Box Crush Test and the Chalmers DST
Ian Chalmers January 2015Click here to download a copy of this paper in PDF format.
What happens when corrugated board is crushed?
Figure 3 shows the relationship between caliper, MDTS and corrugated board crush using 29 sample pieces of board from the same sheet. The pieces were crushed to different levels in a machinist’s vice as indicated then caliper and DST measured after 3 hours. Curves obtained like this can also be used as a calibration on any board to give the absolute crush level.
Figure 3: Caliper and MD Torsional Stiffness (DST) versus corrugated board crush
Figure 3 shows how DST is much more sensitive to board crush than caliper. In fact MDTS is one of the most sensitive properties to board crush. MDTS is also sensitive to the quality of the fluting process and the materials used.
Figure 4 shows the ECT results (FEFCO) for the same 29 samples used in Figure 3.
Caliper and ECT are commonly used in corrugating plants to measure crush but figures 3 and 4 show that while Caliper has a good relationship with crush (in strict laboratory conditions), the sensitivity is very low. ECT has a very poor relationship with crush which is understandable because we are damaging the board in the “Z” direction then testing it in the “X” direction.
Figure 4: FEFCO ECT versus percent crush for 29 pieces of board on the same corrugated board samples as Figure 3.
When corrugated board is crushed the engineered structure of the board is damaged. This structure is quantified by MD Torsional Stiffness. So crushing damages MDTS and the other property effects are as a result of this loss of Torsional Stiffness. Caliper loss is often regained on standing but the Torsional Stiffness can never return to previous levels.
