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Inert environment in the kiln


#1

Hi everybody,

Maybe anyone can help me to make a decision - I was considering how
should I prepare my kiln for mokume. It is not manufactured for
making inert gas environment in it and I can’t imagine how does this
system look, but I have heard that instead of this people use
charcoal. I guess these are two incomparable things so I don’t know
what would be better for me as the beginner. What is the prise for
preparing the kiln that it would be possible to make inert
environment in it, maybe I can do it myself? if Yes, how it is done?
And what are the differences between making billet in that
environment and surrounded by charcoal as Mr. Binnion does. I mean
maybe anyone could explain what happens after burning the billet,
what are the consequences in both situations, and is there a big
difference in results using one and another technique. Thank You in
advance!

Best regards,
Giedrius


#2

Electric furnaces are oxidising atmospheres. You can get electric
kilns that can have argon pumped through them to give an inert
atmosphere but they tend to be rather pricey. Gas kilns can be
reducing, oxidising or inert depending upon how the gas/air vents are
set. you can turn an electric kiln into a reducing or inert
atmosphere by placing carbon in the kiln to remove the oxygen. This
shortens the life of the elements considerably but is otherwise easy
and cheap to do. you can also encapsulate your work piece in
something that will keep air away from it, for small pieces I put
them into a sealed quartz tube under vacuum, ( quartz melts at 1400c
so oxy propane torch needed-alright for my scientific bits but very
time consuming. Larger pieces can be wrapped in Ti or Mo foil to act
as a “getter” for the oxygen or you could put your work in a
stainless steel box with a source of carbon for even bigger pieces.
this last mathod reduces the wear and tear on your elements.

Nick


#3

Hello Giedrius;

The first mokume I made was done in a gas kiln, back in 1989. We were
using copper, nickel and brass, which are more reactive to oxidation
than gold alloys, so it would work fine for gold, I would think. I
was at a conference in Buffalo that Bradney Simon put together and
while there, I saw someone demonstrating a simple, small gas forge
designed for knife makers. I think that you could build something
like that with a large coffee can lined with fiber-frax insulation
and fired with a hardware store propane torch pointing into a hole in
the side of the canister. You’d want a pyrometer, and it might be a
bit tricky to hold the temperature evenly, but if you can keep the
billet at 1350 degrees Fahrenheit for an hour, you can bond most
alloys. As long as there is a reducing atmosphere, you won’t need
charcoal or a shielding gas.

David L. Huffman


#4

Hi Giedrius,

At this point I have made close to a thousand mokume billets and
invested a huge amount of time and money researching the process. One
of the biggest issues that stand in the way of a good diffusion
bonded laminate is the presence of oxygen in the firing of the
billet. It doesn’t just affect the surface but the bulk metal as
well, oxygen will travel great distances into the metal matrix at the
high temperatures and long firing times used in solid state diffusion
bonding. The least expensive method for controlling the amount of
oxygen is to wrap the torque plate / billet assembly in a stainless
steel foil bag filled with charcoal. The foil and charcoal work
together to absorb and reduce most of the oxygen present in the bag
and the gas that leaks in during the firing process. Other methods of
inexpensively controlling the atmosphere like placing charcoal in the
electric furnace chamber and adjusting the fuel burners and vents on
a gas kiln for a “reducing” atmosphere are not effective enough for
the production of a high quality billet. You can make mokume in a
kiln or furnace that is not fully oxygen free but your weld quality
and yield rate will be less than you can achieve with the charcoal in
the foil bag method. Even then it is less than perfect but it is
workable. If your billet does not come out of the furnace looking as
clean and bright as it went in then you have oxygen presence and
oxidation problems to a greater or lesser degree depending on how
much oxygen got into the billet. To achieve the total lack of oxygen
a special furnace is required. There are several types of controlled
atmosphere furnaces and none of them are cheap. Try the stainless
foil and charcoal method first. Once you have achieved a level of
skill with that method then you cna decide if the costs (thousands of
dollars) of a controlled atmosphere furnace are something you wish to
invest in.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#5

I’ve seen kilns retrofitted to provide an inert atmosphere using a
stainless stock pot, stainless tubing connected to the lid with
swagelock fittings, fed by a CO2 canister. The lid does not need to
be airtight as the pot is kept flooded by the continuous slow feed of
gas. It works quite well. You could use argon or nitrogen, but CO2
works as well, is slightly safer and is easy to source. Just make
sure the area around your kiln is WELL ventilated to remove the
excess gas.

Harry Hamill


#6

I wouldnt recommend CO2 as it can break down to carbon monoxide upon
oxidation reaction with metals etc. Nitrogen will react with some
molten metals (esp Al) so the best gas is argon. This is not
expensive, the cylinder rental usually works out more.

Nick


#7

I believe for annealing silver when it is rolled down to make sheet,
cracked ammonia is used. So it must give you hydrogen and nitrogen.
Don’t know how to crack ammonia though. Very small hammers?

regards Tim.


