What is a carton compression test?
The carton compression test (CCT) will measure the ability of a carton to withstand pressure from above before deforming. The carton (or package) is put under pressure by testing apparatus to simulate the weight that cartons stacked at the bottom on pallets in a container or a truck can withstand on top without getting crushed and demonstrates to how much they become deformed, too.
You may also hear this test referred to as a ‘package compression test,’ ‘container compression test‘ or ‘box compression test (BCT).‘
Why perform this test?
Cardboard cartons (often known as boxes or packages, too) are affordable, durable, and eco-friendly, but they vary in strength (check packaging types including cardboard containers here). This means that choosing the wrong type of carton could put your products in jeopardy, especially during shipping or storage.
Cardboard with multiple layers of fluting will be stronger than those without, but the compression test gives real data on whether one package will be more resistant to pressure from above when stacked than another.
There is a range of reliability tests to perform in order to assess carton/packaging suitability and reliability, as you can see below in this typical reliability testing plan and you’ll notice that the compression test is highlighted:
What is the carton compression test process?
The process will simulate how much weight the bottom carton will endure when it is stacked on a pallet to check its compressive strength. This is a must for products which are going to be warehoused.
The process will include:
- Calculate your test force that a carton at the foot of the layer stack must be able to withstand without deforming:
Let’s say there are six cartons stacked in a layer stack and each weighs 5.2Kg.
Stack load = (No. of Cartons in Stack – 1) x gross weight
Stack load = (6 – 1) X 5.2 = 26Kg of weight will be on the lowest carton. This box must be able to withstand this calculated test force, otherwise, the stack may collapse, the box may deform, and the product/s inside may be damaged.
- Place the carton between the 2 platens of the machine – carton to be in normal atmospheric conditions, clean, and platens wiped down after each test.
- Use the machine to apply load to this carton – (it will be applied downwards from above).
There are different test types to apply the force:
Machine apply & release test – the box will be subjected to the calculated test force x 1.4
Machine apply and hold test – using only the calculated force
Weight & load spreader – using only the calculated force
- Capture data on the force applied – this will be your result.
- When the carton deforms, stop the test.
Compression test results
The force applied before the carton deformed must be equal or more than the calculated test force that the carton needs to be able to withstand when at the bottom of a stack.
You will also be able to find out:
- Peak load the carton can withstand
- Carton deformation at peak load
- The load at a critical deformation (headspace, etc.)
- Ability of the carton to protect the contents from compression damage
- Time to carton failure
- Time to critical deformation
A note from ISTA about test results:
When conducting the compression test: Box failure that could result in a stacking failure is considered a failed test if the packaged-product may be warehoused during distribution. Box failure is allowed if the packaged-product provided is not warehoused, and at the conclusion of all testing, the product is not damaged according to the Product Damage Tolerance established and the package still meets acceptable package conditions (both of which will be defined by you before testing).
Also, the test may be carried out with or without interior packing in place. If the interior packing is designed to take a proportion of the weight, then it should be included.
Calculating carton compressive strength with the McKee formula
It is possible to estimate the compressive strength of a cardboard carton using the McKee Formula. This is not as accurate as performing the compression test in a lab.
A simplified McKee formula is as follows:
BCT = Box compression test in Pounds
ECT = Edge crush test resistance in kilonewtons per meter (kN/m)
U = box outline in inch
d = thickness of corrugated board in inch
An example video of the test in action
This video from UPS shows them performing a compression test on a cardboard box using a hydraulic compression test system:
As an alternative, it’s also possible to use a mechanical weight and load spreader where the platens are loaded with weights. Here are some of the weights typically used by a lab if following this more traditional method, and you can imagine these being placed on the platens rather than hydraulic pressure being utilized:
A selection of compression test standards
It’s helpful to know the different testing standards, as which labs use may vary:
- ISTA 2A
Packaged-Products weighing 150 lb (68 kg) or Less
- ASTM D642 – 15
Standard Test Method for Determining Compressive Resistance of Shipping Containers, Components, and Unit Loads
- ISO 12048:1994
Packaging — Complete, filled transport packages — Compression and stacking tests using a compression tester
- TAPPI T 804
Compression test of fiberboard shipping containers
What other reliability tests should I do on cartons?
The following would be considered as standard reliability tests for packaging:
Can Sofeast help with this?
Yes, we can. Click here to read about our reliability testing solution and get a quotation.