Freeze Dried?

Paper baggging, Liquid Dishwashing Detergent (LDD) soaking, microwaving, cover in sawdust and wait a month or two, boiling

- so many methods of attempting to control drying problems.

I normally keep a couple of 2 liter cokes in the fridge. But this evening I had to resort to ice cubes since I'd forgotten to restock my cold coca cola supply. The ice cube tray was "full" - with half cubes. Hmmmmm - the tray was filled with water a month or two ago.

Freeze dried . . . Hmmmm.

Anyone pop a green piece in the freezer - for a couple of weeks and check the weigth change?

charlie b

Reply to
charlie b
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Charlie not sure about this I can understand the Loss of Volume of the Ice Cubes as this will be due to "Sublimation" at the Surface of the Ice, but you also will have an Expansion of Water when Frozen = to 9% of its volume, this may distort/destroy the Inner Cell Structure of the Wood?

My thoughts have been towards Vacuum Drying of Timber anyone had ago at this?

Reply to
Richard Stapley

Water -expands- as it freezes. Enough said?

Freeze Drying, uses cold and a vacuum.

Reply to
Ralph E Lindberg

Reply to
TonyM

Actually, freeze drying involves freezing, heating, and vacuuming all at the same time. See:

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Small units are not expensive. The FPL does not mention it. Woodweb says its a bad idea, but then goes on to say it can work.
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Vacuum kilns involve heating the wood, which can be the tricky part.
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Dan

Reply to
Dan Bollinger

The Scientific facts are Water at 0°C in Liquid form has a density of

0.9999grams per cubic centimetre where as Ice at 0°C has a Density of 0.9150g/cm³ which equates to 9% the damage this can do when trapped is well known, how many of you have suffered a Burst Water Pipe?

It is more about the Breaking or Rupturing of Cells, that when the Wood is Thawed and the Moisture Removed [Freezing will not remove Internal Moisture by Sublimation] there is a very real risk of Collapse within the Wood.

In a nut shell we are not discussing a Viable Method for Drying Wood so its back to the proven methods or the Soap Bath.

RVS

Reply to
Richard Stapley

Sublimation: Passing from solid state to gaseous state directly without going through the liquid state.

In a "frost free" freezer, the "gas", in this case water vapor, is removed from the freezing compartment - if it wasn't it would condense and become "frost". So there is some removal of water - directly from ice.

OR - IF the liquid dishwashing detergent (LDD) method actually gets the solution INTO the wood, I doubt it would freeze.

As for the unusual characteristic of water - to expand, rather than to contract, as it cools, (good thing too or we and other liquid water based organisms would never have occurred on this planet) - I believe the expansion value is closer to 4%. That's in the expansion range of many common woods - something solid wood furniture makers have been dealing with for quite a while (imagine trying to make chairs in Egypt).

But back to quick (relative to air drying) drying - perhaps to eliminate the the "ice cracking" potential problem, how about just using the refridgerator part of the fridge?

charliel b

Reply to
charlie b

Hi Richard & Charlie, Sorry I can't resist a warped & silly OT digression, but if a wood bowl could be collapsed by freeze drying then couldn't it be restored by adding water, as are many lyophilized products? We could freeze dry our finished bowls into small amorphous lumps to be restored by the customer to later glory by just adding water. We turners could freeze bowls instead of people to insure their immortality. More likely our lylophilized bowls would end up being chio pets. :)

Ok I said I'm sorry, so back to the subject. I think lyopholizing, ionizing radiation and hypertonic osmotic gradients have all been tried and found not feasible for drying or preserving turning timber. Not to say that some other methods are that much better. :)

Turn to Safety, Arch Fortiter

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Reply to
Arch

I've turned wood frozen for five months at lower temperatures. No difference, because it's not the freeze that counts, it's that frost-free fan that takes the high relative humidity cold air out. It's evaporation, same as all the other things you mention, that dries the wood. If the surface looses faster than can be replaced from within, the wood checks. Look at a piece of meat that's got "freezer burn" if you want to know what's going to happen to the wood.

"Freeze-drying" in commercial parlance has more to do with vacuum than temperature.

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Vacuum drying is used with wood.

Reply to
George

charlie,

Vic Wood in Australia says that they use freeze drying regularly. You put the wood in the freezer long enough to let it fully freeze (probably a few days). You then remove it from the freezer and place it in the refrigator and let the fan draw out the moisture. This takes several more days. (You should weigh it each day until it stops loosing weight.) Now they were using this for rough turned bowls. My wife and I have tried this with some success, when we can find room in our freezer, which is seldom.

