vacuum drying lumber

[c44u]

i have been at it again. thinking and looking at somethings and need your oppion on vac kiln lumber . i have some plans from internet and thinking of building one.have everthing but the pump. Was woundering how much vac to pull in the tube and how fast to do it. have looked in past post . dose anyone operate one and can steer me in the right direction. i have 12 steel tanks that are 3ft diam. and about 10 ft long. will weld 2 end to end  for longer lumber.
any help you can give please. thanks all. jimmy http://carverscompanion.com/Ezine/Vol2Issue4/LynnDiel/LynnDiel.html

[old3dogg]

First of all you are going to suck those tanks in like a beer can if you dont have the right support around them to keep them from collasping.
Doesnt really matter how fast you pull the vacuum.
To do any drying you will need to be under 80 Torr.
A real good vac pump will set you back about 5 grand. You will need the pump to be lined with stainless steel. The acids in a lot of hard woods will eat carbon steel in a matter of weeks.

The "under 80 torr" thing does depend on how you are going to transfer the heat to the wood and on how hot you want to dry.

[Ernie]

When I was a real newbie, this was one of my posts, I never got any replies.

https://forestryforum.com/board/index.php?topic=10605.msg145217#msg145217

With your freezing winters, I still think that it would work, any thoughts about sublimation drying

[Ga_Boy]

C44U,

This post is ment as a primer to get you thinking; not to stop you in your tracks; with that said please read on.


To make a vacuum kiln work one of the first problems you need to solve is your thermodynamics.

The thermodynamics problem is:  How are you going to transfer the heat to the wood?

Convection is out as you are in a vacuum; no air for the heat to travel through.

Now, if you run a discontineous vacuum system then convection is possible.

You will also need to consider the forces acting on you chamber.




Mark

[c44u]

thanks for all the info on this. i need to do more homework i think. try to look a fast post but so much info the search dose not bring up much. if you know of a web site or info place i can go and read, i would thank you for it. i will have my peterson sawmill in 3 mnth or so. and i am tring to get everthing i can afford up and running. i you can think of anything eles please let me know.

[Den Socling]

C44U,

I've heard this so many times that I didn't reply. Here's two facts. A vacuum kiln that can give you good results over and over with different species and different thickness is a complicated machine. If this machine could be built at a price that the smallest of small operators could afford, I would be building it.

I've helped a few people build small, temporary kilns. I've tried to lead people who want to build something that could be used daily with early post here about discontinuous vac and a design that Sergei's company uses. They aren't as fast and they don't dry as well as our kilns but the design is possibly doable for the very handy handyman.

Den

[serg]

Den hi! I do not use technology of faltering vacuum.
Vacuum constant. The diagram process idle time, for all breeds.
Warming up. Vacuum small - an output(exit) of free water. The stage of boiling vacuum 0.092 temperature of boiling 45 С. when humidity in middle of a board will reach(achieve) 25 - 30 %. In this period I do(make) пропарку, the vacuum remains, at humidity of 25-30 % there is a change of pressure(voltage) of a board. It gives to liquidate internal pressure(voltage).
To dry it is possible in one party(set), a stack an oak red, a maple and an ash. Thickness also different 20 and 30 mm, 30 and 40 mm, 50 and 60 mm. Factories require it. It is universal also practice well. Sergey.

[c44u]

thanks den and serg,
this may be an item that is out of my range at this time. if i can not do this what is the next best way to dry in your oppion.
again thank you for takeing time to write

[serg]

Jimmy! Look as did(made) earlier and spoke on your forum about it. One welder, one assistant. Volume of loading of boards 2.5 М3. Ten days vacuum drying is ready to work. You want to dry what wood?
Thickness of boards? Sergey   http://www.vacuums.ru/econom.html

[c44u]

pine (softwood ) oak and a little of other (hard wood ). 1.75 " to 2.25 "  and about 16' max in lengh.

thanks