Thermal spraying is a surface engineering technique that improves or restores the surface of materials. It involves heating coating material like metal, ceramic, polymer powders and spraying them onto a substrate. There are different thermal spraying processes like plasma spraying, detonation spraying, flame spraying and HVOF. The coating material is pre-heated and accelerated towards the substrate where it forms a layer through solidification. Multiple layers are deposited through repetition to achieve the desired coating thickness. The coated surface may then undergo finishing and post-treatment processes. Thermal spraying provides a versatile and cost-effective solution for applying wear and corrosion resistant coatings in various industries.

1. Course code CME397 Course name Surface Engineering
Year/sem 3/6 Unit no 4
Course Instructor: M.Karthikeyan AP/Mech
Thermal spraying process
Objectives:
Thermal spraying is a technology which improves or restores the surface
of a solid material.
The process can be used to apply coatings to a wide range of materials and
components, to provide resistance to: Wear, erosion, cavitation, corrosion,
abrasion or heat.
Types of thermal spraying process:
 Plasma spraying.
 Detonation spraying.
 Wire arc spraying.
 Flame spraying.
 High velocity oxy-fuel coating spraying (HVOF)
 High velocity air fuel (HVAF)
 Warm spraying.
 Cold spraying.
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2. Coating Material Preparation:
The coating material is typically in the form of powder, wire, or rod.
It can be a wide range of materials including metals, ceramics, polymers, and
composites.
The material is selected based on the desired properties of the coating.
Spray Gun Assembly:
The heart of the thermal spraying process is the spray gun.
It consists of several components including a heat source, a material feeder,
a nozzle, and a gas supply system.
The heat source is usually an oxy-fuel flame, an electric arc, or a plasma arc.
The material feeder precisely delivers the coating material into the heat
source.
Heating of Coating Material:
The coating material is fed into the heat source where it is heated to a molten
or semi-molten state.

3. The exact temperature depends on the material being sprayed and the chosen
spraying method.
Acceleration and Propulsion:
Once heated, the molten or semi-molten material is propelled towards the
substrate to be coated.
This propulsion is typically achieved by compressed air, inert gas, or a
combination of both.
The velocity and trajectory of the particles are controlled to ensure uniform
coating deposition.
Impact and Solidification:
As the heated material particles travel towards the substrate, they impact its
surface.
Upon impact, the particles flatten and spread out, forming a thin layer.
Rapid cooling and solidification occur as the particles lose heat to the
substrate and surrounding environment, resulting in the formation of a solid
coating.
Repetition and Layering:
To achieve the desired coating thickness, the spraying process is repeated
multiple times, building up successive layers of material.
Each layer bonds to the previous one, forming a cohesive coating structure.
Finishing and Post-Treatment:

4. After the coating is applied, it may undergo additional processes such as
machining, grinding, or polishing to achieve the desired surface finish.
Some coatings may also require post-treatment steps such as heat treatment
or sealing to enhance their properties further.
Overall, thermal spraying offers a cost-effective and versatile solution for
applying coatings to a wide range of substrates, making it a popular choice in
industries such as aerospace, automotive, energy, and manufacturing.