Silver (Ag) FAQs
Straight answers to the questions people ask most when choosing and using silver brazing rods and wire.
What does the silver percentage in a brazing alloy tell me?
It tells you roughly what sort of alloy it is. Silver brazing alloys range from fairly low to high silver content, and the balance is mainly copper and zinc, sometimes with a little tin or nickel. The silver content affects colour, melting range and how freely the filler flows.
As a general guide, higher silver alloys are whiter and tend to run at lower temperatures and flow more freely into tight joints, while lower silver alloys look more yellow, like brass. The exact melting range and best joint gap are different for every alloy, so read the maker's data sheet rather than relying on the percentage alone.
What do designations such as Ag 155 or Ag 140 mean?
They are classification codes from the international standard for brazing filler metals. Each code identifies a defined alloy composition, so two products carrying the same code should have the same make-up even if they are sold under different names. Older standards used different codes, and some products list both.
The code helps you compare alloys and check that a replacement matches the one in your procedure. It does not tell you the diameter, whether the rod is flux coated or the pack size, so check those separately on the product details.
Why choose a cadmium-free silver brazing alloy?
Older silver brazing alloys often contained cadmium, which gives off highly toxic cadmium oxide fume when it is heated, and overheating makes this worse. The HSE has guidance for people using cadmium-containing brazing products, and serious illness has been recorded after exposure to the fume.
Cadmium-free alloys remove that particular hazard and are the usual choice today. You still need good ventilation or local extraction for the flux and metal oxide fume, and you should be careful with any cadmium plating on the parts, which should be dealt with before heating. Follow the maker's safety data sheet and your risk assessment.
How big should the joint gap be for silver brazing?
Very small. Silver brazing relies on capillary action, which draws the molten filler into a narrow gap, so the parts should fit closely with only a fraction of a millimetre between them. Too wide a gap weakens the joint and can leave voids, while no gap at all stops the filler entering.
The best gap is the one at brazing temperature, not room temperature, and it changes if the two metals expand at different rates. The maker's data sheet gives the recommended gap for each alloy, so use that figure.