SOLDERING AND BRAZING PROCESS

soldering-and-brazing

Soldering is a method to join piping and tubing to fit­tings.
It is in use primarily in plumbing and heating systems utilizing copper and brass piping and fittings.

Soldering, of­ten called soft soldering, is done at temperatures under 800°F, usually in the 361°F to 500°F range.
When soldering or brazing, there is a gap between the two surfaces that are fastened together.
For example, when two lengths of copper tubing are attached, a fitting or coupling may be placed between them into which each pipe slides.
A clearance is required for the tubing to slide into the coupling or fitting.
A filler metal must be used to fill this clearance.
The filler metal adheres to the tubing and fitting to be joined as it fills the gap.
Only the filler metal melts.

The 50/50 tin-lead solder is a suitable filler metal for moderate pressures and temperatures.

A 50/50 tin-lead solder cannot be used for water supply lines because of its lead content.
95/5 tin-antimony solder is for application with more pressure and to make a stronger joint.
Brazing, requiring higher temperatures, is often called silver brazing and is similar to soldering.
It is used to join tub­ing and piping in air-conditioning and refrigeration systems, Do not confuse this with welding brazing.
In brazing pro­cesses, temperatures over 800°F are used.
The differences in temperature are necessary due to the different combinations of alloys used in the filler metals.
Brazing filler metals suitable for joining copper tubing, are alloys containing 15% to 60% silver or copper alloys containing phosphorous.
These are confusions in terms related to brazing as some might refer it as hard solders or silver solders which are often used by technicians, and it is bet­ter to avoid using them.

In soldering and brazing, the base metal (the piping, tub­ing, and fitting) is heated to the melting point of the filler material.
The piping and tubing must not melt.

When two close-fitting, clean, smooth metals are heated to the point where the filler metal melts, this molten metal is drawn into the close-fitting space by capillary attraction.
If the soldering is properly done, the molten solder will be absorbed into the pores of the base metal, adhere to all surfaces, and form a bond.

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