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Sucking swarf and dust through a plastic tube is a fantastic way to generate very high levels of static electricity. 

As with all high-flow extraction, you should take steps to discharge the static electricity that will be generated from it. Discharging static electricity is easy to do and will prevent job failure.

Earthing is an important consideration for all extraction systems, and especially those with higher flow rates. 

How is static electricity generated?

If a material rubs against another material, particles of electric charge (electrons) can be physically transferred from one material to another. 

If one of these materials is an electrical insulator (e.g. extraction hose material) and not earthed, the charge that is transferred is unable to flow anywhere else. Instead, it builds up on the surface of the material. 

Why does your extraction build up static electricity?

As swarf and dust particles flow up the plastic tube, they will rub against each other and the tube, transferring charge and quickly creating a cloud of static electricity.

If there is no discharge path in the extraction system, this static cloud can build to thousands or even tens of thousands of volts. 

What makes static build up worse?

• Higher airflow rate: more particles will travel through the hose every second, meaning more opportunities for them to rub together and transfer charge.

• Longer hose length: the extra distance to the extractor tank means more opportunity for the particles to rub, resulting in a bigger difference in charge between sections of the hose.

• Smaller hose diameter: reducing the diameter of the hose results in a higher surface area to volume ratio for a given volume of air. This means that more air and particles will be in contact with the inner surface of the hose, transferring charge. 

What happens when too much static electricity builds up?

Allowing static to build to high levels can lead to it suddenly and dangerously discharging. At best this will cause job failure, and worst it can damage the electronics.

What is an ESD?

ESD stands for Electrostatic discharge.

A static cloud is always looking to discharge or flow to earth. 

For example, when your skin is charged with static electricity and you touch something metal, like a door handle, the metal is very conductive and will quickly discharge the static electricity. You will feel this as a small shock.

If the static cloud has a higher voltage, it has more intrinsic energy, and that can enable it to “jump”. A larger (i.e. higher voltage) static cloud can jump over larger distances.

Photo by Mike Lewinski on Unsplash

In the case of the unearthed vacuum tube, the static can build to such a high level that the voltage will eventually jump to an earthed piece of metal (typically on SmartBench or on the extractor). But by this time the cloud could have reached tens of thousands of volts. And that’s a problem…

Why is a large ESD bad?

During an ESD event , a wave of electromagnetic energy is released (also known as an EMP). If it’s large enough, it’s very effective at knocking out electronics.

Typically a large ESD charge will either stop the electronics from working temporarily, or cause permanent damage.

For SmartBench, we are able to prevent permanent damage in most cases, but a large ESD will cause the real-time electronics to reset. If SmartBench is in mid-job, this will cause the job to fail.

How to prevent large ESDs

The solution to prevent ESDs is to put an earthing path (a conductor linked to ground) along the area where static would build up. This means that the cloud can quickly discharge as it begins to accumulate, preventing high voltage static clouds and big ESDs.

How to prevent the accumulation of static electricity in your extraction system

Best practice is to attach an exposed conductor (metal wire) along the length of the extraction tube, which is plugged into an earthing point. This creates a flow path for the negatively charged static to run to ground.

When you have earthed your extraction system and tubing, you will no longer have to worry about static.

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