Here Is How a Plasma Water Table Works

Here Is How a Plasma Water Table Works

Understanding the Basics of Plasma Water Table

What Is a Water Table?

A water table also referred to as a water pan or waterbed comprises a tank of water placed beneath the cutting surface. Several vertical metal bars referred to as slats are present above the tank. These bars support the material during cutting.

During the cutting process, the water level is up to 0.25 - 0.125 inches below the bottom of the piece being cut. Certain machines are equipped with pneumatically controlled valves to control the water level. During the cutting process (HD cutting applications) some welders submerge the plate and plasma torch underwater.

Why Cut With Plasma on a Water Table?

When CNC plasma cutting, there are a lot of good reasons for using a water table instead of a dry, or downdraft table.

In CNC plasma cutting, it is essential to control the dust and fumes generated from the cutting process. Using a water table proves a great solution. In this as the metal being cut is located beneath a layer of water, it prevents generating fumes.

A water table is less expensive to purchase, does not require a dust collector (in most areas), reduces noise, eliminates dangerous arc flash, reduces heat distortion, and keeps parts cool, just to name a few. And even though it is an older technology, a substantial number of large gantry CNC plasma and oxy-fuel cutting machines are still sold with water tables.

How Does a Plasma Water Table Work?

Some water tables are simply a tank, filled with water, and burning bars on top. But that will not get you the full advantages of underwater plasma cutting. So, this discussion is about the type of water table that has an adjustable water level, allowing you to submerge the plate and the plasma torch underwater.

The construction of the table is quite simple; a large chamber is built into the table, below the burning bars and a steel tray. The chamber only has openings inside the water table along its bottom edge, so air can be trapped inside, similar to submerging an upside-down bowl. Then by putting air into or letting air out of the chamber, the water in the table is forced up or down.

At a minimum, the water level controls have an air supply valve and an air release valve, which control the compressed air going into and coming out of the chamber. These valves can be simple ball valves operated by hand or can be solenoid valves controlled by the CNC.

To raise the water in the table, the release valve is closed, and then the supply valve is opened. Compressed air pushes into the chamber, forcing the water out through openings along the bottom of the chamber, which results in the water level rising. Once the water has reached the desired level, the air supply valve is closed, and the air release valve remains closed, holding the air in the chamber so the water level stays up.

Plasma Water Table Air with release valve closed

To lower the water level, the release valve is opened while the supply valve remains closed, allowing the air to escape from the chamber. The weight of the water causes it to flow back into the chamber, pushing the air out through the exhaust.

Plasma Water Table Air with release valve open

Underwater Plasma Cutting

The primary reason for using this type of table is for underwater plasma cutting. Depending on the torch design and vintage, you may be able to submerge the torch and cut successfully without any additional hardware. However, most new Oxygen plasma cutting systems with precision plasma capability will require an air-curtain that clamps onto the torch. The air-curtain uses compressed air to create a bubble around the front end of the torch so that the precision arc is protected from the water. Some plasma torches are not designed for use underwater but may still be used to cut a plate that is sitting above the water.

For larger tables, even if you do not ever plan to cut underwater, a water table with water level control is recommended. This allows the water level to be lowered for easier access to clean out small parts that drop between the burning bars.

Oxy-Fuel Cutting on a Water Table

The standard water table with water level control is designed to be used for both plasma and oxy-fuel cutting. When oxy-fuel cutting, the water cannot be above the plate surface, but it can be very close to the bottom of the plate. Also, there must be at least an inch of water depth above the tray under the burning bars, to protect it from damage by the molten metal spray of the oxy-fuel cutting process.

Depending on material type, thickness, and quality requirements, some users prefer to cut with the water closer to the plate, so that the splashing water helps cool the part while cutting, reducing overall heat distortion. Other users want to avoid quenching of the slag that occurs, and therefore prefer to have the water level as far below the plate as possible.

So, whether you are plasma or oxy-fuel cutting, a water table is a simple and affordable alternative to a downdraft table.