(1) Spraying (throwing) rust removal is driven by a high-power motor to rotate the spraying (throwing) blades at high speed, so that steel sand, steel shots, iron wire segments, minerals, and other abrasives are sprayed (throwing) on the surface of the
steel pipe under the action of centrifugal force ) Injection treatment, not only can completely clean up rust, oxides, and dirt but also the steel pipe can achieve the required uniform roughness under the action of violent impact and friction of abrasives.
(2) If the roughness is too small, the adhesion and impact strength of the anti-corrosion layer will decrease. For severe internal pitting, it is not only possible to rely on the high-strength impact of large-grain abrasives but also to polish off corrosion products with small particles to achieve the cleaning effect. At the same time, a reasonable proportion design can not only slow down the wear of abrasives on pipes and nozzles (blades). , and the utilization rate of abrasive can be greatly improved. Usually, the particle size of steel shot is 0.8~1.3mm, and the particle size of steel grit is 0.4~1.0mm, of which 0.5~1.0mm is the main component. The ratio of sand to shot is generally 5~8.
(3) After rust removal, not only the physical adsorption on the surface of the pipe can be expanded, but also the mechanical adhesion between the anti-corrosion layer and the surface of the pipe can be enhanced. Therefore, spraying (throwing) projectile rust removal is an ideal rust removal method for pipeline corrosion. Generally speaking, shot blasting (sand) de-rusting is mainly used for pipe inner surface treatment, and shot blasting (sand) de-rusting is mainly used for pipe outer surface treatment.
(4) In order to obtain a better uniform cleanliness and roughness distribution, the particle size and ratio design of abrasives are very important. If the roughness is too large, the anti-corrosion layer will become thinner at the peak of the anchor pattern; at the same time, because the anchor pattern is too deep, the anti-corrosion layer will easily form bubbles during the anti-corrosion process, which will seriously affect the performance of the anti-corrosion layer.
It should be noted that in actual operation, the ideal ratio of steel grit and steel shot in the abrasive is difficult to achieve because the hard and brittle steel grit has a higher crushing rate than the steel shot. For this reason, the mixed abrasives should be continuously sampled and tested during operation, and new abrasives should be added to the de-rusting machine according to the particle size distribution, and the amount of steel grit should be the main one in the new abrasives added. The de-rusting speed of the steel pipe depends on the type of abrasive and the displacement of the abrasive, that is, the total kinetic energy E applied by the abrasive to the steel pipe per unit of time and the kinetic energy E1 of a single abrasive. When the equipment is fixed, m is a constant, and y is a constant, so E is also continuous, but due to the breaking of the abrasive, m1 changes, so generally the abrasive with a lower loss rate should be selected, which is conducive to improving the cleaning speed and long life. leaf life.
For the construction process of epoxy, vinyl, phenolic, and other anti-corrosion coatings commonly used for steel pipes, the surface of steel pipes is generally required to reach the near-white level (Sa2.5). The practice has proved that almost all scale, rust, and other dirt can be removed by using this level of rust removal, and the depth of the anchor pattern can reach 40~100μm, which fully meets the adhesion requirements between the anti-corrosion layer and the steel pipe while spraying (throwing) The rusting process can achieve near-white (Sa2.5) technical conditions with low operating costs and stable reliability. In order to achieve the ideal de-rusting effect, the abrasive should be selected according to the hardness of the steel pipe surface, the degree of original rust, the required surface roughness, the type of coating, etc. The mixed abrasive of steel grit and steel shot can quickly achieve the ideal de-rusting effect for single-layer epoxy, two-layer, or three-layer polyethylene coating. Steel shot has the effect of strengthening the steel surface, while steel grit has the effect of etching the steel surface. The mixed abrasive of steel grit and steel shot (usually the hardness of steel shot is 40~50HRC, and the hardness of steel grit is 50~60HRC can be used on various steel surfaces, even on C-level and D-level corroded steel surfaces, except Rust works well too.
