Some questions and answers about thermal spray powder coating quality inspection

1. What is the acceptable range for the difference in total carbon (TC), free carbon (FC), and oxygen content (P/O) between different batches?

A: TC (Total Carbon), FC (Free Carbon), and P/O (Powder Oxygen Content) are all controlled within ±100ppm. Oxygen content directly determines the oxide inclusion level in the coating. We have specifically imported carbon-sulfur analyzers and nitrogen-oxygen analyzers, and each batch of powder requires testing.

We retain samples of each batch of powder for archiving. If performance fluctuations occur at the customer's site, we can send the retained samples for comparative analysis and provide a traceability report within 3 working days.

2. Is the particle size analysis performed using laser diffraction or sieving?

A: The difference between the two methods is as follows: The laser method measures the "equivalent sphere diameter," while the sieving method measures the "minimum passing size." For irregular particles, the deviation between the two can reach ±5~10μm. We have both testing methods. Generally, we use the laser method to test agglomerated sintered sprayed powders, and the sieving method to test molten nickel-based, cobalt-based, and iron-based alloy powders. If you need both test reports, we can provide them simultaneously.

3. Does the "true particle size distribution" of the powder match the report?

A: Every batch of powder undergoes quality testing, and samples are retained. If there are any questions about the particle size distribution, it can be tested again. Traceability is available for up to one year.

4.How do you test the hardness of the powder coating?

A: After each batch of self-fluxing alloy powder is formed by oxy-acetylene flame spraying, its hardness is tested using a benchtop hardness tester. Once the hardness is qualified, it is transferred to the finished product warehouse. After each batch of supersonic spraying powder is formed by HVOF spraying, its hardness is tested using a microscopic hardness tester. Once the hardness is qualified, it is transferred to the finished product warehouse.

7. What type of grinding wheel is recommended for polishing WC coating?
A: The answer to this question involves two steps:

① Grinding wheel selection (hardcore recommendation):Rough grinding (removing excess material): Diamond grinding wheels are recommended, with a grit size of #120~#200. Ceramic bonds offer good rigidity and heat resistance, making them suitable for large cutting volumes.

Fine grinding/polishing (final dimensions): Resin-bonded diamond grinding wheels are recommended, with a grit size of #400. Resin bonds provide good elasticity, resulting in a high surface finish and reducing the likelihood of grinding cracks. Then, polish with 800-grit sandpaper and 2000-grit polishing sandpaper. After polishing, use a polishing compound for a final polish to achieve a bright, mirror-like finish.

Caution: CBN grinding wheels are not recommended for grinding WC coatings—CBN's grinding efficiency on WC is far lower than that of diamond.

8. What is the recyclability rate of thermal spray powder? Are there any specific solutions for recycling powder?

A: Powder residue from laser cladding, plasma welding, and oxy-acetylene spraying processes can be mixed into new powder in the correct proportions for continued use. However, adding too much powder will reduce the coating's lifespan. Powder residue from supersonic spraying is not recommended for continued use. We can provide contact information and recycling quotes from at least three precious metal recycling companies.