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

Skip Feed Repeat and Max Print Area

November 15, 2018

Chuck asks,

My question, is there a formula that determines how long of a print area (thru the machine) can be printed without being printed a second time when running skip feed. We have a 66” rotary diecutter with skip feed. We did a test on a sheet size of 79-1/4, mounted a 28″ plate, centered and it did not reprint.

I reached out to a few of my industry contacts. My colleague Dwayne Shrader put together some info for this post.

Max Sheet Length Before Print Repeat

On a 66 inch machine the print is going to repeat every 66 inches from the lead edge of the plate. That’s the key to determining the length of the sheet before repeat… ‘from the lead edge of the plate’.

To determine the maximum sheet before print repeat where …

Cylinder Circumference with plate installed = CC
Lead Edge Offset = LEO
Max sheet Before print Repeat = MBR

Then…CC + LEO = MBR

You say you mounted it in the center, I assume you mean you centered it around the cylinder. So the lead edge of the plate would have been at 19 inches behind zero register… (66 – 28)/2=19. This being true, then CC + LEO = MBR, or 66 + 19 = 85. Therefore, you could run a sheet just under 85 inches before the print would repeat.

Maximum Print Length

Now, determining the maximum print length, is just a little different because the cylinder circumference is not the maximum machine print length. Keep in mind that the lead and trail edge lockup takes up some of the circumference (or print area). On the typical 66 inch cylinder your maximum machine print length is going to be between 61 and 64 inches depending on machine design, lockup type, etc. Your machine manufacturer should be able to provide the maximum through machine print length.

To determine the maximum print length where …

Maximum Machine Print Length = MMPL
Lead Edge Offset of printing plate = LEO
Maximum Printable Length through machine = MPL

Then… MMPL – LEO = MPL.

For example, let’s say the maximum machine print length is 62 inches and the lead edge is offset by 5 inches… 62 – 5 = 57 inches of available print length. Consequently the maximum sheet before repeat would be 71 inches in this case.

Sometimes a converter may have a plate that is made for a normal feed job, but they want to use it to print a larger skip feed job. In this case the plate is mounted in the normal position and then the register is retarded to offset the distance from the lead edge to the start of the print. The same formula for maximum print length is used here as well just substituting the register offset from zero register.

To determine the maximum print length where …

Maximum Machine Print Length = MMPL
Register Offset from Zero = ROZ
Maximum Printable Length through machine = MPL

Then… MMPL – ROZ = MPL.

Hope this is helpful.

Hazmat Labeling, Flammable, Consumer Commodity, UN?

August 10, 2018

Jeff asks –

I have a question regarding the correct markings for a customer of ours that sells marine paints and coatings. Can you please help clarify which markings are required? It is our understanding that the box can have either the Flammable Liquids placard or the Consumer Commodity placard but not both. Also, if using the Flammable Liquids placard are additional UN markings required?

For your first question you are correct. Only one placard can be used, either Flammable Liquids, or Consumer Commodity as long as it falls under the guidelines for Consumer Commodity.

For your second question regarding UN markings, according to phmsa.dot.gov it would appear that yes, the UN markings should be used in addition to the Flammable Liquids placard.

If anyone has any additional information or insight on this topic, please feel free to share it with us.

— Ralph