#8
I wouldnt recommend CO2 as it can break down to carbon monoxide
upon oxidation reaction with metals etc. Nitrogen will react with
some molten metals (esp Al) so the best gas is argon. This is not
expensive, the cylinder rental usually works out more. 

Nick, I am not a chemist but was under the impression that the
reaction series was carbon and oxygen forming CO (carbon monoxide)
which is strongly reducing and will grab any available oxygen or
oxide to convert to CO2 a more stable form of carbon oxide not the
other way around.

CO2 will combine with moisture which is always going to be present
on any surface and form carbonic acid which is a very weak acid but
corrosive none the less and will lead to unclean corroded metal
surfaces.

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#9

A chlorine atmosphere is used in continuous soldering processing of
chain and the like. I never did ask what happens to the chlorine.
Resistance soldering using carbon electrodes always works better
when nitrogen is blown over the piece to be soldered as they usually
cannot be fluxed.

Nick


#10
Don't know how to crack ammonia though. 

Ammonia is heated to the point where it disassociates or "cracks"
into its component atoms before being fed into the furnace.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#11
The least expensive method for controlling the amount of oxygen is
to wrap the torque plate / billet assembly in a stainless steel
foil bag filled with charcoal. 

Where does one buy “stainless steel foil?” How is it sold, in a sheet
or already formed into a bag?

Thank you for sharing your knowledge.

Merylyn


#12

Stainless steel foil is used in the heat treating industry. It is
available in two types for this use. One is type 321 stainless steel
and is the least expensive of the two it will work up to 1600 F which
is above the laminating temperature for most jewelry metals. It comes
in rols that are 12 or 24 " wide and of varying lengths(10, 25, 50,or
100 ft). The second type is 309 stainless steel and is good to 2000F
but quite a bit more expensive. It is quite a bit tougher than
aluminum foil but you can cut it easily with scissors and it forms
fairly easily by hand. Use a rawhide or rubber mallet to seal the
folded edges. A word of warning about the stainless steel foil, it
is.002 in thick and the edge is like a razor blade, think of paper
cut on steroids. Always wear cut resistant gloves of leather or
kevlar when handling the foil to avoid being badly cut.

To find it look for “tool wrap” at a machinery supplier like MSC,
Enco, Travers etc all of which have online sales or my favorite
McMaster-Carr at mcmaster.com

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#13

I use the stainless steel foil Mr. Binnion is referring to and would
agree it works well and also has been used for some time in the die
treating world. I use it to heat treat steel like O1 tool steel
before quenching it.

It works good for making billets of metals. I would re-enforce his
comment about being sharp.It’s like a large piece of razor blade and
at all stages you should wear gloves to reduce the risk of cutting
yourself.

As for the ammonia topic we use anhydrous ammonia as used in the
dairy industry and etc for our ovens.I would suppose this is similar
to the cracked ammonia as to the fact that we use it to disassociate
oxygen from the air as regarding inhibiting fire scale and
oxidization.

These ovens are made to pump the ammonia into the oven and are widely
used in many different industries other than ours.

Daniel Wade
Albuquerque,NM


#14
These ovens are made to pump the ammonia into the oven and are
widely used in many different industries other than ours. 

Ammonia gas flows through a disassociator that heats it to the point
where is breaks down to nitrogen and hydrogen then it is piped into
the furnace. The theory is it is safer to store ammonia than
hydrogen. I am not so certain about that as the ammonia will hurt
you bad and possibly kill you if you get a lung full from a leak so
in either case it is dangerous.

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#15

Daniel,

I use the stainless steel foil Mr. Binnion is referring to and
would agree it works well and also has been used for some time in
the die treating world. I use it to heat treat steel like O1 tool
steel before quenching it. 

A little tip when doing this. Put a little piece of paper in with
the tool steel. As it heats up, it will ignite and consume what ever
oxygen is in the packet, thus reducing oxidation.

Best Regards.
Neil George


#16

G’day

I worked in a laboratory where an inert atmosphere was needed in a
kiln - small furnace - and at first we had a second furnace to crack
ammonia. But someone thought that as we were buying bottled gases,
why couldn’t the suppliers make up a simple mixture of hydrogen and
nitrogen in the correct proportions… Well, they boasted that they
could supply any bottled gas wanted, from pure cyanogen to pure
medical oxygen. So we bought bottled (cylinders) a mix of 3 parts of
hydrogen to one part of nitrogen (Ammonia gas is NH3) which was very
safe and did the job - and wasn’t expensive. The supplier was the
British Oxygen Co. Anhydrous ammonia gas can be very nasty indeed.

Cheers for now,
JohnB of NZ


#17
But someone thought that as we were buying bottled gases, why
couldn't the suppliers make up a simple mixture of hydrogen and
nitrogen in the correct proportions. 

As far as I can tell the main reason that people are using anhydrous
ammonia is that it is cheap in comparison to mixed gas.

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550