Contents 3.1.2.1 The pickling reaction 58 3.1.2.2 Nucleation and crystal growth 64 3.1.2.3 Electrochemical theory of coating formation 92 3.1.3 The Coating and its Properties 94
3.1.3.1 Structure and composition of the phosphate coating 94 3.1.3.2 Adhesion of the coating to metallic substrates 103 3.1.3.3 Physical properties of the coating 105 3.1.3.4 Chemical properties of the coating 106 3.1.4 Effects of Phosphate Coatings on the Properties of the Metal Substrate 110 3.1.5 Phosphating Processes 113 3.2 ‘Non-Coating’ Phosphate Processes 120 3.2.1 Kinetics of Coating Formation 120 3.2.2 Composition of Alkali Phosphate Baths 124 3.2.3 The Coating and its Properties 126 3.2.3.1 Formation and composition of the coating 126 3.2.3.2 Physical and chemical properties of the coating 129 3.2.4 Processes for ‘Non-coating’ Phosphating 130 3.3 Phosphating in Non-aqueous Media 130 3.3.1 Corrosion Processes in Non-aqueous Media 130 3.3.2 Systems Based on Halogenated Hydrocarbons 131 3.3.3 Systems Based on Halogen-free Solvents 131 3.3.4 Phosphating Reaction Lubricants 131 3.3.5 Wash Primers 132 3.3.6 Phosphoric Acid Containing Post-treatment Compounds 133 3.4 Phosphating Followed by Heat Treatment 133 4. TECHNICAL APPLICA nONS OF PHOSPHATING 137 4.1 General Comments on the Process 137 4.2 Corrosion Protection with no Subsequent Treatment 138 4.3 Corrosion Protection with Additional Post-treatment 140 4.3.1 Post-treatment with Inorganic Compounds 141 4.3.2 Post-treatment with Oils and Waxes 142 4.3.2.1 General comments on post-treatment with oils and waxes 142 4.3.2.2 Synergistic effects of phosphate coatings and corrosion protective oils 144 4.3.2.3 Practical applications of oil or wax-treated phosphate coatings 145 4.3.3 Post-treatment with Specialised Paints 146 4.3.4 Technical Implementation of Phosphating for Corrosion Protection with or without Post-treatment 147 4.4 Phosphating as a Base for Paint or Organic Coatings 149 4.4.1 Pretreatments for Liquid Paint Application 149 4.4.1.1 General comments 149 4.4.1. 2 Synergistic effects of phosphate coating and paint films 151 4.4.1.3 Practical applications 154 4.4.2 Pretreatments for Electrocoating 155 4.4.2.1 General comments on electro coating 156 4.4.2.2 Physico-chemical reactions in anodic electrocoating 4.4.2.3 Synergistic effects of phosphating and anodic electrocoating 157 4.4.2.4 Practical applications of anodic electrocoating 167 4.4.2.5 General comments on cathodic electrocoating 167 4.4.2.6 Physico-chemical reactions taking place in cathodic electrocoating 168 4.4.2.7 Synergistic effects of phosphate coatings with cathodic electrocoating 169 4.4.2.8 Practical applications in conjunction with cathodic electro coating 176 4.4.3 Technical Aspects of Phosphating for Conventional Painting or Electrocoating 176 4.4.3.1 Spray processes 176 4.4.3.2 Immersion processes 179 4.4.3.3 High-pressure spraying 180 4.4.3.4 Phosphating of motor vehicle bodies prior to painting 180 4.4.4 Pretreatment for Powder-coating 181 4.4.4.1 General comments on powder-coating 181 4.4.4.2 Synergistic effects between surface pretreatment and powder-coating 183 4.4.4.3 Practical applications 191 4.4.5 Sheet Steel as a Paint Substrate 191 4.4.5.1 Manufacture of cold-roBed steel strip 192 4.4.5.2 Variations in the corrosion resistance of phosphated and painted cold-roBed steel 194 4.4.6 Pre-coated Steel Sheet as a Substrate for Painting 198 4.4.7 Basis Metal for Coil Coating 200 4.4.7.1 Phosphating 200 4.4.7.2 Organic coating materials 205 4.4.7.3 Practical aspects of continuous strip coating 206 4.4.7.4 Applications of coated strip 210 4.5 Phosphating to Facilitate Cold Forming of Metals 211 4.5.1 General Overview 211 4.5.1.1 Effect of friction in cold forming 212 4.5.1.2 Synergistic effects of lubricants and phosphate coatings 212 4.5.1.3 Adhesion and deformability of phosphate coatings 214 4.5.1.4 Phosphating processes for cold deformation of metals 216 4.5.1.5 Effect of the phosphate coating on the formed work 220 4.5.1.6 Surface treatment after cold-forming 220 4.5.2 Drawing of Wire and other Profiles 222 4.5.2.1 General 222 4.5.2.2 Starting materials 223 4.5.2.3 Machinery and equipment 226 4.5.2.4 Tools 227 4.5.2.5 Phosphating 228 4.5.2.6 Implementation of the phosphating process 230 4.5.2.7 Lubricants 231 4.5.2.8 Example of the process sequence 233 4.5.3 Drawing of Tubes and Hollow Sections 233 4.5.3.1 General 233 4.5.3.2 Starting materials 234 4.5.3.3 Drawing processes 234 4.5.3.4 Drawing machinery 236 4.5.3.5 Tools 237 4.5.3.6 Phosphating 238 4.5.3.7 Implementation of the phosphating process 