What are the 3 methods of thermal spraying?
Most industrial buyers search "thermal spraying methods" when they face severe wear problems. They find HVOF, plasma spray, and arc spray on Google, compare three options, and assume one of them fits their cement mill, crusher liner, or chute application. Then they contact me, describe high-impact abrasion conditions, and ask for a plasma spraying machine quote—without realizing they just described a fusion-bonding requirement, not a thermal spray application.
Thermal spraying has three main methods: HVOF (High-Velocity Oxygen Fuel), plasma spraying, and arc spraying. All three create coatings through mechanical bonding. However, for high-wear industrial applications involving impact and abrasion, these methods often fail to meet performance requirements because mechanical bonding lacks the bond strength and wear life that fusion-based processes like hardfacing, plasma transferred arc, and laser cladding provide.
If you searched this question because you need to extend wear life on crusher parts, mill liners, or bulk handling equipment, this article will help you understand why thermal spraying may not solve your problem—and which surface engineering process category actually matches your wear environment and cost expectations. I have handled hundreds of inquiries where buyers confused process terminology, purchased wrong equipment, or selected coatings that delaminated within weeks because they optimized within the wrong process category.
What is thermal spraying and how does it actually work?
Thermal spraying is a coating process. You heat powder or wire material to a molten or semi-molten state, then accelerate particles through a spray gun and deposit them onto a base surface. The particles hit the surface, flatten, cool, and stack into a coating layer. This is called mechanical bonding because the coating locks onto surface roughness rather than fusing into the base metal microstructure.
Thermal spraying creates coatings by mechanically locking molten particles onto roughened surfaces. The bond depends on surface preparation and particle impact velocity, not metallurgical fusion. This bonding mechanism limits coating performance under impact, thermal cycling, and high-stress wear conditions.
The key limitation is bond strength. When I explain this to customers, I use a simple analogy: imagine stacking wet sand on a rough concrete surface versus melting metal into the concrete structure. Thermal spraying is the wet sand model. If you apply shear force, thermal shock, or repeated impact, the coating can separate from the base because there is no atomic-level connection between coating and substrate. For aerospace turbine blades or electronics heat sinks, this is acceptable because those applications avoid impact loading. For cement plant chutes, mining conveyor parts, or crusher wear plates, mechanical bonding creates a failure risk that most procurement teams do not anticipate when they search "thermal spraying methods" and assume it solves abrasion problems.
Thermal spraying also requires strict surface preparation. You must grit blast the base metal to create anchor profile, control surface cleanliness, and deposit coating immediately after preparation to avoid oxidation. Any contamination, inadequate roughness, or delayed spraying reduces bond quality. I have seen customers receive thermal spray quotes from suppliers who skip these preparation requirements, then wonder why coatings flake off during installation or within the first maintenance cycle.
What are the 3 main thermal spraying methods and when do they actually fit industrial wear applications?
When buyers search "3 methods of thermal spraying," they usually find HVOF, plasma spraying, and arc spraying. Each method uses different heat sources and particle velocities, which affect coating density, bond strength, and cost. However, the real question is not which thermal spraying method is best, but whether thermal spraying is the right process category for your wear condition.
The three main thermal spraying methods are HVOF (High-Velocity Oxygen Fuel), plasma spraying, and arc spraying. HVOF delivers the highest particle velocity and densest coatings. Plasma spraying offers the widest material compatibility. Arc spraying provides the lowest cost per kilogram deposited but lower coating quality.
HVOF (High-Velocity Oxygen Fuel) spraying
HVOF spraying uses a combustion chamber where fuel gas and oxygen burn at high pressure. The combustion accelerates powder particles to velocities between 400 and 800 meters per second. High velocity creates dense coatings with low porosity and strong mechanical bonding. HVOF is the premium thermal spraying method. It produces the best coating quality within the thermal spray category.
Industries use HVOF for aerospace engine components, oil and gas valve seats, paper mill calendar rolls, and pump shafts. These applications need corrosion resistance, moderate wear resistance, and dimensional restoration without excessive heat input into the base material. However, HVOF coatings still rely on mechanical bonding. When you introduce impact loading or flexural stress, coatings can still delaminate because there is no metallurgical fusion with the substrate.
