Burn out time in Olympic kiln

Jewelry Discussion
1

Dear Ganoksin members,

I was wondering if anyone could please help me program my new kiln? I
purchased a programable Olympic kiln, model 129. I was told that this
kiln was originally designed for burnout. I have the Kerr chart for
burnout:

5 hour Cycle (for flasks up to 2 1/2" X 2 1/2") preheat to 300
degrees.

1 hour - 300 F
1 hour - 700 F
2 hour - 1350 F
1 hour - (ladies/ intricate design 900- 1000: gents or heavy pieces
700 -900)

8 hour Cycle (3 1/2" X4")
Preheat to 300 degrees

2 hour - 300 F
2 hour - 700 F
3 hour - 1350F
1 hour -(ladies/ intricate design 900- 1000: gents or heavy pieces
700 -900)

12 hour Cycle (4"-8")
Preheat to 300 degrees
2 hours - 300F
2 hours - 600F
2 hours - 900 F
4 hours - 1350F
2 hours - (ladies/ intricate design 900- 1000: gents or heavy pieces
700 -900)

I called Kerr and they told me that the kiln should increase by 9
degree increments and that should be included in the 5, 8 or 12
hours. If that is the case, where do you rob the time from?

I’m thinking that the 1 hour at 300 needs to stay the same and the
last 1 or 2 hours needs to stay the same. Does the 9 degrees /
minute come out of the other times? Or does the 5 hour cycle actually
take more time?

If anyone has a different program that they use that is successful,
I would appreciate the advise.

Thank you,
Bobbie Blakely

2

Bobby,

I have a programmable kiln that was meant primarily for PMC. I have
used it for nothing but burn outs. I programmed it for the 8 hour
burn out following Kerr’s times and temperatures. The 8 hour program
actually takes closer to 9 + hours and I have not had any bad burn
outs what so ever. Even organics seem to burn out clean using this
programming cycle. It just takes more than 8 hours when you add in
the time it takes for the changes in temperatures.

I avoid the brain damage by putting in the temperature (as per Kerr)

  • hold for the time recommended (as per Kerr), then go to the next
    temperature - hold for that time period and so on and so forth until
    it is ready for casting. That is just me though. I don’t have any
    time restrictions.

I like 1000 deg. F to 1100 deg. F for centrifugal casting for the
final temperature and 900 deg. F for vacuum casting.

Good luck,

Ken Moore
www.kenworx.com

3

I forgot one more bit of When programming for the final
temperature I make the hold time 3 hours. That way is doesn’t start
to cool down before I am finished casting. I still wait the 1 hour
at the final temperature before casting.

Ken Moore
www.kenworx.com

4

Bobby,

What can I say?

After sleeping on it I remembered that I program the rate of
temperature change to FULL. On my kiln if I increase the temperature
per minute to the max amount it says FULL.

By using the FULL rate it takes the minimum amount of time to
increase or decrease in temperature.

I hope all of these pieces of info will help.

Ken Moore
www.kenworx.com

5

Hi Ken,

Thank you so much for your help. I definitely have a tendency to
over think things. Especially since I have been having porosity
problems.

When we cast the new kiln for the first time, we used the Kerr
chart, it took longer but that was fine. The burnout was the best we
have had. Our kiln doesn’t have the ability to set the ramp time to
full.

I am pretty sure now that my porosity problem is in the designs and
the spruing.

Another question that I have is do you put different size cans in
the same burnout. Or only all the same size cans for each burnout?

Thanks again,
Bobbie

6

Bobbie,

I use any where from 2 1/2" flasks to 4’ flasks and up to 4" tall. I
can only do 4 of the 4" diameter flasks because my kiln is too small
for more.

I do the 8 hour burnout for mixed sizes as well as for all the same
size.

I have had porosity problems at first as well. Things that I have
found effect it is:

  1. The type of silver. I primarily use silver casting shot from
    Sante Fe Jewelry Supply that is their #58, (I believe that is the
    number). It is supposed to be anti-porosity and anti-firescale. I
    also
    use Sterling Silver as well.

  2. I try to use at least 50% virgin casting shot or more if I can. I
    do a lot of fabrication and I always save my filings and misc. pieces
    to use in casting.

  3. I use a small branch of apple wood to stir my silver during
    melting. I like the way it smells when it burns and it helps remove
    some of the free oxygen that may be in the molten silver.

  4. One thing that I learned the hard way was not to over heat my
    silver before pouring. I seemed to boil like and it did some real
    weird things like have bits of copper that seemed to come out of the
    Sterling or else it was contaminated. Just the same try not to over
    heat your silver.

Actually I have a paper that I put together to share with my fellow
students at our Senior Center Jewelry class. It has specific
instructions for mixing the investment and other I have
gleamed from friends, from books that I have cited where I had the
on to give credit due and from just experimenting and
trial and error. If you have Microsoft Word I can e-mail you a copy
of it if you would like. I don’t want to take any credit for the
paper other that just putting down my experiences on paper. Those
that were in our last casting class thought it was a great
reference.

I hope this will help,

Ken Moore
www.kenworx.com

7

Ken

I try to use at least 50% virgin casting shot or more if I can. I
do a lot of fabrication and I always save my filings and misc.
pieces to use in casting.

I’m really bad, rarely do I manage 50% new metal, (sometimes just a
token amount.) But there is NO way I’d try to cast filings, dirty
dirty and then some, almost as bad as polishing sweeps. Clean bench
scrap is usually ok. Refiners do have their uses.

If you boil the metal you deserve far worse than a little porosity
:slight_smile:

I have found that 90% of porosity is caused by spruing and flask
temperature. It is really hard to have sprues which are too fat
other than the fact that fat sprues and big buttons make the 50%
thing hard to do. If your wax is 10mm thick a flask temperature of
1100 F is not a good idea, try 600 (for sterling)

Jeff.
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand

8

Jeff,

I can’t say that I always use at least 50% virgin silver. I use the
Neutec sprues and sprue bases. The button is very big, so I tend to
re-use them much of the time. I make sure I get them as clean as
possible before the re-use. I rarely actually use filings. Most of
the scrap I use is odd pieces of wire and sheet. On occasion I get a
piece that has really stretched my patience and for my therapy it
becomes a melted ball of metal.

I have only boiled my metal once and that was a rookie’s (and I
still am a rookie), mistake. I was just trying to share. !:sunglasses:

I will have to try 600 sometime. I have always feared that the
silver will quench too soon. Other than the Neutec main sprue I
normally use 8 gauge connecting sprues. I always try to use a sprue
or multiple sprues at least as large as the largest thickness of the
piece I am trying to cast.

Thank for the input.

Ken Moore
www.kenworx.com

9

Ken,

Thanks again for the helpful advise.

Porosity problems

I try to use at least 50% virgin casting shot..

I only use new casting grain.

I use a small branch of apple wood

I will try this, it sounds interesting.

I have a paper that I put together to share with my fellow students
at our Senior Center Jewelry class. If you have Microsoft Word I can
e- mail you a copy of it if you would like.

I would love a copy.
Thank you very much.
Bobbie

10

Hi,

Along with asking all of you at Ganoksin, I had sent out several
e-mails asking the burnout question and received valuable
in return. Here is the 5 hours and 8 hours cycles sent
graciously from Kerr.

Bobbie