Some questions during operation of thermal spraying
1. Selection of coating materials:
The principle of choice
1: According to the work environment of the workpiece being coated, selecting the material that meet the functional requirements.
2: Selecting the material which have similar thermal expansion coefficient with matrix material.
3: Adapting to spraying process and equipment.
4: Low cost, source.
The main purposes of thermal spray coating are as following: (1) corrosion-resistant coatings. (2) wear-resistant coatings. (3) friction-reducing and sealing coatings. (4) high-temperature thermal barrier coatings. (5) Insulation or conductive coating. (6) Size repair coating, and so on. Different purposes should be different coatings.
2. What is the thermal spraying surface pre-treatment
Thermal spray surface pre-treatment is generally divided into three steps: surface preparation, surface cleaning and surface roughening.
(1) Surface preparation
One is to make the surface of the workpiece suitable for coating deposition and increase the bonding area.
The second is to help overcome the shrinkage stress of the coating. Some parts of the workpiece are pre-processed to disperse the local stress of the coating and increase the shear resistance of the coating.
(2) Surface cleaning
Solvent cleaning, alkaline cleaning and heating degreasing are often used to remove surface oil and maintain cleanliness. Commonly cleaning solvents are: gasoline, acetone, carbon tetrachloride and trichlorohexene. Alkaline cleaning is often used for large repair parts.
(3) Sand blasting treatment: (This is an important pretreatment method for thermal spraying.)
Sandblasting makes the clean surface to form a uniform and uneven rough surface to facilitate the mechanical bonding of the coating. Using clean compressed air to drive the clean sand to spray on the surface of the workpiece, it can cause compressive stress on the substrate surface , remove the surface oxide film, and cause distortion of some of the surface metal, which is conducive to the physical combination of the coating. The substrate metal can get a clean, rough and highly active surface after sandblasting.
3. The thicker of the spray surface, the better?
Some customers think that the thicker of coating, the better. The thickness determines the durability. In most cases we recommend a coating thickness of 0.15-0.2mm, not more than 0.3mm, and a spray thickness at most 2mm. After the thickness of the coating exceeds 0.5 mm, the bonding strength will decrease and the cost will become higher. The coating can ensure the bonding strength and deposition efficiency only under rough conditions. As the thickness of the coating increases, the surface roughness decreases and the coating quality also decreases.
