Archive for the ‘Design and Structure’ Category

Corrugated Performance In Sub-Zero Temps

January 28, 2020

Jeff asks,

I have a client who is asking for specific information about corrugated performance at low temperatures (-20 degrees Celsius) for extended periods of time (up to 6 months).  I have not been given specific information about the contents of the boxes, but I suspect it to be clinical trial materials or something similar.  I expect them to be looking for some sort of performance guarantee.  Current board grade is 32 ECT C Flute.  Outside liner would be virgin paper.  The remainder of the box (medium and inside liner) is recycled paper.

Anything you can provide to help me with this?  Or can you direct me to the right place?  Thanks in advance for any help you can offer.

There just is not much out there. Here is a Link to the last industry wide study on freezer storage which is over 70 years old, but still relevant. Note the added box strengths in the chart. Also here is a link to the most recent report from the PMMI on the storage of Corrugated Packaging.

As you stated, the contents of the box is critical and also is the introduction of any moist air from repeated open and closing of the storage unit. Use of aqueous or UV coatings will certainly provide extended resistance to moisture on the boxes’ surface. However, what generally happens is the glue line is attacked by changes in atmospheric conditions. This is where we often see failure under these conditions.

Does any of our other followers have any knowledge or experiences they can care to share on this subject? How about adhesives and sub-zero temperatures? How does temperature affect the difference adhesives we use in the corrugated industry?

— Ralph

Measuring Force to Break PDQ Perforation

April 10, 2019

Pete asks,

We have been working with several different perf styles to provide ease of opening for retail ready PDQ style trays. There is a variety of different sizes and the majority of the items are earmarked for Walmart stores. While our execution has been successful we do not have an effective process to measure the force required to open the boxes to ensure consistency. Are there any tests to can recommend or any laboratories capable of testing the variables we are trying to measure?

Very good question Pete! You might review TAPPI T-813 which discusses the tensile test for the manufacturer’s joint. There are also jigs for compression testers that will measure the force necessary to bend a crease through a certain distance, usually to a 90 degree angle.  Also check TAPPI 577 and 829 for ideas.

Another option may be to use a burst test at the point of the perf. TAPPI T-810 describes the burst testing method. The question would be whether conventional equipment would have a satisfactory range of operation/measure or would the bursting strength of the perforation be below the recommended operating range of the equipment.

Now let’s toss this one out to our readers to see what their thoughts and experience may be. Has anyone done this type of testing, or is anyone aware of a specific method for testing the force necessary to break a perf?

– 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!