71 ECT board: what it holds
71 ECT board carries 71 lb per inch of edge in an edge crush test. Built into a 12 × 12 × 12 in BC double wall box, the simplified McKee formula puts its compression strength near 1,531 lbf.
Estimated box compression by flute
| Inside size, in | BC double wall | EB double wall |
|---|---|---|
| 8 × 6 × 4 | 1,170 | 955 |
| 10 × 8 × 6 | 1,326 | 1,083 |
| 12 × 12 × 12 | 1,531 | 1,250 |
| 14 × 10 × 8 | 1,531 | 1,250 |
| 16 × 12 × 10 | 1,654 | 1,350 |
| 18 × 12 × 12 | 1,712 | 1,398 |
| 18 × 18 × 18 | 1,876 | 1,531 |
| 20 × 16 × 14 | 1,876 | 1,531 |
| 24 × 18 × 18 | 2,026 | 1,654 |
| 24 × 24 × 24 | 2,166 | 1,768 |
Working load after storage
McKee gives the strength of a new, dry box. In storage it loses strength. Using Packgent's default storage losses (an assumption, see method), this is the most the bottom BC double wall box can carry at each age:
| Inside size, in | 0 days | 10 days | 30 days | 90 days | 180 days |
|---|---|---|---|---|---|
| 8 × 6 | 1,170 | 737 | 702 | 643 | 585 |
| 10 × 8 | 1,326 | 836 | 796 | 729 | 663 |
| 12 × 12 | 1,531 | 965 | 919 | 842 | 766 |
| 14 × 10 | 1,531 | 965 | 919 | 842 | 766 |
| 16 × 12 | 1,654 | 1,042 | 992 | 910 | 827 |
| 18 × 12 | 1,712 | 1,079 | 1,027 | 942 | 856 |
Neighbouring grades
In McKee, BCT scales directly with ECT, so the percentage change in strength equals the change in ECT.
Freight rule limits
NMFC Item 222 ties each grade to a maximum gross weight and size for LTL shipping. Packgent has not published those limits yet because they could not be checked against the current tariff. See the Item 222 page for status.
Sources
- TAPPI T 811: Edgewise compressive strength of corrugated fibreboard (short column test)
- McKee, R.C., Gander, J.W. & Wachuta, J.R. (1963). "Compression strength formula for corrugated boxes." Paperboard Packaging 48(8): 149–159
- Flute calipers: Foster (1997), Wiley Encyclopedia of Packaging Technology
Last reviewed . See all sources and how Packgent computes.