Supersonic Spraying Technology

In China, High Velocity Oxygen Fuel (HVOF) spraying is commonly referred to as supersonic flame spraying. This technique is gradually replacing plasma spraying and other spraying processes, becoming an important method in thermal spraying.

Principle:
High-velocity oxygen Fuel (HVOF) spraying involves the continuous combustion of an oxidizing gas and fuel gas in a combustion chamber. The combustion generates high pressure in the chamber, and through the expansion nozzle connected to the chamber's exit, a high-speed flame is produced. The spraying material is injected into this high-speed jet, where it is heated and accelerated before being sprayed onto the pretreated substrate surface to form a coating.

Coating and Process Characteristics:
The HVOF spraying process, due to its distinct characteristics (extremely high flame velocity and relatively low temperature), results in coatings and spraying processes with several features:
1. High Flame and Particle Velocity: The flame speed exceeds 1800 m/s, and particle velocity ranges from 300 to 650 m/s.
2. Uniform Powder Heating: Powder is injected axially or radially into the combustion chamber, allowing the powder to remain in the flame for a relatively long time, ensuring full melting and producing a concentrated spray stream.
3. High Particle Flight Speed and Short Contact Time with Air: The flying powder particles have a high speed and limited interaction with the surrounding atmosphere, minimizing the reaction with air. This reduces the loss of active elements in the spraying material, which is particularly beneficial for carbide materials, preventing decomposition and decarburization.
4. Fine Powder and Smooth Coating: The powder size used in HVOF spraying generally ranges from 10 to 45 μm, which is considered fine powder. The high particle speed and full melting during spraying result in good deformation of the coating, leading to a smooth surface with low roughness.
5. Dense Coating with High Bond Strength: Typically, the porosity of an HVOF coating is less than 2%, and the bond strength exceeds 70 MPa.