The use of sodium hydroxide aqueous solution alone to remove the chemical oxide film tends to be ineffective. . Mainly in the uneven surface, hair. If it is immersed in the degreaser containing surfactant for 5 to 10 minutes before the sodium hydroxide is removed from the membrane, it is directly (without water washing) into a 25 to 50 g/L sodium hydroxide solution (30 to 40°C). The chemical oxide film can be rapidly removed, and the surface roughness is not affected and is uniform.