Cost is another consideration. HVOF equipment requires high fuel consumption, expensive powder feedstock, and controlled spray environments. When I receive inquiries from cement plants or mining operations asking for HVOF quotes on large wear surfaces like mill liners or chute sections, I redirect the conversation toward hardfacing or plasma transferred arc cladding because the cost and performance trade-off does not favor HVOF in those applications. HVOF may deliver 0.3 to 0.5 millimeters of coating per pass, while hardfacing can deposit 3 to 6 millimeters of metallurgically bonded hard material in fewer passes with better impact resistance.
Plasma spraying (thermal spray, not plasma hardfacing)
Plasma spraying uses an electric arc to ionize gas into plasma. The plasma reaches temperatures between 8,000 and 15,000 degrees Celsius, which melts powder particles as they pass through the plasma jet. The molten particles deposit onto the substrate and form a coating. Plasma spraying can handle a wide range of materials, including ceramics, carbides, and refractory metals that other thermal spray methods cannot process.
This method is common in thermal barrier coatings for gas turbines, biomedical implant surfaces, and electronics thermal management. However, plasma spraying produces coatings with higher porosity than HVOF. The lower particle velocity means weaker mechanical bonding. For high-wear industrial applications, plasma spraying rarely meets performance requirements because porosity creates weak points under abrasive particle penetration and impact creates coating separation at the bond interface.
The terminology confusion happens here. Many buyers search "plasma spraying" when they actually need plasma transferred arc (PTA) hardfacing. These are completely different processes. Plasma spraying creates mechanical bonding and deposits coatings 0.1 to 0.5 millimeters thick. PTA hardfacing creates metallurgical bonding and deposits hard layers 1 to 5 millimeters thick with fusion into the base material. When customers send me RFQs asking for "plasma spraying equipment" but describe crusher liner repair or mill shell protection, I know they need PTA hardfacing systems, not thermal spray equipment. The performance gap between these two processes is the difference between a coating that lasts two weeks and a hardfacing layer that lasts two years under the same wear conditions.
Arc spraying
Arc spraying uses two conductive wires as electrodes. An electric arc melts the wire tips, and compressed air atomizes the molten metal and propels droplets onto the surface. This method is the simplest and cheapest thermal spraying option. It requires low equipment cost, uses inexpensive wire feedstock, and achieves high deposition rates.
Arc spraying is widely used for corrosion protection on bridges, storage tanks, and structural steel. The coating quality is lower than HVOF or plasma spraying. Arc spray coatings have high porosity, rough surface finish, and weak bonding strength. For wear applications, arc spraying rarely performs well because porosity accelerates abrasive wear and weak bonding allows coating loss under sliding or impact conditions.
When buyers contact me asking for arc spraying solutions on cement mill internals or crusher wear parts, I explain that arc spraying will not survive the wear environment. The cost advantage disappears when coatings fail within the first month of operation and require recoating or replacement. In those cases, hardfacing with flux-cored arc welding or submerged arc welding delivers better wear life, stronger bonding, and lower lifecycle cost even though initial deposition cost is higher.
| Method | Particle Velocity | Coating Density | Bond Strength | Material Range | Typical Application |
|---|---|---|---|---|---|
| HVOF | 400-800 m/s | High | Highest in thermal spray | Metals, carbides | Aerospace, pump shafts, valve seats |
| Plasma Spraying | 100-300 m/s | Medium | Medium | Metals, ceramics, carbides | Thermal barriers, biomedical coatings |
| Arc Spraying | 100-150 m/s | Low | Lowest in thermal spray | Conductive metals | Corrosion protection, structural steel |
Why do buyers confuse thermal spraying with hardfacing and cladding processes?
The confusion comes from terminology overlap and search engine results. When buyers search "plasma spraying," Google returns results for both plasma thermal spraying and plasma transferred arc hardfacing. When they search "overlay coating," results include both thermal spray overlays and weld overlay hardfacing. The terms sound similar, but the bonding mechanisms, performance ranges, and equipment requirements are completely different.
Buyers confuse thermal spraying with hardfacing because search results mix both process categories and use similar terminology. However, thermal spraying creates mechanical bonding while hardfacing creates metallurgical fusion. This bonding difference determines whether coatings survive impact, thermal cycling, and high-stress abrasion in real industrial wear conditions.
