Best practices for safe tipping

This blogpost is the second in a series of blogposts about tipping safety and tipping trailer stability. The information given in this post builds further on the first blogpost in the series that focusses on the physics involved and it is highly recommended to read the first blogpost first before starting with this one. 

Click here to read the first blogpost of this series:

The physics of tipping trailers

Conclusions from the previous blogpost (the physics of tipping trailers)

The physics are clear about what makes tipping safe:

1. The base of support (ground surface) must be kept as level as possible;
2. The center of gravity of the vehicle must be kept as low as possible.

So, let’s zoom in on both and go over the things that can be done to maximize safety.

Keeping everything level

This seems easy at first glance: just tip only on perfectly level ground and in theory, nothing can go wrong. Unfortunateley there are some variables at play that are not always obvious.

Ground surface

The ground surface underneath a tipping trailer needs to be flat to begin with. When tipping, the weight on the trailer’s wheels increases for a short time, so the ground must also be strong enough to handle this. It’s important to remember that even solid-looking surfaces can quickly become soft and unsafe when they get wet.

If a ground surface seems loose or not compacted enough, it’s probably unsafe to tip, even if driving on that surface is still possible.

The trailer

The ground isn't the only thing supporting the weight when tipping. Between the trailer's center of gravity and the ground there are several important parts, including:

• The body
• The tipping hinges and cylinder trunnions
• The chassis (frame)
• The suspension system
• The tires

All of these parts work together to support the trailer and if any of these parts are worn, damaged, or asymmetrical in any way, they make the trailer less stable and unsafe.

To keep the trailer stable, it’s essential to perform regular maintenance and visual inspections. Pay special attention to:

• The tires, checking for proper air pressure and any damage
• The suspension, especially the rubber bushings and axle bodies
• The overall condition of the chassis and body

Regular checks can help prevent issues and keep the trailer safe during tipping.

The truck

The front of the trailer is fully supported by the truck, so the truck plays an important role in keeping the trailer stable while tipping. It’s very important that the truck and trailer are lined up correctly.

If the truck and trailer are at an angle relative to each other, there's asymetrical deformation in the front end of the chassis because the fifth wheel can only rotate around one axis relative to the truck and the cylinder is mountend in front of the fifth wheel on the chassis. This means that the weight pushing down on the tipping cylinder will push one front corner of the chassis further down than the other, which introduces asymetrical load on one of the most important structural parts of your tipper: the cyclinder hinges. 

For safe tipping, make sure the truck and trailer are perfectly aligned, with all wheels pointing straight. This helps maintain stability and prevents accidents.

Load distribution

Make sure that the load is evenly distributed in the body at the time of loading. Having more load on one side than the other shifts the center of gravity by default and of course, this is something that must be avoided at all times. Pay special attention to the loading process when the trailer is loaded by means of a bulldozer and when the loading machine operator cannot see inside the body.

Conclusions on how to keep your tipper level

To keep the trailer stable and safe while tipping, remember these key points:

• Check that the ground is level and solid before unloading.
• Regularly maintain the trailer and inspect all parts that carry weight.
• Make sure the load is evenly distributed when loading.
• Keep the truck and trailer as straight as possible during tipping.
• Be aware that high winds can affect stability and reduce safety.

Keeping the center of gravity low

Keeping the trailer's center of gravity low is important for stability so the lower the angle needed to unload, the safer it is.

The tipping angle needed depends on the type of load. Two main factors affect this:

• How easily the load slides over itself
• How easily the load slides down the trailer floor

The angle required for tipping is the one at which the load begins to slide off or down, depending on which happens first.

How easily the load slides off itself

The correct scientific term for this material property comes from the bulk shipping sector and is called “angle of repose”. It describes the steepest angle at which a material can pile up without sliding. The angle of repose is very closely linked to the “flowability” of the load and therefore the tipping angle needed for the load to fall out if it doesn’t slide down the trailer floor. The lower the angle of repose, the better the flowability of the material.

A lower angle of repose is better for safe tipping. Figuring out the exact angle requires scientific testing, so we won’t go into that, but here’s what we know from research:

The angle of repose depends mostly on how rough the particles are and how much moisture the load contains.

For example, dry grain has a lower angle of repose than wet sand, meaning it’s easier to unload.

How well the load slides off the body floor

This is again a material characteristic that is well-described scientifically, called friction.

Friction is how much two contacting materials oppose movement relative to each other, in our case the bulk load and the aluminium or steel of the tipper body. More friction means that higher forces are needed to get the load to move, or in other words, a higher tipping angle is needed.

Calculating the exact friction between the body and a certain load would again be too complex to do on-the-spot, but it’s again useful to know that moisture content does matter.

Think about how dry chalk behaves compared to wet chalk. Also note that freezing outside temperatures can make moist load types freeze to the body, which is bad news for safe tipping.

Conclusions on how to keep the center of gravity low

How steep you need the body to tip before the load starts to discharge is very dependent on the characteristics of the specific load that’s transported.

However, there are a lot of cues drivers can use to gain insight in these variables before tipping, and most of these checks can be done on-site where the loading happens.

If it’s possible, take a good look at the heaps that are on-site when loading. This will give you an idea of the angle of repose.

If the load type allows it, it can also be a good idea to grab some of the load in your hand to guesstimate the friction between load and body, and to get an idea about how steep the angle of repose could be. If the load falls through your fingers, the load is dry and you’re probably fine. If you can make a ball with the load, the load is moist and you’re at risk.

In summary: The ultimate checklist for drivers and operators

Of course, on-site safety rules are there for a reason and should always be obeyed first and foremost. However, these rules usually only cover on-site safety and do not mention the best practices we see from our perspective as a tipping trailer manufacturer.

Tipping safety, or in other words, keeping your tipper as level as possible and making sure that the center of gravity stays as low as possible seems very simple at first, but a lot of variables are important.

Based on all this information, we can extract a practical checklist for drivers and operators that greatly improves on-site safety. We have broken down this list of topics based on the logical steps most drivers will be confronted with:

Checks before starting your day:

• Trailer tire damage and tire pressure;
• Trailer suspension condition;
• Trailer maintenance level.

Checks while loading

• Angle of repose of the load;
• Friction between load and body material;
• Load distribution inside the body.

Checks while driving

• Rain;
• Outside temperature;
• Wind speed.

Checks before unloading

• Is the ground surface level and flat?
• Is the ground surface stable enough to support the higher axle loads while tipping?
• Are all truck and trailer axles in a straight line?

This blogpost is all about what drivers and operators can do to increase the safety margin when tipping, and a big part of that is about the condition of the trailer that’s used. Of course, as a manufacturer of tipping trailers, we have a responsibility to maximize safety by design in every tipper we manufacture.

Click here to read all about why a STAS tipper is the most stable tipping trailer available.

Or click here to read all about the physics behind tipping a tipping trailer.