Vacuum Drying in a Bag

[logboy]

Do you know what isimitibiti was using?

[Den Socling]

No I don't know what he used but a "chamber" might be made from plastic sheathing with duct taped seems. The tricky part would be the connection for the pump.

[logboy]

I dont think the bags or the connection would be an issue as long as one of these would work. The down side would be the "softening point" of 150 degrees. The hot box would need to be kept below that temp.  What kind of vacuum

http://www.veneersupplies.com/categories/Vacuum__Press__Items/Vacuum__Bags__%26__More/Dura-Max__Extreme%E2%84%A2__Vacuum__Bags/

[Den Socling]

Those bags look like they might fit the bill. But odd sizes. Too big.

Many species will reach 7% at 140'F. A couple, like Black Walnut burl, needs 180'F.

I usually run the vacuum around 55 Torr (55mm Hg). A chamber pressure of 65 will work. If you go above 65, the boiling point (and wood temperature) goes above 110'F.

[logboy]

I was checking over your chart and 65 Torr correlates  to 109 degrees F. So theoretically with a "chamber" temp of 125 the wood would be at the required temp and yet still not soften the bags.

What kind of vacuum pump would be necessary to correctly run this setup? I kept reading about oil/water mixture problems. Is a different pump the solution, or a condenser of some sort?

[Den Socling]

If your wood is wet, evaporation keeps the temperature at a level set by chamber pressure. So, if you have 65 Torr, the wood can't go above 110. If you were heating in a bath of 125, the extra energy would speed up drying.

I use shell and tube heat exchangers as condensers. I use liquid ring vacuum pumps because they can take some water if any gets past the condenser. There are dry, screw pumps but they cost two or three times that of liquid ring. The thing about drying in a bag is that a tiny pump would do.

[logboy]

If I am reading right from the other posters the pump would not need to be run continuously either. Some sort of small pump hooked up to a basic timer in a thermostat controlled hot box might do the trick.

[Den Socling]

That's correct.