Common quality problems and treatment opinions of furniture paint painting 3 - whitish
After selecting the matrix material, blasting abrasive, and particle size, the sandblasting process can begin. Key parameters of the sandblasting process include air pressure, nozzle diameter, spray angle, distance from the surface, blasting duration, environmental conditions, and dust extraction system. The table illustrates how abrasive grain size and air pressure affect surface roughness when using aluminum oxide as the blasting media. It shows that larger abrasive particles and higher air pressure lead to increased surface roughness, while smaller particles and lower pressure result in smoother surfaces. When using the same abrasive and air pressure, the surface roughness tends to be higher on harder or stiffer substrates, such as aluminum or mild steel.
The effect of blasting time and air pressure on surface roughness is also significant. As air pressure increases, surface roughness rises sharply. In contrast, the impact of blasting time initially shows a steep linear increase within the first 30 minutes, after which further extension of the time has minimal effect on roughness.
The optimal sandblasting angle is typically 70 degrees relative to the horizontal line, with a recommended range of 80 to 45 degrees. A vertical angle (greater than 90 degrees) should be avoided, as it causes abrasive rebound and reduces efficiency. On the other hand, angles less than 45 degrees may negatively affect the blasting quality. Maintaining a consistent blasting angle throughout the process is essential for uniform results.
When performing scanning sandblasting, each pass should overlap approximately one shot of the previous pass, moving continuously from one end of the workpiece to the other. The second pass should overlap the first, and this alternating pattern should continue until the desired surface roughness is achieved.
The blasting distance—the distance between the nozzle and the workpiece surface—varies depending on the type and size of the abrasive, nozzle diameter, and machine performance. It generally ranges from 102 mm to 304 mm. For softer materials or thin-walled components, a greater distance is preferred, while harder, thicker parts or large coatings require shorter distances. After blasting, dry, oil-free compressed air is used to remove loose particles from the surface. The freshly blasted surface must remain free from contamination, as oils, fingerprints, or moisture can impair coating adhesion. Coating should be applied as soon as possible after blasting to prevent oxidation or moisture absorption, especially for steel substrates. In normal conditions, the interval should not exceed 4 hours, and in wet weather, it should be limited to 2 hours.
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