FURNACE BRAZING

In-line brazing using precision controlled atmosphere belt furnaces

What is furnace brazing? Furnace brazing joins metal parts by heating them and using a filler metal with a lower melting point than the pieces being joined. The filler material flows between the surfaces of the closely fitted joint due to capillary action. The interaction between the molten metal and the base materials forms a metallurgical bond as the filler material cools and solidifies.

The materials selected, atmosphere, rate of heating, peak brazing temperature, and process time are interrelated; and each of the process conditions must be precisely controlled to ensure a reliable joint. To minimize the oxidation of metal it is important to have inert process atmosphere. This is accomplished by using dry nitrogen, sometimes mixed with hydrogen, to ensure that this is a low oxygen level. Additionally, the process gas needs to have low moisture content.

Brazing profiles: blue = aluminum, red=copper and brass

Brazing Furnace Thermal Profiles

The blue profile to the left is for brazing aluminum heat exchangers. The brazing furnace process requires a ramp-up in temperature at a rate of 50°C/min to a  peak temperature of 680°C, followed by a fast cooline using eductors (patented high-temperature cooling technology) and a water jacket. The process gas is nitrogen with a dewpoint of -20°F or better. The red profile to the left is for brazing copper and brass. The process requires a ramp-up in temperature of 100°C/min to a peak temperature of 715°C, followed by atmosphere cooling jets and water cooled eductor coolers. The process gas can be dissociated ammonia, hydrogen, or forming gas.

BTU Controlled Atmosphere Muffle Furnaces (TCA) are optimized for furnace brazing. The furnaces are fully customizable to meet varying process/production requirements. Key features include:

• Muffle construction for high purity N₂/H₂ atmosphere operation
  • <2ppm O₂ Inert atmosphere
  • National Fire Protection Association NFPA 86, NFPA-79 and UL508a safe atmosphere compliant
  • Made in the USA with high quality materials for maximum reliability
• Left Center Right Trim
  • Improves part uniformity and yield
  • Uniform eutectic across plates
• Gas Barrier*
  • Superior atmosphere separation
  • <2ppm O2 Inert atmosphere
• Cooling Eductors*
  • Shorter foot prints
  • Controlled cooling of heavy loads

*May only be required for most demanding applications based on load/profile