Copper 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. Copper powders are used in high temperature brazing at temperatures of above 900°C.
Copper powders, brass powders and bronze
powders in paste form are used as filler metals for brazing steel and copper
alloy parts. A brazing alloy paste consists of metal powder (55-90%) and a
neutral binder (10-35%). It may also contain up to 10% flux. Fluxing is not
required, for example, in certain controlled-atmosphere brazing operations.
Pastes range in consistency from those that can be sprayed to those resembling
putty.
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
.
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.
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 (about 1100°C) 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 973-405-6247 to discuss your specific needs.