Thermal Spraying - Advantages,Applications,Disadvantages

 

What is Thermal spraying ?

Thermal Spraying metal coatings are depositions of metal which has been melted immediately prior to projection onto the substrate.

Thermal Spraying covers a wide range of techniques in which material is heated rapidly on a hot gaseous medium and simultaneously projected at high velocity onto a surface, to produce a coating.

The range of alloys that can be sprayed is immense based mainly on Nickel, Cobalt, Aluminum and Iron but containing elements as diverse as boron, molybdenum and tungsten in fact it would be true to say that an alloy can be provided for almost any application.
Sprayed metal coatings have been used for a number of years and exposure tests have proved them to be superior to conventional paint coating.

How is the alloy sprayed ?

The alloy is sprayed via a torch that is connected to a gas source such as oxygen and acetylene.
The delivery system of the torch is dependant on its manufacturer, however two main methods are employed:

• Micro-pulverised alloy powder purchased in containers that fits onto the torch

• Alloy in wire form that is either ground by the torch and fed into the flame or simply atomised in the flame itself

What materials can be coated ?

Almost all metals can be coated sometimes with a thickness' of as much as 25mm although cost would prohibit thick coatings on large components. Here is a list of some of the materials that can be coated.

• Carbon Steels including tool steels such as D3,D2,O1 etc.
• Stainless Steels
• Titanium
• Cast Irons
• Cast Steels
• Certain Bronzes and Brasses
• Certain Magnesium Alloys

Applications

• Enhance wear and/or corrosion resistance
• Provide specific frictional characteristics to the surface
• Use for dimensional restoration
• Uses as thermal barrier, thermal conductor, electrical conductor or resistor
• Uses as electromagnetical shielding, enhance or retard of radiation

 Advantages

• Extremely wide variety of materials that can be used to make a coating
• Ability of most of the thermal spray processes to apply a coating substrate without significantly heating
• Ability to strip or recoat worn or damaged coatings without changing the properties or dimensions of the part
• Very cost effective especially on large components with small wear areas
• Ideal in breakdown situations where spare parts are unavailable
• High deposition rates.
• Low substrate heating.
• Less expensive to operate.

Disadvantages

1.  Line-of-sight nature of these processes. They can only coat what the torch or gun can see.
2. Size limitations prohibiting the coating of small, deep cavities into which a torch or gun will not fit.