By guest author, Ron Mines FAIP*
Last year I participated in a training day at Woolworths Minchinbury DC (in Sydney), facilitated by IDG, the Australian Institute of Packaging AIP and Woolworths. The previous day, most of the trainees had gone to a Woolworths supermarket to see how shelf-friendly packaging (SFP) was being used in the storeroom and with shelf loading. Many questions were raised during the day about the best board grade to use for outer boxes.
The paradox for Woolworths, and other retailers, is that the stores want stable, but easy-to-handle outer packaging that is:
- easy to open and load to shelves, and
- has waste outers/trays that are also easy to deal with.
However, the DC wants a more robust, tough and durable pack:
- that can withstand rough manual handling and automatic order picking, as well as
- the rigours of their carousel which delivers the outers to store roller conveyors, then
- survive variable pallet load stacking that can add all sorts of dynamic loads to the pack.
It’s also not my intention to touch on the additional costs for suppliers to the grocery industry — this article is about the best board grade.
Ultimately, every packing exercise is unique and requires considerable understanding of pack configuration and packing method. Anywhere in the supply chain — from the box maker to the transport company who delivers finished product to the DC — has the singular potential to cause shelf-friendly packaging to fail. This is particularly the case with outers that are perforated for easy opening.
Working through a perforated box example…
So let’s just deal with perforated boxes, which come in RSC (regular slotted carton) or wrap-around variants mostly.
The supermarket industry wants a single facing of the product on the shelf. This means that in most cases, the box design will end up with perforations across the narrow front of the box, then the perfs will continue at an angle towards the back of the box in one form or another, and then across the back.
Typically in a compression stack, column-stacked boxes with perfs as described above, with no other dynamic forces applied (side or end-shock typically from conveyor stops or movement on the truck when braking, to name but just two of the risks) will reduce the top-to-bottom compression strength by around 40% from the original pack.
Allowing for other issues — including too much die cutting pressure by the boxmaker, damage occurring when erecting and packing, poor palletising and rough handling in the DC — where does the Packaging Technologist set the safety factor?
To illustrate this, I have run an exercise on a soft-pouch 12-pack, where each pouch weighs 500g and the box weighs 200g.
Figure 1: This pack weighs 6.2 kg, stacked five high so the weight on the bottom box is 25kg (no safety factors allocated). As a two-pallet high stack, the net weight on the bottom box is 55kg.
Figure 2: The safety factor when this job was an unperforated regular slotted carton (RSC) was fairly high because the packed pouches are non-supporting in the pack. Let’s choose a safety factor of 4.5 for one pallet high and 6.8 for two pallets high, which was established to cover all of the rigours the box must withstand from the time it’s fed onto the packing machine, until it reaches the supermarket shelf.
Figure 3: At one pallet high, the value for the weight on the bottom box is 112 kg. As a two-pallet-high stack, this same value is 318 kg.
Figure 4: The next step is to determine what safety factor should be applied with all of the new factors of making and handling a perforated box. So for this type of pack, which is not refrigerated, a Packaging Technologist would arrive at a safety factor of 6.3 for one pallet high.
Figure 5: Now the value for the weight on the bottom box is 156kg; a safety factor of 8.5 for two pallets high is determined.
Figure 6: The value of the net weight on the bottom box is now 466kg.
Great, so now that’s established, add 40% to the box strength needed, to establish the boxes’ approximate theoretical carrying capacity required to get product safely onto the store shelves.
So why was it necessary to add 40% when we have already adjusted the safety factor? Because safety factor increases only account for the added potential for failure. The strength increase is still needed to compensate for the direct loss in top-to-bottom compression strength.
The top-to-bottom compression strength now needed for one pallet high is 218kg and for two pallets high is 652kg.
Now the Packaging Technologist can go to the Boxmaker and ask them to determine the best board grade for the pack. This should then be a process of determining the most suitable flute type, then board combination to achieve the required top-to-bottom compression strength.
Through trial and assessment, a measure of confidence can be established, allowing for all of the potentials that have been built into the safety factor.
This article was originally written by the Australian Institute of Packaging (AIP) and was first published in What’s New In Food Manufacturing & Technology (online). (This is a slightly edited version.)
You may also find this article from our Thought Leader series on SRP and its impact on manufacturers interesting, and this blog on at creating shelf-ready packaging retailers and consumers will love.
* Ron Mines FAIP, known as “The Boxologist”, is a consultant to the box and packaging industry. His 40+ years of experience and close industry involvement, give him considerable credibility among his peers. He is a passionate advocate of the AIP and the many benefits of its membership. Ron believes that knowledge is power, and his philosophy is to pass on his knowledge gained over many years. Ron runs specialised training programs for boxmakers and box users, as well as providing technical and other support throughout the industry.