Abstract: Part of liquefied carbon dioxide is subjected to adiabatic expansion so that the remainder becomes snow-like dry ice due to heat of vaporization and heat of sublimation while a liquid is being sprayed to produce snow-like frozen liquid. The snow-like dry ice and the snow-like frozen liquid are mixed and the mixture is compressed and pelletized to produce hard particles each of which consists of a particle of snow-like dry ice coated with snow-like frozen liquid. Thus obtained particles are projected by compressed air or water under high pressure against an object to be cleaned. Wet type abrasive blasting can be effected because when the particles are projected against the object, the frozen liquid coating the surfaces of snow-like dry-ice particles is broken.

Abstract: Dry-ice particles are blasted against an object to be cleaned under the presence of ice particles, whereby drawbacks in the case of blasting the dry-ice particles alone can be eliminated.

Abstract: A liquid containing abrasives is projected through nozzles under high pressure upon the surface of an object to be treated such as sheet steel to descale and clean the surface thereof, and the projected abrasive liquid is recovered so that abrasives of suitable particle sizes may be reused. The jet liquid is a mixture of high pressure liquid and slurry abrasives which are substantially uniform in density and granular size. The mixed slurry after projection against the sheet steel workpiece is returned to a vertical style classifier before it settles to the bottom of the collecting tank. The scales which are removed from the sheet steel workpiece are separated out in the classifier while at the same time the density and the granular sizes of the abrasives are made uniform. In addition, the minuscule abrasives are caused to overflow from the classifier while the liquid and the slurry abrasives made uniform in density and granular size are conveyed to the nozzles.