What is thermal spraying?

Where the health risks of welding have been extensively described, thermal spraying is an underexposed activity. While this way of working may involve similar risks. A triptych about these activities with attention to exposure and health risks. Part one briefly explains what thermal spraying is.

Kick and kick

Thermal spraying is a very long-standing process developed in the early 1912s by Dr. MU Schoop and his colleagues. The process was patented in XNUMX. In the XNUMXs and XNUMXs, various techniques were developed with which coatings can be applied to materials via thermal spraying. It is also called in the Netherlands kicking .

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Image by vinayr16 from Pixabay

Molten material

In thermal spraying, adding a topcoat to a substrate by spraying a molten material onto that substrate at high speed. Melting of the material can be done in different ways (flame, welding arc, plasma). The material to be sprayed is powder or a wire that is heated to the melting point. The molten particles are sprayed by means of compressed air or oxygen to the substrate where they solidify again into an adhesive layer. An advantage is that the substrate can remain relatively cool and there is therefore no chance of deformation.

With thermal spraying, a coating is built up layer by layer. The syringe moves with respect to the substrate. This can be done manually, with a sprayer moving the sprayer over the surface, but can also be automated. Then it is usually carried out by a robotic arm.

Different processes

Applied thermal spraying processes are:

ProcessTypeDescriptionSpecific process
Spray warmFlame sprayingheating by combustion of a fuel-oxygen mixtureautogenous wire spraying
   autogenous powder spraying
   explosive spray
   High Velocity Oxy Fuel Coating Spraying (HVOF)1
 Electric sprayingenergy derived from electrical energy usually through an arc dischargeelectric wire spraying
 Plasma sprayingheating by arc, with gas injectionPlasma spraying2  
   low pressure plasma spraying
Spray coldCold Spray or Gas Dynamic Spray (GDS)  small metal powder particles are accelerated to speeds of up to 600 m / s, causing them to deform plastically on impact and cause adhesion.3   

1 With HVOF, a mixture of gas or liquid together with oxygen and the powder is fed into a combustion chamber. The heat partially melts the powder and is thus sprayed onto a surface
2 Gas is brought to such a high temperature that it ionizes and becomes electrically conductive. This allows the spraying of almost any metal or ceramic on a wide variety of materials with exceptional bond strength and minimal substrate deformation.
3 During this process, the substrate does not get warmer than 90⁰C, so that no deformation or structural change occurs.

Materials and sectors

A recent systematic review (Antonini et al. 2020) provides an overview of the materials that are melted to apply a coating. The different techniques that are used are discussed in detail in the article.

MaterialCharacteristicsComposition
Pure metalsCorrosion protection, electrical conduction, heat conductionZn, Cu, Ti, Al
SteelResistance to wear, economicalFe 35N 20Cr 2Si, Fe 28Cr 5C 1Mn, Fe 13Cr
Complex connectionHigh temperature, corrosion protectionNiCoCrAlY, NiCrAlY, CoCrAlY
Self fluxing alloysGreat hardness, strong bond, wear resistanceNiCrBSiC, NiCoCrBSiC
CarbidesWear and erosion protectionWC 12Ni, WC 10Ni 5Cr
OxidesHigh hardness, resistant to rust / oxidation and wearAl2O3, Cr2O3

Sectors in which thermal spraying is used include:

  • Automotive industry,
  • production of gas and other energy turbines,
  • production of orthopedic implants,
  • aircraft industry,
  • production of machines,
  • production of machine parts such as rollers, rollers, electronic sensors and antennas,
  • consumer goods such as pans, steel plates etc.

Sources

https://nl.wikipedia.org/wiki/Thermisch_spuiten

Antonini, JM, McKinney, WG, Lee, EG, & Afshari, AA (2020). Review of the physicochemical properties and associated health effects of aerosols generated during thermal spray coating processesToxicology and Industrial Health, 0748233720977975. (abstract only)

The following articles deal with exposure to thermal spraying and the health risks

Read also

Exposure to thermal spraying

Thermal spraying and health risks