Table 1 also identifies the specific gravity of the various abrasives. Cleaning efficiency is determined by the energy impacted by the abrasive to the surface of the substrate. This is due to the physical law of kinetic energy: E= ½ mv2. In this formula , E is energy; v is velocity of the abrasive particle; and m is the mass of the abrasive particle, which is proportional to its specific gravity. The most efficient and fastest cleaning is achieved by abrasives with the highest specific gravity.
Several points can be made about velocity, the other factor in the equation, and about nozzle pressure, which determines the velocity of the abrasive. Most abrasives will fracture upon impact at nozzle pressures above 100 psi (7 bar), which typically produces a velocity of 450 mph (depending on the size of the nozzle, etc). When an abrasive breaks down, energy transfer is reduced. Pressures above 100 psi do not add a great deal to the performance of the abrasive. The main advantage of very high pressures is the speed with which blasting can be done.