Package engineering design and resources to avoid product crushing 1

[edwardmatos]

[I originally posted this on the eFunda forum, but only realised after posting how inactive that forum is! I have now requested that the eFunda post be deleted to avoid double posting.]

Hello. A batch of our products we recently produced reached the user in damaged boxing because the corrugated cardboard boxes we put them in were clearly not up to the job of being stacked up in transport. This is in the Far East, so communication with our box supplier isn't great - and so we figured that we should do some calculations at our end to make sure this doesn't happen again.

Does anyone know of any resources from which I can learn a bit about packaging engineering, and refer to typical data tables, to ensure that our new box design will not be crushed? I suppose I will need to learn a bit about cardboard weights vs. stacking strengths, different box designs, and safety margins for applying in the case of imperfect stacking alignment, as well as dynamic loads.

To give it the right perspective, I'm looking at two boxes with the following internal dimension requirements:

365 x 185 x 75 mm - 1.35kg
180 x 180 x 50 mm - 0.70kg

For the first one I am able to arrange the contents such that I can put a "brace" halfway along the length of the box, to prop up the middle section.

I'm no expert in packaging and logistics (yet!) but I gather a typical pallet height for an efficient fit into a container is 2.2m heigh. So, accounting for a bit of extra space for box thickness, and assuming we're stacking them with their largest face on the horizontally plane, we're looking at a stack 27 units high for box 1, and 40 units high for box 2. At a bare minimum (not including safety margins for misaligned stacking and dynamic loads) the bottom box for number 1 needs to withstand 37kg (550Pa), and the bottom box for number 2 needs to withstand 28kg (870Pa). Without knowing anything about cardboard boxes, I imagine a box that can sustain those kind of loads must only come at a hefty premium. Unless there's some sort of lattice effect that gives the bottom boxes extra strength once they're packaged in outer cartons and bound together with tight cling film as you see on palletised goods? Otherwise, presumably there's also an optimisation in trading off cardboard thickness vs. wasted empty shipping space in your container?

Lot's of questions... A reference to a good online resource or book would suffice as a very helpful answer. Many thanks in advance for any help provided.

Edward Matos
AMIMechE

http://iosolar.com

 

[SlideRuleEra]

Review the information and links at the "Packaging Society" website:

http://www.iom3.org/packaging-society

In particular, see these books at the link below:

"Packaging Technology - Fundamentals, Materials and Processes"

"Fundamentals of Packaging Technology"

"Packaging - The Facts"

http://www.iom3.org/packaging-books

Another source may the be the "Package Designer Software" from The Air Force Packaging Technology and Engineering Facility:

http://www.wpafb.af.mil/library/factsheets/factsheet.asp?id=21045

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[edwardmatos]

Hello SlideRuleEra. Apologies for the slow reply, and thanks so much for your comprehensive post. I did look at some of the literature available and thought to come back and post some conclusions. Basically, you can quite easily calculate the force per cm of vertical cardboard perimeter and compare that to typical "edge crush test" results, but there are a large number of different environment-dependent safety factors. If you want a quick conservative result, you end up with a huge safety factor, leading to intuitively overly-large boxes. (That "intuition" coming from simply looking at similar product boxing and cartons in and around the back of an electronics store - they're not in the bomb-proof thickness that my overly-conservative calculations would suggest.) So the quick answer is that, if you're looking for a cost effective design, and don't know much about the environment the boxes will be submitted to, there are simply too many environmental safety factors to try and rely on a calculation without prior experience. Best trust the judgement of the manufacturer, and maybe decrease the height of the pallet stack a little if you want to make sure they've got it right. In future batches I can trial some thinner boxes...

Edward Matos
AMIMechE

http://iosolar.com