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Walnut Drying Question

Started by Glenn1, April 25, 2015, 06:45:44 PM

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Glenn1

I have a load of walnut in the kiln that has been air dried to 16%.  It's been in the kiln for 3 days now and here are the readings.

Using the weight scale, I have one sample at 12% and one at 9%.  When I use the probes into the center of a board, I get 16% and when I use the probes on a lateral side, I get a reading of 6%.  The weight measurement makes sense since it averages the 16% and the 6%.  I am wondering if the difference of 10% between inside and edge is too much.  I had raised the temperature but just dropped it to 100% to see if I can get the percentages to get more even.  Any thoughts or suggestions?
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

scsmith42

Glenn, lumber dries from the outside in.  The last place to dry is the center of the board (measured from both the face and the edge).  It is not uncommon for MC% measurements taken from the edge of the board to be lower then the center of the board shortly after you start a kiln run.

Your most accurate reading will usually be taken from the face of the board, in the middle of it, with the probes extended down to the center of the board.

16% 4/4 and 5/4 BW will probably take 7 days - give or take - to dry down below 8% in a low temp DH kiln.  8/4 a little longer.
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

Den Socling

In vacuum kilns, I run walnut to much higher temperature than Red Oak, for example. If you have any figured wood in a board, the twisted grain will dry much slower than surrounding wood in the same board. If you have figure at someplace like feather in crotch, take it easy and give it time to equalize.

Ga_Boy

Scott and Den posted what I was going to say.  Wood is a natural product as such it does not dry in a uniform fashion. 

weighing samples to calculate MC is based on the average MC of the material, some places my have a higher MC and some places may have a lower MC.  This is why you equalize the charge.

10 Acers in the Blue Ridge Mountains

Glenn1

Please let me paraphrase to be sure that I understand.  Using the probes only on the sides, it is 6%.  I don't need to be concerned about casehardening?
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

WDH

Not if it went in the kiln at 16%.  At that M%, you can dry walnut fast and hard.  Below 25% moisture content, you can let the compressor run full out till there is little to no more water being extracted.  Catching the water in a bucket lets you know how much water is coming out on a daily basis.
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Glenn1

In three days of running the kiln, I picked up a grand total of 1 gallon.

(1/4 gallon, 1/2 gallon , 1/4 gallon)
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

WDH

Set your dry bulb at 120 degrees and your wet bulb at 75 degrees.

What are your set-points now?
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

GeneWengert-WoodDoc

The shell to core variation is not an issue.  As an example, when drying oak, it is not unusual to have the shell close to 20% MC (right at the surface) and the core over 50% MC.  Also, I have never seen any published values on the maximum shell to core.  In fact, it would be impossible to measure th core when the average is much over 20% MC.

As mentioned, at 16% MC you can go all out, as defects, except cup, all occur at much higher MCs.  That also includes casehardening (also called drying stress), which occurs above 50% MC.  Obviously, casehardening is a stress situation and is not related to the MC of the shell.

You will find that if you want the AVERAGE MC of a piece of lumber, (which is what the weight system gives) drive the tip of the pins 1/5 (for planed) and 1/4 (for rough) of the thickness deep.  This is true for all brands of moisture meters, for insulated and uninsulated pins, and for permanent pins or temporary pins.  Even so, test after test has shown that moisture meters come close at low MCs, but the weight system is the best.  Above 25% MC, the pins do not work well, as the reading is off by often 20% MC or more.

So, why is drying so slow?  Sometimes we do see that the water appears to be locked in the lumber, even though the humidity in the kiln is low...I assume you do have around 20% RH.  You can read about this in DRYING HARDWOOD LUMBER, page 102.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Cazzhrdwd

Quote from: GeneWengert-WoodDoc on April 25, 2015, 09:42:01 PM


So, why is drying so slow?  Sometimes we do see that the water appears to be locked in the lumber, even though the humidity in the kiln is low...

