101103_Brazing_&_Adhesives

101103_Brazing_&_Adhesives - Introduction to Brazing...

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Introduction to Brazing • BRAZING is a group of welding processes that produces coalescence of materials by heating them to the brazing temperature in the presence of a filler metal having a liquidus above 450ºC (840ºF) and below the solidus of the base metal. The filler metal is distributed between the closely fitted faying surfaces of the joint by capillary action. -from AWS A3.0, Definitions
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Introduction to Brazing • This means – Brazing joins materials (not only metals) – Brazing uses a filler that melts over 450ºC (842 ºF) – Brazing doesn’t melt the base material – The filler metal wicks into the gap between the pieces being joined, and ‘glues’ them together.
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Difference between Welding and Brazing • Welding works by adding molten metal to a joint- and a portion of the base metal is melted.
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• Brazing works by adding molten metal to a joint- and none of the base metal is melted. Difference between Welding and Brazing
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Characteristics of Brazing • Brazing gives a strong permanent joint – Lower temperature than welding – Less distortion than welding – BRAZING IS GOOD FOR DISSIMILAR MATERIALS like copper to steel, or steel to cemented carbide. These could not be welded. (The molten metals don’t mix, like oil and water, OR they’ll crack when they freeze.)
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Components of Brazing •HEAT • FILLER, OR BRAZE METAL •PROTE CT ION
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Components of Brazing •HEAT – Needed to melt the filler – Best if the part melts the filler, since if the heat source melts the filler and the part is cold, the filler may freeze before it completely wicks. – Sources of heat include torch, induction, resistance: and furnace. This serves as a convenient classifier.
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Components of Brazing •HEAT Torch, induction, resistance: – Both manual OR automated. Heat is applied locally, by an operator OR a machine, and the filler flows into the joint. Filler is fed into joint, or joint is pre-assembled. – Concerns are heat flow, heating time, and consistency from part to part, lot to lot, week to week.
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Components of Brazing • FILLER – Specified in AWS A5.8 – There is a great variety of filler metals, with a great variety of melting points and freezing points. – The filler can come as foil, wire, rods, powder, preforms, or paste. The paste is made of small particles of filler metal mixed with flux.
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Components of Brazing •FLUX – Flux is used to: • CLEAN (removes surface oxides) • PROTECT (keeps air from oxidizing filler) – Flux comes in several forms: • Paste, applied manually • Paste, mixed with braze filler • Preforms, attached to braze filler
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Procedure of Brazing
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Procedure of Brazing
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Procedure of Brazing
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Procedure of Brazing
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Procedure of Brazing
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Procedure of Brazing
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Procedure of Brazing
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• Post brazing cleaning – Flux is a mixture of florides, borates, and other salts that melt, then clean and protect the joint. Flux is generally cleaned off in hot water after
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This document was uploaded on 12/19/2010.

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101103_Brazing_&_Adhesives - Introduction to Brazing...

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