Results and Conclusions:
Tests were run with 3 different fluxes used.
Test 1 had the surface coating removed with a sand blaster from the surface before the solder heat cycle.
The solder joint was formed but the flux is too flammable. The solder flow was a bit uneven and did favor one side. This is also due to the part being heated previously. The previous heat cycles left the surface slightly warped and uneven. The coil was positioned lower after the initial start of the test melted the top of the tube. Coil position will need to be kept at the center of the tube to prevent damage to the top of the tube and to keep it from overheating the galvanized steel. The power for this test was turned on and off to prevent the overheating of the tube even after the coil was lowered to the center of the tube.
Test 2 had a surface that was not sand blasted but was previously heated and had some alloy already at and around the solder joint. The coil was positioned at the center of the brass tube and the power on this test was turned on and ran for the entire 15 second cycle without overheating the parts. Resulted in a good solder joint with an improved spread of alloy around the part. Additional alloy over flow was from previous alloy over flow. One piece of the alloy did not entirely melt but the solder joint area was fully covered by the alloy. The flux in this test showed an improvement over test 1.
Test 3 was ran on the steel pans that had a wall mounted location for the brass tube. This part was previously untested and was not exposed to any heat, alloy or flux (new part). The pan had an additional pan inside to help keep the brass tube in the correct location. This added additional mass to the part and created an additional heat sink. This does help keep the steel from overheating. This test did have the power turned on and off to keep the brass tube from overheating. The flux used in this test showed the best results and significantly improved solder flow around the brass tube. Even with the slightly rounded base, the solder did not run off and flowed around the brass tube.
This process can be achieved with a 2 kW system in similar time cycles. With lower power, there is a lower risk of overheating and damaging the parts. A longer heat cycle at a lower power will also allow the heat to spread out evenly across the part and promote better solder alloy flow.
A temperature controller and temperature monitoring system is recommended to eliminate the possibility of overheating and damaging to the parts.