Paulina asks:
I’m hoping you can give me some insight.
Why is it that ECT can be well above min. but fail BCT?We use the McKee formula for our expected.
What a great question!
ECT is a very good indicator of BCT when the components are perfectly combined and converted without damage to the medium. The entire corrugated structure and all the scores and slots need to be manufactured properly as well. ECT is only one of two primary predicators of initial box performance. The other one is flexural stiffness best measured by four point bending.
To begin to answer your question in more detail, one would have to know the causes of the box failures. We can look at the failure mechanisms and take corrective action. You did not imply in your question that we needed to consider box failure in the distribution environment?
What ECT does not tell us, because it is a dynamic test, is the performance of the corrugated box under dead loads or static weight. It is not a sensitive test! That’s why I am such a proponent of the DST method of corrugated testing. DST gives us a clearer picture of what has happened to the medium in the combining and converting operations. And, there is a difference between semichemical and recycled mediums.
Have you taken FCT and ECT samples from the failed box? Do you have pictures to share? It is a specific or general question?
If you can answer these questions for me we can generate a more definitive answer.
—Ralph
askralph 
November 6, 2013 at 12:56 am
If I may be permitted to add my 2 cents to Ralph’s explanation :
ECT is a Material Test or Material Specification.
BCT is a Performance Test or Performance Specification.
GOOD ECT = GOOD BOARD QUALITY
But BCT = Good Box. Which includes the Box Design and other manufacturing parameters.
I may have a good ECT but my box is either too long or too high and hence is not dimensionally as stable as it could be.
The quality and finish of the punching, slotting and scoring mean a lot to the box quality as a whole.
If you are stapling the joint, then even the gap between the staples can play a role in the BCT value. The stapling joint in usually the weakest link. How weak you want it to be is controlled by the gap between the staples. This cannot be predicted by an ECT test.
That is why the new hi-speed fully automatic lines are coming with glued joint. The glued joint may be slightly expensive compared to the stapled joint but will give much more strength and will drastically increase production speeds.
I use a very simple example to explain this entire concept to the non-tech guys here.
Think in terms of a brick house.
We buy the best of bricks to make our house. Consider that as ECT tested bricks. Wonderful quality.
But the architect who designs the house or the mason who lays the bricks and cement is not so perfect.
What will be the end result? A not-so-perfect house made from a bunch of perfect bricks. A potential disaster.
ECT is a great test for carton which cannot be tested for BCT due to either size of the carton or cost of the BCT machine itself.
ECT and the McKee’s formula (to calculate BCT from ECT) is perfect if everything else if perfect too.
In India, we stress more on BCT as our BCT machines are relatively cheaper.
BCT is the final performance approval test. If its PASS, everything is going to be OK. No doubts remain in ones mind after this test.
And come one, BCT is even more practical to understand.
If I tell you that the BCT of your carton is 1500 lbs. You can imagine what it means and co-relate it easily with stacking loads.
But what if I say that your ECT is 20 KN/Mtr ?
Its a tad difficult to co-relate with real life.
Yes you can say 20 KN/mtr is better than my competitor’s 18 KN/mtr. But can you ever understand what 20 KN /mtr would feel to a carton ? Nope….
Hope I was of any help to you.
I am not a consultant or possess as much experience as Ralph and many others here.
But my company manufactures Packaging Testing Equipment in India (www.PackTest.com) since about 24 years now and I have been in this industry for just around 16 years working on solving problems of our industry.
Another novice article I have written on “Performance of a Carton” can be read from http://www.slideshare.net/rohitchawlaindia/performance-of-a-carton-a5-simple
Best Regards,
Rohit Chawla