Incidentally, one trick I learned from the World of Wood, the magazine of the International Wood Collector's Society, in an article it says to stand the wood vertical in the way that it grew and there will be minimum checking. We've tried this with some Madrone pieces about 5 feet long. They have been standing for six months now with little or no cracking. This is only one trial. The information supposedly came from an old logger, who said to stand your sawn boards on end while they dry and there will be minimum warping and checking. It isn't going to be fast, but it may be a way to save your collected timber from self destruction.

Fred Holder

Reply to
Fred Holder

Bound water would not freeze. Unbound water would require a temperature far lower than the home freezer unit. Remember your HS chemistry where they talked about freezing point depression in solutions? Then, of course, there's no way cellulose cell walls are going to break, not that they need to, there being no live tissue inside, and holes in them anyway.

Reply to
George

The Scientific fact of the matter is - the analagy is not scientific at all. The anatomy (cellular structure) of the xylem and phloem in any plant, and especially the hardwoods, is extremely complex and far stronger and more flexible than household pipe. Nor is the liquid contained in the living tissue water. It is a complex mixture of solutes in water that changes both the freezing point and properties of the system. Moreover, there is both bound and free water in wood. Think about it, northern trees experience repeated cycles of freezing and thawing each spring and fall. Green wood cut isn't so different from green wood in the tree.

Actually, we are. My shop is located in an unheated barn. Winter temperatures range from below freezing to below zero. I routinely cut slabs from green wood and allow them to dry while frozen. Rough turned blanks sit on the floor covered by shavings frozen. They are repeately subjected to thaw/freeze cycles as I heat the workshop to work and then let it go back to sub freezing. I have experienced NO cracking that wasn't due to wind shakes. I even tried putting the pith dead center through both sides in a number of blanks to see what would happen. Either no or minimal cracking. My experience is that it works.

It's also been reported on other message boards that putting a green, rough turned blank into the freezer for several days/weeks prevents both cracking and to some extent warping/distortion. So it's working for other people as well.

Reply to
ebd

in solutions?

You need to take a look at the molar concentration of sap and the freezing point depression per mole.

Reply to
ebd

...

Considering how easily Madrone cracks, it's an interesting data point

Reply to
Ralph E Lindberg

Holymolar Charlie! Look what two bottles of Coca Cola and a tray of half size ice cubes can lead to. At this point in your thread I am unsure whether or not to fix up my old freezer chest for drying wood since I don't need it for keeping fish anymore. Best to keep following the thread, trying to understand the inputs and hoping you will summarize what to do at the end.

I remember HS chemistry, something about rearranging letters & numbers separated by an arrow and a little about a piece of chicken wire with the same symbols attached with equal signs at the corners. It was taught by the same man who taught us shop (we had a Delta lathe) and typewriting and I didn't learn much, so rcw helps me with all three. :)

Turn to Safety, Arch Fortiter

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Reply to
Arch

Freezing point depression makes it highly unlikely he can freeze the sugar water in the wood.

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If you could, and if there was any alteration in wood structure because of it, there wouldn't be a tree left standing in the north, where it gets much colder than any freezer made for commercial use. That's why the tree reduces the amount of water it contains in the winter, to concentrate the solution, and make the freezing point lower. The fan, of course removes humidified air, which accelerates water loss. Leave out of the freezer, and you'll get the same. Note also, as in the other posts, that water escapes at a lower rate in a cool situation.

Reply to
George

This analogy doesn't "hold water", scientifically : ). Muscle and wood tissue, while both complex cellularly, are vastly diffierent structurally, physiologically, and chemically. Way too much to go into here. You are correct that the process that produces freezer burn is surface dehydration. However, due to a number of factors related to the cellular structure of muscle, movement of subsurface water to the surface is virtually nonexistant while frozen. The cellular structure of wood is far more conducive to water movement along the grain while frozen. Freezer burn is a film of cell destruction covering the surface, while checking is separation of tissue along stress lines with minimal cell damage. The two are nothing alike.

Also, differences in elasticity, plasticity, compressive strength, etc, etc, etc make any comparison between muscle and wood tissues a non-starter, except in Biology classes. The properties that distinguish the difference between muscle and wood tissues are huge. We don't burn t-bones to barbecue mesquite and trees can't walk. : )

When all is said and done, a fair number of people have successfully used freezing to prevent checking, myself included. I don't think anyone claims that it works for all species of wood, under every condition that could exist. But it does work, at least under some conditions, for some species of wood.

