Episode 5: Friction coefficient on the truck – What really counts?

If you are on the Rothschenk website, it can be assumed that you have more or less heard of the subject of load securing. If you do more research on the Internet, you will stumble across forums, information pages from consultants and trainers, other manufacturers and dealers, major testing institutions and, last but not least, groups in the social media – all on the subject of load securing.

Particularly in the groups, people argue with great zeal that a belt should be added here and that the belt should be three centimeters further away there in order to achieve the ideal angle. Of course, the self-proclaimed gurus then come into play, whose Latin ends pretty quickly and they then argue with wild insults and unfounded theses.

But where, as the old saying goes, is the “dog buried”?

Clean loading areas

In every load securing training course, at every load securing event, at every load securing lecture, you always hear one thing: “the loading surface must be clean to achieve the highest possible friction“. Even a good anti-slip mat cannot fulfill its purpose if it is placed on a dirty loading area.

But what is clean?

If five people look at a loading area, there will probably be ten different opinions.
If a very clean person looks at it, he would probably prefer to take a bucket of cleaning agent and possibly even disinfectant to disinfect the loading area.

However, if a very messy person gets into the same predicament, the threshold for cleanliness is most likely very far away. Then the self-proclaimed practitioner comes into play with the sentence: “I’ve seen worse”.

This loading area is definitely not clean. It has probably not been swept for a very long time.

The practitioner actually mentioned that he had seen worse soiling than this.

Examination

It is actually very easy to determine a clean loading area. – The loading employee watches as the driver sweeps the entire loading area with a broom.

A broom with black or brown bristles is a useful tool for this. You should not use a street sweeper, as it often does not sweep as cleanly.

Some also use a compressor to blow off the loading area. However, it can often be observed that the dirt settles in a different place due to the turbulence. It is therefore better to dispense with the technology and use a conventional broom.

Which type of sweeper?

You also have to pay attention to what type of sweeper the driver is. Here I differentiate between three different types:

1. The clean one – this removes as much as possible from the loading area and sweeps the vehicle from front to back.
2. The lazy one – he leaves everything on the loading area, even the anti-slip mats that have already been laid out, and then sweeps over the mats.
3. The muddy one – this one has already laid out his anti-slip mats and now takes a hand brush, folds up the mat, sweeps only where the mat is lying and puts it down again.

A “tool kit” should be available in every loading area. On the far right of the picture is a broom with a black bristle.

Effects

Let’s start from the back. The “sloppy one” works very meticulously and also ensures that physics is right and that friction is probably relatively high. However, there could be problems of argumentation during a traffic check if the inspectors assume that the loading area is dirty because the rest of the vehicle has not been swept off.

In most cases, a policeman would be reassured by the “lazyone”, but from a physical point of view, there are dirt particles between the friction partners, so that things could go wrong in the event of emergency braking or evasive action. That’s why the “clean one” is of course our personal No. 1, as this is the only way to do justice to physics and the control officer.

Excuses… and measures

The time factor is also always an issue when it comes to cleanliness. This is why we often hear statements such as “We load … trucks a day, if we have to check that too, then we can load 10 fewer vehicles a day”.

The fact is, if the person loading the vehicle watches every driver sweep the loading area, then 5 to 15 minutes have passed pretty quickly per vehicle and this adds up over the course of the day. But there is another way.

One option is a driver’s routing slip, which the driver receives when registering. It states that the driver must sweep the loading area before entering the loading area. If it is called up and is clean, then the goal is achieved.

However, if he has not swept the loading area, one measure would be to send him back to the waiting position. Such a measure has already helped many companies to “educate” drivers and make them follow instructions.

But there is also another possibility. If the person loading the vehicle notices that the loading area is dirty, they will instruct the driver to sweep the loading area clean. Then it drives back into the warehouse and picks up the next load. If the loading area is clean, loading can begin immediately; if it is not, the employee positions the load in a free space and picks up the next item, and this process is repeated until the loading area is clean.

Time is money?

The drivers would often rather spend 45 minutes discussing why the loading area is not clean than 5 minutes sweeping it up. Such a discussion is also quickly explained with a driver’s routing slip or with a work instruction “BECAUSE IT IS STATED THERE” and the loading personnel must adhere to the employer’s work instructions. In many cases, it also makes sense to inform the shipping company that there are difficulties with one or the other.

The clean loading surface is also a basis for form-fit load securing in a Code XL body.

A Code XL certificate always contains a list of the circumstances under which the structure can withstand the forces applied. Right at the beginning of the list you will find “Sliding friction coefficient of at least µD = 0.3”. This 0.3 can only be realized if the loading area is swept clean.

To put all this into figures, here is a comparison: We assume that a wooden crate with a mass of 5,000 kg is loaded onto the bed of a truck.

If the loading surface is in a swept clean condition, a coefficient of sliding friction of µD = 0.3 (30%) can normally be assumed. This means that the frictional force is 5,000 daN x 0.3 = 1,500 daN .

If anti-slip mats (ARM) are used, which are then correctly laid out on the clean loading surface, the frictional force is 5,000 daN x 0.6 = 3,000 daN.

However, if the loading surface is dirty, it is largely irrelevant whether there are ARMs between the load and the loading surface or not, as the coefficient of sliding friction may only be µD = 0.1.

The frictional force is therefore only 5,000 daN x 0.1 = 500 daN. This may not seem so dramatic at first glance, but in combination with a tie-down lashing, it is possible that more than 50 lashing straps would be necessary to actually secure this crate.

Conclusion

If we don’t get it organized that the loading surfaces are clean before loading, in most cases we don’t need to talk about belts, chains & co, unless you manage to really secure a load with a friction µD ≤ 0.1 in the end.

Yours, Christian Schmid

Lara Hüser