CONSIDERATIONS FOR CREATING A STABLE PALLET STACK
Filling pallets may appear straightforward, but it’s not always as easy as it looks cautions Pacepacker’s Commercial & Information Systems Manager Paul Wilkinson.
If you’re currently stacking pallets by hand, have you analysed the manual handling aspects of the people performing this vital function? There are many questions to ask. How high can your operatives safely reach? How many times do they have to twist? How heavy is each case or sack? Is the finished stack stable enough for transportation?
More complex patterns, combined with revisions by the Health & Safety Executive (HSE) to the L23 manual handling guidance (Manual Handling Operations; Regulations 1992), is proving to be catalyst for automating palletising operations.
Manual handling risks
Manual handling hazards are wide ranging. Although application driven, unusually shaped or unstable loads, excessive weights, stooping and twisting in cramped workspaces can increase the likelihood of a workforce injury.
When assessing risks, palletising operations are advised to study first the weight of what’s being lifted and the frequency and distance that the load is being carried. For lifting, it can be helpful to use the 5x5x5 equation – does the load mass weigh more than 5kg, is it carried further than 5 metres and does the person do this activity more than 5 times a month? If the answer is yes, this could imply a significant lifting activity.
In terms of manual weight handling limits, even with the new HSE guidance there are no hard and fast rules. The recent revisions suggest that when lifting at waist height, it’s around 25kg for men and 16kg for women. The trouble is, pallet layers start at ankle height and often reach above shoulder height, and the advisable weight limits drop significantly to around 10kg for men and 7kg for women. Many bulk loads, from sacks of rice to cases of beverages, exceed these advised limits. And if you look at bulk animal supplies, such as bedding hay, stacks can reach up to 2.4 metres, which is impossible to manually stack safely.
The art of creating stable stacks
Whether you are palletising bags, pouches, cartons, boxes, pails, buckets or drums, the ultimate stability of your stack is paramount. Of course, you want to be an efficient operation and getting as much product onto the pallet as possible within the appropriate weight and height limits plays a part in this, but not at the detriment of other people’s safety. Outside of these primary aims, other factors to consider are bar code scanning or the ease of picking or de-packing the stack by the customer.
Leaving gaps between boxes can help to create a stable stack, and an automated programme can do this repetitive task consistently. Retailers are also calling for more mixed pallet loads in an effort to pare down stockroom inventories. A robot can be configured to differentiate light from heavy packages, which means they can palletise a variety of case sizes of products on one pallet without compromising the stability.
There’s also an emerging trend for the double stacking of palletised loads. Although this technique increases your storage capacity, to do double stacking successfully depends upon the base pallet load being sufficiently strong to carry the load of the pallet above. All sides of the bottom stack, which articulated robotic arms can successfully accomplish, must evenly share the weight of the upper pallet.
There are a whole host of stacking patterns. The actual design will ultimately depend on the where the pallet is destined, e.g. shipping container patterns would be different those for a wholesaler or retailer. Again, stability is vital and in most pallets you won’t see the same pattern repeated layer upon layer. Like building a brick wall, most cases are arranged to interlock. One exception tends to when stacking rigid cardboard boxes of similar size. Here, it can actually increase the rigidity of the overall pallet if each row is mirrored. For those heading to the retail stores, packaging labels are also orientated to face outwards on all four sides.
When programming the perfect pattern, you also need to consider the pallet type and size. The most common standard pallet remains the 1 x 1.2 m, yet there are even variations within this. Do the straps run parallel to the long or short edge? Are all four sides fitted with skid bases and is the pallet configured for 4-way or 2-way entry?
Tricky products can cause problems
Sacks tend to be lumpy compared with plastic crates or cardboard boxes. Also, plastic sacks can be more slippery than paper. In many cases, a person building a pallet can compensate for slight variations in outer package shape and pallet stability. Nevertheless, a strong pallet binding with wrap or strapping may be advisable to avert potential disaster.
Palletising location and climate can also have an effect. For example, when stacking bags of frozen product condensation can form and even ice up, which can make packs and sacks slippery.
Systems today can also be surprisingly compact. The Cartesian options on the market today can be installed into tight spaces at the end of line packing process where the lack of space previously eliminated the idea of automating palletising.
Many complaints about automated palletising systems can be attributed to incorrect fill level of products being stacked, how the product has been settled prior to picking up, programming or end of arm tooling. Like any readily available commodity, a palletising robot ‘out of the box’ will accomplish very little. It’s the ancillaries, applications knowledge, software and set-up you apply to it that make all the difference!
Pacepacker’s award-winning Pallet+ can assist customers to speed up the process and accuracy when re-programming palletising patterns. Catering to fast-changing product formats, packaging shapes and sizes, Pallet+ enables factory operatives to change, store and recall new or revised robotic palletising and case loading recipes in several minutes versus over an hour with usual robot teach pendants.
For more information please contact:
Paul Wilkinson, Business Development Manager
T:+44 (0)1371 811544
F:+44 (0)1371 811621