Addison asks,
In regards to crush, is there a direct correlation between change in caliper of the board and change in ECT of the board after going through a machine? To ask in another way, if ECT testing is not readily available, can change in caliper be used to identify excessive degradation due to crush?
Caliper is a very poor quality control measure and even more so for edge crush. Depending on the flute and the quality of the medium, you can crush the board severely with significant ECT loss yet the spring back of the combined board and the recordable caliper will show very little loss from target.
You may want to investigate a DST tester.
—Ralph
askralph 
February 14, 2017 at 3:49 pm
Ralph,
You are absolutely correct!
Bill Heintz
Sent from my iPhone
February 15, 2017 at 4:20 pm
Stiffness and bending tests can be difficult to perform on converted boxes because the slightest inter-flute buckle can invalidate the result. You could test ECT, but significant damage can happen to the flutes before that number dips. The corrugator is the place to check. If you are ready to invest, I would go with a table-top compression tester and moisture oven. Tell the guys to watch their temperatures, keep a good (board) moisture profile, test flat crush and pin adhesion… trend those numbers up and you’re protecting BCT, not just ECT. You could also trend ECT but not at the stacker with inconsistent board moisture.
For the converting presses, have them measure board caliper coming and going. No, it does not reveal all of the damage that could happen… but it’s quick, easy, and it does tell us when things are getting really bad.
Oh yes, and stop running 23# (112g) medium in every board and on old-school corrugators not up to the task.
February 22, 2017 at 12:18 pm
Spring back of crushed boards shows little change in caliper e.g. see my Bioresources paper however, caliper is an accurate ( < 1%) precise measurement if the measurement is done down to a micron i.e. 0.04 inches. The first peak in board flat crush, dubbed as"hardness" , is also sensitive to any board crushing to the same degree as DST as shown in my Appita paper.