Will the uneven coating thickness of supersonic spraying affect the performance of the workpiece? How to determine whether the spray gun of the supersonic spraying equipment needs to be replaced if it wears out after long-term use? ​

Will the uneven coating thickness of supersonic spraying affect the performance of the workpiece? How to determine whether the spray gun of the supersonic spraying equipment needs to be replaced if it wears out after long-term use?

Will the uneven coating thickness of supersonic spraying affect the performance of the workpiece?

The uneven coating thickness of supersonic spraying will affect the performance of the workpiece, and the specific degree of impact depends on the size of the uneven difference, the application scenario and performance requirements of the workpiece, mainly reflected in the following aspects:

Mechanical performance damage: On workpieces under load (such as gears and bearings), areas with thicker coatings may crack due to excessive internal stress, while thinner areas may experience premature wear or corrosion of the substrate due to insufficient protection. For example, if the coating thickness difference of the machine tool guide rail exceeds 0.1mm, it will cause uneven distribution of contact stress between the guide rail and the slider, accelerate local wear, and shorten the service life.

Decreased sealing and fitting performance: For workpieces with sealing requirements (such as valve cores and piston rings), uneven coating thickness can cause the sealing surface to not fit tightly, resulting in gaps and medium leakage. In precision matched components such as shafts and bushings, thickness differences can alter the fit clearance. Areas that are too thick may cause assembly interference, while areas that are too thin may experience vibration and abnormal noise due to excessive clearance, affecting overall operational accuracy.

Imbalance between corrosion resistance and wear resistance: Areas with thinner coatings are difficult to form effective protective barriers, and are easily corroded in corrosive environments, leading to substrate corrosion; Thicker areas may have a decrease in wear resistance due to loose tissue, resulting in rapid local wear. For example, if the thickness difference of the anti-corrosion coating of chemical equipment exceeds 50 μ m, weak parts will rust within 6 months, which will damage the overall anti-corrosion effect.

Unstable thermal and electrical properties: Coatings used for thermal or electrical conductivity (such as heat sink coatings, electrode coatings), uneven thickness can lead to uneven thermal resistance or resistance distribution, affecting heat transfer or current conduction efficiency. Under high temperature conditions, thickness differences may also generate thermal stress due to different coefficients of thermal expansion, leading to coating cracking or peeling.

Dynamic performance is affected: Uneven coating thickness on high-speed rotating or reciprocating workpieces (such as turbine blades, piston rods) can lead to imbalanced mass distribution, centrifugal force deviation or vibration, increased equipment operating noise and energy consumption, and in severe cases, may cause mechanical failures.

Therefore, for high-precision and high demand workpieces, the coating thickness deviation should be controlled within ± 0.05mm; Under normal working conditions, the deviation should not exceed ± 0.1mm. If it exceeds this range, it needs to be repaired by secondary spraying or grinding to ensure uniform coating thickness and ensure the performance of the workpiece.

How to determine whether the spray gun of the supersonic spraying equipment needs to be replaced if it wears out after long-term use?

After long-term use, if the spray gun of the supersonic spraying equipment wears out, the following indicators can be used to determine whether it needs to be replaced:

Observing changes in coating quality: If there are obvious defects in the sprayed coating (such as increased porosity, decreased bonding strength, and increased surface roughness), and no improvement is observed after adjusting process parameters (such as gas ratio and powder feeding amount), it may be due to abnormal flame morphology or uneven powder atomization caused by gun wear. For example, if the bonding strength of the originally qualified coating was 50MPa, but decreased to below 30MPa after wear and multiple tests showed no improvement, it indicates that the spray gun can no longer meet the requirements for use.

Check the dimensions of key components of the spray gun: measure the outlet diameter of the spray gun nozzle. If the diameter increases by more than 10% compared to the new nozzle after wear (such as the original diameter of 8mm, reaching 8.8mm or more after wear), it will cause a decrease in flame velocity and uneven energy distribution; Check the Laval nozzle inside the spray gun (the core component of supersonic spraying). If there are obvious scratches, deformations, or throat diameter wear exceeding 0.2mm in the throat or expansion section, it will disrupt the formation of supersonic airflow and affect the particle effect.

Monitoring equipment operating parameters: After the spray gun wears out, the consumption of gas and oxygen may increase abnormally (exceeding 15% of normal usage), and the fluctuation amplitude of flame temperature and pressure may increase (such as temperature fluctuations exceeding ± 50 ℃); When the stability of powder delivery decreases and the powder flow rate fluctuates, leading to increased unevenness in coating thickness, and these parameters are abnormal and cannot be restored through debugging, it is necessary to consider replacing the spray gun.

Observe the location and degree of wear: If there are grooves or deformations on the sealing surface of the spray gun, causing gas or powder leakage, and replacing the seal still cannot solve the problem; If the connection between the gun body and the nozzle is worn or loose, and there is obvious shaking (radial jumping exceeding 0.1mm), it will affect the spraying accuracy. At this time, the spray gun must be replaced. For detachable spray gun components (such as nozzles and mixing chambers), if performance cannot be restored after individual replacement, the spray gun needs to be replaced as a whole.

Reference usage cycle and maintenance records: Based on the frequency and workload of equipment use, if the spray gun has exceeded the recommended usage cycle (such as cumulative spraying area exceeding 1000 square meters, or continuous use for more than 6 months), and there have been multiple coating quality problems that have been repaired, it indicates that the spray gun has entered the late stage of wear and continued use may pose risks. It is recommended to replace the spray gun with a new one to ensure spraying stability.

In addition, when the spray gun has irreparable cracks, severe deformation, or when the cost of replacing worn parts approaches the price of a new spray gun, it should be replaced in a timely manner to avoid affecting production efficiency and coating quality due to equipment failure.