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ASPN - Active Screen Plasma Nitriding

In addition to Carburizing and coatings, Nitriding has developed into a process that will be desired long into the future.

The most important nitriding technologies of today are

  • Salt bath nitriding
  • Gas nitriding
  • DC plasma nitriding (DCPN)

Each of these processes is in use today, but having its individual strength and weakness, as shown in the diagram below. Gas Nitriding has a current market share of about 75% and is the dominate technology.

The market share of the DCPN technology is constantly growing due to improved safety and environmental impact. Gas nitriding needs ammonia as a process media and this is quite often forbidden to use in production areas. This process (gas nitriding) also produces hazardous-gas byproducts which cannot be allowed to escape to the atmosphere or work area. Plasma nitriding completely eliminates these issues as it works with a safe nitrogen gas.

The DCPN process also has limitations which are mainly based on the effects resulting from the formation of an electrical field, as:

  • Hollow-cathode effect: When parts are placed very close together or if they contain deep holes of small diameter, the overall discharge current can increase so much so that local melting takes place -> very stringent distances between the parts have to be respected, small holes have to be plugged, proper loading is an issue
  • Arcing: Can produce very high local temperatures and cause localized melting and/or sputtering of material from this point on the surface. This effect could happen by organic degassing in a localized area of a component's surface, by the presence of non-metallic inclusion in the work piece material -> a perfect degreasing of the parts is needed

  • “Edge effect” with components containing sharp corners or of complex geometries, can cause different nitriding effects and brittleness risk
  • Temperature control and uniformity: Is an issue to treat components with different cross sections and does not allow to run mixed loads with different part sizes and geometries

The ASPN technology avoids all of these obstacles and issues. The active screen acts as a radiation heater and as there is no direct glow discharge at the component, there is no overheating happening and any effect caused by the electrical field is eliminated. This enables proper temperature control and uniformity and allows mixing of parts with different dimensions with the same time - which increases the process efficiency [up to 50% more load density]. Even bulk loads can be treated uniformly and efficiently which is not possible with the DCPN process.

A further exciting possibility is the use of the ASPN technology is to nitride non-conductive materials such as rubber or polymers.

The principles of a DCPN and an ASPN furnace are shown in the next two pictures.

Direct Current Plasma Nitriding

Active Screen Plasma Nitriding

Load examples for ASPN Plasma Nitriding

Gear wheels

Piles of flanges

Mixed Load

Piston rings

Piston rings

For more information about the ASPN Technology please see Opens external link in new windowhttp://www.plasma-metal.lu