Jim Fuller

[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.

[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?

[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?

[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]

"Orange, VA"? I drive by there weekly between VB and the cabin in Highland County. Practically neighbors!

[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?

[jimF]

Yes, as most of you know typically a kiln charge is monitored by moisture content (MC) either by weighing a sample or having electrodes inserted into the board to measure the electrical resistance to infer the MC.  The MC is used to infer the stress level in the lumber.  However, MC is a poor indicator of stress level.  To get a handle on how stress levels progress during drying, researchers obtain samples through the whole drying process.  This is achieved by cutting cross-sections from the board, which is then turned so the end grain is face up and the long dimension ( width of the board) is measured.  Ten slices are then sliced and each slice is measured before any moisture is lost.  The measurement is accomplished using calipers or similar instruments. Comparing the initial and second measurement of each slice you can determine the degrees of compression or tension that was in that slice.  Looking at all the slices, can give a good idea of the stress gradient though the thickness of the board.  Below is one cross-section sliced and glued back together. You can see the difference lengths of each slice on the right side, indicating the degree of strain that is relieved by the slicing process.



 

This was accomplished in the 1960's for oak, maple and pine during the drying process and after conditioning.  It gets progressively uncomfortable to obtain the samples in the kiln as the schedule progresses, but possible.  This was not performed during conditioning because the temperature is 180F and 90+%RH, which causes instant scorching of flesh.  Until curiosity got the better of me.  It required firefighters SCUBA gear and other protective clothing.  While this is possible for research, it is not practical for production.  Equipment can be mounted on the lumber to obtain remote real time measurements which also enables to advance the schedule quicker than monitoring MC because the moment the stresses reduce can be observed instead of waiting for a rough inference of stresses by MC.  While the measurements don't give the strain difference between slices the over all shrinkage rates do indicate the stress levels.

[Okrafarmer]

So-- how does it help you to know the stress level at any given time? And is the stress level for all the wood in the charge essentially the same, or does it vary significantly from board to board? If you take a measurement on one board, does it hold true for the whole charge, or what if you just happened to choose a board that wasn't structurally representative of the lot?

[GeneWengert-WoodDoc]

I do agree with Jim's technical explanations in the several previous postings.  I do not believe that by knowing the stress, you can dry better at a commercial level, as we would also have to know the strength of the wood at the given temperature and MC, plus we would have to test a multitude of pieces to,find the one most likely to be damaged.  If we were drying air-dried lumber, I am not certain that stress is that important any more.  Is stress level important when drying soft maple, yp, syp, etc. at any MC?  I would like to,hear if I am missing something here.

Regarding the "soak" treatment (or step schedule), when you look at the drying rate of individual samples when using a step schedule, you do not see steps in the rate.  Rather, we see a rather smooth curve.  With computer controls, we can smooth the steps in temperature and RH and make an even smoother drying rate.

But when using drying rate or stress, it would seem that the key is determining the safe rate or stress level for  99.9% of the pieces.  Without that knowledge, we would have to be conservative, and that would put us back toward the more conservative, conventional drying schedules of today.  One might also argue that air drying is so uncontrolled that it should be discontinued in favor of a controlled drying process...at some point, cost enters the picture and so proper conventional drying becomes attractiVe.

[Ironwood]

Good to see such a great "collective" knowlege here, Den/Jim/Gene.....speaks well of the FF, Congrats Jeff ,  and now I am "subsrcibed".

I missed this thread early on,...been fairly busy as of late.


Regards Ironwood

[jimF]

Okrafarmer,
You bring up the variability within a charge.  This is no different than any method chosen to monitor the progress of a charge. You have to choose your samples carefully in a MC based schedule, ensure airflow in the kiln is uniform, the lumber is somewhat uniform in MC, the same thickness, that you can detect bacterially infected lumber.  There is nothing different fundamentally in how wood dries from one monitoring system to another monitoring system.  Also, after uniformity of the charge is addressed, knowing how lumber dries is important.  The entering side of the stack dries faster than the exiting side, and if the airflow is reversed the center is drying slowest.  So by putting the samples on the edge of the stack you are monitoring the most critical area.

[jimF]

 Gene,
You say "I do not believe that by knowing the stress, you can dry better at a commercial level,".  By being able to monitor stress level you can greatly reduce the drying time, by 35-50%, and at the same time increase the quality – reduced residual drying stresses and improved brightness.  Both are very important for commercial drying.   Reducing drying time is important for commercial drying of any appearance grade species.  Drying stresses are especially important in air drying because usually they contain more surface checks than lumber put green in the kiln.  Once lumber has existing surface checks, they are prone to extent further into the board if not carefully dried.

In regards to your statement that many different species would dry differently, there are hundreds of possible schedules using the Forest Products Laboratory's system of schedules, but only a few are actually used.  Most commercial species are put into only a few groups.  Therefore, not many new stress-based schedules would need to be developed. 

As to the uniformity within a charge, all of the many trials I performed they were very uniform in stress levels throughout the charge.

The way I discovered the stress-based method was an attempt to study the drying stresses by computer modeling of drying rates and stresses/strengths.  Even in computer modeling you must include variability of properties.  All the attempts at modeling have been using material property values obtained in predetermined way instead of simulating a real situation in the kiln.  The stress based method looks at shrinkage rates and bypasses specific strength values and thereby reduces the extent of needed research and computer simulation.  Continued research in modeling would be interesting and may provide additional useful information to combine with the shrinkage rate system.

As to the "soak" treatment of step schedules, these schedules do produce progressive step drying rates.  The problem is interpreting the data.  The data obtained with the step schedules are discrete discontinuous data points which are easy to draw a nice smooth curve from point to point.  However, when obtaining continuous MC or shrinkage data during step schedule drying, both step MC and shrinkage data are obtained.  Currently, the continuously MC based monitoring systems used in commercial drying now uses continuously changing temperature and RH which does smooth out the drying rate.

The stress based monitoring system is what was declared as needed back in the 1950's by R. Reitz at the Forest Products Laboratory. And it works!

While this post addresses Den's question on some technical aspects of one monitoring method , I want to emphasize that all drying systems, air-drying through commercial conventional drying are valid and have their respected place.

[GeneWengert-WoodDoc]

I understand better now.  Thanks.

I would think that your method would not apply well to structural softwoods, as they already are dried with advanced concepts and we find that time is extended mainly due to variation of conditions within the kiln.  Plus, most softwood people do not seem very concerned about quality...look at how poorly they stack, for example.

With hardwoods, about 50% of the wood dried is oak and nearly all is air dried first, as air drying is less expensive than kiln drying and the number of kilns required is less, etc.  So, would we see a 35-50% time benefit in drying air dried oak, not counting equalization or conditioning?  I am assuming no hotter than 160 F and the lowest EMC of 5.0% EMCs.

[jimF]

That is correct, stress based monitoring is not appropriate for structural grade lumber.  Surface checks and such are not a concern for such.
You could see a large reduction is drying time with pre-air-drier lumber when the conditions would reach 160F and 5% EMC.  The lumber does experiences peak stress and stress reversal the same as green lumber.