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Brazing Stainless Steel Tubes

Brazing stainless steel tubesResearch Objective
To braze two lengths of stainless steel tubing together at low temperature within 20 seconds

Parts & Materials Description
(2) .350 O.D. steel tubes, one with a slight flare at edge; BAg-24 brazing wire, black flux

Temperature Required

Induction Heating Equipment
7.5 kW RF power supply, 4-turn helical inductor (coil) with 1.5” O.D.

Operating Frequency
279 kHz

Heating Procedure
The testing was done in an open air atmosphere. A specially-designed, four turn helical inductor was used to provide optimal heating to the joint area. Initial tests were conducted with bare parts and temperature sensing paints to establish time-to-temperature and heating profiles. The BAg-24 brazing wire was shaped into preforms to fit the O.D of the straight tubing section. Black flux was also applied to both tubes. The two tube sections were then fit together with the braze preforms up against the flared tube section. After RF power was applied for 18 seconds, braze wire reached a temperature of 1330°F. The wire then melted and flowed into the joint. RF power was maintained for another two seconds to ensure that all the braze wire melted.

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