I. Several knowledge points about the quality of steel drum painting
1. Corrosion mechanism of steel drum surface
Steel drums are exposed to the atmosphere, and the basic elements of corrosion degradation are water vapor (moisture) and air (oxygen). The region where steel (Fe) loses electrons into ions (Fe2+) forms an anode, and the region where steel electrons are trapped The cathode is formed, the anode undergoes corrosion degradation (formation of iron oxide), and the cathode captures additional electrons without degradation reaction, which is the most basic steel barrel corrosion mechanism. Other factors, such as surface foreign matter (dust, oxide), salinity, acidity, wet time of steel drum exposure, exposure to ambient temperature and humidity, and contact of steel drums with other metals, can affect the corrosion rate and extent of steel drums. .
2. The purpose of surface treatment before steel drum painting
The purpose of the surface treatment of the steel drum is to obtain good adhesion between the steel drum and the paint film coating. Generally, two factors directly affect the final effect of the surface treatment. One is the cleanliness, that is, the degree of surface pollutant removal. The pollutants include oil stains, scale, rust, water vapor, dust, etc., and the other is roughness, including the shape of the roughness, the small or deep water, and the density of the roughness. There is a consensus that the presence of contaminants will affect (reduce) the adhesion of the coating, as the contaminants block the direct contact of the coating with the surface of the steel drum, and reasonable surface roughness will increase the adhesion of the coating because Roughness increases the surface area of the steel drum, which increases the contact area between the coating and the surface of the steel drum.
In the on-site coating inspection, the two methods of visual inspection of the roughness standard control board (may also require finger tactile coordination judgment) and instrument measurement are used to determine whether the roughness level after surface treatment meets the quality requirements of the specification. Commonly used roughness standard control boards include: ISO 8503-1, RUGOTEST NO.3 and Keane-Tator. The commonly used roughness measuring instruments for on-site inspection include pointer roughness measuring instrument and extension paper height measuring instrument.
4, the relationship between coating wetting properties and adhesion
Wettability is a property of (liquid) coatings, especially for steel drums coated with only one layer of coating. Coatings with good wettability can penetrate the surface more fully to make the coating and the surface of the steel drum. Contact surface, which increases the adhesion between the two. Coatings with poor wetting properties should not be used as steel drum coatings. Because weak wetting does not ensure that the coating is in contact with the surface of the steel drum, it may result in a weaker coating and adhesion to the surface of the steel drum.