GUIDES

A practical guide to overstack and understack shingles

Learn why understack shingles are required for some 4-corner cartons and how the right packing system maintains productivity and ergonomics.

ERGOSA

A practical guide to overstack and understack shingles Image

Understanding Shingles & Packing Systems

A Practical Guide for Folder-Gluer Operations

Overstacked or Understacked Shingle?

A shingle is the overlapping stream of folded cartons exiting a folder-gluer's delivery belt.

Diagram comparing overstack and understack carton shingles exiting a folder-gluer, showing that gravity discharge is possible with overstack but blocked with understack

All standard packing systems are designed for overstack shingles. Most packers use gravity to drop boxes into a case, which does not work with an understack shingle.
Overstack shingle of folded cartons exiting a folder-gluer on a green conveyor belt, with each new carton overlapping the previous one from above.

Overstacked shingle exiting the folder-gluer.

Overstack Shingle:

Each new box is stacked on top of the previous one.
Standard for 99% of production runs.
Compatible with all packing systems.

Diagram showing an overstack shingle forming at the folder-gluer exit, with each new folded carton placed on top of the previous one.

Understack Shingle

Each new box is stacked under the previous one.
Required for certain 4-corner box styles.
Boxes cannot fall by gravity — limits packing options.

Diagram showing an understack shingle of folded cartons exiting a folder-gluer, with each new carton sliding beneath the previous one.

Why Are Understack Shingles Used?

With certain 4-corner boxes, the front flap can spring open as it exits the folder-gluer, creating a hook point that catches the next incoming box — causing a jam or crash. When this happens, the operator must switch to understack mode to keep production running smoothly.

Factors that increase the likelihood of this include the rigidity of the carton, the size of the flaps, and the resulting spring effect.

Illustration of a partially folded four-corner carton with raised flaps and IMPACK branding.

IMPACK’s ERGOSA Semi-Automatic Packer: The Only Packer Built for Understack

The ERGOSA is the only packing system capable of handling understack shingles with no extra customisation and no added cost. It features a specialized mode for optimized packing of each box type.

The ERGOSA’s Vertical Mode is specifically designed for 4-corner boxes and allows you to pack from an understack shingle without needing to turn or invert your boxes.

IMPACK ERGOSA semi-automatic packer configured in vertical mode, with an open case at the packing station and a blue conveyor belt.

ERGOSA: One packer, both shingle types — no compromises.

Illustration showing manual wrist rotation to reorient a bundle of folded cartons before placing it vertically into an open case.

Key benefit: the ERGOSA offers optimized packing of other box types exiting the folder-gluer in the overstacked method including the option to turn the box to re-orient the glued edge. Automatic box turning eliminates wrist movements.

Overstack or understack?

Discover how ERGOSA adapts to your carton flow while improving packing ergonomics.