Plasma Processes

Plasma Processes

Conventional plasma spray, commonly referred to as atmospheric plasma spray (APS), is the most versatile method for applying thermal spray coatings. The plasma arc that gives the process its name, is generated in the torch by superheating inert gas in a DC arc. The plasma temperatures in the powder heating region can range from about 6,000-20,000°C (11,000-36,000°F), which is more than the melting range of most substances. This makes it a great choice for ceramics and other materials that have high melting points.

See our Solution

How Plasma Spray Works

How Plasma Spray Works

The plasma spray process begins when the control console sends regulated inert gas (usually argon) to the rear of the plasma torch (SG100). The arc gas then flows through the gas injector and into the arc chamber, which consists of an axially aligned tungsten cathode and copper anode. Depending on process parameters, the configuration of the gas injector will impart a laminar or vortex flow to the gas. Once the gas is flowing, the control console then signals for water cooling to the torch. While the tungsten cathode can operate near its melting point, the plasma torch is water-cooled to minimize cathode and anode erosion, as well as preventing the torch from melting down. Next, a DC arc is struck between the cathode and anode by a high-frequency generator and then maintained by a DC power supply. As the inert gas passes through the arc, it expands rapidly, reaching temperatures that are much higher than those created by other thermal spray processes. Additionally, a secondary gas (helium, nitrogen, or hydrogen) is introduced to the arc gas, providing a significant energy boost to the plasma stream. This expansion of gas accelerates through the anode and causes the plasma jet to become subsonic or supersonic depending on the torch configuration. The supersonic expansion increases particle velocity, while subsonic velocities slow particle velocity and increase particle dwell time. The coating material, in the form of powder, is then metered out by a powder feeder and carried to the torch in suspension via a carrier gas. It is then injected into the plasma jet where it is softened and propelled onto the workpiece, causing a high integrity coating, with excellent bonding.

Plasma Torch Nomenclature

  1. Powder and carrier gas
  2. DC Power (+) and water outlet
  3. DC Power (-) and water inlet
  4. Arc Gas
  5. Cathode
  6. Anode

Where Plasma Spray Excels

Chrome Oxide Sprayed with SG-100 Torch

Where Plasma Spray Excels

Having the ability to control the many facets of the plasma spray process, gives this process the ability to not only spray a wide range of materials, from metallics to ceramics but also allows them to be sprayed on virtually any material. With minimal coating distortion, both large and small components can be thermally sprayed. Once parameters are established, the plasma torch can run for hours without stopping. Making this process ideal for long runs, as the material can be applied nearly continuously. The high degree of melting and particle velocity yields higher deposit densities and bond strengths than both flame and electric arc. Making plasma coatings perfect for protection and refinishing applications.

  • Coatings are dense, with good adhesion
  • Has the ability to spray a wide range of materials
  • Can spray ceramics efficiently
  • Can virtually run continuously, minus maintenance
  • Has lower oxide content and porosity than flame and electric arc
  • Minimal substrate distortion on both small and large components
  • Sprayed substrates can be made from a variety of materials, such as plastics, metals, and ceramics
  • Build-up can be from a few micrometers thick to a few millimeters

Plasma Spray Applications

Plasma Spray Applications

Thermach thermal spray equipment is a smart, reliable choice for coatings, in the factory and in the field. Here are the applications where Plasma Spray is typically used.

  • Corrosion Protection
  • Wear Resistance
  • Heat and Oxidation Resistance
  • Inert chemical resistance
  • Thermal Barriers
  • Electrical Resistivity and conductivity
  • Anti-galling
  • Part Restoration
  • Aerospace
  • Automotive
  • Biomedical
  • Chemical
  • Electronics
  • Marine
  • Industrial