SurTec 759 Acidic Bright Zinc Process

Transcription

1 Protection upgraded SurTec 759 Acidic Bright Zinc Process Properties produces very bright and ductile zinc layers highly concentrated additives, very economic consumption excellent covering and throwing power, good metal distribution suited for rack plating with air or rack agitation, also appropriate for barrel plating tolerates low and high process temperatures (cloud point approx. 80 C) designed as pure potassium electrolyte; ammonium or mixed electrolytes are possible on request runs with high and low zinc content easy to passivate rather insensitive to overdosage or drag-in of impurities IMDS-number: Application The zinc process SurTec 759 includes the following products: SurTec 759 I Carrier contains surfactants and additives which improve the metal distribution; it is used for make-up and maintenance for the replenishment of drag-out losses SurTec 759 II Brightener is used only for make-up and controls the brightness of the zinc layer SurTec 759 M Maintenance Additive contains carrier and brightener additives in the correct ratio of electroplating consumption (dosing according to Ampere hours) make-up values: zinc chloride 60 g/l (50-70 g/l) potassium chloride 205 g/l ( g/l) boric acid 25 g/l (20-25 g/l) SurTec 759 I Carrier 30 ml/l (25-40 ml/l) SurTec 759 II Brightener 1.0 ml/l ( ml/l) analytical values: zinc 30 g/l (20-40 g/l) chloride 130 g/l (Zn g/l) boric acid 25 g/l (20-25 g/l) SurTec 759 I Carrier 30 ml/l (25-40 ml/l) SurTec 759 II Brightener 1.0 ml/l ( ml/l) page 1

2 make-up: Steps for make-up: 1. Fill warm deionised water (50 % of the final volume) into the tank. 2. Add and dissolve zinc chloride and boric acid. 3. Add potassium chloride. 4. Fill up to 90 % of the final volume. 5. Adjust the ph-value (with½ conc. HCl resp. with 10 % KOH). 6. Add and admix SurTec 759 I. 7. Add and admix SurTec 759 II. 8. Fill up to the final volume. 9. Start the continuous filtration. temperature: 30 C (20-60 C) ph-value: 5.5 ( ) adjust with ½ conc. hydrochloric acid resp. with 10 % KOH solution current density: 1.5 A/dm 2 (0.5-4 A/dm 2 ) plating speed: 0.25 µm/min at 1 A/dm 2 anodes: pure zinc % plates at titan hooks or pellets in titan baskets agitation: tank material: filtration: heating: cooling: exhaust: hint: recommended: air agitation with oil-free compressed air, recommended for barrel processes as well (see Iron, page 3) additionally or exclusively rack movement / barrel rotation is possible steel with acid resistant plastic coating continuously, with 1-5 cycles/hour only for warm zinc process necessary due to its temperature tolerance, SurTec 759 needs no cooling required for worker's protection Dosage devices must not contain any PVC components (e.g. valves); suitable materials: PP or PE. recommended process sequence (for iron parts): 1. hot degreasing emulsifying: SurTec SurTec 415 demulsifying: SurTec SurTec hydrochloric acid pickling with SurTec anodic electrolytical cleaning SurTec neutralisation SurTec Acidic Bright Zinc Process SurTec activation in 1 %vol hydrochloric acid 7. passivation, e.g. Chromiting SurTec hot air drying Between each step, there has to be rinsed. The rinsing methods have to be adapted to the plating line. page 2

