The box compression test measures the compressive strength of boxes made of corrugated fiberboard as well as wooden boxes and crates. It provides a plot of deformation vs compressive force.

The BCT value is a measure of the strength of a shipping container and is measured in kN Kilonewton or pounds of force: deflection or deformation is measured in mm or inches.

Contents 1 Test Procedures 2 Factors potentially affecting test results 3 Estimations 4 Field Stacking 5 Relevant Standards 6 References 7 See also

[edit] Test Procedures

A common method of conducting the test, as described in several published standard test methods, is to compress a box at a constant rate of 1/2 inch (12.5 mm) per minute between two rigid platens. The platens can be fixed so that they remain parallel or one can be pivoted or "floating". The test can be conducted on empty or filled boxes, with or without a box closure. Conditioning to standard temperature and humidity is important.

The results of the constant rate of compression test can be:

• The peak load
• The deformation at peak load
• The load at a critical deformation (head space, etc)
• The ability of a box to protect the contents from compression damage
• etc

The dynamic loads have some relationship with expected field loads.^[1]: often factors of 4 or 5 are used to estimate the allowable working load on boxes.

A test can also be conducted with platens that are not mechanically driven but are free to move with a fixed mass (or fixed force) loaded upon them. The results of static load testing can be:

• The time to failure
• The time to a critical deformation
• The ability of a box to protect the contents from compression damage
• etc

As with any laboratory testing field validation is necessary to determine suitability.

[edit] Factors potentially affecting test results

• Size and construction of the specific shipping container under test
• Grade and flute structure of corrugated fiberboard
• moisture content of the corrugated board (based on relative humidity)^[2]
• Orientation of the box during the test
• Inner supports, if used during testing (wood, corrugated board, cushioning)
• Contents (when box is tested with contents)
• Box closure
• Whether the compression machine has "fixed" or "floating" (swiveled) platens.
• Previous handling or testing of box^[3]
• etc

[edit] Estimations

Corrugated fiberboard can be evaluated by many material test methods including an Edge Crush Test (ECT). There have been efforts to estimate the compression strength of a box (usually empty, regular singelwall slotted containers, top-to-bottom) based on various board properties. Some have involved finite element analysis.^[4] One of the commonly referenced empirical estimations was puplished by McKee in 1963.^[5] This used the board ECT, the MD and CD flexural stiffness, the box perimeter, and the box depth. Simplifications have used a formula involving the board ECT, the board thickness, and the box perimeter. Most estimations do not relate well to other box orientations, box styles, or to filled boxes.

[edit] Field Stacking

Box compression testing is a means of evaluating boxes, stacks of boxes, and unit loads under controlled conditions. Field conditions of stacking and dynamic compression do not have the same degree of control. The temperature and atmopheric moisture are often uncontrolled ambient conditions. The stacking of boxes might not be aligned vertically, greatly reducing strength.^[6] Other handling or factors (stretch wrap, etc) may reduce the box strength. Contents and inner components may or may not be factors.

Many packaging engineers find it beneficial to periodically audit warehouses and visit customer's package receiving operations. When field performance is observed or documented to have problems, a new cycle of design and testing may be justified.

[edit] Relevant Standards

• ASTM Standard D642 Test Method for Determining Compressive Resistance of Shipping Containers, Components, and Unit Loads.
• ASTM Standard D4577 Test Method for Compression Resistance of a Container Under Constant Load
• ASTM Standard D7030 Test Method for Short Term Creep Performance of Corrrugated Fiberboard Containers Under Constant Load Using a Compression Test Machine
• German Standard DIN 55440-1 Packaging Test; compression test; test with a constant conveyance-speed

[edit] References

• Brody, A. L., and Marsh, K, S., "Encyclopedia of Packaging Technology", John Wiley & Sons, 1997, ISBN 0-471-06397-5
• Soroka, W, "Fundamentals of Packaging Technology", IoPP, 2002, ISBN 1-930268-25-4

[edit] See also

• Corrugated box
• Corrugated fiberboard