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Author Topic: Discontinuous Vacuum Kiln  (Read 6869 times)

Offline HaroldCR

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Discontinuous Vacuum Kiln
« on: April 17, 2016, 02:43:35 PM »
 Haven't seen any discussion of this type Kiln. The reasoning behind the design is, relieving stress as the lumber dries quicker than air-solar-large scale drying. Anyone ever heard of "Freeze drying" ??

Before my world kind of fell apart, we were in the process of building such a kiln. We had made a deal on a used 4' dia X 12' Propane tank. One end was to be cut off and a hinge device attached to make the door swing and land flatly against the stop flange. A sliding locking ring would be built, so it could be rotated encapsulating locking pawls to create a super tight fitting door. We had a metal supply/machine shop a few miles from home, and were planning to have them roll 2 pieces of 3" X 1 1/2" return, channel iron, so we could weld it around the tank to alleviate crushing from air pressure differential. We would build the door mechanism.

 The tank would be set in a mostly sunny area and painted black, of course.

 A special type of vacuum pump would be incorporated in the system, that would not allow excessive moisture to be pulled into the pump, eventually destroying it. We had bought a couple of these pumps, cheaply, on ebay. We had in fact bought 2 complete vacuum systems, including valves and vacuum tanks which were filters for removing condensation.

 2 angle iron rails would be welded inside the tank as tracks for the carriage. On the bottom of the tank, below the tracks and in from the door, would be installed a vacuum sealing valve. This would be for draining condensed water from the wood as the vacuum would draw it out. Heat sensor mounts and bar measuring gauges would be installed, also, to monitor the stages of drying.

 We were being coached by a guru of Vacuum Kiln designing. The project fell apart before we could get it built. I had hopes of doing the same down here, in CR, but, the rainy season would not permit satisfactory results.

 The way the kiln would function, is, in the morning, the sun would start to heat the tank, and the vacuum pump would draw the heated air out of the wood, carrying moisture with it. A preset bar measurement would be used to shut down the vacuum pump and hold the vacuum at a set level. A timer would be used to start-stop the pump.

 What this would be doing, is, "sweating" the moisture out of the lumber. A timer could be incorporated in the system, so, as the sun was setting, the drain valve could be opened and the water drained out, ALSO, allowing fresh air into the chamber, so the lumber had a chance to "relax" from the vacuum draw and relieve tension from the process. It would also allow what moisture was still present in the lumber, to "equalize", further relaxing the fibers of the wood.

 This type kiln would solve a few problems. It would do away with excess handling of lumber from the mill, to a forklift or whatever, stacking for air drying and then, restacking later, as the lumber dried. In our case, it would also deter theft, as we were located close to a main road and people knew our lumber was valuable.

 So, no air drying, and no harsh drying schedule. Stack on the carriage for the kiln right off the mill and start the drying process. Most of our logs were full of holes, so, drying was not necessary, unlike solid wood. The holes allowed the Pecky Cypress to be dry within a few days so we could then transfer it home to find markets. I found a great market within 6 miles from home and they took all we could produce, wet, right off the mill, so, we stacked it right on the trailer off the mill. We had not yet found a way to locate the solid logs on the river bottom, so, what few we did find, were to be experimented with.

 Everyone that has read this far must be thinking, "I saw all day every day, so, this system is too small for me". That would be correct thinking. However, sitting on a few Mdbt of lumber, waiting for it to dry, ties up a LOT of money. The guru and us figured it would be 30 days or so to dry the lumber. Also, I had spotted a Propane delivery truck in a junkyard, with that big tank on it. The tank was over 7' dia. and over 16' long. THAT would hold a bunch of lumber. That would take a LOT of time away from normal drying and even Solar Kilns. Also, this was a way for a small operator to obtain a cash flow.

  I DID build a solar kiln here, but, people don't want or need "dry" lumber here. 14-16% is fine in the humid tropics.

Offline furu

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Re: Discontinuous Vacuum Kiln
« Reply #1 on: April 17, 2016, 07:19:42 PM »
Interesting read and description.  It would have been  nice to see it in operation.  Sorry you never had the chance to make a go of it. 

