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Has anyone tried to heat treat bamboo using steam at atmospheric pressure or slightly pressurized? This is often done with wood to dry and treat it as I understand. Just curious as this came up in a discussion with a fishing buddy today at work. (Frank Paul) I have never heard of anyone trying this, but I suspect it might just work. I have steam bent some oak for boat building, and it does appear to have hardened when it dries out. (Tom Smithwick) Steam at atmospheric pressure is only 212 degrees Fahrenheit. With the typical temperatures used for heat treating being in the 350 degrees Fahrenheit range I think you would have to go to superheated high pressure steam to get to the temperature. The steam used in drying wood is used both to transfer heat during the first portion of the drying cycle, and more importantly to keep the humidity of the kiln high enough that the wood does not dry to fast. The humidity is gradually lowered while the temperature is kept warm and the air kept moving in the kiln. Near the end of the drying cycle, most of the heat is introduced by heat exchangers, with a little steam used to control the humidity. Somewhere I have the Forest Products Kiln Operators Manual and could look up the humidity/temperature schedules. Steam may usable in straightening nodes, but the temperature still may not be high enough. I think this has been hashed out on the list from time to time. (Kurt Clement)
My question is about ovens and moisture. I understand that its intention is to temper and remove residual moisture from the bamboo. Most of the ovens I have found are closed systems. So it seems to me that as it is heating the moisture out, the moisture circulates and a percentage of moisture must get reintroduced back in to the bamboo since there is no type of moisture venting. Now I know the moisture vapor will escape when you open the door to flip the bamboo, but again it seems the moisture prior to that can make its way back into the bamboo. What are your thoughts on this? Am I making a mountain out of a mole hill? Jerry, your thoughts? (Paul McRoberts) Mine is the simplest of the heat gun types. It's a tube with a gun of the end. Moisture just blows out the end of the oven. Temps are relatively easy to maintain throughout the oven, and it's up and out of the way when you're not using it. (Mike Shay) Leave the door open a crack. (John Channer) Mine is a heat gun oven similar to the one in "The Best of the Planing Form", a small tube, in which the section is hung, inside a bigger tube. The heat gun blows down through the big tube and up through the small one, which is open at both ends. (Neil Savage) Remember that hot air will hold more moisture than cold air will. When you elevate the temperature in the oven, that's what is drawing the moisture from the cane. The heat, if it eventually gets high enough, will result in some chemical changes in the cane, but it also has a lower relative humidity the higher the temperature goes. You can still saturate the air inside the oven if you have a high moisture content, or a lot of cane, and all you have to do is crack the oven door open for a bit. (Mark Wendt) I was hoping Mark would respond ... Important..? Not very, in my estimation. The main purpose of heat treating is to temper. Unless you soak your strips and immediately throw them in the oven (I don't know why I'd do that) I can't see the saturation point in being reached in any oven I've seen. The volume of air vs. the amount of water in the bamboo. Many studies have shown that the bamboo will soon (within a year or so) absorb free H2O and reach a point of equilibrium with whatever relative humidity it lives in. Water will be driven out as a natural byproduct of the temps we use to temper. As soon as you take the sticks out of the oven they begin to reacquire H2O. I'd rather keep the door closed and keep my temperature stable. (Jerry Foster) My oven is a heated Pyrex glass tube, open at both ends. I like the idea of moisture being able to escape readily. (Chad Wigham)
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