Method for removal of surface contaminants from metal substrates

摘要

A method is disclosed for removing water soluble salts from a metal substrate in a wet blast system in which a bicarbonate abrasive is blasted in a pressurized water stream against the surface of the metal substrate to prepare the surface for the application of a coating. The method includes the steps as indicated in FIG. 3 in which a high pressure wet blast pressurized water and sodium bicarbonate abrasive is first applied by a nozzle (14) against the surface of the metal substrate with the water soluble salts being removed or neutralized. Iron salts are present where the metal substrate is of a ferrous material such as iron or steel. Next, pressurized water without abrasive is applied by the nozzle (14) against the surface of the metal substrate for washing the surface clean and removing the neutralized water soluble salts. The water for the wet blast system is of a very high purity characterized by a conductivity of between 0.5 and ten (10) micromohs/cm. To confirm the removal of the salts to an amount less than one (1) ppm, a ferricyanide testing is performed on the surface of the metal substrate. An apparatus for carrying out the method is shown in FIG. 2.