iDRY Vacuum Kilns

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thermometer for vacuum kiln

Started by wd4000, April 21, 2014, 06:29:12 PM

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wd4000

What type of thermometer do you use for a vacuum kiln?
I was think one that could be driven into the wood?
Any suggestions.
Thank you

Den Socling

wd4000,
I have used RTD's in wood but I'll tell you something. While the wood is wet, the temperature of the wood is set by the boiling point of the water in the wood. And the boiling point is set by the chamber pressure (vacuum). Not until you are under FSP does the wood start to heat.
Den
PS Welcome to the forum.

Magicman

Welcome to the Forestry Forum, wd4000.
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

wd4000

Thanks to both of you for the welcome.
So Den are you saying to use a thermometer that would detect the temperature inside of the chamber, not the wood?
I know I have a lot to learn about how to properly use a vacuum kiln, like what is FSP.

I am usually drying rough milled lumber to a MC of 6 or 7 .
From what I have gathered the wood inside the chamber should be at 140 before pulling a vacuum.
Then when the temperature goes down, shut it off, bring the temp. back up and start again.

Where would you suggest to purchase a RTD?
I see you sell vacuum kilns, do you also sell parts?
Please keep in mind my kiln is small. i built it from a piece of ABS water line that is 7' long and 15" ID.

Thanks in advance for your help.

Den Socling

Well congratulations! You are doing "discontinuous vacuum". I tried to lead this group through the process a couple years ago. Where did you get the instructions?

An RTD is an electronic temperature sensor. You could buy one here:  http://www.omega.com/toc_asp/sectionSC.asp?section=C&book=temperature&gclid=CLWTp6r39L0CFYc7OgodeDYASg
Or we could supply what you need. I run the vac kiln business but my son runs the controller business. You can email him at garrettsocling@pcspecialties.com You are about right on those temperature cycles but you would want to start oaks at lower temperature than 140'F. What I would like to see is an automated system that switches back and forth but a very small system probably wouldn't justify the price. What I was talking about here was using reinforced propane tanks.

FSP is fiber saturation point. That is a theoretical point where there is no "free" water left in the wood but the wood fiber is still saturated. In a vacuum kiln, the evaporation of free water keeps the wood cool. When the free water is gone, the wood temperature begins to rise. So, in your discontinuous vac kiln, an RTD in the wood would be a great help.

wd4000

Yes it is discontinuous vacuum. I pieced together instructions form different woodworking forums on the internet,(wish I had found this one before I started).
Their is a local guy that wrote a book on it but in looking at it I did not think it really addressed the subject matter very thoroughly.

I will defiantly but the RTD from you. What I would like is something that has a probe separate from the readout and connects with some sort of water resistant coupling. Should I email your son? If so please alert him to look for an email from me. I would mount the readout on the vacuum tube. I think it would be a lot easier to insert into the wood that way.

I am interested in an automated system, what do you need from me to get the ball rolling?

One last question how many watts per cubic foot should I allow for the heating element?

Thanks a lot Den.


Den Socling

The RTD is a stainless steel rod with Teflon cables attached. You could simply drill a hole in your chamber then seal the hole with something like silicon rubber. Outside, it will connect to a meter or controller. I suggest the controller for automated control. The controller can be fitted with relay outputs. You can use the relays to open or close the bleed valve, start/stop the vacuum pump and start/stop the heat. You can email Garrett. I'll tell him what's up.

Den Socling

And I've been trying to remember how many watts are needed to dry the "typical" board foot. Can't remember and can't find my old WoodMizer manual that had my notes.

boardmaker

@wd4000

I'm very interested in your kiln.  I've thought a lot about a discontinuous kiln.

Curious, are you just using an electric heating element to heat the air during a nonvacuum cycle?

@Den
Is there a way to pull a light vacuum, but still have enough air in the system to heat the wood.  But, not hot enough to cause serious degrade.  Maybe, 25" of vacuum?

Den Socling

Our kilns run around 28" (55 mmHg absolute). That boils water at 104'F.

wd4000

Boardmaker I am using a barrel heater. But I think I need to increase the amount of heat, so I may need to add another one, or possibly get a different heating method altogether.

wd4000

Den I will get in touch with Garrett today.
Thank you.

Den Socling

Good luck. He left on his Triumph MC!

wd4000

Good for him.
Glad to see some still has the sense to enjoy while you can.

Den Socling

wd4000,
The salt and pepper mills surprised us today. They are absolutely beautiful. Garrett grabbed them in a hurry.  :) He couldn't wait to get them home and filled. Thank you very much.
Den

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