Sandblasting surface technology

Sandblasting surface technology

The surface of the workpiece shall be carefully treated before it is sprayed or coated (paint or other anticorrosive materials), which is called pretreatment.

　　 The quality of pretreatment affects the adhesion, appearance, moisture and corrosion resistance of the coating, because the best coating (layer) is adhered to the surface being carefully cleaned. If the pretreatment is not done well, the corrosion will continue to spread under the coating, making the coating flake off. After careful cleaning of the surface and the general simple (manual sandpaper or brush) cleaning of the workpiece, with the sun method for coating comparison, life can differ 4-5 times. There are many ways to clean surfaces, but the most commonly accepted are: a. solvent cleaning b. pickling c. hand tools d. power tools.
 　　 In these ways, each method has its own scope of application, but in all surface cleaning methods, sandblasting method is the most thorough, the most general, the most extensive way, the reason is: A sandblasting than other methods of the workpiece surface cleaning speed and thorough best.

　　 B no other process allows you to choose between the four accepted and generally accepted degrees of cleanliness.

Second, sandblasting, compressed air is used for the dynamic formation of high-speed injection beam, the spraying material (copper ore, quartz sand, iron sand, sea sand, silicon carbide, etc.), such as high speed jet to need to deal with the surface, the surface appearance of components changes, due to the abrasive effect on impact on the surface of the workpiece and cutting, make get some cleanliness and different roughness of workpiece surface, make the workpiece can improve the mechanical properties of the surface, thus improved the artifacts to fatigue, increased its adhesion between the coating and, extend the durability of the coating, but also to the flow of paint and decoration.

Compared with other pretreatment processes (such as pickling and tool cleaning) 1) sandblasting is the most thorough, universal, rapid and efficient cleaning method.

　　 2) sandblasting treatment can be arbitrarily selected between different roughness, while other processes cannot achieve this. Manual polishing can make the rough surface, but the speed is too slow, while chemical solvent cleaning can clean the surface too smooth, which is not conducive to the adhesion of the coating.

Sand blasting application

(a) the workpiece processing before plating, adhesive workpiece sandblasting to scale on the surface of the workpiece and all dirt removed, and the surface it is very important to set up the basis of the schema (usually the so-called hair side), but also by changing different particle size of abrasive, to varying degrees of roughness, greatly improve the workpiece and the adhesion strength of the coating, plating materials.
Or to make the bonding parts adhere more firmly, better quality.

Sandblasting can clean up all the dirt (such as oxide skin, oil stains and other residues) on the surface of castings and forgings after heat treatment, and improve the surface finish of the workpiece and beautify the workpiece.
   
Sandblasting cleaning can make the workpiece showing uniform metal color, make the workpiece appearance more beautiful, to achieve the role of beautification and decoration.

(3) machining parts burr cleaning and surface beautification sandblasting can clean the surface of the workpiece small burr, and make the surface of the workpiece more flat, eliminate the harm of burr, improve the grade of the workpiece.
And sandblasting can make small round corners at the junction of the workpiece surface, making the workpiece more beautiful and more precise.

(4) improve the mechanical properties of the mechanical parts after sandblasting, the mechanical parts can produce a uniform fine concave and convex surface on the surface of the parts (basic diagram), so that the lubricating oil can be stored, so as to improve the lubrication conditions, and reduce noise to improve the mechanical service life.


1. Polishing the surface of various workpiece to make the surface of the workpiece more beautiful.

2. Make the workpiece smooth and non-reflective.
　　 For some special purpose workpiece, sandblasting can achieve different reflective or matte at will. Such as stainless steel workpiece, wood furniture surface matte, frosted glass surface pattern, and cloth surface of the wool processing.
By striking the surface of the workpiece with sand balls, the stress is eliminated and the surface strength of the workpiece is increased, such as the surface treatment of springs, machining tools and aircraft blades.

Clean up the class

　 That is, cleanliness. There are two representative international standards: one is "SSPC-" formulated by the United States in 1985; The second type is "Sa-" formulated by Sweden in 1976, which is divided into four grades: Sa1, Sa2, Sa2.5 and Sa3. It is the international common standard, and is detailed as follows: Sa1 -- equivalent to sspc-sp7 of the United States.
The use of a simple manual brush, sand cloth polishing method, this is the four medium cleanliness of the lowest level, the protection of the coating is only slightly better than the use of untreated workpiece. Sa1 treatment technical standards: the surface of the workpiece shall not be visible oil, grease, residual oxide, rust spots, and residual paint and other dirt. The Sa1 level is also called the manual brush cleaning level. Sa2 - equivalent to sspc-sp6.
The use of sandblasting cleaning method, which is the lowest level of sandblasting treatment, that is, the general requirements, but the protection of the coating is much better than manual brushing cleaning. Technical standards for Sa2 treatment: the surface of the workpiece shall be free from grease, dirt, oxide, rust, paint, oxide, corrosion, and other foreign materials (except the defects), but the defects shall not exceed 33% of the surface per square meter, including slight shadows; Slight decolorization caused by defect and corrosion; Oxide skin and paint defects. If the original surface of the workpiece has a dent, then slight corrosion and paint will remain at the bottom of the dent. Level Sa2 is also known as commodity clearance level (or industrial level).
　　Sa2.5 -- a level commonly used in industry and acceptable as a technical requirement and standard for acceptance.The Sa2.5 class is also called the near white cleaning class. Technical standard of Sa2.5 treatment: same as the first half of Sa2, but the defect is limited to no more than 5% of the surface per square meter, including slight shadow; Slight decolorization caused by defect and corrosion; Oxide skin and paint defects.
　　Sa3 - equivalent to sspc-sp5, is the highest processing level in the industry, also known as white cleaning level (or white level).Sa3 level processing technical standard: same as Sa2.5 level but 5% of shadow, defect, rust, etc. have to exist.

Sandblasting roughness

This is usually referred to as the roughness, sandblasting sand particles impact and rebound outward, the impact of thousands of an inch of the surface of the indentation, called the basic schema. Springback can make certain surfaces a few thousandths of an inch higher. The low ones are called "valleys" and the high ones are called "peaks". Each sand particle hitting the surface causes a "valley" and a "peak". It's called MILL. A MILL is 1/1000 of a second.
　　 The formed base schematic value shall be 30% of the total coating system, and shall not exceed 1/3 of the thickness of the dry film coating. Generally, the corrosion resistance shall be between 50-70 (um).
 　　 1 micron (um) =0.001 mm (mm) 1 micron =0.001 s =0.0254 mm (mm)

Appendix C comparison of international common surface treatment standards

Steel Structure Painting Council (SSPC)

National Association of Corrosion Engineers (NACE)

British standard ISO 8501-1 / BSI BS 7079

The Swedish Standard

GB-3092 / GB-8923-88

Comparison of surface treatment standards