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.
- 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
Grades correspond to their chemical composition and are directly related to corrosion resistance and mechanical properties. Surface finishes are the result of mechanical or physio-chemical treatment of the steel surface and can be reproduced on different grades of stainless steel.
As a roofing and façade material stainless steel is easily shaped using conventional methods such as forming, bending, shearing, drilling and punching. It can be installed using techniques such as welding, brazing, riveting, mechanical fixing and adhesive bonding. Due to the metal’s light weight it can be installed in long tray lengths and provides comparable performance to other metals at thinner gauges. This can make a consideration contribution to the reduction of building envelope weight.
Stainless steel can be used on flat or curved surfaces and to form complex shapes such as domes and cupolas. It is not susceptible to fracturing at low temperatures.
Terne coatings on sheet or strip for external cladding, roofing and flashings confer a lead patina appearance to the surface, enabling them to be used as a substitute for lead sheet on buildings such as churches. Terne-coated stainless steels are defined in BS EN 502 and BS EN 508-3 as ‘stainless steel continuously hot dip coated with a lead-tin alloy’.
- 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.
“Stainless Steel – for design, structure and protection against the elements.”
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