An industry requirement exists for the standard to calculate or predict corrugated boxes’ or rigid pack performance in the dynamic or static conditions in which these packaging are regularly transported and stored. The ECT, compression strength test, and stack load, all tests understand the value of packaging load-bearing capacity during transit. Every test standard approximately has the same type of testing method, but a packaging engineer must calculate according to their suitability. I will explain only the needed section of the test where exactly necessitate findings.
Initially, questions arise – why all these tests for the stack load-bearing study. What are the differences between all these strength calculation tests?
So, first, we will understand what ECT means is?
The ECT can only be performed on the corrugated fiber boxes, and it means Edge Crush Test, which is a dynamic test & performed on the corrugated box’s specified cut sample.
The test is performed on the Edge Crush Tester machine and performed to calculate crushing resistance strength on the cut sample and get the value of resistance on the particular cut samples.
The McKee formula is then used to calculate the total corrugated box compression strength value with our outcome value from the machine.
It gives, how much load can bear on the bottom of the box?
*The ECT Value is often provided on the BMC (Box Manufacturer’s Certificate).
The simplified McKee formula above provides a quick estimate that should rate an actual box’s strength.
Many performance parameters we ignored in the calculation with this formula:
a. The miss-out estimate of the gluing or stapling strength of the joints in the box.
b. We need to cut the sample for calculating the Edge crush test, but we can’t ignore the lesser or higher moisture in the whole box and box’s particular part.
c. If the somewhere minor bend is there in the box, it can’t give the box’s specific strength value with a small piece of sample.
d. This test was only performed for board or corrugated fiber boxes.
e. If we cut the sample in 90° rotation of the corrugated box, the crushing strength value is different due to the paper grain direction.
Compression Strength of the box
It is also another test of dynamic load test where actual compression is measured with the load given at a particular speed with the compression machine. These values of the test can be taken as a real strength of the box or rigid packaging.
So, what are the pros and cons of this compression strength calculation with the compression testing machine?
It gives the exact value of compression strength of the outer packaging material with the machine.
No need to verify with another test methodology for the stack load-bearing capacity.
The test can be performed for the bottle, box, drum, and other rigid packs.
Same here; the test can also affect by a bend in the box.
Paper grain direction also affects the compression strength value.
Stack Load Test:
This test is a static load test, or we can say it will give us the exact physical strength of the pack. The original packaging is filled with the product and placed on the stack as per standard or safety or stacking requirement for 24hrs observations. Based on this, we will decide the packaging strength.
As per the given standard, the calculation is based on visual analysis.
Some limitations of the Stack load testing:
a. If packaging deformed during a stack load test, we can’t know how much packaging deformation will accept.
b. There is no such exact measure for improving packaging if our pack fails in a stack load test.
c. We can’t justify the safety factor value in a stack load test.
d. If the secondary container is boxes or any rigid pack, the value can’t give the strength in just 24 hrs.
But there are also some points to keep in mind during the calculation of the strength.
a. When we do packaging of bottles | rigid pack in a corrugated box, inside the corrugated container works as a stacking medium and supports enhancing the stacking strength, increasing or improving the stability. Like if a bottle is in the box, it will add the value of compression strength at the transits time only.
b. Climate condition also affects the compression value when environmental conditions change as the goods are transported to different geographical locations, the compression strength of the boxes changes.
c. What type of specific safety factors is to assume? No detailed data is given. It depends on the condition of the road and transport way (air, rail or sea)
d. Handling also the most crucial factor to be considered for the performance during the stack load test.
e. Paper grain direction also plays a vital role; it needs to be checked at the supplier’s end whether he is making the boxes as per the prescribed grain direction or not.
f. How long it will sustain the stack load. (No such standard has the measuring of life during stacking)
Reference of test standards:
IS 7063-2: Methods of test for corrugated fibreboard, Part 2: Edgewise crush resistance of the board
ASTM D5639 / D5639M Standard Practice for Selection of Corrugated Fibreboard Materials and Box Construction Based on Performance Requirements
ASTM D7030 – 04(2017) Standard Test Method for Short Term Creep Performance of Corrugated Fiberboard Containers Under Constant Load Using a Compression Test Machine
ASTM D4577 – 19 Standard Test Method for Compression Resistance of a Container Under Constant Load
ASTM D642 – 20 Standard Test Method for Determining Compressive Resistance of Shipping Containers, Components, and Unit Loads
Test Method TAPPI/ANSI T 804 om-20 -Compression test of fiberboard shipping containers
ISO 12048:1994 Packaging — Complete, filled transport packages — Compression and stacking tests using a compression tester
ISO/TC 122/SC 3 Performance requirements and tests for means of packaging, packages, and unit loads (as required by ISO/TC 122)