What am I missing?

[customsawyer]

Received a email from JYC HF Vacuum dry kilns. Didn't trust the email enough to click on the link so I googled them. If I'm seeing things right in the pictures then they don't use any stickers. Just what looks like a metal plate about every 5 or 6 layers. I feel sure that I have mentioned this before but I hate to sticker lumber. Back to my question. How does the moisture get out of the boards that are dead stacked to 6 inches deep? Do these actually work really well? 

[kantuckid]

In another "sticker idea twist": There's a guy on FB WM group who's experimenting with sawing PVC pipe in half for KD stickers. Seems pricy to me. 

[K-Guy]

It's Chinese kiln and shows you have much to learn, Grasshopper!  :D

The vacuum basically sucks the water out of the wood.

[Ianab]

Yeah, vacuum kilns work on a different process. They don't need airflow to carry the moisture away because they are physically pumping all the air (and water vapour) out of the chamber.


The idea is that at very low pressure water evaporates at a much lower temperature. Pull enough vacuum and water will boil at room temperature, or even sublimate directly from ice at below freezing temps in a "hard" vacuum.


But the problem is that it still takes energy (heat) to allow the water to vaporise. In a conventional kiln you heat the air, blow it though the stack, and that both provides the energy needed and carries away the moisture. But you can't do that in a vacuum, so some sort of heating plates or pads are used to directly warm the wood. If you didn't the stack would soon turn into a big wood popsicle and the drying process would stall. (No air to carry more warmth to the wood)


Advantages are that it's fast, and you can dry thicker or more difficult species with less risk of degrade.
Disadvantages is that it's expensive, the kiln chamber has to be a sturdy pressure vessel able to handle a vacuum without imploding, and you have to have heat pads, vacuum pump and some fancy controls.

[customsawyer]

Of course I have much to learn. That's why I hang around here.

[moodnacreek]

I think Woodmizer did this with electric blankets in a vacuum chamber. Can't see how anything would dry flat.

[Ianab]

The wood is still constrained in a stack, pretty much the same as if it was on stickers. Stickers in regular drying are only needed because you need to blow warm air over all the boards as evenly as possible. In a vacuum there is no air flow, the water vaporises in the wood and wafts out, pulled by the vacuum pump. Because there is no high temperature involved there is less stress on the wood than a conventional kiln, especially if you start pushing the schedule. 

If you want to get even more high tech, you can send microwave radio energy (like an MW Oven) into the kiln chamber to warm the water and help it evaporate, but that's getting into real rocket science territory.  :P

[Don P]

Most of those were actually RFV, radio frequency/ vacuum. I worked in two shops that had RF glue machines. I can't remember the frequency but FM radio was a no go in the shop. I think one was 10kw and the other 15. They were basically a college radio station broadcasting from a slick plastic covered aluminum plate in the bed through the panels we were gluing and into the same plate on top which was the ground return side. The radio frequency simply got the electrons in the wet glue excited and making heat. RFV was doing the same thing. As you can imagine it was making the meter spin but it put out pallets of panels per day. It's almost a microwave at a safer frequency. One of those presses used firehose for the "pistons" for both side and top pressure. something I've wondered about for drying, wrap the stack in firehose and pump it up.

[Ianab]

It's almost a microwave at a safer frequency.

Lower frequency radio would also penetrate the wood better. I mention microwave because it's the same principle, but the higher the frequency the less penetration. 

[customsawyer]

Thanks guys. Starting to make sense now.

[YellowHammer]

I think it may also depend on the type of vacuum kiln.  For example, and someone help me out here, the people who I know that run the IDry, which is a type of hybrid, because the heat is applied with heated air by heat strips and the vacuum is relatively moderate (equivalent to only 30,000 ft), then sticker stacking is a requirement.  I've never talked to anybody who owns a hybrid that doesn't need to sticker.  

Is this true?  

