Episode 9: AccelerationsPosts by Thomas Bauer
Accelerations are a physical phenomenon that surrounds us all the time. We often do not notice it and if we do, it hurts, e.g. when you knock yourself on the thumb with a hammer.
With this load securement blog post I would like to draw a line from everyday situations to special requirements when transporting with sea containers or by truck.
About the author:
In a series of specialist articles from the field, on topics relating to containers and trucks, you will receive first-hand professional knowledge.
How to secure cargo correctly and what are the basics of cargo securing?
They are developed and presented by Sigurd Ehringer, owner of SE-LogCon:
- VDI certified instructor for load securing
- Reference book author
- 8 years Project Manager
- 12 years with the Bundeswehr (company commander)
- 20 years of sales experience
- since 1996 consultant/trainer in logistics
- 44 years instructor/trainer in various fields
Episode 9: Accelerations
In physics, one speaks of a uniformly accelerated translation with or without an initial speed.
The acceleration (a) is calculated by dividing the speed (v) by the time (t). The unit of acceleration is m/s2.
Often, changes in speed are caused by braking, which in physics is called deceleration. The calculation is the same, only the sign changes from + to -.
In practice, there is also the important element of weight/mass. Surely one or the other has already got the answer to the question about load securement: It's so heavy, it can't move at all. And that is exactly where the problem lies, because the mass has the property of wanting to maintain its current state and opposes any change with a force.
Anyone can observe this phenomenon on the conveyor belt of a discounter. The articles are moved each time the belt is moved up and slowed down. Stacked shopping goods slip, bottles fall over or start rolling. Exactly the same thing happens with transports.
Anyone can test the relationship between mass and acceleration using the following example in practice.
Take a 120 mm nail and a 500 g hammer. Put the nail with the point on a block and then place the hammer on the nail head.
Result, the nail will be minimally and insignificantly pressed into the soft wood. If the hammer is removed again, the nail usually falls over again.
From a physical point of view, only the force that results from the hammer weight multiplied by the acceleration due to gravity is effective.
The practitioner will lift the hammer, accelerate towards the nail head and hopefully hit it.
This additional acceleration increases the force generated significantly:
Force (F) = mass (m) * acceleration (a)
Upon impact, the hammer brakes abruptly and the force drives the nail into the wood. Depending on the acceleration, the weight of the hammer and the friction in the wood, several blows will be required.
Depending on the situation, the practitioner will use a different hammer to generate the required force.
Of course, there is also a certain amount of technology involved. Anyone who has ever hit the "Lukas" knows what I'm talking about.
This basic principle is hidden behind many load securement situations. E.g. when a load is not stowed positively on the bulkhead and the truck driver has to brake. The load is traveling at the current speed (phase 2) and is accelerated negatively when braking (phase 3). The greater the speed and the longer the path on which it can gain momentum, the greater the force of the impact on the front wall.
Physically this is expressed using a formula for calculating the energy. This formula also includes the speed squared (V2).
Perhaps one or the other also remembers a question from his driving license: How does the braking distance change when the speed doubles?
Answer: it quadruples. That is just because of the speed squared. So the energy (force of the impact on the front wall) increases with the speed.
The load always moves when the acceleration / deceleration is greater than the friction (coefficient of friction µ). This means that as long as the accelerations / decelerations are smaller than the friction between the load and the loading surface, the load remains in place. Only when they get bigger does the load move jerkily.
As a rule, there is no gradual transition. However, loading units at risk of tipping first begin to tip over and then slide. This can be demonstrated well with driving tests.
This example clearly shows that anti-slip mats alone are only a theoretical improvement in load securement. They must be supplemented by additional measures such as lashing down.
So it comes down to preventing cargo from moving.The form fit is the simplest solution. It should be noted, however, that the cargo movements all must be prevented in every direction, because the movement in the acceleration / deceleration direction is usually followed by a reaction in the opposite direction. Sometimes the securing of the cargo towards the rear is questioned.
The main part of this backward acceleration comes as a reaction to the emergency braking (rebound effect), because the energy inherent in the load is not completely used.
The following is an example from a test drive. The load weighs approx. 1200 kg, the speed is approx. 25 km/h.
After a video runtime of 5 seconds, the brakes come out of 25 km/h and the 1200 kg load tips forward because it was not stowed positively on the box pallet.
During truck transport, this process, the emergency braking with 0.8 g, usually only takes place once. When transporting by container ship, which can also achieve an acceleration of 0.8 g when rolling, this movement can occur 2-3 times per minute. These permanent accelerations represent, among other things, the special feature of the container.
The responsible shipper is therefore required to assess the specific situation on the truck or in the container, estimate or calculate the forces and then take the necessary measures. Of course, gap fillers have to withstand constant stress. For example, cardboard spacers are rather unsuitable in a damp environment.
Precautionary measures, in order of effectiveness, are:
- Stow positively
- Fill in the gaps to create a form fit
- Direct lashing is also a form-fitting method
- Combine direct lashing with anti-slip mats
- Tie-down lashing with anti-slip mats
Your Sigurd Ehringer.
Physics simply explained. You can very much underestimate what mass and speed mean when you are out and about in traffic.
On our own account:
Rothschenk. That's us.
Rothschenk is a manufacturer of load securing equipment for overseas containers. In the tranquil town of Aub in central Franconia, we develop, test and sell our own load securing equipment such as dunnage bags/padding, Lashing restraint systems, Edge Protectors, Anti-slip Mats, Lashing Straps and drum securement. You can get a small insight into our product world in our Online Shop: [R] SHOP24.
We develop for our customers, to whom also large corporations e.g. from the CHEMICALS-, BEVERAGES- and Automotive industry belong, individual load securing. Therefore we are used to come up with new products and solutions in our own research and test department.
We stand for quality "Made in Germany„. Not only in development, but also in production. Because we are the only manufacturer for load securing with our own production site in Germany. Real "Made in Germany" even.
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