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Aluminum & its alloys

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Bright annealing

Coiled aluminium alloys and foils were traditionally heat treated in an exothermic generated atmosphere or in air. Aluminium alloys that contain even very small amounts of Mg and/or Mn will form surface oxides unless the atmosphere in the annealing furnace is free of moisture and oxygen.

Another problem that control of the annealing atmosphere helps to overcome or avoid is oil staining by oil-base roll lubricants that do not burn off at lower annealing temperatures. If the oxygen content of the furnace atmosphere is kept very low during such annealing, the oil will not oxidize and stain the work.

Additionally the use of air and exothermic gas can produce explosive conditions in the furnace atmosphere. Depending on the amount of rolling coils coating the lubricants surface, an explosive condition could result in the furnace during vaporization of the lubricants in an air atmosphere. In addition, the variation in atmosphere composition can produce oil staining unexpectedly.

Furthermore, exothermic generators have high maintenance costs and sometimes cause production losses due to equipment breakdown.

Consequently, nearly all heat treaters of aluminium use a pure nitrogen atmosphere supplied by liquid stored nitrogen tanks.

Nitrogen purges the oxygen out of the furnace, eliminates the risk of explosion due to oil vapors and avoids the formation of flammable atmospheres containing toxic components such as CO, as found in exothermic atmospheres.

Messer Process = Neutrotherm

Source: Ebner Industrieofenbau

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Sintering

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�?.

Aluminum 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 alloys to be sintered, in addition to pure nitrogen, hydrogen/nitrogen mixtures are used.

Messer Processes =  Hydrotherm, Neutrotherm

Source: European Powder Metallurgy Association

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Brazing

Aluminium brazing is the preferred process for the production of automotive heat exchangers such as radiators, condensers, evaporators and heater cores.

This process, the so-called NOCOLOK® Flux brazing process, is carried out in continuous belt furnaces under pure nitrogen.

Nitrogen is introduced in the critical brazing section of the furnace and flows towards the entrance and exit. This prevents the ingress of contaminants from outside into the furnace. As the component enters the critical brazing zone, furnace atmosphere becomes established, i.e. the dew point is ≤ –40°C and the O2 concentration is < 100 ppm. These conditions are necessary for optimum brazing results.

Messer Process = Neutrotherm

Source: Seco-Warwick