How to ensure the quality of plasma spraying?

How to ensure the quality of plasma spraying?

The following are methods to ensure the quality of plasma spraying:

1、 Selection of spraying materials

Select appropriate spraying materials according to application requirements:

Consider the functional requirements of the coating, such as wear resistance, corrosion resistance, high temperature resistance, etc., and choose powder materials with corresponding properties. For components that require high wear resistance, hard alloy powders such as tungsten carbide can be chosen; For occasions with high corrosion resistance requirements, ceramic materials such as alumina and zirconia can be used.

Ensure the quality stability of powder materials, including chemical composition, particle size distribution, particle shape, etc. The purity of the powder should be high and the impurity content should be low to ensure the performance of the coating. The particle size distribution should be uniform to avoid particles that are too coarse or too fine affecting the spraying effect.

Storage and Handling of Powder Materials:

Powder should be stored in a dry and clean environment to avoid moisture and contamination. Sealed containers or specialized powder storage equipment can be used to prevent the powder from deteriorating due to contact with air and moisture.

Before use, screen and dry the powder to remove impurities and moisture, ensuring its flowability and spraying performance. For powders that are prone to moisture absorption, appropriate preheating treatment can be carried out before spraying to improve the dryness of the powder.

2、 Spray equipment debugging

Selection and maintenance of plasma spraying equipment:

Select appropriate plasma spraying equipment according to the requirements of the spraying task. Consider factors such as equipment power, spray gun type, powder feeding system, etc., to ensure that the equipment can meet the quality and production efficiency requirements of the coating.

Regularly maintain and upkeep the equipment, check the wear and tear of components such as spray guns, electrodes, and powder feeding tubes, and replace damaged parts in a timely manner. Keep the equipment clean to prevent dust, impurities, etc. from affecting the spraying process.

Optimization settings for equipment parameters:

Adjust the parameters of the plasma spray gun, such as current, voltage, gas flow rate, etc. The current and voltage determine the energy of the plasma arc, affecting the melting and spraying effect of the powder. The gas flow rate affects the stability and spraying speed of the plasma arc.

Optimize the parameters of the powder feeding system, such as powder feeding speed, powder feeding method, etc. The powder feeding speed should match the spraying speed to ensure that the powder can be evenly sprayed onto the surface of the workpiece. The powder feeding method can be selected according to the characteristics of the powder and coating requirements, such as axial feeding, radial feeding, etc.

3、 Spray coating process control

Surface treatment of workpiece:

Before spraying, strict treatment should be carried out on the surface of the workpiece to ensure the bonding strength between the coating and the workpiece. Surface treatment includes steps such as cleaning, sandblasting, and roughening. Cleaning can remove impurities such as oil stains and dust from the surface of the workpiece; Sandblasting can increase surface roughness and improve coating adhesion; Coarsening treatment can further improve the bonding performance between the coating and the workpiece.

Inspect the surface treated workpiece to ensure that the surface is clean, free of oil stains, rust, and the roughness meets the requirements. For workpieces with special requirements, surface activation treatment can be carried out to improve the bonding strength of the coating.

Process control during spraying:

Control the spraying distance and angle. The spraying distance should be moderate, generally between 100-150 millimeters. Being too close can cause the coating to overheat and deform, while being too far away can affect the melting and bonding effect of the powder. The spraying angle should be adjusted according to the shape and requirements of the workpiece to ensure that the coating evenly covers the surface of the workpiece.

Maintain a stable spraying speed. Spraying too fast can lead to uneven coating thickness, while spraying too slow can affect production efficiency. Maintain stable spraying speed by controlling the movement speed and powder feeding speed of the spray gun.

When performing multi-layer spraying, attention should be paid to controlling the interlayer temperature. After each layer of spraying, the coating should be allowed to cool appropriately to avoid cracking or peeling due to high temperature. At the same time, to ensure good bonding between layers, methods such as cross spraying can be used to improve the bonding strength between layers.

4、 Quality Inspection and Control

Coating performance testing:

Perform performance testing on the sprayed coating, including thickness measurement, hardness testing, bonding strength testing, porosity testing, etc. Thickness measurement can use equipment such as micrometers and coating thickness gauges to ensure that the coating thickness meets the requirements. Hardness testing can use micro hardness testers to detect the hardness distribution of coatings. Combined strength testing can use methods such as tensile testing and shear testing to evaluate the bonding strength between the coating and the workpiece. Porosity detection can determine the porosity in the coating through metallographic analysis, penetration testing, and other methods.

Evaluate the quality of the coating based on the test results. If quality problems are found in the coating, such as uneven thickness, insufficient hardness, low bonding strength, etc., the reasons should be analyzed in a timely manner and corresponding improvement measures should be taken.

Process quality control:

Establish a strict quality control system to monitor every step of the spraying process. Develop detailed operating procedures and quality standards to ensure that operators strictly follow the requirements for operation.

Conduct quality inspections during the process, such as checking powder materials, workpiece surface treatment, spraying parameters, etc., to promptly identify problems and make adjustments. Focus on monitoring key processes, such as debugging spray guns and controlling parameters during the spraying process.

Record various data during the spraying process, including equipment parameters, process parameters, quality inspection results, etc. Through data analysis, summarize experiences and lessons learned, continuously optimize spraying processes, and improve coating quality.