Important Corrugated Terms to Understand

You are only as good as the materials you use. At KBPC we work with a variety of different sheet feeders to find the best possible performance/price for the sheets we use to produce the packaging our customers rely on. 

Recent changes in the market, and the constant effort to drive the total fiber content of paper down have made our commitment to consistently review key quality requirements with our suppliers even more important. This process involves a lot of careful evaluation of a lot of characteristics.

Let’s review some of these and explore their properties.

ECT: We all know it - but do we understand it? Box compression loss will vary with supply chain elements, trucking, storage, warehouse, climate, but the deterioration rates vary by actual amounts of board crush or flute degradation and the use of semichemical or recycled mediums as well. These must factor into performance evaluations.

Caliper: This is the amount of spring back or recovered thickness after crushing. While fluting is a resilient material and recovers from much of the sever deformation that occurs during combining and/or converting, its inherent strength contribution to the corrugated may be significantly compromised by compression. We implemented end of the line caliper testing some time ago to help identify sheets that failed to recover sufficiently form the converting process.

Flat Crush: This is measure of actual combined board crush verses the potential resistance to crushing as predicted from the Concora strength of the medium. This, however, is not a good predictor of actual board crush. A more difficult real world test that we have had to work hard to simulate in the design process, but cannot really determine in production.

Pin Adhesion:Determines the strength of the bonds between the liner(s) and the medium(s) and is a good test to identify delamination failures.

Four Point Bending Stiffness: Measures the rigidity of the combined board and the sidewall wall robustness of the corrugated box. This gives you a lot of real world performance characteristics.

Torsional Stiffness:Relatively new to the US, but known elsewhere. This maybe the single best overall determinant of board strength.

Warp:Should have no more than 1/8 deviation from flatness per foot.