Drying really thick wood safely?

[Curlywoods]

This question is really meant for Den as I am curious if a vacuum kiln would dry really thick wood with less degrade than a conventional or DH kiln would?  

  It seems that I am always asked for 4"-5"  thick woods for bedposts, large table legs, etc, and can never find a good source for my customers.  

  All of the thick stock that I have ever seen that was dried in a normal kiln was severely checked.  Can really thick woods be dried with minimal degrade in a kiln?

[old3dogg]

Mike.
Most thick species of hard wood can be dried in a vac kiln with good results.
Wood with a lot of figure and knots can give you trouble but if you are carefull it will come out ok.
I use to dry a lot of 4" thick Cherry and Soft Maple with less than 6% kiln degrade.
I have seen some of the wood that has come out of Dens kilns and I have to say that he knows what he is doing.
Drying slabs is hard to do if you have hart in them.If they are hart free the process is simple.
Mike.

[Den Socling]

In a conventional or DH kiln, you always have a humidity "gradient" that moves water from the surface of the wood to the air which carries it away. With a vacuum kiln, you can have a pressure gradient as well as a humidity gradient. With our kilns, I can keep the humidity gradient at zero if I want. Then, all drying is done with pressure gradient. Pressure gradient moves water from inside the wood and not the just the surface. It slows drying to use pressure gradient alone but, if you are drying difficult and expensive wood, who cares about a couple days.

[rerednaw]

Den, if you keep humiduty gradient at zero and use only pressure gradien, water from wood are moved as a water or as a vapour ?

[Den Socling]

You can't have the humidity gradient at exactly zero. There is always some small gradient. But using the pressure gradient, water is moved as vapor.

[serg]

Den, all on a forum hello! I have taken main principle of management of drying to provide optimum process. To receive high efficiency in a combination to high quality of the dried up boards. At usual air drying speed of drying is defined(determined) by a difference parcialnogo pressure pair on a surface of boards and an environment of environment(Wednesday), the agent of drying. Intensity of diffusion of a stream of a moisture on a surface of boards, no less than diffusion of a stream inside a board. It is defined(determined) by the molecular phenomena limiting his(its) speed. Regulation of this size make due to change of parameters of the agent of drying, namely a difference. At vacuum drying speed of process is defined(determined) the DIFFERENCE of the GENERAL(COMMON) (superfluous) PRESSURE of the STEAM-AIR MIX INSIDE the BOARD (In the centre of section a board) and the GENERAL(COMMON) PRESSURE in an environment. In this case the house painter a stream of a moisture from the centre on Wednesday of the greater or smaller intensity (formulas of the equation does not translate) Measurement of superfluous pressure of a steam-air mix inside wood takes place represents the certain difficulties. Therefore speed of process at vacuum drying can be adjusted the attitude(relation) of the current humidity of wood to equilibrium. The current humidity is measured by the gauges established on surfaces a board, equilibrium humidity can be defined(determined) under the diagram depending on pressure and temperature of environment(Wednesday). Supervising and adjusting size этх the data it is possible to support optimum process of drying of boards. Sergey.

[rerednaw]

Den, if we have humiditi gradient near (or exactly) at zero (this mean what humiditi  of all air in kiln is near 100%) where vapor provided by pressure gradient find place ? In air ? But air already have 100% humidity.

[Den Socling]

If you are vaporizing water, how can you maintain a vacuum if you aren't removing vapor from the chamber?