240 4.5.3.8 Lubricants 240 4.5.3.9 Examples of applications 241 4.5.3.10 Post-treatment of drawn tubing 242 4.5.4 Cold Extrusion 242 4.5.4.1 General 242 4.5.4.2 Starting ma terials 243 4.5.4.3 Machinery 244 4.5.4.4 Tools 245 4.5.4.5 Phosphating 245 4.5.4.6 Implementation of the phosphating process 246 4.5.4.7 Lubricants 247 4.5.4.8 Examples of the manufacture of finishe products 248 4.5.5 Deep Drawing 250 4.5.5.1 General 250 4.5.5.2 Machinery and tools 252 4.5.5.3 Steel sheet for drawing and deep drawing 253 4.5.5.4 Phosphating 254 4.5.5.5 Lubricants 256 4.5.5.6 Examples of applications 257 4.6 Improvement of Sliding Properties 258 4.7 Electrical Insulation 260 5. PHOSPHATING PLANT 265 5.1 Process Units 265 5.1.1 Tanks for Treatment Solutions 265 5.1.1.1 Tanks for immersion phosphating 265 5.1.1.2 Tanks for spray phosphating 269 5.1.2 Bath Heating 269 5.1.3 Mechanical Handling Equipment 274 5.1.4 Spray Equipment 276 5.1.5 Liquid Dosing Installations 277 5.1.6 Drying 278 5.1.7 Sludge Removal 278 5.1.8 Storage, Transport and Dosing of Chemicals 279 5.1.9 Materials for Plant Construction 281 5.1.10 Process Feed Water, Rinse Tanks and Water Supply 281 5.2 Treatment Plants 282 5.2.1 Immersion Plants for Individual Components 282 5.2.2 Spray Plants for Individual Components 288 5.2.3 Conveyor-type Plants 288 5.2.4 Plants for Continuous Treatment of Wire 288 5.2.5 Steam and High-pressure Treatment 288 5.2.6 Manual and Special Application Plant 293 5.2.7 Plant Maintenance 293 6. TREATMENT OF EFFLUENTS FROM PHOSPHATING PLANTS 294 6.1 Legal Req uiremen ts 294 6.1.1 Federal Republic of Germany 294 6.1.2 United Kingdom 296 6.1.3 United States of America 296 6.2 General Overview of Effluent Materials 298 6.3 Effluent Management 299 6.4 Effluent Treatment Methods 299 6.4.1 Neutralisation 299 6.4.2 Chromate Removal 301 6.4.3 Nitrite Removal 301 6.4.4 Rinsewater Recycling using lon-exchangers 302 6.4.5 Emulsion Breaking 6.4.6 Thickening of Effluent Sludges 6.5 Effluent Treatment Plants 6.5.1 Batch Treatment 6.5.2 Continuous Treatment 6.6 Zinc Phosphating Plants with Closed Loop Operation 306 6.7 Effluent Monitoring and Analytical Control 307 7. TECHNIQUES FOR THE CHARACTERISATION OF PHOSPHATE COATINGS 308 7.1 Determination of Coating Weight 309 7.1.1 Coating Weight Determination by Strip and Weigh Method 309 7.1.2 Coating Weight Determination by Stripping without We~h~g 7.1.3 Coating Weight Determination of Post-treated Phosphate Coatings 7.1.4 Coating Weight Determination using Infra-red Absorption 7.2 Estimation of Metal Removal during Etching 313 7.3 Coating Thickness Measurement 313 7.3.1 Destructive Thickness Measuring Methods 314 7.3.2 Non-destructive Thickness Measuring Methods 314 7.4 Relationship between Coating Thickness and Coating Weight 316 7.5 Determination of Porosity and Pore Distribution 316 7.6 Determination of Surface Roughness 318 7.7 Determination of Crystal Size 320 7.8 Determination of the Phase Structure 320 7.9 Determination of Electrical Properties 322 7.10 Analysis and Identification of Phosphate Coatings on Metals 323 7.10.1 Determination of Phosphate 325 7.10.2 Determination of Manganese 325 7.10.3 Determination of Zinc 325 7.10.4 Determination of Calcium 325 7.11 Determination of Carbon in the Surface of Steel 8. ANALYTICAL CONTROL OF PROCESS CHEMICALS 327 8.1 Determination of Free Acid 8.2 Determination of Total Phosphate 8.3 Determination of Total Acid or Pointage 8.4 Determination of Acidity Ratio 8.5 Point of Incipient Precipitation (PIP) 8.6 Other Analytical Methods 8.7 Automatic Process Control 8.8 Concentrate Testing 9. TECHNICAL ASSESSMENT OF PHOSPHATE COATINGS 9.1 Tests for Corrosion Protection 9.1.1 Manifestations of Corrosion 9.1. 2 Test Methods for Corrosion Protection 9.1.2.1 Long-term tests 9.1. 2.2 Salt spray test 9.1.2.3 Water condensate test 9.1.2.4 Water condensate test in sulphur dioxid atmosphere 9.1.2.5 Tests for filiform corrosion 9.1.2.6 Detergent test 9.1.2.7 Testing under cyclic conditions 9.1.2.8 Corrosion testing of assem bled vehicles 9.1.2.9 Miscellaneous short-term and electrochemical tests 9.2 Adhesion Testing 9.2.1 Mandrel Bend Test 9.2.2 Cross-hatch Test 9.2.3 Erichsen Test 9.2.4 Impact Tests 9.2.5 Cup Drawing Test 9.2.6 T-bend Test 9.2.7 Stone Chipping Test 9.3 Combined Adhesion and Corrosion Tests 9.4 Testing Surface Friction Properties 9.5 Testing Electrical Insulation Properties 10. STANDARDS RELATING TO PHOSPHATING 10.1 Federal Republic of Germany 10.2 United Kingdom 10.3 Italy 10.4 Japan 10.5 Sweden 10.6 United States of America 11. REFERENCES 12. SUBJECT INDEX
