Dickson Weatherproof Nail/CDC Coatings
Nails to be galvanized were contaminated with cutting oil from an upstream process. The nails were cleaned prior to galvanizing in a 150°F-200°F bath containing alkali- and surfactant-based cleaners. The final cleaning step involved a sulfuric acid dip. Nails that were not properly cleaned resulted in poor adhesion of the coating. These nails had to be stripped in the sulfuric acid and then recleaned as described previously. During a modification to the upstream machines that was intended to increase the productivity, it was noted that the cutting oil was no longer needed. Since the nails entering the galvanizing process were cleaner, only a brief surface preparation in the galvanizing tumbler was required. Since this surface preparation step in the initial step in the galvanizing process anyway, no loss of production or increase in chemical use was observed. Some adhesion problems still occasionally arose, so there was reluctance to eliminating the cleaning line entirely. Further experiments showed that, by increasing the drying oven temperature slightly, the adhesion problems could be completely eliminated. This allowed for the elimination of the cleaning line and the acid-stripping bath.
This project eliminated the generation of 9.4 tons per year of sulfuric acid waste and about three tons per year of caustic waste. In addition, the generation of an oily wastewater was eliminated and control of the wastewater treatment system improved.
Details of Reductions
Additional Information :
A savings of $4,200 per year was realized from the reduction in the use of sulfuric acid and the elimination of the caustic cleaner. Other cost savings include about $500 per year in cutting fluid and about $5,000 per year in natural gas used to heat the caustic tank.