iDRY Vacuum Kilns

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Jim Fuller

Started by Den Socling, September 11, 2012, 12:34:45 PM

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Den Socling

Jim Fuller is a member who is quite the expert when it comes to wood structure, drying, instrumentation and so on. He has written a book and sent me an advance copy. I was afraid that it might be ponderous reading when he asked me to review it. Instead I found it easy to read and it is full of useful information. Having Jim as the author and a member gives us a great opportunity. We can read and discuss with the author! I hope Jim pops in here and tells us when and where copies of his book will be available. I think he should notice the subject.  :D

jimF

Thank you Den for the nice review. With you so busy, I did not expect such a quick turn around with the review.  We went to the shore for my daughter to try out surfing.  It was a success: no sharks, whales, jellyfish, broken bones nor concussions!
The focus of writing the book is to provide helpful information pertaining to all aspects of drying:  air drying, small kilns, how wood behaves to moisture after drying etc. The material is for individual woodworkers, furniture shops, commercial driers. Not knowing how many people would be interested and to hold down the costs, the chosen print format has been print on demand with loose cone binding.
Finishing vacation, so I will be getting with the printer this week to finalize the details.

Jim

jueston

this sounds like a very interesting book and i look forward to it becoming available.

Den Socling

Jim, I found "aspirated pits" interesting. You can tell when you're going to get a bad load out of a vac kiln. The clue is that it doesn't want to dry. Not until temperature is dangerously high will the wood come dry. Then you unload firewood. I wonder if this is due to aspirated pits?

jimF

That could be one cause, but not all species have bordered pits and only bordered pits can become aspirated.
Bacteria in bacterial infected wood produces a slim barrier in an effort to maintain a wet environment for it to continue reproducing, which also can significantly retard moisture loss. 
The water in the wood can also contain dissolved gases.  When a vacuum is applied, the dissolved gases can come out of solution and form air pockets. Because of surface tension or capillary action, the water cannot pass through the air pocket and block any flow of water.
Higher temperatures will promote liquid water to become vapor and enable the water to penetrate the pit membrane, cell wall, slime barrier or air pockets more easily.
Bacterial infected wood is weaker than normal wood and elevated temperatures weaken the wood material even more, promoting checks.  With any cause of reduced water migration,a steep moisture gradient developes.  And thereby causing the drying stresses to be sharper.  Also causing checks.  All leading to firewood.

Okrafarmer

I've had good success with air-drying and kiln-drying bacteria-laced ambrosia red maple. Maybe red maple is just a forgiving species.

Do you have a section of the book that talks about how to reduce or eliminate case-hardening? Any mention about the various things people apply to wood to try to reduce it?

And it would be great to have instructions or info for many different species too.

I will look forward to buying the book! I would like to have that kind of info at my fingertips.
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jimF

a quick reply while on break.
yes, the book includes a discussion on stress relief.

jimF

There is a thorough discuss on drying stresses and within that stress relief.  It does not include any thing applied to the wood to eliminate casehardening, as I know of none.  People have tried to coat the wood to reduce the occurrence of surface checks caused by drying stresses.  One study use diluted white glue with some success if the lumber is green and the surface had not experienced any drying.
There is some mention of drying behavioral differences between species to show generalities.  However, there are too many species just in the US to list them all.

beenthere

JimF
Do you have links to the book reviews?
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

jimF

Den has initiated this thread with his review.  To give you a sense of the book, I'm including the Table of Contents.

Drying Wood
Structures of Wood
     Structures That Influence How Water Moves
     Structures That Influence Shrinkage
Water and Water Movement in Wood
     Wood and Water
     Water Movement Within Wood
     Air and Water
     Water Movement From the Wood
     Putting the Above Together 
Shrinkage & Drying Stresses:and How They Develop
     Shrinkage and Swelling
     Drying Stresses
     Some Possible Complications
     The point to ponder
Which System Should I Use
    Air-Drying
    Low Temperature
    Conventional Temperature
    Comparing Systems
Useful Equipment
    Temperature and Relative Humidity
    Air Flow
    MC Determination
Preparing the Wood
    Single or Few Pieces of Wood
    Stacks of Wood
Drying the Wood
    Stages of Drying
    Single or Few Pieces of Wood
    Stacks of Wood
        Air-Drying
        Forced-Air Drying
        Kiln-Drying
            Solar Kiln-Drying
            Conventional  Kiln-Drying
     Modifying Schedules
     Operating Equipment
     Tests, Defects & Remedies or Corrections
Storage of Dry Wood
    Single or Few Pieces
    For Large Volumes of Wood
Additional Applications
    Drying Situations
    Situations After Drying

Den Socling

It's time to change the direction of this thread. It is against Forestry Forum rules to market a product in a board other than the "for sale" section. Jim's a member who wrote a book. I got a copy and I found it informative. Period.

