Back in the cobwebs of my feeble brain I seem to remember something like this. What was the name of the file? Greg At 07:39 PM 8/30/2002, you wrote: >>Yes, I believe it is. That's why I am confused. It seems that the intent >>is to dry down the board to a specific moisture content. Since this is >>the case why is an instrument that measures the moisture content of the >>air being discussed? Again, respectfully, what am I missing? >> >>Greg Newell > > >The connection Greg, the connection. If you know the temperature and >relative humidity, you can compute the equilibrium moisture content of a >piece of wood that has been in that temperature and humidity long enough >to reach equilibrium, moisturizationally. The rate at which the MC in a >piece of wood changes is relative to the difference in MC of the wood, and >in the surrounding air. The greater the difference, the faster the >moisture exchange between the two. Wood left in 70°F air at 40%RH will >eventually stabilize at about 7.7%MC. But you don't know at what rate. If >you are kiln drying and want an absolute minimum cycle time, you don't >have time to sit around with a yard full of green 16/4 wood waiting for >the stuff in the kiln to reach EMC, so you jack up the temperature to >provide a greater moisture potential differential and measure it directly >with a probe from time to time until it hits the target MC and pull it out >before it passes on to ultimate mummification. In a piano shop, drying out >an 8mm thick spruce panel, the drying time is considerably less and you >probably aren't processing 10,000 board feet at a time, so you can afford >another day for it to stabilize in it's own time in the box. That being >the case, if you'll keep an eye on the temperature and RH% in the box, and >compare the MC computation from those measurements with your target EMC, >you just have to leave the sucker alone and wait for the wood to get to >that MC all by itself. You can leave it in there for two weeks, >justifiably assuming that anything that thin that hasn't reached >equilibrium by then probably never will, or you can use your handy >homemade faux soundboard MC indicator instead of a probe to get an >adequate indication of the MC of the panel without poking holes in it with >a $200 instrument who's calibration is most likely in doubt anyway, most >especially at low MC levels. > >Didn't I send you a copy of my Excel MC compuationalizationating worksheet? > >Ron N Greg Newell mailto:gnewell@ameritech.net
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