I am seeing Idry's come up for sale and some are getting in my price range.  Like Customsawyer, not being required to sticker and unstick would certainly fall into the "Take Steps to Save Steps" category, but I don't know if it applies to all of them.

[Walnut Beast]

Sounds like somebody might be getting a I dry sometime 

[boonesyard]

YH,

You are correct, an Idry is a sort of Hybrid Vacuum kiln that does not completely vacate all air. A fan is still used to move air in the chamber, therefore stickers are still required for circulation. 

A vacuum is measured in Hg, or inches of mercury. Barometric pressure at sea level is just under 30 Hg, and my Idry is set to create a vacuum down to about 8Hg which is the pressure at about 32,000 ft. At that altitude, water boils at about 148 deg. which allows more of the BTUs entering the kiln chamber to be used to directly evaporate water, which increases efficiency thereby speeding up the process. 

[scsmith42]

Good explanation above.

Vacuum kilns can be broadly divided into two categories - low vacuum and deep vacuum. Low vacuum kilns such as the iDry still have some atmosphere present in the kiln to convect heat, so an internal heat source and stickers are used.

Deep vacuum kilns have no atmosphere inside to convect heat, so a source such as a heat exchanger plate or electric blankets in-between the layers, or microwaves are used to supply the heat.

Jake, the one that you referenced uses microwaves.

[customsawyer]

Most lumber is aggravating to sticker, to say the least. Some of the big slabs that I produce, like the pecan we cut at the project, or 9/4x26x16 pine slabs I go through so much of, are getting down right brutal. I've never cared for stickering lumber but the older I get the less I like it. So when looking at the pictures of this kiln I will admit it peaked my interest. Must be getting even lazier in my old age.

[scsmith42]

Unfortunately in RF Vacuum kilns you still have to place anode plates in-between the layers of lumber, but I don't think every single layer.

[YellowHammer]

If they use microwaves and Jake gets one, then at the next Project, he can dry wood and cook chicken and pizza in 3 minutes.   8) 8)

[Don P]

You can really burn the cookies with RF. I discovered lichtenberg more than once before my boss knew it was cool  :D

I was cleaning one of the aluminum platens out back of the shop, didn't finish and left it out back overnight. When my boss arrived the next morning he said a 90 lb shopping cart lady was jumping up and down on it trying to fold it up into her cart, this was a 4x8 sheet of 1/4" , it would have taken her several folds, but I ddn't leave that temptation out again.

I don't think there is any free lunch laborwise, vacuum just means you get to rinse and repeat faster, or the real niche is thick and hard to dry stuff. For normal value, normal dimension wood, the big boys do not dry that way. I imagine the juice isn't worth the squeeze. If you have timberframers or slab furniture makers deep enough to pay for it, it would probably be a busy machine.

[Walnut Beast]

The company looks to be pretty big and interesting

[customsawyer]

In the pictures I saw on their website it looked like a heat plate every 8 layers of 4/4 lumber. I normally put 20 layers on a pallet but would be able to bump it up to 24 without stickers. Normally do 12 layers of 9/4 lumber could maybe bump it up to 16 without stickers on a pallet. Might also speed up turn around time too. This would increase storage in that I wouldn't need all of the air drying room. Sounds great in theory but I would prefer one of y'all buy one first and let me know how well it improves your business.

[scsmith42]

Jake, I'll buy one if you'll finance it!   :D

[customsawyer]

25% interest will also need a credit app. with loooooooots of references. Probably like 99% percent down or something like that. 

[scsmith42]

25% interest will also need a credit app. with loooooooots of references. Probably like 99% percent down or something like that.

I didn't know that you owned one of those Payday Loan companies!  :D

[GAB]

25% interest will also need a credit app. with loooooooots of references. Probably like 99% percent down or something like that.

I didn't know that you owned one of those Payday Loan companies!  :D

Who knows, that just might be his next career.
GAB

[customsawyer]

Scott you better jump on it quick before the interest rates go up again.