Re: [TCML] DUMB QUESTION OF THE DAY

[Quarkster <quarkster@xxxxxxx>]

Ed -
   
  Actually, brazing tungsten is quite easy. Almost all brazing alloys will "wet" both cupro-nickel (the outer layer of modern composite dimes) and tungsten. Brazing tungsten does NOT require that the workpiece get any hotter then the melting point of the brazing alloy.
   
  For small workpieces like yours, a propane torch should be adequate, as long as it can provide enough heat to get the parts to a dull red color. The melting point of the silver-bearing brazing alloys starts around 1100F, well within the capability of a propane torch with a good nozzle. The nozzle characteristics of "Home Depot" type propane torches are highly variable; some can produce a perfect flame with a needle-like inner cone, while others can only generate a crude "brush" type flame. You want the needle-type flame to give you pin-point control of the hottest part. Apply brazing flux to both parts BEFORE you start to heat them, or the surfaces will oxidize before you reach the point where the filler metal will flow and wet the surfaces. Larger workpieces will require a MAPP gas torch, or an oxy-acetylene rig. There are literally scores of brazing alloys that will work for this type of application, but the silver-bearing alloys will have the lowest melting points and
 are easiest to work with. See:http://www.silvaloy.com/hiag.php for some info on various Ag brazing alloys & their melting points.
   
  If you are working with an oxy-acetylene rig, or a MAPP gas torch that allows you to adjust the fuel-oxidizer ratio, adjust the mixture to a neutral or slightly reducing flame to minimize the risk of oxidizing the surfaces of the workpiece before they get up to brazing temperature.
   
  I've silver-brazed a fair amount of tungsten rod of various sized into machined brass electrode holders for static and rotary gap electrodes with good results. A bead-blast or sand-blast cabinet works great for cleaning off residual flux and surface heat-discoloration, but you can also use a heated solution of phosphoric acid ("Lime Away" or similar household cleaners).
   
  Regards,
  Herr Zapp
   
   bunnykiller <bunnikillr@xxxxxxx> wrote:
  Hey Ed...

Brazing Tungsten is one of the more difficult metals to achieve. When 
brazing, both the parent and daughter metal have to go to a point of 
"wettness" to allow the brazing compound to grab ahold of the mating 
surfaces. Tungsten, being that it has such a high melting point, is 
going to be difficult to meet the wet point of the metal with standard 
propane/MAPP gas applications. Oxy/Acetylene does produce the heat 
needed but it also adds too much oxygen to the surfaces of the metals 
and quickly creates oxides. Even with high quality fluxes, the oxygen 
content is still excessive and the flux is unable to hide the metals 
from the oxygen, thus resulting in a weak bond. Seems that a method of 
submersing the 2 metals in a flux bath and an electrical weld would 
probably be the best bet for home brew situations.

Im interested in what application you have in mind for this dime n wire 
spark gap...

Scot D

(SNIP)

 
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