Method for electrochemical phosphating of metal surfaces

• US 6,346,186 B1
• Filed: 08/07/2000
• Issued: 02/12/2002
• Est. Priority Date: 08/29/1996
• Status: Expired due to Term

• Current Assignee: Chemetall GmbH (BASF SE)
• Original Assignee: Danfoss A/S
• Inventors: Steenberg, Thomas, Christensen, Erik, Bjerrum, Niels Janniksen
• Primary Examiner(s): Mayekar, Kishor
• Application Number:
  US09/633,748
• Time in Patent Office: 554 Days
• Field of Search: 205/318, 205/320, 205/198, 72/41, 72/46
• US Class Current: 205/318
• CPC Class Codes: C25D 11/36 Phosphatising
• CPC Class Codes: C25D 9/10 on iron or steel
• CPC Class Codes: F16L 5/02 Sealing

Abstract

A method for electrochemical phosphating of metal surfaces, particularly stainless steel, in connection with cold forming of metal workpieces, which method provides the cold formed workpiece with a lubricant after phosphating, involves an electrochemical phosphating through a cathodic process applying an aqueous phosphating solution containing

0.5 to 100 g Ca²⁺/l

0.5 to 100 g Zn²⁺/l

5 to 100 g PO₄³⁻/l

0 to 100 g NO₃⁻/l

0 to 100 g ClO₃⁻/l and

0 to 50 g F⁻ or Cl⁻/l

by which the temperature of the solution is between 0 and 95° C., the pH-value of the solution is between 0.5 and 5, and the current density is between 0.1 and 250 mA/cm². This gives a good lubrication effect, a good adhesion to the metal surface, particularly stainless steel, and a more expedient texture than ordinary phosphating.

Claims

1. Method for electrochemical phosphating of metal surfaces used with cold forming of metal workpieces, comprising effecting an electrochemical phosphating through a cathodic process using an aqueous phosphating solution containing

0.5 to 100 g Ca²⁺/l

0.5 to 100 g Zn²⁺/l

5 to 100 g PO₄³⁻

/l

0 to 100 g NO₃⁻

/l

0 to 100 g ClO₃⁻

/l and

0 to 50 g F⁻

or Cl⁻

/l

with the ratio of Ca⁺⁺/Zn⁺⁺ being larger than 1, and where the temperature of the solution is between 0 and 95°

C., the pH-value of the solution is between 0.5 and 5, and the current density is between 0.1 and 250 mA/cm², and then applying a lubricant to the workpiece.

2. Method according to claim 1 in which the lubricant comprises molybdenum disulphide or sodium stearate.

3. Method according to claim 1, in which the temperature of the solution is approx. 25°

C., the pH-value is 1 to 4, and the current density is 5 to 250 mA/cm².

4. Method according to claim 1, in which the aqueous phosphating solution contains

to 20 g Ca²⁺/l

2 to 10 g Zn²⁺/l

to 90 g PO₄3−

/l

20 to 50 g NO₃⁻

/l

0 to 40 g ClO₃⁻

/l and

0 to 5 g F⁻

/l.

5. Method according to claim 1, in which the aqueous phosphating solution further contains 0 to 100 g of a water soluble polymer per litre.

6. Method according to claim 5 in which the water soluble polymer comprises at least one of polyvinyl alcohol, polyethylene glycol and polyethylene oxide.

7. A method of preparing a workpiece, comprising the steps of application of an aqueous phosphating solution as set forth in claim 1 for electrochemical phosphating of metal surfaces of the metal workpiece, and then providing the workpiece to be cold formed with a lubricant after phosphating.

8. A method according to claim 7, in which the lubricant comprises molybdenum disulphide or sodium stearate.

9. A method according to claim 7, in which the phosphating solution further contains 0 to 100 g of a water soluble polymer per litre.

10. A method according to claim 9 in which the water soluble polymer comprises at least one of polyvinyl alcohol, polyethylene glycol and polyethylene oxide.