Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 28 of 331

2. Fresh water rinsing: The purpose of this stage is to flush all remaining organic soil from the part and neu- tralize alkalinity and prevent pH con- tamination of the next stage. Many systems do not have adequately sized rinse tank volumes or overflow ca- pacity to effectively flush and neu- tralize. Part density and configuration dictate the most suitable overflow rate. Control at this stage consists of mon- itoring pH and total dissolved solids. 3. Phosphating: Iron phosphating is the most common form of conversion coating in general industry for today's new coatings. The cleaned and rinsed part enters the phosphating stage and receives a uniform acidic attack. Unlike three-stage systems where the chem- istry relies both on removal of soil and phosphate deposition, the five-stage system employs a single function: phosphating. This allows a wider range of chemistries for phosphating and the ability to use ingredients that produce a much higher quality phos- phate coating. Similar chemical reactions occur at the substrate–solution interface.The deposition of phosphate is not only more uniform, it is also heavier in na- ture and quality. Most five-stage iron phosphates deliver 40–70 mg/ft2 of coating. 4. Fresh water rinsing: The purpose of stage four is to flush any remaining phosphate solution and prevent the subsequent stage from becoming con- taminated. 5. Seal rinsing: The purpose of final seal rinsing, regardless of whether it's the final stage in either a three- or five- stage system, is to remove unreacted phosphate and other contaminants, cover bare spots in the coating, pre- vent the surface from flash rusting, and extend salt spray performance. There are three types of seal rinse: deionized water rinses, acidified rins- es, and reactive rinses. stay ahead of the game with STEELCOTE, A Brite's superior line of Phosphate/ Pre-Treatment Chemistry X Superior Technology • Reduced Costs • Consistent Quality X Product Innovation • Low Temperature Phosphates • Phosphate Free Conversion Coatings X Superior Service • Solving Complex Finishing Problems • Rapid In Plant Service TOLL FREE: 1.888.8A BRITE 27 Li STRIKEne up a with...

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