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I think I've case hardened some walnut 6/4 and 8/4 boards. I'm getting a consistent 8-10% mcv reading on the surface but 15-20% at the center of the wood. Anybody have some suggestions on how to get the water out of these beautiful boards? I'm using an EBAC LD300 and thought I was ready to spike the temp after doing some quick readings and coming up with the 8-10% mcv.
David M.
I would not assume casehardening has occurred, though it may have. You are not as close to the end of your drying cycle as you thought, so a definite moisture gradient should be expected. The EBAC DH kilns are operated at low temperatures, so if you have not allowed the RH to get too low during the process serious degrade is unlikely. What are you using for a kiln schedule? How have you been monitoring the drying progress?
On a general note, kiln schedules work best with a single thickness of material.
Here are a couple of links discussing case hardening: http://www.woodweb.com/knowledge_bas...xplained.html; http://www.forestryforum.com/board/i...?topic=49318.0
Hi Kevin,Quote:
Originally Posted by Kevin Jenness
Thanks for the feed back. The tech at EBAC had me progressively increase the temperature and on time until it maxed out at 50C and was on a constant setting. I bumped up the temp and 0n time when there was no or minimal water exiting the kiln. The wood was in the kiln for 4-5 weeks and I wasn't seeing any water in the "exhaust tube" and assumed it was finished drying. I did a quick MC check on a couple of boards (along the accessible edges) and was getting readings of 8-9%. I pulled the wood out and did some more checking and found areas that were dry and ares that weren't. (I think part of my issue is improper air flow in the kiln). I'm going to resolve the airflow issues and put the wood back in the kiln and hopefully get a more consistent drying to a usuable 8%..
It's been a steep learning curve on proper drying. A local sawyer with two DH kilns told me that he doesn't put anything in the kiln til it air dries to 25% or less? I think another mistake I made with the walnut was rushing it into the kiln at a higher MC.
I also pre-air-dry to below 20% before putting the wood into my dehumidification kiln. All the bad things that can happen in drying have already happened at that point since the wood is past the fiber saturation point which is about (25% to 30% moisture content depending on species). Then, you can run the kiln flat out to bring the down to the target moisture content. For me, that takes about 6 to 9 days depending on the species. That includes a 24 hour period of sterilization at 150 degrees at the end.