Mixture of Species

[AliciaS]

We dry Lodgepole, Ponderosa, and occasionally Sugar Pine separately in the kilns.  Then we mix those species going through our moulder to create our Reserve Pine product.  When these species go through the moulder they are metered by a Wagner Omega inline moisture meter set and calibrated for just one species, usually Ponderosa.  How much will this affect the overall moisture and deviation of those readings?  I would think it must, as the specific gravity and densities are different.

(Posted on behalf of an industry dry kiln superintendent.)

[MichaelM]

For every 0.04 increase in specific gravity, the moisture content reading will increase by 1%  (if the MC is actually constant).  PP, LB, and SP have average specific gravities (at 12% MC, from Wood Handbook) of 0.41, 0.41, and 0.36, respectively.   On the average, the sugar pine may be reading a percent+ low compared to its actual moisture content. 

I suppose a non-meter issue could be wets in the sugar pine.

Would it be difficult to do a separate calibration for each species?   Not that you would run that way if they are mixed, but in an hour or two it would answer your question better than my theoretical answer.

[TimothyD]

Very good information, Mike.
I would also like to point out that even within species, there is variability of s.g., such that mixing these species together with close average s.g. values will result in an overall distribution only slightly wider than the individual s.g. distributions.  What this means is that the vast majority of all the boards will still be within the same MC "envelope" as they would otherwise be using a segregation strategy.  The farther the average s.g. averages are between the individual species, the greater the effect will be, but as Mike pointed out these are not that far apart from one another.