MEMBER'S QUESTION:

We use the calculations for BCT and ECT that are in the Fibre Box Handbook.  Do you know if those calculations are fairly accurate or do you have another way of calculating that information?

Also, we just tested 33/23/33med/23/33 for ECT and BCT.  The ECT result is 54 and the BCT result is 1,222 lbs.  Do you have any advice that would deter us from running 33 lb medium as the middle liner? The dimension of the box is 21.5 x 12 x 10 1/8.  The boxes are stacked 5 above the bottom box and hold 43 lbs. of material in each box.

ASKRALPH! RESPONDS:

The formulas in the FBA Handbook are the way to go!  I used a simplified version of the same formulas myself.  If you tell me the dimension of the box I can tell you if you were with the theoretical range of predicted BCT based on the components  and the ECT that you obtained after the press.

Medium as a facing is fine.  You could possibly loose a little stiffness in the side walls and a little more compression in the entire structure since moisture pickup in high RH condituions may be greater with the medium.  There are other AICC members that use three plies of medium in certain application and others that use three plies of linerboard, but for very different applications.  It’s all about the wonderful engineered design of the corrugated structure.

The theoretical range in ECT given the variation of the ring crush of the components is 40 to 58.  You were in the top quartile in ECT.  Compression potentials with that given range in ECT start at 980# top-to-bottom and goes up to 1420#.  This assumes that the board caliper was 0.260 inches. You were in the middle range in cox compression and your safety factor was 5.