I have to raise the temp to 160 with compressor off to get that last remaining moisture out, its always been that way for my kiln.
96 Woodmizer LT40Super  Woodmizer 5 head moulder

Glenn1

Quote from: WDH on April 25, 2015, 08:30:25 PM
Set your dry bulb at 120 degrees and your wet bulb at 75 degrees.

What are your set-points now?


110db and 80wb
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

Den Socling

That's interesting, Cazz. In our vacuum kilns, 140 gives me 7% with Red Oak but I run walnut up to 160.

WDH

You are just dealing with recalcitrant water  :)
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

GeneWengert-WoodDoc

I also suggest raising the temperature...140 F minimum and even 160 F until the water begins to move.  Then you can return to somewhat lower temperatures.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Glenn1

Quote from: GeneWengert-WoodDoc on April 26, 2015, 12:18:38 PM
I also suggest raising the temperature...140 F minimum and even 160 F until the water begins to move.  Then you can return to somewhat lower temperatures.

Doc,  It's only an L53    ;D    ;D...   It's now up to 120db and 89wb.  I'll leave it that way for awhile and watch the water coming out. 
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

Glenn1

Had to change the sock today on the wb.  Is it normal to have it dried out after 3 days?  I am using distilled water.   Thanks for all the great comments!
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

beenthere

That is normal to run out of water if the evaporation rate is high, which comes from low relative humidity. All part of the game to keep the sock wet. ;)
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

GeneWengert-WoodDoc

It is reasonable to wash the socks once or twice with regular laundry.

Try to avoid running out of water...maybe install a mother or a larger reservoir.  If the sock does dry out, put a fresh sock on.  In this case, a dry sock does indicate that you do indeed have low RH in the kiln.

If there is little humidity in the kiln air, the cold coils can get really cold and could freeze up, at which point the efficiency is poor.  If the compressor is controlled by the WB (many are not), then it is also possible that the compressor is not running 100% of the time.  Likewise, ice on the coils can result in the compressor shutting off.  Obviously, you cannot remove water when the DH is not compressing! In my experience, slow drying after air drying, especially with thick stock, is not very uncommon...it happens a lot.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Glenn1

Doc, not sure how I am going to wash the sock as I just cut away the part that had gotten hard.  Must be another way?  By the way, the RH inside the kiln is 10%.

Thanks
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

Den Socling

10% is outside the range of accuracy of all but the best meters.

WDH

I replenish the water for the sock twice a day.  If it gets crusty, you do have to cut off the crusty part.  A mother reservoir is a good idea.  I need to do that. 

On my L53, if the temp reaches 135 degrees, there is a high temp shut off on the compressor, and that will shut the compressor down.  You have to remove the wood and take the side panel off to access the re-set button.  A major pain in the butt log, for sure.

Drying 9/4 white oak has about driven me crazy.  You just about cannot get water out of that stuff.
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Den Socling

For what it's worth, I go to 150 to get the final couple percent White Oak.

YellowHammer

Walnut likes to hold water and has to be hammered, 120 to 125F, compressor at 100% in its last stage.
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

Glenn1

Quote from: YellowHammer on April 26, 2015, 10:24:03 PM
Walnut likes to hold water and has to be hammered, 120 to 125F, compressor at 100% in its last stage.

Will a 5 pound mallet do the trick?   smiley_smash
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

Cazzhrdwd

I suppose I'm not doing it correct, but it doesn't matter what I dry, I always get down to 10-15 percent and can't get the rest of the water out. Now I get there as soon as the schedule will allow, then raise the temp to 160. 150 doesn't do it, it has to be at 160. Its at that temp for about 12 hours, then I just open the door slightly and 8-12 hours later, the load is at 6-8%. I used to get down to the lower MC and just wait for it to finish, not anymore, I need it done and on to the next one. Now I have my first 200m., I put my first load of rustic oak in a week ago. I wanted to try it on some junk oak first before I put in FAS. Nyle says it will take 38 days and I suspect I'll have to turn up the heat on this one too, can't fool around, I've got to get to the next load!
96 Woodmizer LT40Super  Woodmizer 5 head moulder

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