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Spraying equipment SPRAY EQUIPMENT
Combustion chamber
The combustion chamber of a supersonic spray system is the core component of the equipment. Its function is to generate a high-temperature, high-pressure gas flow—whose velocity can exceed 2,000 m/s—through the intense combustion of fuel and oxygen, thereby accelerating the spray material to supersonic speeds. Due to its prolonged exposure to extreme conditions—including temperatures exceeding 2,000°C, pressures in the megapascal range, and high-speed particle erosion—the combustion chamber has become one of the most vulnerable components in supersonic spray equipment.
Product Description
Supersonic Spray Wear-Resistant Parts — Combustion chamber
The combustion chamber for supersonic spraying is the core component of the equipment. Its function is to generate a high-temperature, high-pressure gas flow—whose velocity can reach—through the intense combustion of fuel and oxygen. 2000 m/s as described above), the spraying material is accelerated to supersonic speeds. Due to prolonged exposure to... Extreme heat ( 2000℃ Above), high pressure (several megapascals), and high-speed particle erosion Under these operating conditions, the combustion chamber becomes one of the most easily damaged components in supersonic spraying equipment. The following will discuss... Structural principles, core materials, failure mechanisms, fault diagnosis, maintenance strategies Analyze across five dimensions.
I. Structural Principles and Core Functions
(1) Structural Design Features
The combustion chamber is typically made of High-temperature alloy substrate and Ceramic lining The component includes key structural elements such as fuel nozzles, oxygen inlets, and powder feed channels. Its design must meet the following requirements:
- Maximizing combustion efficiency : Through the Laval nozzle structure (convergence - expansion type), enabling the combustion flame to reach sonic speed in the throat and achieve supersonic flow (Mach number > 1) at the nozzle exit. 5 ).
- Airflow Stability Control The inner wall roughness needs... ≤Ra0.8μm Avoid airflow disturbances that could cause spray particles to disperse.
- Cooling System Integration Adopting a circular water-cooling channel or an air-cooling structure to ensure that the wall temperature is kept within the material’s tolerance range (e.g., nickel-based alloys). ≤1000℃ ).
(2) Core Features
- Energy conversion
Convert the chemical energy of fuel into high-temperature kinetic energy, providing supersonic acceleration power for spraying materials—for example, the energy released by burning aviation kerosene can raise the flame temperature to... 3000℃ ).
- Particle Heating and Acceleration
The spray powder is heated to a semi-molten state in the combustion chamber (temperature >). 2000℃ ), and accelerated to via a supersonic airflow. 300-650m/s forming a dense coating.
- Process parameter control
By adjusting the fuel / Parameters such as oxygen ratio, powder feed rate, and cooling water flow rate control the bonding strength of the coating. ≥70MPa ) and porosity ( ≤1% ).
II. Core Materials and Selection Criteria
(1) Comparison of Mainstream Materials and Their Performance
|
Material Type |
Typical ingredients |
Temperature resistance limit ( ℃) |
Core Advantages |
Typical application scenarios |
|
Nickel-based superalloy |
Inconel 625 、 Hastelloy X |
1100 |
High-temperature oxidation resistance, thermal fatigue resistance |
Conventional Supersonic Spraying (e.g., Carbon Steel, Stainless Steel) |
|
Ceramic coating |
WC-10Co4Cr、 Al₂O₃-ZrO₂ |
1600 |
High hardness ( 1392HV ) Wear and corrosion resistance |
Spraying hard alloys or corrosion-resistant coatings |
|
Metal-ceramic composite material |
WC-Ni、 Cr₃C₂-NiCr |
1400 |
Combining metallic ductility with ceramic hardness |
High-load, wear-resistant applications (such as mining machinery) |
|
Ultra-high-temperature alloy |
Niobium alloy, molybdenum alloy |
2200 |
Extreme temperature resistance (e.g., in aerospace engine combustion chambers) |
Special high-temperature experimental environment |
(2) Key Factors in Selection
- Temperature matching
- Normal operating conditions (such as spraying) WC-Co Coating: Select nickel-based alloy + Ceramic lining;
- Ultra-high-temperature applications (such as thermal spraying of metal ceramics): Choose niobium alloys or surface coatings. Zirconium dioxide Coating.
- Chemical compatibility
- When spraying fluorine- and chlorine-containing materials: Choose surface coating. Cr₃C₂-NiCr The combustion chamber, designed to prevent corrosion.
- Particle erosion intensity
- Spraying large particles (> 50 μm ) or high-hardness materials (such as tungsten carbide): select WC-10Co4Cr Coating, its porosity ≤1.3% It can withstand high-frequency impacts.
