Load safety in practice
Stopping the Slippery Slide
Article in CHEMIE TECHNIK magazine, September 2009
Load safety is often underestimated in practice. Barrels slipping from pallets, damaged trailers or even IBCs lost on the road – the cause for these unwanted situations is frequently insufficient load securing. Key factors are the anti-slip mats placed between cargo and load surface. These are also used for securing intermediate layers.
Once panels, containers or barrels start sliding on a lorry, there is often no stopping them.
The consequence: Damage to the product and – what might be even worse – danger to road traffic and users. The responsibility lies by no means solely with the driver. Above all, the onus is on the logistics specialists in charge of the loading process, who (for example in a chemical company) are responsible for securing the loads on a lorry properly.
And here, friction plays the pivotal role: Only when the load’s resistance to shifting on its base is greater than the forces involved in acceleration, braking or occurring in bends, will the load be secure.
This is most often achieved by a combination of slip-inhibiting materials and so-called “friction-locked securing methods” such as lashing down of the loads with straps. Slip-inhibiting materials used are often pads or strips from elastomers but also the relatively new anti-slip mats from coated paper. These have to be used, according to VDI (Association of German Engineers) standard 2700 Part 15, in such a way that they are “externally visible without the load having to be lifted or shifted.” In addition, the coefficient of sliding friction of the materials must be at least µ 0.4, or at least µ 0.6 for the transport of paper rolls.
For the selection of anti-slip mats, a number of issues need to be considered, among them the composition of load surface and cargo, as well as their weight, materials and dimensions. The above-mentioned part 15 of VDI standard 2700 describes the options, handling and safety requirements as well as inspection and discard criteria of slip-inhibiting materials and anti-slip mats in particular.
Dirt can become a safety issue. An especially sensitive issue that is often given little attention in practice are the discard criteria.
Anti-slip mats are frequently re-used too often. But the mats should – according to VDI standard 2700 Part 15 – no longer be used if one of the following conditions applies:
• Permanent deformation or pressure marks
• Tears
• Surface abrasion
• Cracked areas of material
• Swollen areas
• Damage due to contact with aggressive substances
• Embrittlement
Among others, the consignor/sender is responsible for the correct securing of loads on lorries. Anti-slip mats prevent slipping of cargo on pallets or on the load surface. The discard criteria are an issue that is often overlooked in practice.
According to VDI standard 2700 Part 15, anti-slip mats should no longer be used if they show any signs of dirt which could affect functionality.
But how should the logistics specialist or the driver check if dirt is “affecting functionality”?
“Part 15 poses more questions than it answers,” the Nordpack product manager criticises, and points out another sore point:
“Testing certificates for the coefficient of sliding friction seldom correspond to actual practice in terms of contact area and weights tested.” The product manager cites the securing of steel coils as an unsolved problem illustrating the issue – here, pads of anti-slip mats with a coefficient of sliding friction of at least µ 0.6 are sold “but this application was never tested.”
“We have tried to get a testing certificate for their application together with our customer. It was quite a surprise to actually receive the certificate in the end. Euro pallets, pallet cages and paper rolls were tested, but steel coils – negative. Enormous weight on the smallest contact area and lightly oiled tin – I have yet to see an independent practice certificate for this,” the product manager says.
An additional effect is that thin and soft anti-slip mat pads roll up with pulling and sliding of the load creating dangerous rolling friction. Here, for example, the coefficients of sliding friction are as low as µ 0.3. This often happens for instance as soon as pallets are pushed into the correct position by a forklift on loading.
Avoiding squashed fingers
Another problematic area is handling: Time and again, occupational accidents in the form of crushed fingers happen during positioning of pads and elastomer strips. In addition, selective placement of slip-inhibiting material results in a significant workload.
As a rule, at least six pads have to be placed on each pallet. “A Rhineland chemical company has therefore decided to equip their lorries with a complete covering of Safetygrip anti-slip mats, also on grounds of cost,” the product manager reports. The material is based on paper or cardboard coated on both sides with slip-inhibiting latex and is replaced every time. Used material is disposed of as waste paper.
As the mats cover the entire area, the material can be relatively thin: It is offered in strengths of 0.4 to 2.2 mm. In comparison: Rubber pads have to be at least 3 mm thick to ensure there is no contact between cargo and load surface. As the newest development in load safety, the manufacturer has developed an anti-slip mat based on corrugated cardboard specifically for drums. This structure deals with the problem of rimmed steel drums that quickly begin to slide because of their small contact area. The wavy material interlocks with the barrel and thus additionally increases the frictional resistance to the rim. According to the manufacturer this achieves slip angles of 28° or more even without any stretching or strapping.
Contact www.chemietechnik.de
Quoting the reference number, a free load securing video (DVD) may be ordered.
Further information CT 603