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Ask the Experts Metals

How can I prevent copper filler metal from spreading away from the brazed joints in my steel parts?

Tom Philips
Sr. Principal Applications Engineer

In furnace brazing, this tendency for the melted copper filler to flash and spread is generally caused by one of four factors:

  • Your brazing zone temperature is set too high. Copper melts at 1984ºF. For carbon steel brazing, the brazing zone should be set at 2050 ± 10ºF.
  • The reducing power of your atmosphere is too high, caused by too low a dew point or too high a concentration of hydrogen in the brazing zone. For carbon steels in a muffle type furnace, dew points should range from -10º F to +10ºF, with 5% hydrogen.
  • The joint gap is too wide, producing lower capillary forces for the melted copper to flow into the joint; this causes the copper to flow away from the joint.
  • The part is in the "hot zone" of your furnace for too long.

You can help prevent this tendency by avoiding these scenarios.

For a free copy of our technology guide, "Introduction to Furnace Brazing," please call us at 800-654-4567.
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