Carbide Inserts for Rotary Electrodes

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Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

Jon -

Most older commercial TIG welding systems utilized a simple spark-gap RF
generator for starting the arc. These RF generators utilized replaceable
screw-in tungsten electrodes. These electrodes consist of small tungsten
disks 3/8" or 1/2" in diameter brazed to a short section of brass rod with a
threaded stud opposite the tungsten disk. These electrodes screw into heavy
brass blocks that serve as heat sinks and connection points. Somewhere I
have the part number for the inserts used by Lincoln Electric for their
older systems; I'll try to locate the data. Last time I checked,  these
replaceable tungsten electrodes were about $12 each.

Some of the "commercially" made rotary spark gaps use these screw-in
elements as replaceable inserts for both the flying and stationary
electrodes.

Many manufacturers of industrial tungsten carbide cutting tools offer
carbide "inserts" in the form of flat disks, 1/4" to 1" in diameter, with
thickness from .1" to about .25". These are very easy to silver-braze to
sections of brass rod to make carbide-faced spark-gap electrodes. An
oxy-acetylene torch is required to get everything hot enough, especially if
1/2" diameter or larger brass rod is used. I've used both paste brazing
alloy (mixture of flux and powdered brazing alloy) and thin foil; SilFos is
one of the alloys commonly used for brazing tungsten carbide cutting inserts
onto the tool shank.

In a spark-gap application,  tungsten carbide is not as erosion resistant as
pure tungsten is, but if you can get slightly used insert disks for a few
dollars a pound they may be more cost-effective than paying $$$ for the pure
tungsten electrodes.

Remember that for flying electrodes used in RSG applications you must keep
the flying electrodes well below red heat to prevent melting of the brazing
alloy securing the carbide disk, which typically has a melting point of
1200 - 1400 degrees F. In any case, a scatter shield should always be used
around the rotating parts or any RSG.

Scott Hanson