The Detonation-Gun uses measured quantities of oxygen, acetylene and particles of a coating material, detonated by a timed spark in the firing chamber. The resultant high-speed gas stream heats up the coating particles to a plastic state and throws them from the gun barrel at supersonic velocity (upto 1200m/s).
This action joins the coating material to the surface of the workpiece with a tenacious mechanical bond. Bond strengths in excess of 10,000 psi are obtained. Coating hardness can go upto 1350 VHN.
Rapid-fire detonations, during automatically controlled passes across the workpiece, build up the coating to a specified thickness. Although temperatures around 3500 ℃ is reached inside the gun, the workpiece remains below 100 ℃, this eliminates the possibility of microstructure changes in precision parts. Also metallurgical properties in the substrate remain unchanged.
This coating has got excellent bond strength, toughness, wear resistance and very less porosity.
Advantages of the Process
Compared to other thermal spray processes D-Gun coating is highly cost effective way to add superior performance qualities to a given substrate and extend product life and increase performance.
- A wide variety of materials can be sprayed on all suitable base materials.
- Dense microstructures with smooth surface finish. Much smoother finish could be obtained after grinding. Coatings feature very high dimensional accuracy.
- Excellent bond strength coatings (highest in any thermal spray variant) and low substrate temperature.
- Controlled residual compressive stress and enhanced fracture toughness.
- Better impact wear / fretting wear and erosion resistance than any other thermal spray coatings.
- Hardness of 68-72 Rockwell hardness could be achieved for the ceramic / carbide coatings.
Coating Powder's Spectrum
| Powder | Coating Hardness, VHN | Operating Temperature ℃ |
Application Field |
| Al2O3 | 1100 | 980 | Heat & wear resistant high temperature protective coatings Ensuring high chemical stability and oxidation resistance. |
| Al2 O3-TiO2 | 950 | 700 | Heat, wear and corrosion resistant coatings. Good sliding wear resistance. |
| WC-Co | 1200 | 560 | High wear-, improved mechanical impact and heat shock - resistance. |
| WC-Co Cr | 1150 | 560 | High wear resistance coupled with corrosion reisistance specially for gas compressor application. |
| WC-Ni | 1100 | 700 | High wear resistance and erosion resistance, impact strength. |
| Cr3C3 - NiCr | 875 | 900 | High wear-resistance at high temperature, corrosion- and erosion-resistance. |
| NiCrAlY | 400 | 1300 | Corrosion resistant bond coat for high temperature applications. |
| CoCrAlY | 400 | 1200 | Corrosion resistant bond coat for high temperature applications. |
| NiCr | 200 | 1350 | Corrosion-and oxidation resistant bond coat for high temp. applications. |
| NiAl | 300 | 1350 | Good oxidation and corrosion resistance properties at high temperatures. Good for general repair & build-up. |
A wide range of powders covering pure metals alloys ceramic oxides, carbides, their blends and composites are readily available for development of coatings based on the need and application
Comparison of properties of D-Gun Coating with respect to other thermal spraying
| Process Name | Flame Temp ℃ | Substrate Temp ℃ | Particle Velocity, m/s. | Porosity,% | Bond Strength (PSI) | Oxide Content % |
| Detonation Gun | 3890 | 40-100 | Up to 1200 | 0.1 - 1.0 | Extremely high | 0.1 |
| HVOF | 2500-3100 | 100-300 | 500-1000 | 1.0 - 2.0 | Very high | 0.2 |
| Plasma Spray | 5500-8300 | 100-400 | 200-600 | 1.0 - 10.0 | Very high | 0.1 - 1.0 |
| Wire ARC | 4000-6000 | 500-800 | 240 | 10 - 20.0 | High | 0.5 - 3.0 |
| Flame Spray | 2500 | 500-700 | 30-180 | 10 - 30.0 | High | 4 - 6.0 |
Comparison of Hardchrome with DETONATION (D-GUN) Sprayed Ceramic and Carbide Coating
| Properties | Hard Chrome | D-Gun Coated Ceramic coating | D-Gun Coated Carbide coating |
| Surface Hardness | Max. 60Rc | 980 - 1020 VHN (69 Rc) | 1150 - 1250 VHN (72 Rc) |
| Temperature of Operation during service | 180 ℃ | Up to 800 ℃ | Up to 540 ℃ for Tunsten Carbide Upto 900C for Chromium Carbide |
| Chemical Stability | Good | Excellent, due to the inert nature of ceramic material. | Good |
| Bond Strength | 2500psi (Electro deposition technique) | 5500psi Very high velocity thermal spray coating technique. (D-Gun has the highest bond strength of all thermal spray processes in ceramic coating) | Excess of 10,000 psi (highest bond strength coatings among all thermal spray variants) |
| Surface Roughness (Ra) | Smooth and metallic finish. | Ceramic coating can match the Ra of hard chrome. 0.4 m Ra can be obtained | 0.15 m Ra and even less with lapping can be obtained. Excellent metallic finish. |
| Scratch Resistance | OK but does not have abrasion resistance. | Excellent due to very high hardness retention and has very good abrasion resistance. | Excellent abrasion resistance. |
| Impact resistance | Very low | Not good as it can take only mild loads hit directly | Very good due to the metallic nature of the bonding material and high bond strength. |
| Chances of "Peel Out" of coated layer | Yes - during service | No due to high bonding. Ceramic coating only wears out over a period of time and does not peel out unlike hard chrome coatings. | No chance of a peel out during service due to extremely high bonding. |