Home made vac kiln

[Den Socling]

You may remember a few years ago when I tried to lead interested members through building a kiln from a propane tank. Well a guy in England was paying attention. Look at this.



 

Still a lot to do but he and his partner are doing a great job.

[beenthere]

Progress is good. Are they now drying or just to the stage of getting the chamber ready?

[Den Socling]

Not drying yet. They are gathering up parts for cooling, vacuum and heating systems. I was trying to lead the FF in building a discontinuous vac. These guys are going for the whole 9 (10) yards. It will be continuous drying like my kilns.

[LeeB]

Please educate me on the difference.

[Ianab]

Please educate me on the difference.

A problem with a vac kiln is that as the water evaporates it cools the wood. (insert some thermodynamic science here)

The wood quickly gets so cold that the drying, and movement of water though the wood pretty much stops. Because the kiln is close to a vacuum heat cant be carried in via warm air like a non-vac kiln.

So in a conventional vac kiln you need some sort of heating pads or plates, often with hot water, to carry heat energy directly to the wood via conduction. This complicates life and add a lot of cost.

The idea with an intermittent vac kiln would be to pull a vacumm and evaporate some moisture. Then let warm air back in, warm the wood up again, rinse and repeat, loosing a percentage of moisture each cycle. Does away with the complication of the heated plates needing to be in contact with the wood etc.

Ian

[LeeB]

Thank you, thank you. Thank you very much.

[Den Socling]

Here's a picture of a continuous vac kiln loaded with 12/4 HM. It dries in about 13 days. Discontinuous vacs take 6 to 20 times as long depending on species and thickness.



 

Here is a pair of discontinuous vac kilns that we converted to continuous by adding heating plates.



 

[GeneWengert-WoodDoc]

I would think that with a discontinuous chamber, the wood would have to be stickered.  Otherwise, how would you get heat into a large pile of lumber.  I do believe Den is correct is saying that a discontinuous dryer will take much longer...from a thermodynamics point of view, it takes a heck of a lot of heat to evaporate water, so you would find that heating wood 20 to 30 F will not provide much energy for evaporation.  Technically, the specific heat of wood is 1/1000 of the heat of evaporation.

[Den Socling]

I have had a lot of people say to me that they wanted to build their own kiln but I have never imagined anybody like these guys in  the UK. They are working on the kiln in their spare time and look at the job they are doing.



 



 



 



 



 



 



 

[beenthere]

Looks great Den.
Lacks some commentary of just what we are seeing in the pics (no.s 4 & 5 in particular). Or are you wondering too? ;)

[Den Socling]

#4 & #5 show an amazing job of building a shell and tube heat exchanger. I told them they would need a condenser to keep warm vapors out of their vacuum pump. I described the single pass shell and tube they needed. They couldn't find one so, no problem, we'll build one. As you can see, they have done a beautiful job in stainless steel.

The last picture is John Howard and his partner. I have communicated only through email so I don't know which is John. They both look young!

[WoodenHead]

That is very nice work.

Do the discontinuous vacuum kilns have some of the same advantages as a continuous vac kiln?  (example: colour of the wood)  How do drying times compare to dehumidification kilns?  What will these guys be using to heat the wood?

[serg]

Good work! Den. I could not understand it is your technology Vacuum drying? If yes, then you can do these cameras all over the world without leaving America?

[GeneWengert-WoodDoc]

I have had the opportunity to work with Den and the key to vacuum drying today is certainly good equipment AND, maybe more important, special, well developed operating conditions.  Den excels in both.

[Den Socling]

The color from a discontinuous vac can't be bright since you heat intermittently with hot air.
They intend to make aluminum heating plates. I would have said impossible 4 months ago!

Hi Sergie. This kiln will use exactly the same technology that I use here. I have described details and I have given them diagrams.

Thank you, Gene.

[Fla._Deadheader]

 I was one of those guys Den was coaching. If not for wife dying, we would probably still be at it. Den was really getting into helping and giving excellent advice. I probably never thanked him enough, so Den, thanks again for all the time you spent.

We had a pressure treating plant that we passed by, on our trips to the logging camp, so, we stopped in and received the grand tour. Tank was a double long propane tank, 4' dia. saw the vacuum system and how quick the vacuum would draw the water out of the wood, and then, flood the tank with the treating chemicals. Gave us a good view of what we needed to do.  We were a 2 man dog and pony show, so, we had limited time for such things, but, big plans.  : ;D

Tanks I found were 4' dia X 15' long. Had spotted some larger ones up in Georgia, but then, things fell apart.

My plan, on paper, progressed to once the kiln was built, I would have it in the sun, in Florida, lots of sun, and even had designed 2 solar mirrors, to reflect more rays of heating against the kiln tank. Then, I, along with Shop teacher, bought some vacuum pumps, tanks, plumbing, valves, etc. Last I knew Shop Teacher still had the stuff, but, was talking scrapping it all.

Anyway, I had thought of how slow the discharging and recharging of the kiln would be, so, had figured on 2 propane tanks, while the kiln was working, the second tank would be drawn down. Then, once the kiln tank was drained, it could be quickly drawn down. Figuring that an empty tank would have more volume available, than a tightly stacked full of wood, tank, would have a quicker transfer of vacuum.

I had planned to try to do this during the night, so the kiln would be ready for heat first thing in the mornings. Also planned to burn all waste from the mill, to supply quicker heating to the kiln, and, have hot water circulating.

So much for plans when things jump out in front of life.

