Archive for the ‘Containerboard’ Category

Corrugated Shelf Life, Storage and Usage Temps, Toxicity?

April 9, 2019

Chris asks:

Do you have any resources for the following information regarding corrugated containers?

As the answers would appear to be specific to the material composition, these would be for plain C-Flute kraft containers.

  • Shelf Life
  • Service Temp Range
  • Storage Temp
  • Toxicity

These questions are asked quite often on Ask-Ralph. This may not be a complete answer to your question, but it is a start to the dialogue.

Corrugated under compression (loaded and stacked) ages/deteriorates at a different rate than KD boxes on a pallet. Environment, fill load, stacked load, potential crush during converting all contribute to the deterioration rate of a loaded box.

Ideally, whether loaded or stored as knock downs, corrugated should be stored at 72 degrees and 50% RH.  That’s a perfect world and few of us live in a perfect world. Any fluctuations in these conditions can reduce the fibre to fibre bonding and strength of the adhesive bond. Temperature does effect stored corrugated, but it’s the combination of temperature and humidity that has the greatest effect. High temps (90 plus degrees F) and low humidity and you’re likely to start to see score cracking and brittle paper issues. High temps and high humidity and you’re likely to start seeing bond breakdown and an increase of the compressive creep rate leading to increased chances of failure under load.

At extreme low temps and you may start to experience recharacterizations of adhesive that can lead to failures at joints and even at the liner to medium bonds. Same holds true here with humidity though it may not be as severe as with high temps.

General rule of thumb, if it is comfortable to work in, it’s probably good for corrugated. We don’t like to be hot and sweaty or numb from cold… neither does corrugated.

As far as toxicity, corrugated is considered an indirect food additive by the FDA and is detailed in 49 CFR.  Therefore, no toxicity for plain kraft. If there are inks or coatings involved, then you have to look that them on an individual basis.

Now there’s a start to the discussion. What input do our readers have?

— Ralph

Calculating Theoretical Box Compression

April 9, 2019

Steve asks:

How can you calculate a theoretical box compression value if you know the ECT value of the combined board, you have the dimensions of the box and can figure out the Square root of the perimeter? What is the formula we should use?

You have everything listed above except one important factor, the caliper. You need the caliper and then you’re all set. So the formula you would want to use is 5.87 x ECT x (the square root of (caliper x box perimeter)).

(Steve has provided caliper and other the carton specs as)

  • multiplier = 5.87
  • ECT value = 154.7
  • Perimeter = 148”
  • Caliper = .4375” (AA DW)

So our equation would look like this,

Predicted BCT = 5.87 x 154.7 x (√ (.4375 x 148)) = 7307.11 lbs.

Or… 5.87 x 154.7 x 8.0467 = 7307.11 lbs

Just a note, rounding can have a significant effect on the result. It may be better to round down than to round up for the sake of safety.

— Ralph

Tuck Top vs Tuck with Locking Tab, or Friction Tuck

March 1, 2019

Rich asks,

I have a customer who orders a lock bottom box with a tuck top from us. It ends up at distribution in Walmart and Walmart is having issues with the top flap coming open. It does not get taped closed. They are asking if we have packaging engineers that can provide documented test results or studies on performance changing it to a tuck top with a locking tab, or friction lock tuck top tab, or extending the tuck on the top tuck. Have you seen anything like that or are you aware of any hard documentation that says how much it changes the function of the top tuck? Thanks for your help with this.

I would start by checking with your sheet supplier and/or their containerboard provider to see if they have any information regarding the information you are looking for. Often integrated companies do these types of studies. Some will be willing to share and others are not as open to sharing their results. I have an associate in Canada that may want to weigh in on this issue. I’ll touch base with him and then update this post with any input he may have. I also searched through my George Maltenforts’ books, but found no discussions or reported research in this area.

However I do believe that a friction fit is the best way to go short of some type of press applied coating.

— Ralph

Calculating Partition Strength

February 28, 2019

Rodrigo asks;

Calculating Partition StrengthI’m trying to figure out the stacking strength of the partitions shown in the picture (How much weight can be held on top). A corrugated board bed is set on top covering all of it. Products are located inside the 4 cells of the partition. I would like to know what is the process or logic of calculating the maximum weight it can hold before it collapses. Resistance used is 26 ECT.

If I see correctly the pieces are set at an angle so we cannot determine compression strength because the elements are not fully vertical. (left-most sections in the image)  What is more significant here is the torsion or flexing of the components. Because of the distance between connecting points, failure is more likely to come from the twisting action of the components than an edge-wise crush. It’s just like a vehicle traveling over a rough road and all four wheels and suspension act independently of each other.  If the pallet of the load is uneven or starts to shift, then angular forces can be applied potentially causing the long spans to flex and collapse.

We can’t tell exactly how large your partition assembly is, but do you have access to a compression tester with a footprint large enough to test at least one square?

— Ralph


Tom adds,

Consider pointing Rodrigo to the book Corrugated Shipping Containers An Engineering Approach by George G. Maltenfort. Chapter 7 of the book discusses compression strength estimation for boxes with inserts and shows 25 different styles. These are not the partition shown in your question but MIGHT give him a place to start your predictive work or at least highlight attributes he needs to consider.

Thanks Tom!