Mr. Zowada,
I have been enjoying your articles in Knives Illustrated. It is
refreshing to get a perspective on knife making that isn't filtered
through "party lines". Keep up the good work.
I've been reading quite a bit about the making of Damascus steel. I was
wondering, what is the purpose of the flux in welding? I have heard
several opinions as to the reasons for its use and for different
formulas. Can I make it myself?
Thank you,
J.W.
Duluth, MN
J.W.
Thank you for your kind words. I'm just a guy who makes knives, and
wants to help others see that it isn't that hard to do.
Flux is used during the welding process to clean and protect the
surface of the steel. It isn't magic and it isn't glue. When steel is
heated into the forging range, a surface oxide forms. This is commonly
known as "scale". In the steels used by knife makers, it is usually
iron oxide or a combination of iron and nickel oxides. These oxides can
build in thickness over time and completely prevent successful welding.
The flux is put on the surfaces of the steel being welded. It is
usually applied just before the "welding heat". The flux will then
combine with and dissolve the oxides already on the surface of the
steel, forming a runny liquid. This liquid coating protects the surface
of the steel from further oxidation.
The steel is then brought to welding temperature. A slightly reducing
atmosphere in the forge will also help prevent further oxidation. At
the proper welding temperature the flux, will flow over the surface of
the billet and sort of "shimmer". The best description I have heard of
how this looks was by Bill Moran, "It looks like butter starting to
melt under the sun". The steel is then removed from the forge and the
weld is closed with a hammer or press. If the welded surfaces were
prepared properly, the flux and dissolved oxides will be forced out of
the weld seam as the weld is closed.
Some oxides are particularly difficult to deal with. They stick to the
surface of the steel and are quite resistant to the flux. The worst of
these seems to be nickel. If you weld L6, A203E, 15N20, Nickel 200 or
meteorite you will have more problems getting the welds to "stick". The
easiest method of removing the scale from these alloys is to grind it
off. I prefer to do the grinding hot, right after the billet is creased
for folding. This conserves the heat in the steel, saving re-heating
time.
My procedure looks like this:
1. Heat to 1700F in slightly oxidizing flame.
2. Sprinkle flux on surfaces to be welded.
3. Heat to 2100F in slightly reducing flame.
4. Close weld, forge billet to double length.
5. Cut through center of billet to create a "hinge"
for next fold.
6. Grind off scale from next weld surfaces
7. Fold billet in half.
8. Repeat
Notice that the only heating is at steps #1 and #3. This method is very
efficient since everything is done hot. A 160 layer billet usually
takes about 50 minutes.
There are several formulas for welding fluxes. In the past some of them
were closely guarded secrets. I guess that some still are. Several
years ago a well-known knife maker offered a substantial cash prize to
any one who could guess his "secret" liquid welding flux. I guess too
many people got a little too close because nothing more was ever said�
Most fluxes used today have borax as their primary ingredient. This is
sometimes mixed with sand, iron filings, florspar and other materials
to meet the needs or desires of the blacksmith. Some smiths prefer
anhydrous borax to the regular stuff. It will flow better on the steel
at lower temperatures.
I find that I mostly stick with plain old 20 Mule Team Borax from the
grocery store. It is inexpensive and easy to find. Some of the
commercial or anhydrous borax/florspar mixes do work better. They flow
at lower temperatures and protect the billet better. But, I have a lot
of practice and am used to 20 Mule Team's quirks. If you use straight
20 Mule Team Borax, apply the flux in the bright orange or 1700F range.
Otherwise it will foam, froth and fall off your billet. Maybe I am just
too lazy (or cheap) to use something better.
I hope this helps.
Tim Zowada
4509 E. Bear River Rd.
Boyne Falls, MI 49713
tim@tzknives.com