Thursday, May 14, 2015

Edge Crush Test vs. Box Compression Test

Edge Crush Test vs. Box Compression Test (aka ECT vs. BCT): New Performance Metrics for Corrugated Square Off

by Rob Kaszubowski, CPP

As packaging consultants we are constantly faced with the challenge of learning a client’s vernacular and acronyms – as well as common acronyms within the packaging industry. For years the standard for corrugated packaging has been the ECT or Edge Crush Test. Edge crush slowly surpassed Mullen burst as the standard metric for corrugated strength. (Read more about ECT vs. Mullen Burst Here).  The ECT value is then utilized to help calculate the “theoretical box compression strength” which is derived from the McKee formula which dates back to the 1960’s.

Lately though, the more common term around the industry is now the BCT value or Box Compression Test. This value is often tied to a company’s packaging specification as part of their performance spec requirements.  That means that depending on a number of factors (the weight of the box contents, stacking pattern, safety factor, length of storage, storage conditions, etc.) a company may call out a target compression value that their secondary packaging must meet as a minimum threshold for performance.

So for example, a very simple requirement in the past may have been:
§  Box style = RSC
§  Size = 15 x 12 x 10
§  Material = 44# C ECT Kraft
Now that same company may specify the BCT (Box Compression Test) value:
§  Box style = RSC
§  Size = 15 x 12 x 10
§  BCT = 940 lbs

At the end of the day the customer doesn’t care what makes up this box, or what the paper combinations are. They just want to be sure that it can hold 940 pounds and make it through their supply chain with their products unscathed.

To perform the ECT test, a 2” x 2” swatch of corrugated is cut from a sample sheet stock. It is placed in an edge crush tester machine and thus the ECT value is obtained.  
Common ECT target values include:
§  26 (B or C flute)
§  32 (B or C flute)
§  44 (B or C flute)
§  55 C flute
§  42 BC flute
§  48 BC flute
§  51 BC flute
§  61 BC flute
§  71 BC flute

Corrugated board consists of three combined layers of paper: a single face liner, medium, and double face liner. Just as there are multiple ways to slice up a pizza, there are also multiple combinations of paper that can equal a certain ECT value. The weight of the paper liners used typically depends on what paper weights the supplying paper mills typically carry and source to the corrugators.  The amount of recycled content or virgin fiber can also be a factor in the final ECT value.

liner/ medium/ liner
Anatomy of Corrugated Board
So as companies look to standardize their packaging and consolidate sourcing they are looking towards a much more simplified corrugated box specification: one that no longer calls out the ECT value, but rather the BCT value. Packaging engineers and procurement teams are stating: I don’t care what you make the box out of, as long it meets my minimum strength thresholds. This shift in the market should ultimately make it easier for suppliers to focus on running paper combinations that they run well and run fast and deliver an optimized product.

If you have questions about what your minimum BCT values or stacking safety factors should be for your secondary or tertiary packaging, contact the packaging engineering team at Chainalytics.

14 comments:

  1. It's a really nice website. Useful information and correct information

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  2. Thank you for the beautiful site

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  3. Hi, a very useful article. Won't the method of sealing the box also make an impact on the BCT value ? We had seen that if we hot melt glue the box, that provides 30% more BCT value in comparison to taping the flaps. Can you pl throw some light on this ?

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  4. Hi Sajith - that is definitely an interesting hypothesis. However, I can't say that we've done any specific performance testing on adhesive closure vs. tape on the box flaps. I'll keep you posted if we come across any such results.

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  5. Hi, is there a formula on how to convert ECT to BCT? our supplier declares ECT but our QC needs BCT. how will I compute?

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    1. Traditionally, one can use the McKee formula to utilize the ECT value (plus caliper of the board, and box perimeter) to derive a calculated BCT (box compression) value.

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  6. I want to know different between BCT result and bursting strength result.Please,kindly reply to me.Thanks.

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    1. Hi Chue,

      Thanks for the note. BCT (or box compression test) measures the top to bottom strength of an assembled box or package. Burst strength measures the amount of force required to puncture through the corrugated materials. These are essentially different metrics and means to evaluate corrugated and box strength and cannot necessarily be used for an apples to apples comparison.

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  7. HI rob
    what do you mean by box perimeter? is the perimeter of flat cardboard rectangle?

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    1. No absolutely not, the box perimeter means when the board converted into a CFB box, we Need the actual Box perimeter to determine the BCT which contain length width and height.

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    2. Hi, I have read the comments and found it interesting.
      Right now in our company, I have a plan to determine whether we are using an over specs box or just the appropriate one. Can you tell me on how I'm gonna do it? We have 425kgf BCT.

      Thanks.

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    3. Kerr maybe you can reach out to us and we can discuss via phone or email?

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  8. Box Perimeter is the total edges of box opening when setup. Hope that makes sense.

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  9. I am beginner eBay seller.I typically sell china and crystal and usually double box my packages. My question is related to ECT in this first example. For instance, I might send a set of glasses packed first in a 12”x12”x6" box with an ECT of 32 lbs/in. (Assume that the glasses are well packed internally and pass the “Shake” Test so that there is nothing you can hear or feel during the “shake” test). Then this first box in packed in a larger 16” x 16” x 10” with a Burst Test of 200 lbs/in (no ECT noted on this box). I have also filled around the first box so it is completely surrounded with 2” of styrofoam pellets to insure that it will also pass my “shake” test.
    Question: With this type of double boxing have I increased anything for the first box (ECT or Burst Test)?

    The second example is for Weight Limits. For instance, the first box has a Gross Weight Limit of 65 lbs and its actual weight is 80 lbs. I then pack it in another box with the same Gross Weight Limit of 65 lbs. This second box and filler adds 2 lbs.
    Question: Did I gain anything by double boxing for the increased weight of the first box. Is the box now technically “legal” to meet the combined weight?

    Will appreciate your answer. RC

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