I wanted to try that down here, but, that never got past the talking stage. ?

[WoodenHead]

I misread the post.  I thought they were making a discontinuous vacuum kiln.  Will they be using your controls, Den?

[Den Socling]

No on the controls. As we have gone along, I've described how the PLC needs interfaced to various actuated valves and sensors. They will write their own program.

[StSomewhere]

Hey Fla_deadheader can you put me in touch with your partner if he is thinking of scrapping it all?

[John.Howard]

For anyone interested, I'm the one being advised by Den. The decision to build a vacuum kiln was not one I took lightly, and if I had known at the time how much it was going to cost and how long it was going to take, well, there's no way I would have started this project. In this instance therefore, my ignorance was a virtue, for by the time I realised how expensive it was becoming, I felt we had gone too far to turn back.

My need for a vacuum kiln came about from a desire to build traditional timber frames, with infill panels instead of external cladding (so the frame can be seen from the outside like our medieval buildings). The problem with timber framing is that it is a medieval construction technique that doesn't sit too well with modern living. People nowadays expect to live in centrally heated houses, which further exacerbates the shrinkage and causes major distortion in the wood. Lime washing is no longer part of the spring cleaning as it was in medieval times, which would have filled any small gaps that had opened up, and no one has time to air dry the timbers. Because of the fact that green Oak, our traditional timber for framing, will shrink around 8% tangentially, it is not suitable for a panel infill frame, although some companies do manage to do it using expanding gaskets, you still get the shrinkage on the joints. It is possible to buy 'air dried Oak' (though of dubious moisture content as it has been air dried for between 1 - 3 years and as Oak dries at a rate of roughly 1" per year, on large section timbers, that isn't enough) but I couldn't find anywhere that sells seasoned curved timber, the use of which is one of the defining aspects of the traditional British style. We use curved wind braces, which cause the most problems with shrinkage; when you cut a shoulder at an angle there is more wood to shrink on the thicker side than the tapered side, creating an uneven gap. Not only does this look bad, but if the shoulder shrinks away it is no longer doing it's job and so all the work is taken up by the pegs.

Anyway, after a lot of research on drying, I discovered the only way to dry large section timbers was with a vacuum kiln.

The role that forums such as this play in maintaining and spreading human knowledge is vital. That I can still read discussions you guys were having almost a decade ago, and learn from them, I see as very important and, for me, what the internet is all about. I've read so many posts, I feel like I know half of you already! Crucially for me, because of this forum I was able to contact Den Socling. His willingness to help and generosity with his knowledge have been amazing. He is a top man. If we manage to pull this off, the vacuum kiln and the timber frames, I will see my contacting him as a pivotal moment in my life. Thank you Den. I've always tried to restrain the questioning! And your correspondence has led me to go off and research and learn about many things (most of which there is more information about online than there is about vacuum kilns!). Your information and your kind words have been greatly appreciated.

We've got to the stage now where we are both (my best friend and I) having to take some time to sort out some personal things. Things we neglected in our single-mindedness to get the kiln built! It's been pretty much all consuming and has led to a few bank fines! I've been pretty obsessed with vacuum kilns this year and didn't keep an eye on anything else. We now have to earn more money to finish the project, but it is still very much our priority.

Building the vacuum kiln has been very stressful, but we've also really enjoyed it. When the time comes that we pull a dimensionally stable piece of Oak out of it, that will be a cause for celebration!

By the way, I'm the one on the left in the picture...

[Den Socling]

There's one thing you forgot to mention, John. I tried and tried to talk you out of this project.  ;)

[John.Howard]

Ha,ha,ha! It was too late, Den. I'd already decided it was the only way forward!

[customsawyer]

Welcome to the forum John. Great job on the build. The only problem I have is that now you have me thinking. smiley_sidelightbulb

[scsmith42]

Welcome to the forum John. Great job on the build. The only problem I have is that now you have me thinking. smiley_sidelightbulb

Yeah, me too, and I already have a couple of 1000 gallon propane tanks....

[John.Howard]

Thanks for the welcome. I'd love to see other home made vac kilns! I have to warn you though, as Den warned me, this is an expensive tool. I've tried to build it as cheaply as I possibly could, using recycled materials where possible, fabricating what we could and generally not using top-of-the-range equipment from companies such as SIHI, which is what Den uses, but even still we're looking at a £10,000 machine in materials alone! I just hope it all works out.

We've still got a few issues to resolve. Specifically the door. We were very careful to keep the amount of distortion on the flange to a minimum. We borrowed a plasma cutter and welded the flange in small sections, so as to put as little heat into the 10mm sheet (which is what we cut it out of) as possible. Because of that the flange needed no further dressing and we were confident it would give a good seal with the 8mm neoprene gasket we bought. The first time we put the gasket in, we did the door up nice and tight to see what it was like. Then we left it for a couple of weeks...
When we went to open the door, we expected it to just open. But it didn't. We hadn't pulled a vacuum or anything, just done it up tight, and when we undid all the bolts it remained completely stuck! We hitched up the forklift truck to try and pull it open, but it just pulled the tank along! We tried chaining the tank to the concrete base and yanking at it with the truck and that just bent the handle!! We tried wooden wedges, but ended up beating in metal wedged to get it open! We haven't done it up with the gasket in since. I don't know if it's because I painted the flange with flexible paint or just the suction created by the compression of the neoprene. We have a couple of ideas how to solve it but they're not ideal. Anyone got any suggestions?? Other than not doing it up so tight!