I see this confusion pattern every week. A procurement manager from a cement plant sends an inquiry asking for "plasma spraying equipment" to repair kiln tires or mill liners. The RFQ description includes high-impact abrasion, thermal cycling between 200 and 400 degrees Celsius, and material removal rates measured in millimeters per month. These are hardfacing conditions, not thermal spray conditions. When I respond explaining the difference between plasma spraying and PTA hardfacing, many buyers realize they used the wrong search term and that their previous thermal spray attempts failed because they selected equipment and processes that could never meet their performance requirements.
The second confusion point is bond strength. Thermal spraying relies on mechanical interlocking between coating and roughened substrate. Hardfacing and cladding rely on metallurgical fusion where the deposited material melts into the base metal and forms a metallurgical bond through shared microstructure. Under impact loading, mechanical bonds can fail through shear or peeling. Metallurgical bonds resist these failure modes because the coating and substrate are metallurgically continuous. This is why crusher liners, mill liners, chute plates, and conveyor components use hardfacing, not thermal spraying.
The third confusion point is deposit thickness. Thermal spraying typically deposits coatings between 0.05 and 0.5 millimeters thick. Hardfacing deposits layers between 1 and 10 millimeters thick. When wear rates exceed 1 millimeter per year, thermal spray coatings cannot provide sufficient material reserve. Buyers who do not understand this thickness difference purchase thermal spray equipment, deposit thin coatings, and then contact suppliers complaining about premature coating failure without realizing they selected a process category that was never designed for their wear rate.
When should you choose fusion-based cladding instead of thermal spraying?
If your application involves impact loading, abrasive wear with particle sizes larger than 1 millimeter, thermal cycling, or flexural stress, you should evaluate fusion-based processes first. Fusion-based processes include hardfacing (FCAW, GMAW, SAW), plasma transferred arc cladding, and laser cladding. All these processes create metallurgical bonding by melting deposited material into the base metal.
You should choose fusion-based cladding over thermal spraying when your application includes impact loading, high abrasive wear rates, thermal cycling, or requires deposit thickness greater than 1 millimeter. Fusion bonding delivers higher bond strength, thicker deposits, and better resistance to delamination under severe wear conditions.
At HALDEN, we supply hardfacing machines, plasma transferred arc systems, and laser cladding equipment specifically because most industrial wear applications require fusion bonding, not mechanical bonding. When customers describe wear conditions on cement mill liners, crusher jaws, coal pulverizer rings, or steel plant transfer chutes, the wear mechanisms almost always include impact and high-stress abrasion. Thermal spraying cannot survive these conditions. Even HVOF coatings, which deliver the best mechanical bonding within thermal spray, will delaminate under repeated impact because mechanical bonds cannot absorb impact energy without separation.
Hardfacing with flux-cored arc welding allows deposit thickness between 3 and 10 millimeters. This provides sufficient material reserve for applications where wear rates reach 1 to 3 millimeters per year. Plasma transferred arc cladding delivers dense, metallurgically bonded deposits between 1 and 5 millimeters thick with minimal dilution and heat input. Laser cladding offers precise, low-heat-input fusion bonding for high-value components where dimensional tolerance and minimal base metal distortion are critical.
The cost comparison also favors fusion processes when lifecycle cost is considered. Thermal spraying may have lower cost per kilogram deposited, but if coatings fail within months and require recoating every maintenance cycle, total cost escalates quickly. Hardfacing deposits last years, not months, under the same wear conditions. When I help customers calculate lifecycle cost, hardfacing usually delivers 50% to 70% lower total cost compared to repeated thermal spray recoating cycles over a five-year operating period.
| Decision Factor | Thermal Spraying | Fusion-Based Cladding |
|---|---|---|
| Bonding Mechanism | Mechanical | Metallurgical |
| Typical Deposit Thickness | 0.05 - 0.5 mm | 1 - 10 mm |
| Impact Resistance | Low | High |
| Thermal Cycling Resistance | Low | High |
| Abrasive Wear Resistance | Moderate | High |
| Best For | Light wear, corrosion, dimensional restoration | Heavy abrasion, impact, high wear rates |
Conclusion
Thermal spraying has three main methods, but for most high-wear industrial applications, the real decision is not which thermal spraying method to choose—it is whether thermal spraying is the right process category at all. If your wear environment includes impact, abrasion, or thermal cycling, fusion-based processes like hardfacing and cladding will deliver better performance, longer service life, and lower lifecycle cost.
