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.
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.
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.