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Iron Powders for Brazing
Brazing is a joining process whereby a filler
metal or alloy is heated to melting temperature and
distributed between two or more close-fitting parts by capillary action. At its
liquid temperature, the molten filler metal and flux interacts with a thin layer
of the base metal, cooling to form a strong, sealed joint. By definition the
melting temperature of the braze alloy is lower (sometimes substantially) than
the melting temperature of the materials being joined. The brazed joint becomes
a sandwich of different layers, each metallurgically linked to the adjacent
layers. Iron powders are used in high temperature brazing at temperatures of
above 900ºC.
To create high-strength brazes, a brazement can be annealed to homogenize the
grain structure and composition (by diffusion) with that of the parent material
.
High temperature brazing is a joining process carried out under vacuum
or in a controlled (reducing) atmosphere with a brazing temperature
above 900°C. At brazing the brazing filler metal melts and is drawn by
capillarity while molten into the thin space between the base material
(not melted) that are to be joined. When cooled a strong and leak free
metallurgical bond is created.
Application Examples
High temperature brazing is commonly used to join complex shaped stainless steel
parts but also for other base materials like nickel alloys, cupper alloys and
diamonds. Brazing applications are found in automotive, industrial and tool
industry where strength and resistance to corrosion and oxidation
is required.
Heat exchangers for automotive, industrial and domestic use are brazed using
cupper-, nickel- or iron based brazing filler metals. In cases where high
corrosion and oxidation resistance is required nickel brazing is recommended.
Newly developed iron based brazing filler metals is a low cost alternative to
nickel brazing.
Manufacturing Methods
Brazing filler metals are pre-placed
near or in the joint, preferably using a paste. The paste is composed by brazing
filler metal powder mixed with a binder (water or solvent based) with powder
content at about 80-90%. The binder determines the rheological properties of the
paste which is chosen depending on how the paste is applied to the base
material. The brazing paste may be applied by dispensing, screen printing, roller
coating and spraying.
When the
paste is applied to the base material the whole part is heated in a vacuum
furnace (or in reducing atmosphere), the binder is burned off at about 500°C and
at the brazing temperature the brazing filler metal melts and fills the space
between joining parts by capillary forces. When cooling down, a leak free -
metallurgical joint is formed.
Questions? Please call
973-405-6249 to discuss your specific needs.
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