Sandblasting parameter selection and influencing factors

       All substrate surfaces that may be damaged by sandblasting or that have been sprayed must be shielded and protected. Dust or abrasive adhering to the surface of the substrate should be blown off with compressed air before spraying.



The air pressure for sandblasting depends on the material of the substrate, the required surface roughness, the fluidity, weight and particle size of the sand grains, as well as the type of nozzles and sandblasting equipment used, generally 340 ~ 880kPa.



For substrates such as aluminum, copper alloy, bronze and plastic, low wind pressure and soft and fine sand should be used to reduce the possibility of sand embedding. The high wind pressure gas will generate compressive stress, which will lead to the deformation of the substrate of the thin piece, and it is easy to break the sand grains quickly.



For pressure blasting equipment, the following nozzle pressures should be used:



1) Using alumina silicon carbide, flint or slag, the minimum air pressure is 345kPa and the maximum is 414kPa.



2) For gravel, emery or chilled iron sand, the minimum value is 517kPa.



These pressure values are not the pressure of the fan tank, but the pressure measured at the nozzle with a pressure probe.



With siphon (suction) blasting, the maximum nozzle pressure should be:



1) Using alumina, silicon carbide, flint or slag, it is 517kPa.



2) For sand, emery or chilled iron sand, it is 621kPa.



The blasting beam should form a spray angle of 75°-90° with the surface of the substrate. Sandblasting is done by moving from one end to the other.



The distance from the nozzle to the surface of the substrate depends on the particle size and type of abrasive, the size of the nozzle aperture and the processing capacity of the sandblasting machine, and generally fluctuates in the range of 102 ~ 304mm.



In order to obtain a sandblasted surface equivalent to NACE No.1, the structure and uniformity of the sandblasted surface should be visually inspected under strong light, and the entire sandblasted surface is considered to be in a diffuse reflection shape and without reflection. , so as to determine the required blasting time. Excessive blasting times can lead to undesired surface structures.



The speed and cost of blasting are related to the following factors: type of blasting equipment, load capacity and substrate material.



The large-aperture nozzle sandblasting machine has a larger spraying area per unit time than the small-bore nozzle sandblasting machine. However, the choice of nozzle aperture size is limited by the amount of compressed air obtained. Using a continuous pressure sandblasting equipment and 925 iron sand, the air pressure is 703kPa, the surface of different steel substrates is sandblasted and roughened, and the surface is semi-bright or slightly eroded.



Abrasive type and particle size also affect blasting speed. Generally, the larger the grit size, the lower the blasting speed. About 6.8kg of alumina or 11.3kg of chilled iron is required per square foot of sandblasted surface.