MEMBER'S QUESTION:

Hi Ralph,

Occassionally, the question arises "What is a typical or appropriate warranty period for corrugated products?"  We certainly don't advocate forcing customers to accept sub par quality products, however, there are situations which arise where the discussion comes up. Is it different for die cut vs. flexo work?  What about printing, litho lam. etc?
 
This relates to finished boxes that sits at a customer's site for an extended period of time. When finally unbanded for use, they may experience cracking which may have occurred due to their storage conditions,  or in one case recently, a printed and glued "weekender" style display had a weakening of the board in piece just below the glue tab of the piece above.  This compression caused weakness.  They had sat there for 4 months. We probably had crushed them in our banding process, however, it;'s possible that due to time, they took a prominent set that would not have occurred in a shorter time frame. The question was asked " What is the life expectancy or warranty period for a product such as this"  We resoved it by replacing the product at our expense,  but it brings up a few interesting points.
 
 
ASKRALPH RESPONDS:

Great to hear from you.  Thank you for the question.

Your question somewhat precedes an article in the May/June issue of BoxScore.  Review, distribute and save the chart on the Expected Values of Combined Board.  As long as the corrugated products maintain their flat crush, edge crush, and pin adhesion strength values close to what they were when the products were manufactured, then the aged products are the same as new production.

Hi Ralph,
I've read some of your responses to the ASK Ralph service.  I'm a packaging engineer for a US based manufacturer of computers and preferrials.  Products we have build and packaged in China are having box compression failures.  We specify a minimum box compression strength on our drawings.  Test results performed by the supplier at the time of manufacture are passing.  We are using a safety factor of 4.5 to 5.5 that should account for all the environmental and conversion effects acting on the box to degrade it's performance.  However, after arrival at our distribution centers in Americas and Europe, the box is failing under load.

My research so far seems to point to the recycled material China uses in their box board paper.  This material looses it's bond strength after cyclic exposure to high heat and humidity.  BCS at time of manufacture is not the same after this type of exposure, and is much worse that industry experience with typical virgin or re-cycled softwood fiber.

If I could add a minimum stiffness requirement on my drawings (per TAPPI 836), do you think I would have a way to manage the use of recycled content board such that my expected box compression performance is not compromised over time?  If yes, how would I create a table of expected stiffness requirements?  Should it be related to board combo caliper, by flute size, by ECT or Mullen test values, etc?

Thank you for your advice,

ASK!Ralph Responds

Thank you for the inquiry and contacting the AICC.

Where have the boxes failed in the supply chain?  Do you have any pictures that you can share so I can offer an opinion on the type of box compression failure?

MEMBER'S QUESTION:

We have a customer that is currently using a 32 ECT RSC and would like to transition to an HSC for cost savings.  They are under the impression that they will need to upgrade the board construction to maintain the same performance.  Do you have any ideas, data, etc. that does or does not support that theory?

 

Thank you for your help,

 

ASKRALPH! RESPONDS:

 

Now that’s a great question.  The simple answer is that the compression strength of a corrugated box is a product of the ECT strength in the side walls and the flexural stiffness of the vertical panels.  The flaps on a corrugated box are “relatively” useless as far as box performance goes.  Flexural stiffness can be measured, but is highly dependent on the caliper of the combined board.

 

So as long as the dimensions of the box and ECT strength from the combined components do not change than there should not be a performance difference between a RSC and HSC.

 

My source for this information is George Maltenfort’s two books: Corrugated Shipping Containers and Performance and Evaluation of Shipping Containers.  I can send you a pdf of a few pages, but they are rather technical in nature with an engineering perspective.  And, we can always sent the two designs out to an independent lab for evaluation.

MEMBERS QUESTION:

 

I am trying to ascertain the industry standards for determining the effect of humidity on corrugate stored over various periods of time. Can you direct me to a source or provide information that would guide us in this endeavor? We have a client that is going to store corrugate for three to four months in a new facility. The facility is in a little valley area known for its humidity. I have asked them to start monitoring humidity levels and keep baseline data for my office.

 

I have some basic information on humidity effecting corrugated but I need to be in a position to answer any and all questions.