The Plasma cutting is a popular method for cutting metals under dry environmental conditions. However, there are cases in which plasma cutting under water is also advantageous.

We would like to give you an insight into the advantages, but also the disadvantages, of plasma cutting under water. As underwater plasma cutting is a thermal process that is used underwater, our experts will go into some important aspects.

How does plasma cutting work under water?

The principle of plasma cutting under water is similar to plasma cutting above water. An electric arc is created between an electrode and a metal workpiece. This ionizes the gas that is passed through the cutting head and turns it into a plasma. However, unlike the dry surface, there is a layer of water over the workpiece. In most cases, the thickness is between 40 and 70 mm.

The plasma has a high temperature and melts the metal at the interface. The cutting head is equipped with a CNC controlmoves to work the metal precisely. To be able to plasma cut under water, however, the cutting head must be specially designed.

Cutting head for underwater cuts

There are special cutting heads that are designed for plasma cutting under water. These cutting heads have an exceptional design to displace the water during the cutting process and isolate the plasma. When plasma cutting under water, a vortex gas is used to remove the water around the cutting area. This will prevent the water from penetrating the arc and leaving the cutting process behind.

An opening in the cutting head guides the cutting gas and creates a vortex around the cutting nozzle. This allows the cutting head to cut metal quickly and effectively without water hindering the process. However, the water is only displaced in the area where the plasma meets the material. The water hits the material in all other areas, even those that were cut only fractions of a second earlier. The water thus has an influence on the still-warm cut edge.

Eckert Cutting offers CNC cutting machines with the Support HD3000 cutting head. This not only fulfills the requirements for plasma cutting under water. This cutting head has collision protection as well as electronic and mechanical initial detection. High-speed height scanning is also one of its qualities.

Gas for cutting under water

As with plasma cutting over water, a suitable cutting gas is required for the cutting head to perform its work. The most commonly used cutting gas for plasma cutting under water is oxygen. Oxygen is an ideal cutting gas because it can undergo an exothermic reaction with the metal at high temperatures. This can speed up the cutting process below the water surface.

In plasma cutting under water, other gases are used for cutting in addition to oxygen. These include nitrogen, argon and hydrogen. Nitrogen is inert and there are no chemical reactions with the metal to be cut. It is therefore often used to produce a clean and smooth cut edge.

Argon, however, can be used at higher amperages due to its higher plasma density than nitrogen. This means that cuts can be made more quickly. Due to its high thermal conductivity and plasma density, hydrogen is another cutting gas that is used. It enables thicker metals to be cut with greater speed and efficiency.

It is theoretically possible to cut under water without cutting gas. However, it is not recommended. Cutting without cutting gas results in a slower cutting speed and poorer cutting quality. The requirements of the cutting process and the type of metal being cut determine which cutting gas is used.

Under water vs. above water

Underwater plasma cutting differs from plasma cutting above water in a number of important ways.

A major advantage of plasma cutting under water is that the water cools the cutting process. It prevents the cut from burning. If materials are cut in water, this can lead to higher surface quality. Since cutting under water reduces the spread of smoke and sparks, it is also safer than cutting above water. Plasma cutting under water protects people and the environment.

However, plasma cutting under water also has some disadvantages compared to plasma cutting above water. One of the reasons is to regulate the cutting depth, as the water obstructs the view of the cut. Another disadvantage is that cutting under water can be difficult due to the additional pressure. The water also cools down the cutting process and therefore reduces the cutting speed of the CNC cutting machine.

The slag produced during cutting is also cooled quickly by the water compared to dry cutting, making it harder to blow out of the cutting gap. This leads to a comparatively higher roughness of the cut surface and, in some cases, higher post-processing costs compared to dry cutting.

Be aware of safety precautions

Companies must observe certain safety precautions when plasma cutting under water. This way, they can ensure the safety of their employees and compliance with regulations. Here are some crucial elements to keep in mind when plasma cutting underwater:

• Personal protective equipment (PPE) for employees
• Electrical safety through e.g. insulated cutting heads
• ensure water supply and good gas quality
• Ventilation and air purification in the factory hall
• Continuous Training and training (especially for new techniques)

We are happy to advise you

Should you have any further questions on this or any other topic, please do not hesitate to contact Eckert Cutting. Our experts will be happy to advise you including and customized to your requirements.

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