3 Technical Specification (at 20 C) Appearance Density (g/ml) ph-value (conc.) SurTec 759 I liquid, yellowish-brownish, clear ( ) 5.5 (5-6) SurTec 759 II liquid, yellowish, clear ( ) 5.0 (4-6) SurTec 759 M liquid, yellowish-brownish, clear ( ) 5.5 (5-6) Maintenance and Analysis Check the ph-value regularly. If the ph-value is too low, in the bath a quicker increase of iron can be observed, covering and metal distribution will get worse. A too high ph-value leads to a decrease of zinc as well as to roughness of the layer caused by build-in of metal hydroxides. Furthermore burnings could occur within the high current density range. Iron, if higher than 100 ppm, disturbs the process within the high current density range especially with subsequent blue passivation of the parts. Remove iron(ii) impurities by hydrogen peroxide treatment. Therefore add ml/l hydrogen peroxide solution (diluted 1:10). This will oxidize the dissolved iron(ii) to iron(iii), which precipitates as iron(iii) hydroxide. This precipitate can be removed by filtration. Do not overdose hydrogen peroxide since it leads to rough zinc layers. It is also possible to remove a significant part of iron(ii) by the way of continuous air agitation of the electrolyte, since Fe(II) can also be oxidized to Fe(III) by the oxygen of air. A lack of SurTec 759 I Carrier leads to roughness within the high current density range, high lack may cause blistering. An overdosage of SurTec 759 I will not do any optical or technical harm. But if triple dosage is exceeded, more brightener is needed and problems may occur during subsequent passivation. SurTec 759 M Maintenance Additive is added for replenishment of the consumption of carrier and brightener, which are consumed in the course of the plating process. SurTec 759 M is dosed according to Ampere-hours. An overdosage will lead to greasy brightness, but won't cause problems unless there is a lack of SurTec 759 I Carrier. Without SurTec 759 I brittle zinc layers with flittering may occur. Drag-out losses of SurTec 759 I can be replenished proportional to the addition of potassium chloride. Per 25 kg KCl add 2.5 l SurTec 759 I and kg boric acid. The organic additives can be analysed by HPLC. Analyse and adjust the concentration of zinc, chloride and boric acid regularly. Sample Preparation Take a sample at a homogeneously mixed position and let it cool down to room temperature. If the sample is turbid, let the turbidity settle down and decant or filter the solution. page 3

4 Zinc Analysis by Titration 0.1 mol/l EDTA solution (Titriplex III) buffer solution (100 g/l NaOH ml/l 98 % acetic acid in DI-water) indicator: xylenol orange tetra sodium salt (1 % blended in KNO 3 ) 1. Pipette 5 ml bath sample into a 250 ml Erlenmeyer flask. 2. Dilute with 100 ml deionised water. 3. Add 20 ml buffer solution. 4. Add a spatula tip of indicator. 5. Titrate with 0.1 mol/l EDTA solution from red to yellow. consumption in ml = g/l zinc rise by 1 g/l zinc = addition of 2.1 g/l zinc chloride (water-free) Chloride Analysis by Titration 0.1 mol/l silver nitrate solution indicator: chloride indicator (5 g K 2 Cr 2 O NaHCO 3 ) or potassium chromate solution (5 %) 1. Pipette 1 ml bath sample into a 250 ml Erlenmeyer flask. 2. Dilute with 100 ml deionised water. 3. Add some indicator (ph-value must be between 6.5 and 10.5). 4. Titrate with 0.1 N silver nitrate solution from clear yellow to turbid yellow, until the first sign of a brown shade appears. consumption in ml = g/l chloride rise by 1 g/l chloride = addition of 2 g/l potassium chloride Boric Acid Analysis by Titration 0.1 mol/l NaOH solution mannitol EDTA sodium salt NaOH solution (15 %) 1. Pipette 10 ml bath sample into a 250 ml Erlenmeyer flask. 2. Dilute with 50 ml deionised water. 3. Add 2-4 g EDTA sodium salt. 4. Adjust the ph-value with 15 % NaOH solution to ph Add 2 g mannitol to the clear solution (ph-value decreases). 6. Titrate with 0.1 mol/l NaOH solution back to ph 7.9. consumption in ml = g/l boric acid Lack: Dissolve the required amount of boric acid completely in hot water and add the solution to the plating tank. Take into account the percentage from the raw material specification of the boric acid to be dosed. Excess: If the boric acid content becomes too high it will not dissolve completely. This may cause particles in the bath and roughness in the zinc layer. Remove undissolved boric acid from the bath by filtration. page 4

5 Consumption and Stock Keeping The consumption depends heavily on the drag-out (see chapter maintenance ) as well as on the work out. The following values per 10,000 Ah can be taken as estimated average consumption: SurTec 759 M l In order to prevent delays in the production process, per 1,000 l bath the following amounts should be kept in stock: SurTec 759 I SurTec 759 II SurTec 759 M 50 kg 25 kg 100 kg Product Safety and Ecology Classification and designation are noted in the Material Safety Data Sheets (according to the European legislation). The safety instructions and the instructions for environmental protection have to be followed in order to avoid hazards for people and environment. Please pay attention to the explicit details in our Material Safety Data Sheets. Warranty We are responsible for our products in the context of the valid legal regulations. The warranty exclusively accesses for the delivered state of a product. Warranties and claims for damages after the subsequent treatment of our products do not exist. For details please consider our general terms and conditions. Further Information and Contact If you have any questions concerning the process, please contact your local technical department. For further information and contact details please visit our homepage: 30 November 2015/DK, SiD page 5