Reply to
ebd

Say what? It's loss of moisture and structural collapse. Lipid isn't cellulose and vice versa, but you certainly can see that the _loss of moisture_ which expands the structure is the common thread. Or are you just trying to sound important?

Capillary action, the process by which unbound water is carried by the tree, or pulled by evaporation, depends on adhesion to the walls of the tube, and cohesion of the liquid involved. What happens to the surface of wood where the relative humidity is low is that it loses water to the air to the degree the air is able to accept it which cannot be replaced from the interior by capillary action. That's what causes surface checking - always - and the weakness in structure from the collapse of fibers which have lost their bound water produces initial surface checks, which open until adhesion overcomes cohesion, preventing capillary draw.

Proof is in your woodpile. End checks are self-limiting. Once the dry layer is thick enough, it isolates the interior from further rapid loss, which is why you can trim off the damaged ends and find wood well above the EMC in the interior. Wet the end, re-expand the fiber, and be fooled into thinking the structure is sound to your sorrow.

I have cord upon cord of wood which has been "frozen" all winter, and it's only now beginning to dry again. Since the water couldn't leave, the checks have not grown. Is that what you mean by preventing checking? It may seem news to you, but loggers have known it for years. Keeping the log submerged or soaked will do the same thing, and for the same reason. However, none will have done a thing to prevent checks which will begin on a freshly exposed surface once water can be removed. That's the drying part. Take two pieces of wood, as nearly identical as you can get. Make them from the same stick. Freeze one, not the other, then put them into identical conditions to dry and check for difference. I suggested this to Fred when he spoke of alcohol "drying" as an effective method. There will be no difference in dry time nor in distortion. Of course, if you control the relative humidity by wrapping, as in the "alcohol method" you will have success, if you toss them on the table for three days at 60% RH, you will have failure. Freeze has nothing to do with it - nor does alcohol. It's controlled moisture loss which is the independent variable in your experiment.

Try it.

Reply to
George

Since we' replaying around with the idea of using tissue drying methods on wood, and it seems (more or less) agreeing that they're not comparable, how 'bout this one:

a method used to prepare bio specimens for scanning electron microscopy (SEM) is to replace all of the water in the tissue with alchohol, followed by liquid CO2. The specimen is submerged in liquid CO2, and thressure and temp are cranked up to the triple point (the point where the CO2 gas/liquid phase lines and temperature pressure phase lines intersect) -. Basically at this point, the CO2 transisions from liquid to gas, but the volume does not change. If you remember your basic chemistry.physics, and think about gas laws, it should make sense. If you don't remember it, just take my word for it - its real.

the end result (in bio anyway) is a speciment that is totally dry, but with none of the distortion (shrinking) usually assoicated with liquid loss.

It seems that (in theory anyway) this should work for dessicating wood. I don't know how good the wood would be....0% moisture just doesn't sound like it would be a good thing. (Bio specimens in this state are delicate beyond delicate). Course, all the bio SEM work I've done was in specimens that were in the 5 mm or less size range, so you'd have to be doing some mighty small woodwork.....

this is what happend when a engineer/bio geek starts thinking.......

--JD

Reply to
jd

Excuse me, but loss of moisture never results in expansion. And no, I have no reason to try and sound important. Perhaps you do, but I'm mearly trying to be accurate in replying to a question from someone asking for help.

Actually this mechanism has been proved to be insufficient to explain how water is transported to the tops of redwoods, for example.

Incorrect, actually. Has nothing to do with structural collapse of fibers. Wood shrinks differentially as it dries, setting up stresses that pull the wood apart.

Very poor analogy. We are talking of properly prepared blanks, pith removed and roughed out to a thickness of about 3/4" to 1 1/2" not firewood. Apples and oranges.

I have. It works. Both freezing and alcohol. And actually you are quite wrong about the effect of alcohol. It's used quite extensively in the preparation of tissue for microscopy. The alcohol replaces the water, i.e., dehydrates the tissue, preventing damage or distortion of the tissue. Freezing is likewise used extensively to microtome fresh samples for immediate viewing rather than permanent mount.

Perhaps you are, deliberately or subconciously, missing the critical point. No one is saying to cut a block of wood with pith running through it, put it in the freezer or in alcohol, pull it out and expose it to low humidity and expect it not to check. What we are saying is that if you rough turn a green wood blank to about an inch wall thickness, freeze it or soak it in alcohol long enough for the water to be replaced by the alcohol, and then dry the blank slowly (under cover of shavings or in a paper bag or other method of your choice), the failure rate from checking will be drastically reduced if not eliminated and you can dry more quickly than would be the case without treatment.

Reply to
ebd

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