If you get a copy and there is something you don't agree with or something you don't understand, then come back to this thread and discuss it with Jim. That's all I want to see in this thread.

beenthere

Den
Jim indicates that you are the book reviewer.
What can you, or would you, tell us about your review?

Is it a technical publication, or Jim's thoughts? 
I thought something was mentioned about going out for review, but apparently the book is published.

There are good wood drying handbooks published and even available online in .pdf form. In your opinion, is there additional information in Jim's book?
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Den Socling

It has a lot of general information that you can find on-line. But shrinkage and stress is covered in depth.

Den Socling

Jim, I assume that the lines of RH on the psychrometric chart on the back cover start at 10% on the bottom and are in 10% increments. Correct?

clww

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jimF

Den,
yes, the RH increments are 10% plus the one in the upper righthand corner is 95%.  I will get a properly print graph to you.  Sorry, I caught that mistake after sending your version.

jimF

clww,
Howdy neighbor, Highland county nice area.

Den Socling

Jim,
You state that bound water starts to be removed at as high as 70% MC. I have always believed that but this is the first time I have seen it in writing. With my vac kiln schedules, I might ramp the heat .006 degrees per hour from beginning to end. I never check MC or stop to "soak".
You also mention shrinkage at "19%". Is this the point where nothing but bound water is being removed? I thought that point would be closer to FSP. I realize FSP varies from cell to cell.

jimF

Den,
Yes, shrinkage in the center of the board can start when the center is as high as 70% MC. John McMillen (1963 USDA Forest Products Lab) stated that core shrinkage can occur when the MC is greater than 40%.  I don't remember if that was average MC or core MC.  And Rice and Youngs (1990 Virginia Tech) report shrinkage occurring above Fiber Saturation Point (FSP), the point when bound water starts to be removed.  [These above references were from technical journals.]

Stress level, shrinkage and MC during drying has not been measured simultaneously until my studies in 1994, and this is how such inferences of when bound water removal can  be made.  Also, with most people using conventional kilns or conventional kiln schedules they tend to think in terms of temperature and RH whereas you, using vacuum kilns, tend to think in terms of partial vapor pressure.    The concept of water being pulled (low vapor pressure) from the wood and thereby from the cell wall is more obvious.  In a vacuum kiln, drying slows down as the wood cools from evaporation of water.  That is when you realize you need to add heat.

I think the 19% you are referring to is where, in the book, it compares moisture loss/shrinkage in different layers of a board.  "As the surface dries to about 19%MC, it wants to shrink.  At the same time, the center is not drying and does not want to shrink."  What this is referring to is the surface is shrinking but the center is not during the time when the surface is going from high MC to about 19%.  For nothing but bound water to be being removed, all of the freewater needs to have already been removed.  I know of no way to determine that no freewater is present other than using Magnetic Resonance Imaging (MRI) and I have not performed a study using MRI.  (Relevant to a researcher but irrelevant to a kiln operator.)  I agree with you and would tend to think freewater has been removed by around 25% MC or so.  However, it's not that FSP varies much from cell to cell but that MC varies greatly from cell to cell at any one second, including when average MC is approximately 30% which is not the definition of FSP.  FSP refers to when an individual cell has no freewater.

What do you mean by "stop to 'soak"?

Den Socling

Conventional schedules have increases in temperature that stop until MC drops. That is what I call a soak.

jimF

I think the "soak" is the result of the schedules being developed when the samples were taken out to weigh every day and the controls were advanced manually.  Now, the computer controlled conventional kilns are monitored based on samples being continuously weighed in the kiln.  The software advances the settings based on the loss of weight in smaller increments or more smoothly, similar to you increasing the temperature .006 degree per hour.

Den Socling

When I was involved  with conventional kilns, almost all were run by old control systems. We have trashed a bunch and they weren't replaced computer controls. I suspect that many kilns are run the "old" way. We still sell a controller or two about once a month.

jimF

The old controllers are fine because the traditional schedules are so conservative.  The drawback is that the traditional schedules are unnecessarily slow.  Since these schedules are advanced by monitoring MC; no one really knows what the stress level in the wood is.  This is where, in the book, the prospective of defining the goal of drying versus the concerns during drying is brought up and with that, monitoring the lumber's progress by measuring shrinkage to infer the stress level and advancing the schedule accordingly.

Den Socling

Jim I got my new psychrometric chart. Everybody who runs a conventional kiln should use one. Yours is a beauty. It could be said that it's worth the price of the book. And laminated, too!

Den Socling

Jim. Did you say in your book that a kiln charge can be run by measuring stress? You say that you can measure compression or tension by slicing a sample (figure 27). How do you measure. I would think that the differences in the size of slices would be small. Do you use calipers?

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