Water or downdraft: Controlling fumes during plasma cutting

By Hypertherm
Posted on 08/10/2017 in SPARK the blog, Plasma cutting

Controlling fumes while plasma cutting inside is critical. When using a CNC table you have two choices: water or downdraft. Each has plusses and minuses that should be considered when choosing between the two. Let's start with water.

On a small machine, which we’ll define as any table smaller than 5 by 10 feet, a water based fume control system can consist of a simple tray or pan, about 4 to 10 inches deep that holds water. You can choose to have your water level high so it touches the bottom of the plate being cut, or you can lower the level to leave a few inches between the water and your plate. This is the cheapest, easiest way to trap particulates from the cutting process. However, if you own a larger table, you’ll likely want to opt for a more complex water table design with deeper tanks, removable slat assemblies, and pneumatically controlled mechanisms to help control the water level.

WATER ADVANTAGES

WATER DISADVANTAGES 

  • Very good fume control
  • Less warpage and camber on thin plate and parts
  • Better edge metallurgy on some stainless steel parts
  • Rust will get on slats, plate, and machine components
  • Edge roughness and increased dross if water splashes on part being cut
  • Less productive as slower cutting speeds are needed
  • Difficult to clean table, especially if you let it go more than week
  • Water in unheated shops / cold areas will freeze

When it comes to downdraft tables, the simplest systems close in the area underneath the cutting table slats to create a chamber. A fan or blower then sucks out these trapped fumes, sending them to the outside or into a filtering devise. On an entry level 4 x 4 cutting machine, air flow of about 3,200 to 3,600 cubic feet per minute is required to effectively remove fumes from a 100 amp or smaller plasma system. More complex systems, like those on larger industrial tables, often use zoned systems with a series of mechanical dampers that draw fumes only from the area being cut. There are also downdraft tables with relatively complex self-cleaning features such as chain driven blades at the bottom of the chamber. These blades work to drag the slag and droppings to one end of the table, making cleaning easier.

DOWNDRAFT ADVANTAGES

DOWNDRAFT DISADVANTAGES

  • Better cut quality on steel
  • Rust not an issue
  • No water to freeze
  • Low cost provided you don’t need a filtering device and can simply blow the fumes outside
  • Easier to clean
  • Blowers used to collect fumes will suck out the hot and cold air in your shop; a real problem for those in hot and cold climates
  • More expensive if you need a zoned system or filtration devise

This post is only meant to provide a general overview of fume extraction options. For advice tailored to your particular situation, we strongly recommend contacting an authorized Hypertherm channel partner.