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Thread: Brazing vs. soldering
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17-05-2002, 04:40 PM #1
Brazing vs. soldering
There is a question that I have never seen answered completely. Why are all tube connections in a refrigerating system done with brazing, and never with normal soldering?
To be sure that we are talking about the same thing (English is not my natural language, and I am not very good in foreign languages besides Verilog and C++):
- With brazing I mean connecting two metal surfaces with a filler metal, melting point > 650 °C
- With soldering I mean connecting two metal surfaces with a filler metal, melting point < 350 °C
When I am 'brazing', I am using a powder-like flux and brazing rods containing about 40% silver. When I am soldering, I am using a liquid flux and SnPb or SnAg solder.
Now, both types of connecting metals provide a strong joint. Now I wonder: why is the more expensive and possible more risky method (easier to damage TEV's, for example) of brazing always used? I can imagine a few reasons:
- Strength. Joints at the high pressure side of the circuit must be strong to resist peak pressures. Now, I have already seen hydraulic systems where pipes are conencted using normal solder joints. The pressures in these systems are usually higher than those in any common refrigeration system. A pipe-to-pipe connection using SnAg solder should easily withstand 30 bar peak pressure.
- Heat. Joints in the discharge line must withstand heat and high pressure. I can imagine that normal solder joint gets weak at high temperatures, but those temps are not that high, are they?
- Tightness. Maybe a normal solder joint leaks refrigerant?
Well, what is the reason that those connections need brazing instead of normal soldering?
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