Brazing is considered to occur within a temperature range of 900°F - 2200°F (470°C - 1190°C). Unlike welding, brazing does not melt the base metals, so the brazing temperatures are lower than the melting points of the base metals. This makes brazing a suitable method for joining dissimilar metals.
The recommended brazing temperature should be the lowest possible within the provided range. For most braze alloys, the minimum brazing temperature is usually at least 25ºC (50ºF) above the liquidus temperature. This minimum temperature is crucial when using free-flowing braze alloys, when brazing large gaps, or when working with thin materials. At lower temperatures, the molten braze alloy becomes less reactive with the base metal and more sluggish. The time at the brazing temperature should be sufficient to ensure that all sections of a part and all parts within the load reach the desired temperature. Typically, this time ranges between 5 and 10 minutes but can be longer for heavier loads.
After the brazing soak is complete, the cooling cycle can begin. It is recommended to cool the load to a temperature at least 25ºC (50ºF) below the solidus temperature of the braze alloy before initiating gas quenching, unless a specific heat treatment is required. This ensures that the molten braze alloy has re-solidified and will not be blown away from the joint during the quench.
Once brazing is completed, the work is allowed to slow cool to approximately 980°C (1800°F) to solidify the filler metal. Parts can then be rapidly cooled by gas quenching, usually in the range of 2 bar.
The furnace temperature is gradually increased to the brazing temperature, which typically ranges between 500°C and 1200°C. This gradual increase allows for proper heat distribution and minimizes thermal stresses. The brazing temperature is maintained for a specified amount of time to allow the filler metal to melt, flow, and wet the base metals, creating a strong joint.
After the brazing process, the furnace is slowly cooled to room temperature to minimize thermal stress and distortion. The parts are then inspected for quality, and if necessary, post-brazing treatments such as heat treatment, machining, or surface finishing may be performed to achieve the desired properties and appearance.
For brazing aluminum and aluminum alloys, it is important to maintain vacuum levels of 10-5 mbar (10-5 Torr) or better. The parts are heated to 575-590°C (1070-1100°F), depending on the alloy, with temperature uniformity typically within ±5.5°C (±10°F) or better. The atmosphere in the furnace should be slightly positive when brazing with hydrogen.
For copper, the optimal brazing temperature usually falls between 1,100 and 1,500℉, and the filler metal's temperature is also important in the brazing process.
Overall, the specific temperature for brazing depends on the materials being joined and the type of filler metal used. It is important to follow the recommended temperature ranges and guidelines provided by the manufacturer to ensure a successful brazing process.
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