When to run lumber at planer after pulling charge from kiln?

[jules77]

Hello All,

We have been asked to post the following questions for Dave at Roseburg Forest Products

The questions are based about a practice a former kiln supervisor put into place and we are wondering about it now. The practice is to ALWAYS wait for a minimum of 12 hours after a kiln is finished before running the lumber at the planer.
 
Questions
 
1 – Is there a good reason to wait?
 
2 – Does warm wood affect the inline moisture meter in any way?
 
3 – Does lumber run worse or better if it is still warm?
 
4 – Does lumber continue to shrink while it cools?
 
Thanks for any answers you can supply.

[TimothyD]

Looking at some of the data we have from doing wood temperature delta testing, I would expect that you might see from 1% to 1.5% overestimate in MC going from about 70 degrees F to 110 degrees F.

This result was obtained from doing testing against competitors’ technologies/systems, and I can tell you we are about twice as good in this respect as indicated by our testing.  Wagner has long known the inherent physical issues that affect moisture measurement systems, including the effects due to temperature differences in the wood itself.

From the question, I am thinking that the “12 hour wait” period may be more to equilibration stabilization at the tail end/end of the charge.  I wonder if there might be thermal expansion/contraction concerns? For instance, there may be“sizing” issues if “hot” lumber was planed and then contracted while coming to a more typical temperature equilibrium.

Found this interesting reference when doing a search:
Principles of Lumber-drying and Practical Advice to Dry Kiln Operators; (1914) From www. jgokey.com

Not sure it will be helpful to you, but it is very interesting; it is a reference from 1914 and discusses continuous track kilns!

Regards,
Tim