Technology: how to deal with the surface of high-frequency welded steel pipe(2)

    Following the introduction of yesterday, now we tell the remaining four points for you.
4.2 Spray abrasive
    In order to achieve the desired effect of rust removal, we should choose the abrasive based on the surface hardness of steel pipe, the original extent of corrosion, the required surface roughness, coating types. For the two-layer or three-layer polyethylene coating, we use a mixture of grit and steel shot abrasive blasting easily to achieve the desired effect.
    Steel shot has the effect of strengthening the steel surface, while steel grit have the role of etched surface. A mixture abrasive of grit and steel shot (usually steel shot hardness is 40 ~ 50HRC, grit hardness is 50 ~ 60HRC) can be used for a variety of surfaces, even with C and D levels corrosion of the steel surface, rust removal effect is very effective.
 4.3 Abrasive particle size and the ratio
    In order to obtain a better distribution of uniform cleanliness and roughness, abrasive size and the ratio’s design is very important. Coating roughness is too easily lead to peak the anchor pattern thinning; at the same time as the anchor pattern too dark, in corrosion with coating process is easy to form bubbles, seriously affect the coating performance.
    Roughness level too small will result in coating adhesion and impact strength decreased. For serious pitting inside, not only by high-intensity large abrasive particles impact, must also be polished off by small particles of corrosion products to achieve the cleaning effect. At the same time, a reasonable proportion of the design not only can reduce the wear of steel tubes’ abrasive and nozzles (blades), and the utilization of abrasive can be greatly enhanced. Typically, steel shot of diameter is 0.8 ~ 1.3mm, steel grit particle size is  0.4 ~ 1.0mm, in which 0.5 ~ 1.0mm is the main ingredient. Sand balls ratio is 5 to 8.
    We should be noted that in practice, the ideal ratio of abrasive’s grit and steel shot is difficult to achieve, because hard and brittle steel grits’ crushing rate is higher than steel shot. To this end, the operation should continue sampling mixed abrasive, according to the particle size distribution, mix new abrasive to the rust removal machine, in which mix new abrasives, steel grit number is account for the major.
4.4 Rust removal speed
    Steel tubes’ rust removal speed depend on the type and displacement of abrasive. Generally we should choose a lower loss rate abrasive, this will help improve the cleaning speed and long blade life.
4.5 Clean and preheat    
    Before spray treatment, using cleaning methods to remove grease and fouling of the surface of steel pipe, and using the heating furnace to preheat the tube surface to 40 – 60 ¡æ, make the steel pipe surface keep dry. In the spray processing, due to oil-free steel surface, rust removal effect can enhance, the dry steel pipe surface is also conducive to steel shot, steel grit and rust separate from the oxide skin, so that after removal the steel pipe’s surface is cleaner.    
    We should pay attention to the Importance in the production of surface treatment, strictly control the technological parameter. In the process of actual construction, steel pipe coating peel strength value is much higher than the standards, to ensure the quality of coating. On the basis of the same equipment, greatly improve the technological level, and reduce production costs.

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