Author Topic: moisture content range  (Read 3915 times)

Offline Gilman Blackshear,Ga

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moisture content range
« on: November 17, 2011, 08:24:51 AM »
We have six southern yellow pine facilites located in Georgia (3) and Florida (3). We stamp our dressed wood SPIB KD-19. 
My question is , what should our target goal be in relationship to the total percentage of pieces in a most desired moisture content range? Example : 90% of our wood should be in the 14% to 16 % range.
Is this attainable with southern yellow pine or is this too tight of a range to be realistic?
What do others see as there range of moisture content? Where do you target the greatest % of your wood?
Thanks in advance for feedback

Joe D

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Re: moisture content range
« Reply #1 on: November 17, 2011, 10:39:01 AM »
If you have a KD-19 stamp your maximum MC allowed is 19%. Your question is what should you want your target moisture to be based on 95% of the boards
being below 19%? This depends on the variability you have in your drying, or what we will call your standard deviation. Bending a couple of statistical rules for
95% of your boards being at or below 19% with a 3% standard deviation the target should be 19%-(3%x1.645) or 14.1%, for a standard deviation of 3.5% it
is 19%-(3.5%x1.645) or 13.2% and for a 4% it is 19%-(4%x1.645) or 12.4.2%. Variation when drying SYP at high temps is highly variable, often increasing as the average
increases. At this point you are probably unhappy with my answer. In most cases, when high temperature drying SYP and the standard deviations I see, we need to keep
our average around 13 to 14% so we do not have too many wet pieces.

What I'm saying probably contradicts what you have heard from other individuals as far as when to pull your lumber. But think of the dollar cost of the wet pieces that need
redrying or put in the #4 sort and mold issues. Thus you have to work on drying uniformity, get all of your inputs as constant as possible, lumber entering MC, airflow,
heat distribution etc. Also to counteract the lower MC I'm suggesting stacking and top weights become critical.     

Offline GeorgeCulp

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Re: moisture content range
« Reply #2 on: January 10, 2012, 11:25:11 AM »

Dr. Denig is spot on in his assessment of where you most likely have to be with your MC.
The main question to ask yourself is how do you assess your moisture content levels of your dressed lumber? By pin meter? By in line meter? Who reports these levels? Greaders? QC people?
Determining your level of moisture content of your lumber is whole ballgame in and of itself. In order to get enough  volume to give you and accurate representation of your mc you need an in line system. Once that is achieved there needs to be one person well trained in its operation on how it works, the setup of parameters, and how and when to make setup changes based on varying subspecies of yellow pine (lobloly versus short leaf for example), variations due to the temperature of the wood (cold weather versus hot.) etc.

Once that is achieved you will need to be able to separate the results based not only on thickness and width yet length as well. Also, based on each kiln too.

Once all this is in place you will gain two indicators of your drying level and quality. 1.your standard deviation - it is a good indicator of your drying quality.
2. the percentage pieces of your lumber that are over the maximum allowed mc. In this case 19%. This number will determine whether you should dry your lumber more or less. If you have 0 pieces of lumber above 19% then you are probably overdrying. If you have too high a percentage above 19% you are delivering an "off grade" product to your customer and could suffer a regrade.

The first number - the standard deviation - should be used to assess drying changes.  Be they mechanical (ex. in increase in airflow) or procedural (ex. a change in venting schedule). If the standard deviation goes down then the change was positive, if it goes up then negative.

It all boils down (no pun intended) to accurately assess your mc levels. And that is a whole world in and of itself.

 


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