Michael asks:
Recently, some of my colleagues brought the Chalmers Dimensional Stiffness Tester to my attention through an article in the recent July/August issue of the BoxScore magazine. The potential for the DST is impressive, especially for replacing current testing methods such as ECT, FCT and Caliper.
However, those of use at Niagara Sheets still have questions about the usefulness of the device. Sure, if we were to understand the complexities of MD Torsional Stiffness properties, we could use the DST to quickly evaluate the quality of our corrugated sheets. The question we have is if we were to come across a less-than-desired value of Stiffness, how would we determine the root cause?
The current array of TAPPI standard tests that we conduct all evaluate a specific corrugated property. The Caliper measures the combined thickness to see if the fluted medium, as well as the entire combined board, is of the correct height, which is important for flexural stiffness. The ECT measures the combined edge stiffness qualities of the liners and medium. FCT gives us an idea of how good the formation and strength of the fluted medium is. We also use Pin Adhesion to test the nature and strength of the bond formed from our adhesive.
Each of those tests tell us about a specific property. If the DST is to replace all of these, than how will we be able to determine which of these properties could be the problem should we find a corrugated sample with a low MD Torsional Stiffness?
Our initial thoughts were that the DST could be used as a first line of testing to give a quick overall evaluation of the entire corrugated board. Should a poor value be found, then all the previously mentioned tests would then be utilized to further isolate the problem. This would allow us to benefit from the efficiency of the DST while still allowing us to perform a root cause analysis to determine the specific problem using the standard TAPPI tests.
Please share your thoughts on how DST might allow us to isolate any defects in our corrugated board.
I am interested in hearing from other corrugated sheet and box manufacturing companies about how they use the DST to monitor corrugated quality. It would be helpful for us in evaluating the DST’s real world usefulness.
I have highlighted below what I believe to be the relevant questions from you and your colleagues.
The best method for any corrugator testing program is to record the position of the testing samples both in the MD and CD directions. Issues of non compliance or low values need to be addressed across the machine and in the machine direction. Consideration must be given to parallelism and circumference of all rolls. The test results will set the precedence for the root cause analysis.
Caliper only measures the recovered spring back thinness of the combined board and cannot determine the damage to the fluting in the corrugating operations. We have seen the loss of ECT and BPI in several historical studies and yet the final caliper had been acceptable.
Yes, ECT as a dynamic test does measure vertical compression potential of the finished box, but not the engineered structure’s real load bearing ability and performance duration. Static load bearing is best measured by BPI and flexural stiffness.
Flat crush measures the crush resistance of the medium at the third peak of the curve. The article I sent you a link to, indicates that real corrugated failure begins after the first peak or flatting of the flutes even before the flanks are kinked.
Pin adhesion is always a good test, but shear stiffness should indicate if one has a good bond.
There is a formula for determining the BPI target value which is based on flutes, liners, and the strength differences between recycled and semichemical mediums. Then you will have targets to measure yourself against.
I am not the one at liberty to say who is using the system, you may contact Randy Banks at Sharp International for more details.
—Ralph
askralph 
April 11, 2014 at 8:18 am
Hi Ralph,
I´m having board (double wall) with excelent DST values but PIN ADHESION=0 in the SF. It means that DST is unreliable.to diagnose PIN.
Tks
MARIO
February 21, 2015 at 2:30 pm
Some interesting comments on this new test. From what I’ve read in various forums, it makes me wonder if we’re looking at this test the correct way: It does not seem destined or well-suited to replace ECT, FCT, caliper, or 4-pt bending… and it’s of little use to predict box compression… and with so many variables involved it’s likely not effective at comparing different liner and medium combinations… neither is it a “go or no-go” quality check at the down-stacker…
I think it’s main value is trending continuous improvement efforts on equipment, processes, and materials. If I strip corrugated board to its essentially performance characteristics, I have Edge Crush and 4-pt Bending Resistance. ECT is almost mathematical for what I’m going to get but creating and maintaining flexural stiffness is a battle that has to be fought and won many times over. Watching DST might be a 10,000-foot-view on your improvement efforts and nothing more. It also does not require sample pre-conditioning so that makes things so much faster and easier.
Very, very interesting comments about crappy pin-adhesion not showing up in your DST results. Despite what I said about trending with DST versus looking for a pass/fail, you would think zero pins would jump out of a single test result.
May 16, 2018 at 11:50 am
The DST measures torsional stiffness i.e., resistance of the corrugated board to twisting which is affected mostly by the quality of the fluting. If subjected to out-of-plane crushing, the fluting shanks become creased dropping the caliper by about 1/2 mil or so but lowering the torsional stiffness and FCT hardness significantly. I have discussed the DST in an Appita Journal article and in my book “Physical Testing of Paper” published by Smithers-Pira. Bottom line: it is nice to have, but changes can be also be equally measured with a digital caliper gauge accurate to a micron or the first peak in FCT – Roman Popil, Roman@gatech.edu