Lead is a toxic metal that was used for many years in common household products and municipal services such as plumbing. This metal can be discharged into the air from motorized vehicles and industrial sources and may enter drinking water through the corrosion of aging lead service lines or welding solder. Lead that contaminates drinking water supplies poses serious risks to public health, especially to children. Until 1974, most welding solders used in the United States contained 50 percent lead. In 1986, the U.S. Safe Drinking Water Act Amendments prohibited the use of lead-bearing solders containing more than 0.2% lead in potable water systems. Lead-free silver solder was adopted as a safe alternative.
What Is Silver Solder?
This silver alloy — also known as Sn-Ag-Cu alloy — is rich in tin (Sn), contains 3.0 – 5.0% copper (Cu), and 0.3 – 0.7% silver (Ag). Its make-up forms a strong solder and is often used for mechanical joints. As the Sn-Ag-Cu alloy has a higher melting temperature than lead solder, the parts being joined need to be heated to a higher temperature to enable a strong bond. This lead-free solder can be applied using the same fluxes, joining techniques, and heating equipment for lead-based solders.
Uses of Silver Solder
Silver soldering alloy was introduced to the plumbing industry for joining copper potable water lines. However, the use of this lead-free alloy has expanded to include the building of refrigerator ice dispensers, ice-making machines, juice-dispensing machines, and drinking fountains. This type of solder can join most common metals and is often used in brazing — silver brazing — to create a stronger joint than can be made by soldering.
When to Solder and When to Braze?
The key difference between soldering and brazing is how each works on a joint. Both methods work by flowing a filler metal with a lower melting point than the metals being joined into the joint. However, silver brazing creates joints made with a liquid temperature of more than 450° C — or approximately 840° F, while in silver soldering, the filler metal used has a liquid temperature below this. Neither method involves melting the metal that’s being joined.
Joints created using brazing are typically stronger than those soldered, and brazing is ideal for joining dissimilar metals. Both methods are used with a flux, which chemically cleans the metal during the process. Silver soldering and silver brazing are effective for creating a weather-resistant barrier, as silver is inherently corrosion-resistant. Keeping the joint clearances close and using the minimum amount of filler metal will reduce the joint’s exposure to the atmosphere.
For a lead-free, zinc-free, and antimony-free solder, visit the Canada Metal website. You can choose from various weights and formats and may qualify for same-day shipment.