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Pickling rust
General use of chemical and electrolytic methods for pickling, pipe anti-corrosion chemical pickling only, can remove oxide scale, rust, old coating, and sometimes can be used as a blasting rust after reprocessing. Although chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, its anchorage is light and it is easy to pollute the environment.
Spray (throw) shot rust
Spraying (throwing) shot rust removal is driven by a high-powered motor to rotate the jet (throwing) jets at a high speed so that abrasives such as steel grit, steel shots, wire segments, and minerals are sprayed on the surface of the steel pipe under centrifugal force. Not only can it thoroughly remove rust, oxides, and dirt, but it can also achieve the required uniform roughness under the abrasive impact of abrasive and frictional forces. After spraying (throwing) shot derusting, not only can the physical adsorption of the pipe surface be enlarged, but also the mechanical adhesion of the anti-corrosion layer to the pipe surface can be enhanced. Therefore, spraying (throwing) shot rust removal is the ideal rust removal method for pipeline anti-corrosion. In general, shot peening (sand) rust removal is mainly used for inner surface treatment of tubes. Shot peening (sand) rust removal is mainly used for outer surface treatment of pipes. There are several issues that need to be taken into account when using spray (throw) shot rust removal.
Rust level
For steel pipe commonly used epoxy, vinyl, phenolic and other anti-corrosion coating construction process, it is generally required that the surface of the steel pipe reach near-white level (Sa2.5). Practice has proved that this kind of derusting grade can remove almost all scales, rust, and other contaminants. The depth of the anchoring pattern can reach 40-100 μm, fully satisfying the adhesion requirements of the anticorrosion layer and the steel pipe, and spraying (throwing) the shot The rust process can achieve near-white (Sa2.5) technical conditions with lower operating costs and stable and reliable quality.
Spray (throw) shot abrasive
In order to achieve the desired rust removal effect, the abrasive should be selected based on the hardness of the surface of the steel pipe, the degree of original rust, the required surface roughness, the type of coating, etc., for single-layer epoxy, two-layer or three-layer polyethylene coatings. Mixing abrasives of steel grit and steel pellets can achieve the ideal rust removal effect. Steel shots have the effect of strengthening the steel surface, while steel sand has the effect of etching the steel surface. Mixed abrasives of steel grit and steel shots (usually steel shots with a hardness of 40-50 HRC, steel grit with a hardness of 50-60 HRC can be used on various steel surfaces, even on grade C and D grade corroded steel surfaces Rust removal effect is also very good.
Abrasive particle size and ratio
In order to obtain a better uniform cleanliness and roughness distribution, the abrasive particle size and the ratio design are very important. If the roughness is too large, the anti-corrosion coating may become thinner at the peak of the anchorage pattern. At the same time, due to the deeper anchorage pattern, the anti-corrosion coating may easily form bubbles during the anti-corrosion process, which will seriously affect the performance of the anti-corrosion coating.
If the roughness is too small, the adhesion of the coating and the impact strength will be reduced. For severe internal pitting, high-strength impact cannot only be achieved by large-grained abrasives, but also by small particles to remove corrosion products to achieve cleaning effect. At the same time, a reasonable proportioning design can not only reduce abrasive wear on pipes and nozzles (blades). , And the utilization of abrasives can also be greatly improved. In general, the particle diameter of the steel shot is 0.8-1.3 mm, and the diameter of the steel grit is 0.4-1.0 mm, of which the main ingredient is 0.5-1.0 mm. Sand pills are generally 5-8.
It should be noted that in practice, the ideal ratio of steel grit and steel shots in abrasives is difficult to achieve due to the fact that hard and brittle grit has a higher breakage rate than steel shots. For this reason, the mixed abrasive should be continuously sampled during operation. According to the particle size distribution, new abrasives should be added to the derusting machine, and the amount of steel sand should be the major one among the new abrasives.
Rust removal speed
The derusting speed of the steel pipe depends on the type of abrasive and the displacement of the abrasive, that is, the total kinetic energy E of the abrasive applied to the steel pipe per unit time and the kinetic energy E1 of the single-particle abrasive.
When the equipment is fixed, m is a constant, y is a constant, so E is a constant, but due to abrasive crushing, m1 changes, therefore, generally should choose the abrasive with a lower loss rate, which will help improve the cleaning speed and long The life of the blade.
The main use of wire brush and other tools on the surface of the steel, can remove loose or tilt of the scale, rust, welding slag and so on. Hand tool derusting can reach Sa2 level, and the derusting of power tool can reach Sa3 grade. If the steel plate surface is attached with a solid iron oxide scale, the rust removal effect of the tool is not satisfactory, and the depth of the anchor grain can not reach the anti-corrosion construction requirements.