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Author Topic: Kiln Temp for setting pitch?  (Read 724 times)

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Offline Bigshooter

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Kiln Temp for setting pitch?
« on: April 21, 2017, 06:01:06 pm »
I just talked with a company that make fir doors. He said one crucial part of drying Douglas Fir is to get the kiln up to 185 degrees for 24 hrs to set the pitch. This will stop the pitch from bleeding. Is this true? I thought pitch was almost impossible to stop.

Offline Ianab

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Re: Kiln Temp for setting pitch?
« Reply #1 on: April 21, 2017, 06:58:29 pm »
Heat treating like that should pretty much eliminate any pitch bleeding problems.

What happens is the heat evaporates the lighter compounds in the pitch and drives them out of the wood. The stuff that's left is the heavier compounds, with a higher melting point.  These now wont melt and run, at any sensible temperature, like the mix of light and heavy pitch tends to. 

Then higher temp the wood is kilned too, the hotter the wood has to get later before the resins can liquefy again.
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Offline xlogger

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Re: Kiln Temp for setting pitch?
« Reply #2 on: April 22, 2017, 06:49:15 am »
If I dry some pine and sterilize it at about 140 would the pitch be set there?
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Offline Don P

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Re: Kiln Temp for setting pitch?
« Reply #3 on: April 22, 2017, 07:31:53 am »
It will be "set" to 140. There is a big caveat in all this though.  An analogy might help think about it. Water boils at 212 so all the water will boil out of a kettle on the stove at 212. If the kettle is on the stove for 5 minutes at 212 will it boil dry? Sure if there is just a teaspoon full of water in it but if it is full it'll take longer. The same is true with setting pitch. If the wood is very pitchy or has pitch pockets it will take much longer at the pitch setting temp to cook out those volatiles and set the pitch to that temperature. If the sun sees the wood 140 is probably not going to be enough.

Offline GeneWengert-WoodDoc

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Re: Kiln Temp for setting pitch?
« Reply #4 on: April 23, 2017, 07:41:07 am »
Don P is indeed correct, so that is why we use 24 hours and also why we prefer 180 F or hotter. 

Analogy continued:  If the water is on the stove and the burner is at 220 F, the water will boil slowly, but at 300 F it will boil quickly.

So, 140 F will not remove pitch with low boiling points (meaning pitch that will ooze out at room temperature or so) very quickly and will not evaporate all the "soft" pitch even if done for several days.
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Offline YellowHammer

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Re: Kiln Temp for setting pitch?
« Reply #5 on: April 23, 2017, 08:39:26 am »
I've had pretty good luck with 160 which is as high as I want to go in my Nyle kilns.  Upon inspection, the remaining resin in and on the boards is a very hard crystal like structure.  I haven't seen any drips or runs subsequent to this temp.  Higher is better, I assume, but this works for me.
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Offline Bigshooter

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Re: Kiln Temp for setting pitch?
« Reply #6 on: April 23, 2017, 12:54:57 pm »
So my next question to this is what kind of Kiln do I need to build for this 185 degree pitch setting? I have a building that I am going to convert to a kiln. It is stick framed with a tin roof and a concrete floor. The dimensions are 12' wide, 20' long and a 10' ceiling. 185 is pretty hot for a wood building in my opinion. Should I just build something else ? Convert a sea can?

Offline ScottCC

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Re: Kiln Temp for setting pitch?
« Reply #7 on: April 25, 2017, 09:43:14 pm »
Thanks everyone for the info also, never knew this was possible to be almost able to stop pitch issues in logs.  As far as heat in a wood building, it would pay to continuously insulate interior and that would keep highest of heat away from wood structure for short high heat times.
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Offline GeneWengert-WoodDoc

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Re: Kiln Temp for setting pitch?
« Reply #8 on: April 25, 2017, 10:30:10 pm »
If all you want todo is set the pitch, a wood kiln with insulation will work fine.  The issue with a regular kiln is that high humidities will lead to decay.  Note that the roof in a wood kiln is tricky, as rain and snow can cause decay unless you have a second roof over the top.  In the long run, a reefer might be a good idea if the insulation will withstand the heat.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Bigshooter

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Re: Kiln Temp for setting pitch?
« Reply #9 on: May 22, 2017, 05:04:25 pm »
That's what I'm looking at now is a sea can. Simple to setup, made from steel, so easy to alter.

Offline scsmith42

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Re: Kiln Temp for setting pitch?
« Reply #10 on: May 22, 2017, 09:13:30 pm »
Like Yellowhammer I too set the pitch in pine at 160, but have noticed that it seems to harden about 15 degrees or so lower than the highest temperature that it sees in the kiln.

I have also noticed that the lumber will still leave a lot of sap residue on my millwork equipment (jointer, planer and wide belt sander). 

I presume that this is because the surface temp during the millwork process is higher than the hardened temperature of the sap.
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Offline K-Guy

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Re: Kiln Temp for setting pitch?
« Reply #11 on: May 26, 2017, 02:02:52 pm »
scsmith said:
"Like Yellowhammer I too set the pitch in pine at 160, but have noticed that it seems to harden about 15 degrees or so lower than the highest temperature that it sees in the kiln.

I have also noticed that the lumber will still leave a lot of sap residue on my millwork equipment (jointer, planer and wide belt sander). 

I presume that this is because the surface temp during the millwork process is higher than the hardened temperature of the sap."

That is correct scsmith. Friction will raise it very quickly over 160f.