Jeff Vandenbroeck on mon 18 nov 02
Passing behind my kiln I bumped in the protruding end of my thermocouple.
The porcelain sheath of the probe is broken. Will it still work in these
conditions?
Can the thermocouple be mended?
As I'm in a country where it's already difficult to find screws, can
somebody explain me what I have to order and if I can mend it myself. It's
always a bit scary the first time.
Thanks for your advice.
Jeff
Logan Oplinger on mon 18 nov 02
Dear Jeff,
To obtain a replacement "protection tube" for your thermocouple (TC), a lot
will depend upon who the manufacturer/supplier of your kiln/thermocouple is.
But first, you don't say where the protection tube is broken, or how. Is
the break near the connection head (the part that protrudes outside the
kiln, and where the wires are connected to the TC), or is the break nearer
the enclosed end? Is the break a clean break or are there more than two
pieces? If enough of the enclosed end is left to protect the TC from the
kiln atmosphere, it should be possible to fire with no or minimal damage to
the TC.
It is possible to fire your kiln several times without a protection tube,
and do minimal damage to the TC. However, different firing atmospheres,
and fumes given off by clays/glazes will, over time, tend to alter the
calibration of the TC itself by introducing contaminants into the metal at
the exposed TC junction. This also causes the TC junction to corrode away
if it is of the chromel/alumel type.
If you cannot readily obtain a replacement TC protection tube, the next
best thing would be to make your own from a white high fire porcelain or
even a high purity fireclay that does not contain coloring oxides or other
contaminants. Making your own would allow you to continue firing with
minimal damage to tour TC until you can obtain replacement tube from your
supplier.
Depending on how your TC assembly is manufactured, your supplier may only
provide the complete assembly for replacement. This usually includes the
TC, protection tube, and connection head. The protection tube is often
permanently cemented to the connection head.
One of the best web sites for obtaining information about TCs is at Omega
Engineering (no personal affiliation). Go to:
http://www.omega.com/toc_asp/sectionSC.asp?book=temperature§ion=b
and:
http://www.omega.com/toc_asp/sectionSC.asp?book=temperature§ion=a
Good Luck
Logan Oplinger
Mary O'Connell on mon 18 nov 02
Dear Jeff,
Your now broken porcelain sheath is protection for the thermocouple. Your
thermocouple will still measure the temperature inside your kiln as long as
the tip where the two wires meet and are soldered are still intact. You
must be careful while loading the kiln that you don't disturb the exposed
thermocouple by bumping the end and breaking the connection. I don't know
what country you live in so I don't know how you would go about getting a
new one. I live in the United States and the clay companies here carry
them. You could try making one by making a plaster mold and pouring cone 10
+ porcelain. Important to match thickness of old porcelain sheath.
Hope this was helpful. If you have any other questions please ask.
Mary O'Connell
The Geneva Potter
moconnell@inil.com
----- Original Message -----
From: Jeff Vandenbroeck
To:
Sent: Sunday, November 17, 2002 7:54 PM
Subject: Broken thermocouple
> Passing behind my kiln I bumped in the protruding end of my thermocouple.
>
> The porcelain sheath of the probe is broken. Will it still work in these
> conditions?
>
> Can the thermocouple be mended?
>
> As I'm in a country where it's already difficult to find screws, can
> somebody explain me what I have to order and if I can mend it myself. It's
> always a bit scary the first time.
>
> Thanks for your advice.
>
> Jeff
>
>
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Ron Collins on mon 18 nov 02
This happened to us last week. The thermocouple had three porcelain
sheaths, one broke into thee pieces.
I mended it with a mixture of 1 part karo syrup, (you can us honey), one
part vinegar, and clay (we use a white porcelain clay). Put enough dried
clay so that the mixture looks and acts like slip. I let it dry a day or so
and then have been using it as is. It seems to be working fine. We use the
above mixture to repair any bone dry piece or a piece already bisqued.
Ron and Melinda in Guatemala
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