CHEMICAL METAL PRE-TREATMENT

Transcription

1 Protection upgraded CHEMICAL METAL PRE-TREATMENT Basics and New Developments April 2017 April 18, AGENDA 1 Basics about Chemical Metal Pre-Treatment 2 Cleaning and Pickling 3 Conversion Coating - Phosphating 4 Holistic Approach 5 Summary April 18,

2 BASICS ABOUT CHEMICAL METAL PRE-TREATMENT April 18, BASICS ABOUT CHEMICAL METAL PRE-TREATMENT Purpose of the Pre-Treatment Aim: Achieve adhesion of the subsequent coating (cleaning and pickling) Maintain adhesion and minimise corrosion between coating and part (conversion coating) Defined State of the Surface = clean, free of oxides, free of salts, inert conversion coating Adhesion of the Coating (Paint) = Surface Tension Part > Surface Tension Coating Typically demanded: σs = mn/m the coating can wet the surface and spread σc σs σc = surface tension of coating σs = surface tension of part April 18,

3 BASICS ABOUT CHEMICAL METAL PRE-TREATMENT Properties of the Surface Residues at the Surface April 18, AGENDA 1 Basics about Chemical Metal Pre-Treatment 2 Cleaning and Pickling 3 Conversion Coating - Phosphating 4 Holistic Approach 5 Summary April 18,

4 CLEANING Mechanism Task: remove loosely bound pollutants Vegetable, animal and mineral oils Metal soaps Corrosion inhibitors Pigments Residues of a mechanical treatment Schematic: hydrophobic particles (coal, soot) hydrophilic particles (oxides) builder chips fat, wax, oil, lubricant surfactant April 18, CLEANING Mechanism SINNER Circle Application Time: 5 min ( min) Temperature 60 ºC (RT-80 ºC) Mechanics Assist the Cleaning: Wiping Brushing Spraying Ultra sound Air or part agitation Flooding Builder Substances: Hydroxide Silicate Phosphate Carbonate Borate Alkanol amine fatty acids Surfactants: Non-ionic surfactants Anionic surfactants NaOH, KOH Na 2 H 2 SiO 4 5 H 2 O K 5 P 3 O 10, K 4 P 2 O 7 Na 2 CO 3 Na 2 B 4 O 7 10 H 2 0 April 18,

5 CLEANING Quality and Control Desired Result: Oils, corrosion protection, soaps, pigments are removed Coatings can wet the surface and have good adhesion Wettability of the surface indicates the quality of the cleaning water Hill GmbH April 18, PICKLING Mechanism Task: Remove oxides (scale, rust, corrosion products), formed during mechanical treatment, storage, thermal processes Ingredients: Inorganic acids Surfactants Inhibitors Sulfuric acid / phosphoric acid (dissolve oxides and rust) Non ionic and anionic surfactants (improve the wetting of the surface, removes oils and fat from pores) Triazines (protect the metal bulk) Reaction: Fe 2 O H + 2 Fe H 2 O Fe + 2 H + Fe 2+ + H 2 April 18,

6 PICKLING Alternative Technology Neutral Activation Removing rust at moderate ph of 5-7 No acid fumes, easy to handle, no corrosive chemicals No corrosion during transport Virtually no danger of hydrogen embrittlement April 18, AGENDA 1 Basics about Chemical Metal Pre-Treatment 2 Cleaning and Pickling 3 Conversion Coating - Phosphating 4 Holistic Approach 5 Summary April 18,