I did not really understand the door seal design but sure it would have worked for you. 

Since you beefed-up the outer hull to prevent collapse what had you figured was the vacuum point that the tank would deform significantly without the support?
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Offline HaroldCR

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Re: Discontinuous Vacuum Kiln
« Reply #2 on: April 17, 2016, 09:56:30 PM »

 That's a good question, furu. Unfortunately, I can't remember the actual  differential between atmosphere pressure and vacuum pressure. The thickness of the tank was nearly 1/4", so, as I tend to overbuild things, the channel was an insurance thing. Back then, 2002, it was not an expensive plan.

 On the door flange-seal question, 2---1/2" thick X 2" wide flat bars was to be rolled edgewise to make a circle that would be the same dia as where the door part was cutaway.  One would be welded to the tank and one to the door so they would mate up. On the tank part there was to be a slight offset as the flange was placed back from the front edge of the tank groove left after the welding, so a special rope type seal could be mashed-glued in and the flat flange of the door would mash it really tight as the lock ring was rotated.

 The ring was shaped like a channel and added to the tank side after the flange was welded on.  Place it on the flange, then weld the ends together, so it would slip around the flange without falling off. There would be notches cut in the door side of this ring and slightly tapered metal blocks welded to the door flange.

 As the door was closed, the ring would slip over the blocks and then the ring rotated to make an ever tightening compression of the seal from the door flange. Once sufficient vacuum was attained, there should be no leakage of air into the chamber, until the drain valve was opened.  We figured to have 13-14 blocks spaced at approximately 10" in the approximately 132 inch circumference of the flange. Actual construction would be more exact. We were not machinists, so, drawings were all approximate.  ;D

 Final plan was, if this worked as we thought, we could always add more tanks. This way, a steady supply of dried lumber would always be coming on, and always protected from the open environment.

 Once we made our first run, we could have actual temp measurements, to see if we could reach pitch set and insect killing temps. If not, we could always devise a heated water system and circulate very hot water to reach the actual high temps needed, through piping placed inside the tank, under the track area. The space was figured at placing the rails at 6-8" or so, above the bottom of the curved tank. The carriage would pass over that plumbing.

 Too bad I didn't keep all the drawings we had made up.
 

Offline furu

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Re: Discontinuous Vacuum Kiln
« Reply #3 on: April 17, 2016, 10:28:58 PM »
Got it now.  Thanks.
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Offline bandmiller2

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Re: Discontinuous Vacuum Kiln
« Reply #4 on: April 18, 2016, 12:29:24 AM »
Hal, it would have to work, what worries me is how fast its dewatered and the effects on the wood cells. I know little of kiln drying lumber, always used dry winter air and time. You may not need too deep a vacuum. Once you start pulling a vacuum the door will hold itself closed. Frank C.

Offline HaroldCR

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Re: Discontinuous Vacuum Kiln
« Reply #5 on: April 18, 2016, 12:51:19 AM »
I agree with you, Frank.

 Only thing is I would hate to have the thing look like a Coke can all squished up.

 In a controlled environment, maybe the door could be made to seal without the locking ring. In our shop, I doubt we could effectively control warpage enough for that to take place.

 Releasing the water will be a lot more gentle than baking it out in a steam kiln.

 Red Oak vs White Oak would be a very different schedule.

 The main purpose of this design was that we could PROBABLY dry the 3" thick table slabs to under 10% in 3 months or so. This was an educated guess by the guru. We used to stand these on end and watch the water slowly drain out into puddles. Remember, we were working with waterlogged logs, so, dryer logs should work equally as well, or better.

 NOW lets see if this thread gets some action.  ;D

Offline bandmiller2

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Re: Discontinuous Vacuum Kiln
« Reply #6 on: April 19, 2016, 12:34:21 AM »
Hal, what will you use for a vacuum pump.?? Years ago a friend and neighbor offered me a large vacuum pump at the time I had no use for it and didn't need more clutter in my shed, kinda wish I grabbed it. Would a air compressor pull a usefull vacuum.?? As they said in the navy if something blows it has to suck. Frank C.

