Uplink Tom
Senior Heliman
Location: Boyertown PA
| it'll workI've been silver brazing for years.
from some website:
Note: While modern U.S. usage calls the use of these alloys silver brazing, obsolete U.S. works and many current British sources often use the terms silver soldering or hard soldering to describe the same process. This is a source of continuing confusion, since silver solder is a term also used to describe much weaker alloys used at low temperatures for plumbing work. To avoid confusion, try to refer to an alloy's composition, standardized classification, or melting and flowing temperatures. When in doubt, seek clarification.
Common silver brazing alloys contain as much as 60% silver or as little as 20%, with the remainder made up of metals including copper, zinc, nickel, and tin. Silver brazing alloys melt at temperatures as low as 1145F, greatly reducing the impact on heat treatment of bicycle tubing. There is still a heat affected zone near the joint, but the butting of the tubing provides more material here to make up for its reduced strength. Away from the joint, the lower joint temperature means less heat travels along the tubing, and the heat treatment remains effective. The skill of the brazer also plays an important role in reducing heat damage, since the longer a joint is heated, the more heat is available to damage surrounding material.
Often, silver brazing alloys also include cadmium, a poisonous metal with deadly fumes. Cadmium lowers the brazing temperature and improves handling characteristics slightly, but should only be used by expert workers with commercial grade ventilation equipment. Using it at home in your garage is asking for trouble, so if you want to do silver brazing, look for cadmium-free alloys. All the major manufacturers of silver brazing alloys produce cadmium free fillers.
Silver is also the filler of choice for brazing stainless steels. Most brass fillers will not wet the surface of stainless, and if they do they will produce low-quality joints. Brazing stainless steel takes more practice than brazing ordinary steels, and in some cases special filler alloys are needed to prevent corrosion between the filler metal and the base metal. A small amount of nickel is added to the filler alloy to prevent this sort of corrosion, which can otherwise cause rapid failure of joints continuously or repeatedly exposed to water.
While each manufacturer has its own trade names for its alloys, most alloys sold in the U.S. conform to one of a number of specifications established by the American Welding Society (AWS). A common cadmium-free alloy used in bicycle work is AWS No. BAg-7, which has the same characteristics whether sold as Safety-Silv 56, All State 155, or Silvaloy 355. The alloy is 55 to 57 percent silver, 21 to 23 percent copper, 15 to 19 percent zinc, and 4.5 to 5.5 percent tin.
Nickel Silver Brazing
One final class of brazing filler that should be mentioned is nickel silver alloy. Despite the name, this is not a silver alloy at all, but mainly nickel and copper. It has a much higher melting point than genuine silver alloys, and should not be used on heat treated tubing.
On the other hand, nickel silver is stronger than brass filler, often much stronger, and some nickel silvers will work well on some alloys of stainless steel. All State specifically recommends one of its nickel silver alloys, No. 11, for brazing bicycle frames, and this alloy does make strong, reliable frame joints. According to his Manual, this is Tim Paterek's preferred fillet brazing alloy, too. It has a very wide working range, from 1200 F to 1750 F, and a tensile strength of up to 85,000 psi.
Heli's just mock me then crash.....C5, C30, B400, Q50, 9C |
