Brazing and soldering


Brasing and soldering are processes for joining metallic components in the solid state by means of a fusible filler metal (brasing or soldering alloy which must “wet” the two parts perfectly). The operation does not involve melting of the base metals.The operation is known as “soldering” when the melting point of the filler metal is less than 450°C, and “brasing” when it is higher than this value. In the case of roofing, it’s a soldering operation. 

General information

The soldering of stainless steel is carried out using a soldering iron, copper pan and a filler metal using a filler made of lead and tin with a minimum tin content of 28%. It is also possible to use a pure tin at a temperature of 230°C or a tin- silver mix between temperatures of 215°C and 250°C. 
In order to improve the capillarity and the correct adhesion of the surface to solder, it is important to degrease these areas with a pickling flux.
The only approved pickling flux is a diluted orthophosphoric acide based product. The use of pikcling flux containing florides or chlorides (as used for Zinc and Copper) is to be avoided due to the risk of corroding the stainless steel.
A correct soldering bead depends on:
> the cleanliness of the parts to be soldered together
> the cleanliness and geometry of the soldering iron
> the type of pickling flux used
> the filler metal
Practical advice
> Use the pickling flux sparingly.
> Avoid areas not to be soldered from coming into contact with the pickling flux.
> Clean and weather the soldering iron by placing it into the pickling flux for one or two seconds.
> Use tools set aside for soldering stainless steel only.
> Use a soldering iron adjusted to the correct temperature in order to melt the filler metal.
> Avoid using an ammoniac stone.
> Conduct the soldering process in two stages
- first smooth uniform bead to ensure the solder “takes”
- second ribbed or edged bead to ensure the strength and resistance of the solder.
> Rince the soldering beads in clean water upon completion in order to remove any residue of the flux which can be corrosive in a concentrated form over time.
> For valleys wider than 500mm, it is important to rivet before soldering. The rivets should be placed at 5 to 10 cm intervals.
Repairing the solder on tin coated stainless steel
> Abrase the surface in order to prepare a “key” on the base metal.
> Clean the area with diluted orthophosphoric acid.
> Coat the area with the filler metal (lead-tin filler).
> Recoat using diluted orthophosphoric acid.
> Solder as per new material taking the same precautions.