Wood Drying Topics > Moisture Variability

Re drying H4 radiata pine

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aj:
We are re drying h4 radaita pine at 90 over 60 70hrs with 16hrs EQ in that. but its coming out 10 to 12% m/c  but inside 20 and over. any help would be great thanks aj

PhilM:
My understanding is that H4 is an Australian grade which describes a treated post for in-ground usage and sized 100mm x 100mm nominal (approximately a 4” x 4” in the US).

Is this a Kiln Dry After Treatment (KDAT) process?  If so, were the timbers treated with a full cell process, leaving a lot of liquid in the wood cells, and resulting in a longer drying time than the green lumber (before preservative treatment)?

It may simply be that drying 4” thick pine at 90C dry bulb/ 60C wet bulb (this is 194F / 140F) for 70 hours is simply not long enough.  KDAT of southern yellow pine is often not done if it cannot be done at temperature above 212F because of the lengthy time required.

Importantly, with this very wet material, you need to make sure that you are maximizing air flow efficiency by baffling the kiln load well to insure that the air flow is moving through the stack (and not around the ends of the stacks). This will both speed drying and minimize moisture variability.

HencoV:
I think 90/60 is too harsh if you run a single set point from start to finish. Your steam usage is probably also very high, and your vents stay 100% open for most of the drying cycle. My experience is that you seal in the moisture if you go to 90/60 too quickly.(whille still above FSP) If your kiln controls don't allow for multiple stages, I'll rather go for a RH% between 33 -36%. You will probably dry faster, with less variation and better quality, which requires less Eq at the end.

MichaelM:
When you said the wet material was in the middle of the load, I first associated this with airflow that is too low (as Phil suggested).  Phil had many other good comments.  I would also tend to agree that a 44F wet-bulb depression throughout is a little high.  Starting out a little more gently and doing the last 15 to 25% of the cycle at a 25 or 30F wbd might help.
Mike M.

aj:
Thank, It was in side the board not the stack thanks.

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