Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

Issue link: https://metalfinishing.epubxp.com/i/49721

Contents of this Issue

Navigation

Page 135 of 707

Zinc die castings may be treated in a specially blended acid solution, commonly referred to as immersion chemical polishing. This process facilitates surface preparation by deburring, smoothening, leveling, and brightening. Common base metal defects, such as nodules and pores, are effectively worked out. A typical solu- tion consists of: 42° Be` nitric acid (20-30%), 66° F (18-46° Be` sulfuric acid (20-25%), ammo- nium bifluoride (20-40%), and nonionic or amphoteric surfactant (>0.5%). Application: 65-115° C). Maintaining temperature is critical to avoid etching or dulling the surface. Immersion time depends on particular surface requirements. Organic soils (grease, oils, buffing compound, mold release, etc.) should be removed in a suitable soak or ultrasonic cleaner before the chemical pol- ishing step. Thorough rinsing is understood between steps. Copper strike as per formulas given for zincated aluminum. Castings should be sealed with at least 0.03 to 0.05 mil. Additional copper as plated to 0.08 to 0.14 mil before application of nickel plating. 134

Articles in this issue

view archives of Metal Finishing Guide Book - 2011-2012 Surface Finishing Guidebook