Before applying a protective coating (paint or other anti-corrosion material) to a workpiece, the surface must be carefully prepared, a process known as pre-treatment.
1. Pre-treatment
Before applying a protective coating (paint or other anti-corrosion material) to a workpiece, the surface must be carefully prepared, a process known as pre-treatment. The quality of pre-treatment affects the coating's adhesion, appearance, and resistance to moisture and corrosion. The best coatings adhere to a carefully cleaned surface. Poor pre-treatment can allow rust to spread beneath the coating, causing it to flake off. The lifespan of a coating exposed to sunlight can be 4-5 times greater on a carefully cleaned surface than on a surface that has been simply cleaned by hand (with sandpaper or a brush). There are many methods for surface cleaning, but the most commonly accepted are:
A. Solvent cleaning B. Acid cleaning C. Hand tools D. Power tools
Each of these methods has its own scope of application, but of all surface cleaning methods, sandblasting is the most thorough, versatile, and widespread method. The reasons are: A. Sandblasting cleans the workpiece surface faster and more thoroughly than other methods. B. No other process method allows you to choose between four recognized and generally accepted levels of cleanliness.
Sandblasting uses compressed air as a power source to create a high-speed jet beam, directing abrasive (copper ore sand, quartz sand, iron sand, sea sand, corundum, etc.) at the surface of the workpiece being treated. This process alters the surface appearance of the workpiece. The impact and cutting action of the abrasive imparts a certain degree of cleanliness and varying degrees of roughness to the workpiece surface, improving its mechanical properties. This enhances the workpiece's fatigue resistance, strengthens the adhesion between the workpiece and the coating, prolongs the durability of the coating, and facilitates leveling and decorative effects.
Comparison with Other Pretreatment Processes (such as Pickling and Tool Cleaning)
1) Sandblasting is the most thorough, versatile, rapid, and efficient cleaning method.
2) Sandblasting allows for a wide range of roughness levels, which is not possible with other processes. Manual sanding can produce a rough surface, but this is too slow, while chemical solvent cleaning can create an overly smooth surface, hindering coating adhesion.
Sandblasting Applications
(1) Pretreatment of Workpieces Before Coating and Bonding
Sandblasting removes all impurities, including scale, from the workpiece surface and creates a crucial surface pattern (commonly known as a rough surface). By varying the grit size of abrasives, varying degrees of roughness can be achieved, significantly improving the bond between the workpiece and the coating or plating material. Alternatively, it can strengthen the bond between bonded parts and enhance quality.
(2) Cleaning and Polishing the Rough Surfaces of Castings and Forgings, and Workpieces After Heat Treatment
Sandblasting removes all impurities (such as scale, oil, and other residues) from the surfaces of castings and forgings, as well as those after heat treatment. It also polishes the surface to enhance its smoothness and beautify the workpiece. Sandblasting can reveal a uniform, consistent metallic color, enhancing the appearance and achieving a decorative effect.
(3) Deburring and Surface Beautification of Machined Parts
Sandblasting can remove tiny burrs from the surface of a workpiece and smooth it out, eliminating the harmful effects of burrs and improving the quality of the workpiece. Sandblasting can also create subtle radiused corners at the interface of the workpiece, making the workpiece appear more aesthetically pleasing and more precise.
(4) Improving the Mechanical Properties of Parts
Sandblasting can create uniform, finely contoured surfaces on the surface of mechanical parts (basic diagram), which trap lubricating oil, improve lubrication conditions, reduce noise, and increase the service life of the machine.
(5) Finishing
1. Polishing various workpiece surfaces for a more aesthetically pleasing finish.
2. Enabling workpieces to achieve a smooth, non-reflective finish.
For certain special-purpose workpieces, sandblasting can achieve varying degrees of reflectivity or matte finish. Examples include matte finishes for stainless steel and wooden furniture, patterns on frosted glass, and roughening fabric surfaces. (VI) Stress Relief and Surface Strengthening
Shots are used to strike the workpiece surface to eliminate stress and increase surface strength. This is used for surface treatment of workpieces such as springs, machining tools, and aircraft blades.
