Common Defect Prevention Measures for Thermal Spray Coating

Thermal spray coatings are widely used in a variety of industries to provide surface protection, wear resistance, and thermal insulation. However, like any other manufacturing process, thermal spray coating can suffer from defects that can reduce the effectiveness of the coating.??Here are some common defect prevention measures for thermal spray coatings:

1. Coating peeling, flaking

① The surface roughness is not enough or there is dust adsorption, which reduces the adhesion of the sprayed coating; the surface roughening of the workpiece and the cleaning before spraying should be strengthened.

②The workpiece contains grease, and the grease overflows during spraying, such as the crankshaft of ductile iron; strictly remove the oil stain before spraying, and perform proper baking.

③ There is visible oil and water in the compressed air; try to reduce the oil and water in the compressed air, and repair or replace the compressed air device if necessary.

④The spray gun is too far away from the workpiece, and the metal particles are not filled with the workpiece; the distance between the spray gun and the workpiece should be shortened.

⑤ The time interval between turning and roughening, roughening and spraying is too long, and the surface of the workpiece to be sprayed has oxidation phenomenon; the interval time between surface pre-addition, surface roughening, and spraying depth should be shortened.

⑥ When the sprayed coating is processed by a grinding machine, an alumina grinding wheel is used, so that the coating is partially overheated and oxidized; the grinding wheel should be properly selected to take cooling measures.

⑦ The flame of the spray gun is not concentrated or deflected, causing the metal particles to not adhere strongly to the surface of the workpiece; the spray gun should be repaired or replaced.

⑧The linear speed of the workpiece and the moving speed of the spray gun are too slow, and the inclusions float on the surface of the workpiece during the spraying process, which reduces the adhesion strength; the linear speed of the workpiece should be adjusted to control the floating objects between spraying.

2. Coating layered

①Using gap spraying, when the standard size is about to be reached, the spraying is not finished once, and the stop spraying time is too long; note that when spraying in gaps, the stop spraying time should be short each time.

② When spraying, the oil and water in the compressed air are splashed on the surface of the workpiece; check whether the air pump and accessories are working normally, and water is often released, especially the oil-water separator should work normally.

③ After each layer is sprayed, a large amount of dust is adsorbed on the surface of the workpiece, so that there is isolation or partial isolation between layers; when spraying, keep it clean and take necessary dust-proof measures.

3. The coating cracks

① When spraying, the spray gun moves too slowly, so that the sprayed coating is too thick and overheats; the normal spray gun moving speed should be maintained, and the spray should not be too thick at one time.

② When spraying, the spray gun is too close to the surface of the workpiece, which will overheat the coating; the distance between the spray gun and the surface of the workpiece should be appropriately opened.

③The shrinkage rate of the spraying material is too large or contains more elements (such as S, P, etc.) that cause thermal cracks; the appropriate spraying material should be selected, and the content of harmful elements should be minimized.

④ The current is too large during arc spraying, and the oxidizing flame is used during flame spraying to make the coating thick and oxidized; the spraying parameters and spraying flame should be reasonably selected.

⑤ The sprayed coating is cooled rapidly and causes cracking; when spraying a thick coating, attention should be paid to the cooling speed.

⑥There is oil mist and water in the compressed air, which reduces the bonding strength of the deep layer; the oil and water in the compressed air should be resolved in time.

⑦ The center of rotation of the workpiece is inaccurate, the sprayed coating is thick or thin, and the shrinkage is uneven during cooling; the concentricity of the center of rotation of the workpiece should be repaired and adjusted.

4. The coating is not wear-resistant

① The spray gun is too far away from the workpiece, the temperature of the metal particles is low, and the bonding force with the surface of the workpiece is small, and some particles fall off during work; the spraying distance should be reasonably selected.

② There are a large number of sand particles embedded in the coating during lapping; the grinding wheel should be selected reasonably.

③The metal wire is fed too fast; the wire feeding speed should be selected reasonably.

④The metal wire material itself is not wear-resistant; qualified spraying materials should be selected.

⑤The air pressure is too low, and the spray gun is too far away from the surface of the workpiece, which reduces the bonding strength; the spraying parameters should be selected reasonably.

How to better prevent defects for Thermal spray coatings

Surface preparation

Proper surface preparation is critical to the success of any coating process. The surface should be cleaned thoroughly to remove all contaminants and any previous coatings.

Material selection

Choosing the right coating material is crucial for preventing defects. The material should be compatible with the substrate and should have the appropriate physical properties to provide the desired performance.

Process control

Maintaining tight process control is essential to prevent defects in thermal spray coatings. This includes controlling the temperature, velocity, and pressure of the spraying process.

Quality control

Regular quality control checks should be conducted during the coating process to detect any defects early on. This includes visual inspections, non-destructive testing, and adhesion testing.

Operator training

Proper training of operators is necessary to ensure that the thermal spray coating process is carried out correctly. This includes training on equipment operation, material handling, and safety procedures.

China Thermal Spray?Technology Factory

As a member of Thermal Spraying Specialized Committee of China Surface Engineering Association, Chuangzhi has been devoted to the R&D and promotion of thermal spraying technology and concentrated on the enterprise management for more than 15 years. Company owns a skilled, high efficiency and high quality R&D and production team, and has acquired many proprietary technology and patent certification.

Chuangzhi has established a whole set of excellent and advanced thermal spraying technology through the introduction of domestic & foreign advanced equipments, such as plasma spraying equipment, HOVF equipment and electric arc spraying equipment, and varieties of finish machining techniques and testing methods. Chuangzhi has passed the quality management system certification ISO9001:2008. With excellent products and technical services, now our products are exported to Europe, the United States, Japan, Taiwan and many other countries and regions.

Chuangzhi persists in the management philosophy of "quality, service and innovation ". Company supplies excellent products and reliable service for clients with continuous innovative technology. We look forward to cooperating with you sincerely.