III. Vulnerability Mechanisms and Typical Failure Modes
(1) Vulnerable Core Causes
|
Failure Type |
Mechanism of action |
Typical Scenarios and Representations |
|
Thermal fatigue crack |
The temperature difference between the inner and outer walls of the combustion chamber > 800℃ This leads to uneven thermal expansion and contraction of the material, resulting in radial cracks. |
Frequent start-stop operations of equipment, insufficient cooling water flow rate (< 5L/min ) |
|
High-temperature oxidation corrosion |
Sulfur in fuel ( S ) Chromium in spray coatings Cr ) Reacts with the alloy to form low-melting-point oxides (such as Nickel sulfide Melting point 797℃ ) |
When spraying stainless steel, a black corrosion layer appears on the inner wall. |
|
Mechanical wear |
Supersonic particles (speed > 600m/s ) Continuous scouring of the inner wall leads to material flaking. |
When spraying tungsten carbide powder, grooves appear on the inner lining surface. |
|
Carbon buildup blockage |
Incomplete fuel combustion or residual powder buildup leads to carbon deposits, which in turn affect airflow distribution. |
Spraying efficiency has declined, and the coating exhibits uneven thickness. |
|
Galvanic corrosion |
Contact between different materials (such as nickel-based alloys and ceramic linings) forms a galvanic cell, accelerating corrosion. |
Pitting corrosion has appeared in the areas where the ceramic lining has come loose. |
(2) Typical Failure Modes
- Inner wall wear
- Appearance: The surface exhibits scratches or pits parallel to the airflow direction, with roughness ranging from... Ra 0.8 μm Increase to Ra 3.2 μm The above.
- Reason: The hardness of the spray particles > HV1000 and the powder feeding rate > 40g/min。
- Ceramic lining spalling
- Performance: The coating in localized areas has separated from the substrate, exposing the underlying metal.
- Reason: Insufficient coating adhesion strength (< 70MPa ) or mismatch in thermal expansion coefficients (e.g., the difference between ceramics and nickel-based alloys exceeds 1 × 10⁻⁶/℃ ).
- Cooling channel blockage
- Performance: The cooling water flow rate dropped sharply, and the wall temperature exceeded the material’s temperature tolerance limit (e.g., nickel-based alloys >). 1100℃ ).
- Reason: Sediment or scale buildup in the water reduces heat dissipation efficiency.
IV. Fault Diagnosis and Detection Methods
(1) Appearance and Performance Inspection
- Visual inspection
- Check whether there is any on the inner wall. Cracks, flaking, carbon buildup Does the ceramic lining have chipped edges or discoloration (such as a change from white to dark brown)?
- Check the water temperature at the outlet of the cooling channel; the temperature difference > 15℃ May indicate a blockage.
- Reverse engineering of spray quality
- If the coating appears Combined strength reduction (< 70MPa )、Porosity exceeds the standard (> 2% ) It could be caused by unstable airflow in the combustion chamber or carbon buildup.
- Nondestructive Testing
- Ultrasonic Testing : Detect the depth of cracks on the inner wall (> 2 mm Needs to be replaced);
- Infrared thermal imaging Monitor the wall temperature distribution and identify locally overheated areas (temperature difference > 50℃ ) Requires focused investigation.
(2) Performance Testing
- Combustion Efficiency Test
- Analyze the composition of exhaust gases: CO Content > 1% Indicates incomplete combustion; fuel adjustment required. / Oxygen ratio.
- Airflow Stability Test
- Use a pitot tube to measure the outlet airflow velocity; the fluctuation exceeds... ±5% The inner wall needs to be inspected for wear or carbon buildup.
V. Maintenance Strategies and Lifetime Optimization
(1) Key Points for Daily Maintenance
- Cleaning and Inspection
- After each work session : Using compressed air (pressure) 0.6–0.8 MPa ) Purge the combustion chamber to remove carbon deposits and powder residues;
- Weekly check Use an endoscope to examine the condition of inner wall wear, with particular attention paid to the area around the powder-feed channel inlet.
- Cooling System Maintenance
- Regularly replace the coolant (recommended every... 50 hours), add a corrosion inhibitor (such as sodium nitrite) to prevent scale formation;
- Monitor the cooling water pump pressure; below. 0.3 MPa The filter needs to be cleaned regularly.
- Coating repair
- For areas with mild wear (depth < 1mm ), using supersonic spraying WC-10Co4Cr Coating repair—after repair, the bond strength must be tested. ≥70MPa ) and porosity ( ≤1% ).
(2) Replacement Standards and Installation Specifications
- Replacement conditions
- Inner wall crack length > 10mm or depth > 3mm；
- Area of ceramic lining spalling > 5 cm² ；
- The cooling channel is blocked, causing the wall temperature to continuously exceed the material’s temperature tolerance limit.
- Installation Key Points
- The new combustion chamber needs to be subjected to... Pre-spraying treatment Spray at the inlet of the powder delivery channel. NiAl Transition layer (thickness 50-100 μm ), enhance coating adhesion;
- During installation, ensure that the cooling channels are leak-free; use... O Fluororubber sealing ring (temperature-resistant) - 20~210℃ ), and apply high-temperature grease (such as perfluoropolyether grease).
(3) Life Extension Technology
- Material upgrade
- Replace the nickel-based alloy combustion chamber with a niobium alloy. + WC-17Co Coating, lifespan can be extended 3-5 Double, especially suitable for high-temperature and wear-resistant applications.
- Structural improvement
- Design of the combustion chamber inner wall Flow guide groove Reduce wear in areas with concentrated particle erosion;
- Adopt Double-layer cooling structure The inner layer is water-cooled, while the outer layer is air-cooled, reducing the temperature difference across the wall.
- Smart Monitoring
- Install temperature and pressure sensors, combine them with machine learning algorithms to predict the combustion chamber’s lifespan, and achieve... Preventive maintenance 。
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