|
Grading green with Metriguard Green Veneer Grader |
| By Harry Moore, PE |
|
Page 1 of 2
Several years back when one of our customers asked, “can you make a machine to grade green veneer” we scratched our heads.
We have been in the business of building veneer graders for structural properties since the 70’s (‘Metriguard’ has evolved into a generic term like ‘Jell-O’ or ‘Kleenex’ to the structural panel people.) Consequently, we are always on the lookout for new product opportunities - but why would anyone care to grade this steaming, volatile, unsuitable-for-any-use material right off the peeler?
Panel producers have tried putting green veneer to use - composing
green veneer into products using water compatible adhesives and no-heat
processes. This has typically resulted in panels that are so twisted
when dry that they might fit in a modern sculpture exhibit. Indeed,
just achieving any form of structural grading at this stage is
challenging and must take into account the effect of the very high
water content on the measurement technique.
So the last time I got a call about building a green veneer grader, I
asked some probing questions – “Where is the return in this.” “If
you’re going to have to dry anyway, why bother doing it when it is much
more difficult”, I inquired of a northwest structural panel producer
and a regular customer.
He made a good case:
“We have much greater peeler than dryer capacity” he said. “So we sell
our excess green material to a local plywood producer.” “They don’t
care about the structural properties of this stuff – the insides of a
piece of plywood can hide a million sins” he repeated.
“So we give them the good with the bad” he said because “we don’t know if it meets structural standards or not when it’s green.”
Later, I checked our trade rag that lists premiums for structural
material and plugged in some typical yield percentages and some
published mill production volume numbers. After a few key presses on
the calculator, what popped out was a return on investment for a
green-veneer grader of less than two months.
And I discovered that this situation was typical: excess peeler
capacity over dryer capacity (have you priced a dryer lately?), a
market (hog fuel?) for non-structural green veneer, a solid premium for
structural material – and this was ignoring the fact that there were
valuable added benefits.
Benefits such as the ability to schedule drying according to product
demand – dry the structural stuff when the order book calls for LVL.
Dry the rest when time permits. And perhaps the most important benefit
– accurate moisture sorting to optimize drying.
You see, the same thing that makes grading green veneer so difficult –
the high moisture - makes it imperative that we get accurate moisture
readings for compensation. We need to know this moisture because the
most telling grading technique – the measurement of stress wave
velocity - is highly influenced by this high moisture.
It turned out that in our bag of tricks we had just what we needed - a
non-contact microwave technique invented at Helsinki University of
Technology (HUT) and licensed by Metriguard. We have been using this
technology for grading dry veneer in our top-of-the line grader.
|
