There is several ways that we can choose to make longitudinal fin tubes for Cu-alloy. And I’m going to introduce the best option among them. We’ve tried many times to get a good result and failed many times too. And finally we found the best way without failure of quality.
The first one is lead soldering. The melting temperature of lead is 327.5°C and the environment of the tube for use is 200°C maximum. Fins are attached to tube surface perfectly without a gap. Lead is melt down and fixes both wall of fins and out surface of tubes. Work is simple and fast. It’s cost effective way to produce the fin tubes. And no need skilled welder for produce. However, when it was repeated the temperature of fluid going up to 95°C and cooled down, the fins were slightly raised up out of tubes. Every metal expands when it gets heat, and shrinks when it loses heat. We thought we could solve this issue because elongation of lead is high. But the result were opposite. The discrepancy of elongation between lead and Cu-alloy tubes wasn’t the issue but the problem was thermal conductivity. Lead is 30㎉/mh°C but Cu is 300~340㎉/mh°C. Lead couldn’t follow up Cu-alloy’s thermal transferability.
The second method is silver soldering. It’s alloy of Silver-Copper-Zinc or Silver-Copper alloy. Melting temperature is between 720~855°C. Work is also simple and fast. Its cost is a little higher than lead soldering but not much. We had a test as the same condition of lead soldering. And we found the same problem. Fins were off. Most of all, fin and tube materials were burned out a little caused by high heat temperature during welding. Aside by material issue, welding condition is not recommendable.
The third method is laser welding. Laser welding is very fast. It melts both fin and tube materials at the same time. Two materials are firmly attached and never detached during experiment. Fluid temperature were 95°C and cooled down. We found no transformation. The only defect is fin material can be burn out in dark color. But material shape is sound without deformation. However, it costs very higher price than soldering method.
The last option is Spot Welding by electric resistance. Mechanism is similar to laser welding. It melts both fin and tube materials at the same time. But it remains no burning mark. Heat transfer efficiency is good. Cost is cheaper than lead soldering but early stage investment is expansive. If continuous manufacturing plan or orders built, this method is highly recommendable among the others.
The Original Posted by Jethro