Archive for the ‘Containerboard’ Category

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

UPDATE:

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!

Student Question about Corrugated Use in North America

November 15, 2018

Christoph asks,

Hi Ralph, I was wondering if you may help me with a few questions. I am a German Master Student studying Printing Technology at CalPoly State University. The topic is about the corrugated packaging market and the most common used papers and purpose of the boards.

Therefore, I would like to ask you if you can provide me with information for the following questions:

  1. Which are the three most produced board qualities (e.g. Brown Kraftliner 35# – recycled fluting 30# – Brown Kraftliner 35#: C-flute) in the Northern American market?
  2. What is the most common purposes for corrugated boxes? (shipping, shelf-ready packaging, …)
  3. On average how many colors are printed on the above requested corrugated board qualities?

I am very thankful for any information you can provide.

 

Hi Christoph, happy to share a little information with a student of the industry.

  1. The most common combined board grade is 33/35 test liner / 23# test medium / 33# test liner.  While virgin kraft linerboard is still present, the US is about 50/50 new verses used fibre.  In Europe this is very different.  Mills that use the newest papermaking technology can use 28/26/23 C flute constructions.  We make heavier boxes here than you do in Europe.
  2. We ship durable and nondurable goods in corrugated packaging.  If you want this broken down by manufacturing segment I can provide that.  The biggest market is food.  Yes there is shelf ready packaging and displays.
  3. On average we probably print three colors via flexo. There is a great deal of four-color work done, but there is still a significant amount of two-color and one-color work being done (think Amazon, Home Shopping Network, etc.). Digital is gaining ground quickly, but it is not the ideal process for most boxes. It has its niche and its popularity is growing especially in the graphic market. However, digital has yet to reach the speeds necessary to make it ideal for high throughput orders. You’ll want to keep your eye on it though as the technology is continually evolving.

— Ralph