Method and apparatus for depositing hard chrome coatings by brush plating

• US 5,453,174 A
• Filed: 01/10/1994
• Issued: 09/26/1995
• Est. Priority Date: 07/16/1992
• Status: Expired due to Fees

• Current Assignee: Klehr Harrison Harvey Branzburg, LLP
• Original Assignee: Electroplating Technologies Limited
• Inventors: Van Anglen, Erik S., Keeney, Harold M.
• Primary Examiner(s): Valentine, Donald R.
• Application Number:
  US08/179,579
• Time in Patent Office: 624 Days
• Field of Search: 204/224 R, 204/225, 204/271, 204/275, 204/217, 204/292-293, 204/237, 204/212, 204/227, 205/117, 205/118
• US Class Current: 205/117
• CPC Class Codes: C25D 5/06 Brush or pad plating

Abstract

Thick layers of hard dense chromium coatings are formed on metal substrates by an electrolytic brush plating operation in which a lead-tin anode is closely positioned to a cathodic workpiece in full anode wrap relationship and the surface of the cathodic workpiece is wiped by an open construction wiper to remove hydrogen bubbles and/or outwardly extending dendritic coating material with minimum contact with and force upon the coating surface. The open wiper construction allows free access to the coated surface at all times of fresh undepleted coating electrolyte and allows hydrogen bubbles and dendritic material to be discharged unimpeded from the wiper structure.

Claims

1. An improved apparatus for selective electrolytic plating of a hard chromium coating upon a cathodic workpiece comprising:

(a) a dielectric electrode support means,

(b) a lead based anodic electrode arranged and constructed for support by said dielectric support means closely spaced to a predetermined surface of a cathodic workpiece to be plated and effecting at all times during electroplating substantially full anode coverage of the area of the surface of the cathodic workpiece to be plated,

(c) an anode wrap material positioned upon the active surface of the anodic electrode in opposition to and contigous with the cathodic workpiece,

(d) conduit means for delivering a chromic acid containing electrolytic solution to the anode wrap material,

(e) means to facilitate substantially continuous relative movement of the anodic electrode with respect to the contiguous surface of the cathodic workpiece with the anode wrap material against such surface to be coated, and

(f) means arranged and adapted to allow continuous feed and replacement of electrolytic solution in the anode wrap material.

2. An improved apparatus in accordance with claim 1 additionally comprising:

(g) an electrolyte supply means for dispensing heated coating electrolyte to the anode wrap material upon the lead base anodic electrode via the conduit means, and

(h) pump and conduit means to move electrolyte from the electrolyte supply means to a porous plastic material forming at least a portion of the anode wrap material and conduit means to move the electrolyte in a continuous circuit from the electrode chamber means to the electrolyte supply means.

3. An improved apparatus in accordance with claim 2 wherein the electrode comprises a lead-tin alloy and the anode wrap material is comprised of:

(i) a porous felt-like polymeric resin material substantially resistant to deterioration by chromic acid positioned adjacent and effectively attached to the active surface of said lead-based electrode, and

(j) an abrasion resistant polymeric resin brush-like material substantially resistant to chromic acid positioned atop and effectively attached to the porous felt-like polymeric resin material in a position for contact with the surface of the workpiece to be coated during a coating operation,

(k) said brush-like material having plastic bristles spaced at distances adapted to form a workpieces contacting structure having sufficient space between the bristles so as to present no substantial barrier to free movement of undepleted electrolytic solution to the workpiece coating surface to replace a solution from which plating has already taken place or to impede free movement of hydrogen bubbles or dendritic material displaced by said bristles from said surface workpiece away from said surface or to impede release of said hydrogen bubbles or dendritic material from within said plastic bristles.

4. An improved apparatus in accordance with claim 3 where the active surface of the lead-based electrode is a pre-electrolyzed surface.

5. An improved apparatus in accordance with claim 2 wherein the anode wrap material is comprised of:

(i) a porous felt-like polymeric resin material substantially resistant to deterioration by chromic acid positioned adjacent and effectively attached to the active surface of said lead-based electrode means, and

(j) an at least somewhat abrasion resistant interconnected continuous fibrous polymeric resin material substantially resistant to chromic acid positioned atop and effectively secured to the porous felt-like resin material in a position for contact with the surface of the workpiece to be coated during a coating operation,

(k) said fibrous polymeric resin material having its component fibers spaced at distances adapted to form a wiper construction having sufficient space between the fibers to present no substantial barrier to free movement of undepleted electrolytic solution to the workpiece surface to replace solution from which plating has already taken place or to impede free movement of hydrogen bubbles or dendrites displaced by said fibers from said workpiece surface away from said surface or to impede release of said hydrogen bubbles or dendritic material from within said plastic polymeric fibers.

6. An improved apparatus in accordance with claim 2 wherein the lead-based electrode is arranged and constructed for movement in a continuous mode or manner over all portions of the surface to be plated at all times.

7. An improved apparatus in accordance with claim 6 wherein the lead-based electrode substantially surrounds an elongated workpiece which is suitably journaled for rotary movement within a dielectric electrode chamber means.

