Homemade Chisels

[abknight@zzzzzz]

Tungsten Carbide info and very techie brazing site.

If I remember correctly Tung Sten equals Heavy Stone. It
can also handle heat and established the success of the
lightbulb as a long lasting hot burning filiment.
Carbides, apparently are something that forms in the
heating of steels or metals which have carbon added to
them, I am not sure.
 From Oliver Sacks' "Uncle Tungsten": a shpere of tungsten
two feet in diameter would wiegh five thousand pounds.
The chemical symbol is W after wolframite, the ore in
which it can be found.  It was found in tin mines and it
wolfed up all the tin in bindings that were very hard to
undo.

http://www.carbideprocessors.com/Brazing/book/index.htm

What follow are a few exerpts that I found interesting.
There is huge info on brazing.  Not so much if any on
sharpening.
"The single greatest cause of braze failure from brazing
is the fact that the saw tip is pushed in too hard and all
the silver solder is forced out the sides.  There needs to
be .003 to .005 inches of silver solder between the
carbide tip and the saw plate.  Anything greater or
thinner will drastically weaken the braze joint. "  But
that is for a saw blade.

Knoop Hardness Ratings
Diamond                                   6,000 - 6,500
Silicon carbide (solid)                2,130 - 2,140
Aluminum oxide (corundum)      1,635 - 1,680
Tungsten carbide (Co binder)    1,000 - 1,500
Hardened steel                             400 -   800

Tungsten carbide is actually grains of tungsten carbide in
a matrix.  Commonly this matrix is cobalt.  This is pretty
handy because you can mix carbon, tungsten and cobalt
together and sinter them.  The tungsten and the carbon
form carbides and the cobalt does not.  You get very hard
grains for wear resistance and the cobalt stays relatively
soft for impact resistance.  These are sometimes called
cemented materials and cemented tungsten carbide because
the tungsten carbide grains are cemented together with
cobalt or other materials such as nickel and nickel-chrome
alloys.

Tungsten carbide is fairly yielding compared to the
ceramics.  You can take tungsten carbide, heat it and bend
it into spirals and curves for cutters, which you cannot
do with ceramics.

Making Tungsten Carbide
Tungsten and carbon powders are blended and carburized in
a furnace at 2700 - 2800 F.  This produces the WC grains.

These grains are combined with Cobalt powder and mixed in
a ball mill.  Tungsten carbide balls are mixed with grains
allowed to run for several days to get even dispersal of
the grains and the cobalt powder.  This powder is then
dried and wax is added as a binder.  The wax holds the
powder together and makes it somewhat slippery so it
presses into shapes well.  Typically 15 to 30 tons of
pressure is used to form the carbide into a tool shape
such as a saw tip.  The parts are typically pressed one of
three ways.  They are rammed in a mold before sintering.
They are isostatically pressed.  Isostatic pressing means
they are surrounded by a liquid or a gas and the pressure
is applied to the liquid.  This transfers the pressures to
the surface of the parts uniformly.  The third pressing
method is hot pressing during sintering.

The shapes are presintered in an atmosphere-controlled
furnace at temperatures of 1,000 - 1,500F.  The wax melts
out and leaves the pieces sort of like a soft chalk.
These chalk pieces can be easily machined although they
are also easy to break and can be chipped here if handled
improperly.

The final step is another sintering step that can take
place in a special atmosphere, a vacuum or both.  The
temperature is typically 2,500 - 2,700 f.

During final sintering the parts will shrink up to 15% in
any dimension and up to 35% in volume.

Exerpted from
http://www.carbideprocessors.com/Brazing/book/03.htm