Thermal Spray Nozzle with Diverging Means for Oxidation Control
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Solution Overview
Problem
High velocity oxygen fuel (HVOF) thermal spray guns face issues with oxidation of powdered materials, reduced spraying accuracy due to radial particle deflection, nozzle erosion, and inability to coat internal surfaces efficiently due to the need for a long barrel and small particle dispersal.
Innovation Solution
A nozzle design with a diverging means that extends outside the combustion chamber, creating a divergence in the combustion gas stream to introduce coating material downstream, reducing oxidation risk and eliminating the need for a barrel, allowing for stable supersonic jets and precise coating of internal surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If powder is injected into the centre of the combustion chamber, then heating occurs, but oxidation of the powdered material occurs
Solution Approach 1:
The combustion chamber is segmented into distinct zones: a combustion zone where fuel burns, a diverging means that creates separated gas streams, and a coating material inlet that introduces powder into the diverged streams. This segmentation allows the powder to be heated by combustion gases without direct contact with the fuel-air mixture, preventing oxidation while maintaining heating effectiveness.
Solution Approach 2:
The diverging means acts as an intermediary structure between the combustion zone and the powder injection point. It creates a divergence in the combustion gas stream, allowing the powder to be introduced into the diverged streams rather than the centre of the combustion chamber. This intermediary structure enables thermal heating while preventing direct exposure to oxidizing conditions.
2Object-affected harmful factors
If powder is injected into the stream of supersonic gases, then oxidation is avoided, but radial particle deflection occurs reducing spraying accuracy
Solution Approach 1:
The diverging means creates different flow conditions in different regions: the divergence region provides axial flow separation that reduces radial deflection, while the coating material inlet provides localized powder introduction into the diverged streams. This local quality modification allows particles to maintain axial trajectory and improve spraying accuracy while avoiding oxidation.
3Temperature
If a long barrel is used to maintain high gas temperatures for sufficient particle heating, then heating is adequate, but the device cannot coat internal surfaces of large components
Solution Approach 1:
The barrel section is extracted/eliminated from the traditional HVOF nozzle design. Instead of using a long barrel to maintain temperature, the invention uses a combustion chamber with a diverging means that creates sustained high-temperature zones without requiring a lengthy barrel. This extraction allows the nozzle to be compact enough to reach internal surfaces while maintaining adequate heating through the diverged gas stream geometry.
4Quantity of substance
If small particles are used, then coating material can be applied, but particles disperse in the gas field and rebound or never reach the article
Solution Approach 1:
The diverging means creates a divergence in the gas stream before the powder is introduced. This preliminary action of creating flow separation and reduction in gas velocity at the divergence point helps contain smaller particles within the gas stream, preventing them from dispersing and rebounding. The powder is introduced into the diverged streams where the reduced velocity and altered flow pattern improve particle delivery accuracy to the substrate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances axial velocity and temperature stability, reduces particle deflection, extends nozzle lifespan, and enables efficient coating of smaller particles, improving deposition efficiency and reducing oxidation, allowing for precise application of coatings to previously inaccessible surfaces.
Implementation Method 1
diverging means, located at least partially within said combustion chamber, for creating a divergence in said stream of combustion gases thereby creating a plurality of streams or an annular stream before converging to a single stream
Implementation Method 2
combustion of the fuel takes place in the combustion chamber and combustion gases expand and pass through a convergent-divergent restriction 16 and on through a barrel 18 before exiting through an exhaust 20
Implementation Method 3
the powdered material must be injected into the stream of supersonic gases
Implementation Method 4
When the rate of flow of combusted gases and powder particles accelerates to supersonic velocities
Implementation Method 5
The shock wave diamonds result in a loss of temperature and expansion on exiting the barrel increases the temperature loss
Implementation Method 6
diverging means extends at least partially outside said combustion chamber through said exhaust
Data Source
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AI summary
A nozzle for a thermal spray gun and a method of thermal spraying are disclosed. The nozzle has a combustion chamber within which fuel is burned to produce a stream of combustion gases. The streams of heated gases exit through a pair of linear exhausts which are located on either side of an aerospike. The streams converge outside the nozzle and powdered coating material is introduced into the converging streams immediately downstream of the aerospike. The coating material is heated and accelerated before impacting on a substrate to be coated.