7 PHOSPHATING General Differences Amorphous Layer Phosphating (Iron Phosphating): Water based solution of phosphate anions Solution contains no metal cations taking part in the layer formation Only cations coming from the base material take part Crystalline Layer Phosphating: Water based solution of phosphate anions and metal cations The cations of the solution take part in the film formation Additionally, cations from the base material can take part Main processes: zinc phosphating, manganese phosphating, zinc calcium phosphating April 18, PHOSPHATING Amorphous Layer Phosphating (Iron Phosphating) Properties Low cost Cleans and phosphates in one step Spray and immersion application Easy processing Cleaning Cleaning/ Phosphating rinse rinse DI-rinse Phosphating rinse rinse DI-rinse Typical Process Sequences Thin coating Suitable for steel With fluorides suitable for zinc and good cleaning for aluminium Much less sludge compared to zinc phosphating Automatic dosing possible (ph-value) amorphous (non-crystalline) structure approx. 0,3 0,8 g/m² April 18,

8 PHOSPHATING Crystalline Layer Phosphating Zinc Phosphating Excellent corrosion protection Good adhesion of coatings Suitable for Fe- und Zn-materials With fluoride suitable for aluminium Short application time Comparison to iron phosphating More difficult to handle Formation of sludge Crystalline Structure of the Layer approx g/m² Cleaning Rinsing Pickling Rinsing Activation Phosphating Rinsing Passivation DIrinse April 18, PHOSPHATING Crystalline Layer Phosphating Biggest Advantage: Corrosion protection between pre-treatment and coating April 18,

9 PHOSPHATING State of the Art The LT-range; Environmentally Sound Innovations SurTec 615 LT Manganese Phosphating Ni ºC SurTec 619 LT Thick layer Zinc Phosphating, forming and corrosion protection SurTec 618 LT Zinc Phosphating pre-paint Additional Passivation SurTec 580 Cr(III), best corrosion protection SurTec 580 NC Cr-free April 18, PHOSPHATING Passivation Additional Passivation Increases Quality The phosphate layer is porous, gaps in the layer are filled Corrosion protection and adhesion are improved Better process stability Metal Phosphate OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH Me Me Me Me Me Me Me OH Me Me Me Me Me Me Me Me Me Me Metal Phosphate OH HO OH Cr OH OH OH HO OH OH OH HO O O Cr O O HO Cr O O Cr Cr Cr Cr Cr Cr Cr Cr Cr Cr Phosphate Cr O O O O O O O O O O O O O Me Me Me Me Me Me Me O O O O O Phosphate Me Me Me Me Me Me Me Me Me Me Me Metal April 18,

10 AGENDA 1 Basics about Chemical Metal Pre-Treatment 2 Cleaning and Pickling 3 Conversion Coating - Phosphating 4 Holistic approach 5 Summary April 18, HOLISTIC APPROACH Contamination Prior to the Metal Pre-Treatment Know the contamination Avoid excess of contamination Take care about storage and transport Apply suitable corrosion protection April 18,

11 HOLISTIC APPROACH Welded Parts Adjust Welding Parameter Glass-like oxides; only to be removed by mechanical treatment Broken oxide skin Oxide skin Metal corrosion April 18, HOLISTIC APPROACH Welded Parts Phosphating Welded Area Broken oxide skin; uniform phosphating Cracks in the oxide skin; only singular phosphate crystals are deposited April 18,

12 HOLISTIC APPROACH Material Defects due to Forming April 18, HOLISTIC APPROACH Blasting Blasting - Best Pre-Treatment? April 18,

13 AGENDA Subline 1 Basics about Chemical Metal Pre-Treatment 2 Cleaning 3 Conversion Coating - Phosphating 4 Holistic Approach 5 Summary April 18, SUMMARY Chemical Pre-Treatment In order to obtain good adhesion and corrosion protection, a pre-treatment is essential Remove contaminants (oils, fats, particles) Remove sorption layers and reaction layers (oxides) Strive for a stable and uniform state of the surface having a high surface tension Deposit a conversion layer provides a temporary corrosion protection (until the coating has been applied) improves the adhesion of successively applied coatings minimises corrosion between metal und coating Holistic approach Be aware about the precondition of the part Minimise contamination during the manufacturing Take care about corrosion protection during the complete manufacturing process Avoid defects in the bulk material April 18,

14 Protection upgraded Thank you. April 18,