8. An improved apparatus in accordance with claim 7 wherein the edges of the dielectric electrode chamber means are in sealing relationship with the surface of the workpiece which is to be coated with chromium and an alternate drainage means is provided.

9. An improved apparatus in accordance with claim 6 wherein the lead-based electrode is made in two adjoining halves and has a ridged and valleyed surface adapted to provide an anode-to-cathode surface ratio of at least about 1.5 to 1.

10. An improved apparatus in accordance with claim 6 wherein the lead-based electrode is formed with other than a circumferential active surface and such surface is arranged and constructed such that it has at least an anode-to-cathode surface ratio of at least about 1.5 to 1.

11. An improved apparatus in accordance with claim 10 wherein a rectifier having a ripple factor no greater than 5% is connected to the lead-based anode.

12. A method of selective plating of a hard chromium coating upon a conductive base material comprising:

(a) substantially completely encompassing a portion of the surface of a metal workpiece to be electrolytically coated with a lead base anode,

(b) adjusting the distance between the surface of the lead-base anode and the surface of the metal workpiece to be coated to be within a range of one eighth of an inch to one inch,

(c) establishing an electrical circuit from a source of direct current between the workpiece acting as a cathode and the lead base anode,

(d) contacting the surface of the metal workpiece to be electrolytically coated with a polymeric wiping means having a relatively open construction arranged and constructed to contact the surface of the metal workpiece simultaneously with coating and dislodge bubbles of hydrogen plus dendritic material from said surface and allow said bubbles and dendritic material to be discharged into the coating bath,

(e) establishing continuous movement between the anode plus the adjacent polymeric material as a whole and the surface of the workpiece to be coated while maintaining at least a portion of the anode surface adjacent at all times to each portion of the surface of the workpiece to be coated, and

(f) continuously maintaining undepleted coating electrolyte between the anode and metal workpiece to maintain fresh solution constantly available at all plating areas between said anode and the metal workpiece.

13. A method in accordance with claim 12 wherein the polymeric wiping means which contacts the relatively moving metal workpiece has the form of a bristle-type brush surface having an open construction that will allow ready passage through and from said bristle structure of hydrogen bubbles and severed dendritic coating material.

14. A method in accordance with claim 13 wherein the polymeric wiping means which contact the surface of the relatively moving metal workpiece takes the form of an open weave polymeric material that will allow ready passage through and from said open weave structure of hydrogen bubbles and severed dendritic coating material.

15. A method in accordance with claim 12 additionally comprising circulating the undepleted coating electrolyte in a continuous circuit between a supply and the coating areas of the metal workpiece at a rate sufficiently rapid to prevent any substantial depletion of a desired concentration of chromium in the electrolyte as plating of chromium proceeds.

16. An improved apparatus for selective electrolytic plating of a hard chrome coating upon a cathodic workpiece comprising:

(a) a dielectric outer shell and support means,

(b) an anode within said dielectric outer shell,

(c) means for supporting a cathodic workpiece adjacent said anode with surfaces to be coated within one eighth inch to one inch of each other,

(d) said anode being arranged and constructed to completely cover the cathodic surface to be chrome coated at all times,

(e) a cathodic surface wiping means having a relatively open construction that does not tend to impede either the discharge from said wiper of hydrogen bubbles or dendritic coating material wiped from the surface of the cathodic workpiece positioned to bear against the surface of said cathodic workpiece, and

(e) means to relatively move the cathodic workpiece surface with respect to the anode and the wiping means.

17. An improved apparatus for selective plating of a hard chromium coating upon a cathodic workpiece in accordance with claim 16 wherein the open construction cathodic surface wiping means is comprised of continuous interconnected polymeric fibrous material.

18. An improved apparatus for selective electrolytic coating in accordance with claim 17 wherein the wiping means is comprised of an open construction fibrous polymeric scraping material having relatively widely spaced individual fibers.

19. An improved apparatus for selective electrolytic coating in accordance with claim 18 wherein the wiping means is comprised of an open weave fibrous woven material.

20. An improved apparatus for selective electrolytic coating in accordance with claim 18 wherein the wiping means is comprised of an open construction knitted material.

21. An improved apparatus for selective electrolytic coating in accordance with claim 18 wherein the wiping means is comprised of an open construction braided material.

22. An improved apparatus for selective plating of a hard chromium coating upon a cathodic workpiece in accordance with claim 16 wherein the open construction cathodic surface wiping material is comprised of discontinuous end connected polymeric fibrous material.

23. An improved apparatus for selective electrolytic coating in accordance with claim 22 wherein the wiping means is comprised of a polymeric brush-type wiper having relatively widely spaced bristles.

24. An improved apparatus for selective electrolytic coating in accordance with claim 16 wherein the wiping means is comprised of a solid polymeric wiping blade.

25. An improved apparatus for selective electrolytic coating in accordance with claim 24 wherein the solid polymeric wiping blade extends substantially across the entire cathodic surface.

26. An improved apparatus for selective electrolytic coating in accordance with claim 24 wherein there are a plurality of solid polymeric wiping blades extending at least partially across the cathodic surface.