In the construction process of epoxy, ethylene, phenolic and other anticorrosive coatings commonly used in steel pipes, the appearance of steel pipes is generally required to reach near white grade (Sa2.5). It has been proved theoretically that all oxidized scales, rusts and other contaminants can be removed by using this kind of rust removal grade. The anchorage depth reaches 40-100 um, which fully meets the requirements of adhesion between the anticorrosive coating and the steel pipe. The spray (throw) rust removal process can reach the near-white level (Sa2.5) technical conditions with lower operating cost and stable and reliable quality.
2 shotcrete (shotcrete) abrasive
为了到达理想的除锈效果，应依据钢管外表的硬度、原始锈蚀水平、请求的外表粗糙度、涂层类型等来选择磨料，关于单层环氧、二层或三层聚乙烯涂层，采用钢砂和钢丸的混合磨料更易到达理想的除锈效果。钢丸有强化钢外表的作用，而钢砂则有刻蚀钢外表的作用。钢砂和钢丸的混合磨料(通常钢丸的硬度为40～50 HRC，钢砂的硬度为50～60 HRC可用于各种钢外表，即便是用在C级和D级锈蚀的钢外表上，除锈效果也很好。
In order to achieve the ideal rust removal effect, Abrasives should be selected according to the hardness of steel pipe surface, the original rust level, the required surface roughness, coating type, etc. For single epoxy, two or three layers of polyethylene coatings, it is easier to achieve the ideal rust removal effect by using a mixture of steel sand and steel balls. Steel shot has the effect of strengthening steel appearance, while steel sand has the effect of etching steel appearance. Mixed abrasives of steel sand and steel shot (usually the hardness of steel shot is 40-50 HRC, the hardness of steel sand is 50-60 HRC) can be used for various steel surfaces, even for C-grade and D-grade corroded steel surfaces, the effect of rust removal is very good.
Particle Size and Proportion of 3 Abrasive
In order to obtain better average cleanliness and roughness dispersion, the design of abrasive particle size and ratio is very important. It is easy to form anticorrosive coatings at the peak of anchor lines when the roughness is too large. At the same time, because the anchor lines are too deep, the anticorrosive coatings are easy to form bubbles in the anticorrosive process, which seriously affects the performance of the anticorrosive coatings.
粗糙度太小会形成防腐层附着力及耐冲击强度降落。关于严重的内部点蚀，不能仅靠大颗粒磨料高强度冲击，还必需靠小颗粒打磨掉腐蚀产物来到达清算效果，同时合理的配比设计不只可减缓磨料对管道及喷嘴(叶片)的磨损，而且磨料的应用率也可大大进步。通常，钢丸的粒径为0.8～1.3 mm，钢砂粒径为0.4～1.0 mm，其中以0.5～1.0 mm为主要成分。砂丸比普通为5～8。
Too small roughness will cause the adhesion and impact strength drop of the anti-corrosion coating. For serious internal pitting corrosion, not only the high-strength impact of large abrasive particles, but also the small abrasive particles must be used to polish the corrosion products to achieve liquidation effect. At the same time, reasonable proportion design can not only slow down the abrasive wear on pipelines and nozzles (blades), but also greatly improve the application rate of abrasives. Usually, the diameter of steel shot is 0.8-1.3 mm and steel sand is 0.4-1.0 mm, in which 0.5-1.0 mm is the main component. The ratio of sand balls is 5 to 8.
China seamless pipeline network recently learned that it should be noted that in practice, the ideal ratio of steel sand and steel shot in abrasive is difficult to reach, because the crushing rate of hard and fragile steel sand is higher than that of steel shot. Therefore, the mixed Abrasives should be sampled from time to time in operation. According to the particle size distribution, new Abrasives should be added to the rust remover, and the amount of steel sand is the main part of the new abrasives.
4. Rust Removal Speed
The speed of rust removal depends on the type of abrasives and the discharge of abrasives, i.e. the total kinetic energy E applied by Abrasives per unit time to the steel tube and the kinetic energy E1 of single abrasive particles.
式中： m ——磨料的喷(抛)量；
In the formula: m - the amount of abrasive spraying (throwing);
V - Abrasive running speed;
M1 - The quality of single abrasive.
M. The size of the crushing rate is related to the abrasive crushing rate, which directly affects the cost of surface disposal operations and the cost of rust removal equipment. When the equipment is fixed, m is constant and Y is constant, so E is also a constant. However, due to the breakage of abrasives and the change of m1, abrasives with low wear rate should be generally selected, which is beneficial to improving clearing speed and long blade life.
5 Cleaning and Preheating
China seamless pipeline network recently learned that before spraying (throwing) disposal, cleaning method was used to remove grease and scale on the surface of the steel pipe, and heating furnace was used to preheat the pipe body to 40-160 C, so that the appearance of the steel pipe adhered to a dry state. In spraying (throwing) disposal, because the steel pipe surface does not contain grease and other dirt, it can enhance the effect of rust removal. The dull steel pipe surface is also conducive to the separation of steel shot, steel sand and rust and oxide scale, so that the steel pipe surface after rust removal becomes cleaner.
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