Copper is used in its pure state mostly in applications that require high heat or electric conductivity, while its alloys (bronzes and brasses) are widely used in several fields thanks to their excellent corrosion and wear resistance. Copper and its alloys have been and still are a great natural resource for the growth of mankind.
The end products of copper fabricators can be generally described as mill products and foundry products. They consist of wire and cable, sheet, strip, plate, rod, bars, tubing, forgings, castings and powder metallurgy shapes. These products made from copper and copper alloys may be heat treated for several purposes such as homogenizing, annealing, stress relieving and precipitation hardening.
Definition according to DIN EN 10052: „Annealing carried out in m medium that allows the original metallic surface finish to be maintained by preventing oxidation of the metal.“
Annealing is a „heat treatment consisting of heating and soaking at a suitable temperature followed by cooling under conditions such that, after return to ambient temperature, the metal will be in a structural state closer to that of equilibrium.“
A medium is an „environment in which the product is placed during a heat treatment operation. The medium can be solid, liquid or gaseous. “
The protective gas consists of nitrogen and hydrogen. The maximum concentration of the hydrogen is approx. 5 %.
Messer process = "Neutrotherm"
The hydrogen content in nitrogen-hydrogen mixture exceeds 5 %.
Messer process = "Hydrotherm"
Definition according to ISO 3252: Sintering is a ”thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding together of the particles.”
Powder metal parts sintered in controlled atmospheres result in efficient binder removal, size control, less sooting and bright surface finish.
It is important to understand the significance of introducing gases into the specific furnace areas where they are most effective. Called zoning, these special atmosphere injection techniques control both the flow pattern and the chemistry of the atmosphere.
Depending on the material to be sintered, in addition to hydrogen/nitrogen mixtures, nitrogen/hydrogen/hydrocarbon or pure hydrogen is recommended.
The Endolin process was developed and patented by Messer. Endo gas is blended with nitrogen to get the desired concentration of active gas components and the mixture is fed directly into the furnace.
Messer Process = "Endolin"
Brazing and high-temperature brazing
Brazing is a joining process wherein metals are bonded together using a filler metal with a melting temperature greater than 450 °C, but lower than the melting temperature of the base metal.
High-temperature brazing is flux-free brazing under exclusion of air (vacuum, protective gas) with filler metals whose melting temperature is above 900 °C.
Depending on the base material, two different types of gas atmospheres are used in furnace brazing using flux and inert gas and in high-temperature brazing:
- Chemically inert atmospheres, which protect the parts being brazed from coming into contact with other gaseous elements, which might react with the metals being joined thereby producing surface films that might inhibit flowing of and wetting by the molten brazing alloy.
- Chemically active atmospheres, which will react, during the brazing cycle, with any surface films present on either the parts to be joined, or the brazing alloy preform, removing them in the process.