Question: In addition to our series production facilities, we also have a sample electroplating facility. We not only carry out initial sampling here, but also decoat and recoat parts for private customers. These are individual pieces and small series. Recently, the range has expanded considerably, which poses a particular challenge when it comes to demetallization. As we are not prepared to purchase an expensive solution from the supplier for every combination of substrate and coating, we are looking for an appropriate collection of recipes.
Answer: Demetallization, also known as stripping, can mainly be divided into chemical and electrochemical processes. However, there are also mechanical processes, such as grinding and sandblasting, which are not included in this category for various reasons.
Chemical demetallization processes do not require a power supply and therefore have low investment costs. However, they incur high operating costs due to the consumption of chemicals. Electrochemical demetallization requires correspondingly higher investment costs and a higher energy input, but can reduce the cost of chemicals and often enables shorter processing times.
Demetallization requirements
- High and consistent stripping speed
- Removal of the coating layer without attacking the base material
- Long service life of the solution
- No or only slight decomposition of the solution
- Solution is harmless to waste water and easy to treat
Recipes
The following table should not be regarded as complete. It serves as a starting point for your own "database" and should also be supplemented by your own experience. Further recipes can be found in relevant specialist literature and articles [1-3].
|
Coating: |
Base metal: |
Electrolyte: |
Concentration: |
°C: |
Chem. or Electr: |
|
Aluminum oxide |
Aluminum oxide |
NaOH |
100 - 200 g/L |
20 |
chemical |
|
lead |
Aluminum |
HNO3 |
500 g/L |
20 |
chemical |
|
lead |
Copper, nickel, brass, steel, silver |
NaOH |
135 g/L |
80 - 90 |
1 V |
|
Bronze, aluminum |
Aluminum |
HNO3 |
500 g/L |
20 |
chemical |
|
bronze |
steel |
NaCN, NaOH |
100 g/L, 20 g/L |
20 |
6 V |
|
Cadmium |
aluminum |
HNO3 |
Conc. |
20 |
chemical |
|
cadmium |
steel |
Ammonium nitrate |
100 g/L |
20 |
1 - 5 A/dm2steelcathodes |
|
cadmium |
steel |
NaCN |
100 g/L |
20 |
2 - 10 A/dm2Steelcathodes |
|
chromium |
Aluminum |
H2SO4 |
700 g/L |
20 |
2 - 10 A/dm2 |
|
chromium |
Copper, brass, nickel |
HCl |
Conc. |
20 |
chemical |
|
chromium |
steel |
NaOH |
100 g/L |
20 |
1 - 10 A/dm2 |
|
chromium |
Cast iron |
NaOH |
70 g/L |
35 |
4 - 10 A/dm2 |
|
chromium |
Zinc, aluminum |
H2SO4 |
Conc. |
20 |
6 V |
|
Copper - Nickel - Chromium |
Steel, aluminum |
H3PO4Triethanolamine |
750 g/L 250 g/L |
65 - 90 |
10 A/dm2 |
|
Gold |
Copper and its alloys |
NaCN Alum |
40 g/L 20 g/L |
20 |
1 - 5 A/dm2 |
|
gold |
Steel Non-ferrous metals |
KCN NaOH |
100 g/L 20 g/L |
20 |
1 - 5 A/dm2 |
|
copper |
Aluminum |
HNO3 |
Conc. |
20 |
Chemical |
|
Copper |
Steel |
Cr-VI oxide H2SO4 |
250 g/L 2.5 - 15 g/L |
20 |
1 - 10 A/dm2 |
|
copper |
steel |
NaOH NaCN |
100 g/L100 g/L |
20 |
1 - 20 A/dm2 |
|
copper |
Zinc |
Na2S |
120 g/L |
20 |
1 - 2 A/dm2 |
|
Brass |
Aluminum |
HNO3 |
500 g/L |
20 |
Chemical |
|
Brass |
Steel |
NaCN NaOH |
100 g/L20 g/L |
20 |
6 V |
|
Nickel |
Aluminum |
HNO3 |
Conc. |
20 |
Chemical |
|
Nickel |
steel |
H2SO4 |
700 g/L |
20 |
2 - 10 A/dm2 |
|
nickel |
Zinc |
H2SO4 |
Conc. |
20 |
5 - 10 A/dm2 |
|
nickel |
tin |
HCl |
Conc. |
20 |
6 V |
|
Phosphate layer |
steel |
NaOH, NaCN Trilon |
150 g/L, 75 g/L 75 g/L |
20 - 45 |
Chemical |
|
silver |
Aluminum |
HNO3 |
Conc. |
20 |
Chemical |
|
silver |
Copper |
H2SO4HNO3 |
900 ml/L conc. 100 ml/L conc. |
20 |
6 - 12 V |
|
silver |
Non-ferrous metals |
NaOH |
100 g/L |
20 |
1 - 6 A/dm2 |
|
Zinc |
Aluminum |
HNO3 |
400 g/L |
20 |
Chemical |
|
Zinc |
Non-ferrous metals |
NaOH |
100 g/L |
20 |
Chemical |
|
Zinc |
steel |
HCl or H2SO4 |
10-20% |
20 |
Chemical |
|
Tin |
Steel |
HCl Antimony oxide |
Conc. 15 g/L |
20 |
Chemical |
Literature
[1]Praktische Galvanotechnik; T.W. Jelinek; 7th edition; Eugen G. Leuze Verlag; ISBN 978-3-87480-277-2
[2]Technology of Electroplating; Bernhard Gaida, Bernd Andreas and Kurt Aßmann; 2nd edition; Eugen G. Leuze Verlag; ISBN 978-3-87480-240-6
[3]Online article archive electroplating Link: https://www.leuze-verlag.de/fachzeitschriften/galvanotechnik/artikelarchiv-gt
