing the nichrome with beryllium- and boron-alloyed solder metal, the brazed metal also dissolves in the solder, so it is necessary to solder without overheating and quickly by strictly following the brazing procedure.
Supplier
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