During the blasting process, the abrasives are ejected at a relatively high speed and hit the surface of the steel substrate. Of course, this speed is not so high that the abrasive will break prematurely before the metal is properly cleaned. Under high compressed air pressure, non-metallic abrasives will be excessively broken and lost, so abrasives such as brown corundum should not use excessively high air pressure. For sandblasting construction, for soft or thin-walled substrates, low wind pressure and slightly finer sand particles should be used to reduce the possibility of sand particles embedding. For pressure type sand blasting equipment, high wind pressure gas will generate large compressive stress. The use of higher nozzle pressure will cause the deformation of the thin substrate, and it will also easily increase the crushing rate of the abrasive and increase the abrasive loss. Table 7-9 lists the use of a pressure-type blasting equipment, with a pressure of o.? MPa, using a nozzle of a given diameter for blasting, and blasting production for different surface conditions. Ability test results. In order to obtain the required blasted surface, a visual inspection of the structure and uniformity of the blasted surface is required to determine the required blasting time. Excessive blasting time can lead to unwanted surface structures.
After the steel substrate is sandblasted, the surface is clean and highly active and absorbs moisture. Therefore, the surface of steel components after sandblasting must never be touched by hand. If you need to touch it, you need to wear clean gloves. The surface response of the steel substrate just after sandblasting is very strong. If the ambient temperature increases and the temperature of the workpiece is lower than the ambient temperature, condensation will occur on the surface of the workpiece and rust will appear. This is often the case when anticorrosive construction is carried out in northern China, especially for some storage tanks. In autumn, due to the large temperature difference between day and night, this situation also occurs during night construction. When pressure sandblasting is used, the long-term operation of the air compressor increases the temperature of the compressed air, and the temperature is higher than: the compressed air of the workpiece easily causes condensation on the surface of the workpiece. Using centrifugal sand blasting process can avoid this phenomenon.
The surface of steel components after sandblasting should be sprayed with a metal coating as soon as possible. The shorter the interval between sandblasting and spraying, the higher the bonding strength of the coating. After the steel substrate is subjected to sandblasting, severe plastic deformation occurs on the surface atomic layer, lattice defects increase, and surface activity and adsorption increase. At this time, the surface of the substrate is very easy to adsorb some dust, dirt and moisture, and it is easy to rust. After the surface of the workpiece substrate is sandblasted, the surface activity is significantly improved, and low-energy electrons can be emitted at room temperature. The measurement of low-energy electrons can quantitatively describe the degree of surface activation. With the extension of the time, the energy and number of low-energy electrons on the substrate surface will gradually decay, and the surface activity will decrease, which will affect the bonding strength of the thermal spray coating.