Offline HaroldCR

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Re: Discontinuous Vacuum Kiln
« Reply #7 on: April 19, 2016, 12:47:40 PM »
 Frank, on anything experimental any vacuum is better then none. It's been forever since I did research on vacuum values. I BELIEVE reaching 30 bar is near impossible without very specialized equipment. 30 bar is near perfect vacuum, IF I remember correctly. Adapting to a typical air compressor intake can be difficult. They are usually a molded orifice for holding filter material.

 When running our dairy farm, we had a vane vacuum pump for the milker claws. It would need draining after each session and it had a glass oiler on it, same as the old gas and steam engines. It would run at 15" ?-pounds-? bar- whatever, limited by adjustable sensors in the vacuum line, set for that number. Internal corrosion is where the problem originates. Liquid ring vacuum pumps are used in destructive pump environments.

 I recently checked ebay and found several liquid ring pumps, from $200.00 and up. Just for experimenting, maybe find an electric vacuum pump used for power steering or power brake assistance from a junker car. Might have to tinker with the adjustment somehow, to get higher vacuum ?? Don't know ?? You will need a heavy tank of some sort to avoid atmospheric crushing as you pull the vacuum. It would be nice to find a clear acrylic container that you could place a moist wood sample inside and seal the container. Pull a vacuum, using a gauge for reference and watch for results.

 I am going to experiment with moist wood in a couple of weeks on a related but totally different project. Hope to have results to post when I get back home from Florida. I'm hoping to find a used-cheap pressure cooker, and use it in reverse. Got to hit up thrift shops. I also have a compressor shaped vacuum pump that was given to me, that I am going to use to pull vacuum on bags that will contain my DIY Solar panels I need to get built. It will mash the air out from between the cells and the material that gets melted and encapsulates the cells to the glass.

 I go up to Fl in 2 days to help my Son and will buy another Chevy Volt Battery for my 3 wheel vehicle build and converting my house and shop to alternative energy, and shit can this expensive stinking power company here.  ;D ;D
« Last Edit: April 19, 2016, 01:07:48 PM by HaroldCR »

Offline HaroldCR

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Re: Discontinuous Vacuum Kiln
« Reply #8 on: April 20, 2016, 06:43:53 PM »

 Kind of surprised there is so little interest in this, as it's a really good way to dry thicker slabs quicker than 1" per year schedules ???

Offline bandmiller2

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Re: Discontinuous Vacuum Kiln
« Reply #9 on: April 21, 2016, 12:07:08 AM »
Hal I don't think there are too many active members here. I have never been too interested in kilns because little of what I cut is used in moisture sensitive applications like furnature. Small shed, barn repair and truck and trailer bed oak are my mainstays. I can see that kilns would be very important in the deep south with its constant high humidity. A kiln would also help with blue stain in pine especially a quick vacuum, "dry em out before they bud out". Frank C.

Offline Stevem

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Re: Discontinuous Vacuum Kiln
« Reply #10 on: April 22, 2016, 02:10:46 PM »
Just a passing thought.
Years ago I had a water truck that sucked water into itself using engine vacuum.  Had a vacuum hose running from engine intake manifold to a unit mounted on on top of the water tank with a shut off valve.  Had to watch out you didn't get too full and suck water into the engine.  Never did.  That water tank unit looked kind of like those little domes on old railroad steam engine boilers and it "rattled" when it was working. Sounded like marbles in a paint can.  No idea what was inside.  15" of vacuum available on a car engine.
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Offline bandmiller2

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Re: Discontinuous Vacuum Kiln
« Reply #11 on: April 23, 2016, 12:15:01 AM »
Steve, its probably a hollow ball so if the water level rises it will block the vacuum line to the engine. Some of the old gasoline fire pumpers used engine vacuum to prime the pump when your drafting from a pond. When diesels came along they had to have a separate vacuum pump to prime. Frank C.

Offline Stevem

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Re: Discontinuous Vacuum Kiln
« Reply #12 on: April 25, 2016, 03:45:29 AM »
Come to think of it when I went to a diesel powered water truck I had to get a trash pump to fill it.  Been awhile.
Stevem
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