Electrolytic tinplating of steel substrate and apparatus

Process for electrolytic tinplating continuous-strip steel, comprising in combination

• A. providing flat-rolled steel strip having substantially-planar opposed surfaces
• B. directing such steel strip for horizontally-oriented travel so as to present a bottom surface and a top surface for plating;
• C. providing a horizontally-oriented halogen-bath electrolytic tinplating line presenting an entry cell providing sole access for such steel strip into such line for plating purposes;
• D. polarizing such steel strip cathodically for travel through such line;
• E. directing horizontally-oriented travel of such steel strip through:
• (i) a plurality of horizontally-oriented electrolytic plating cells containing halogen-bath plating solution, in which
• (ii) stannous ions are provided in solution for electrolytic plating such bottom surface by establishing plating current in soluble tin anode means submerged in such halogen-bath plating solution, and
• (iii)electrolytically completing finish-surface tinplating, to a preselected plating weight, from such submerged anode means onto such bottom surface;
• F. preventing dissolution of surface iron from such steel strip into such halogen-bath plating solution, by
• (i) providing a separate soluble anode means, distinct from such submerged anode means, in such entry cell,
• (ii) simultaneously tinplating such top surface, initiated upon entry into such horizontally-oriented tinplating line with a barrier layer of tin from such separate anode means which is distinct from tinplating of such bottom surface with such barrier layer of tin:
• (iii)preventing access of plating solution to such top surface during travel through such tinplating line.

Apparatus for electrolytically tinplating continuous-strip flat-rolled steel substrate, comprising, in combination

• A. means for providing cold-reduced flat-rolled continuous-strip steel substrate presenting opposed substantially-planar surfaces;
• B. means for preparing such surfaces for tinplating, including
• (i) means for cleansing iron fines and debris associated with cold-reducing such steel, from such surfaces, and
• (ii) means for removing oxide from such cleansed surfaces;
• C. means for directing horizontally-oriented travel of such substrate so as to present a bottom surface and an opposite top surface for plating purposes,
• D. a plating line, including:
• (i) a plurality of horizontally-oriented in-line electrolytic tinplating cells, each including anode means adapted for submersion in plating solution confronting such bottom surface of such substrate for finish-surface tinplating thereof;
• (ii) an entry plating cell which provides sole access, for plating purposes of such substrate, into such plating line, with such entry cell including, in addition to such anode means for tinplating such bottom surface:
• (a) means for controlling plating solution surface level in such entry cell for submerging both surfaces of such substrate during travel through such entry cell, and
• (b) a second-anode means, comprising
• soluble tin pellets adapted to be submersed in such plating solution, confronting such top-surface, in contiguously-spaced relationship therewith;
• E. plating-line roll means directing such substrate into such entry cell, for
• horizontally-oriented travel intermediate anode means and such separate-anode means;
• F. electrical power supply means for establishing plating current in such anode means and, independently, establishing plating current in such separate-anode means, with
• such roll means polarizing such strip cathodically, in relation to both such anode means, and
• G. means for controlling plating current in such submerged anode means and such separate-anode means so as to simultaneously electrolytically tinplate both such bottom and such top surface of such substrate in such entry cell.

Electrolytically tinplated continuous-strip flat-rolled steel substrate having:

• A. a substrate thickness gauge in the range of about 0.005″ to about 0.015″;
• B. a pair of substantially-planar opposed substrate surfaces;
• C. electrolytically applied tinplating on each substrate surface, with each such surface, being electrolytically tinplated simultaneously in a horizontally-oriented plating cell containing acidic stannous-ion electrolyte, and in which
• each such surface is electrolytically tinplated from an independently-powered anode means.

Halogen-bath plating solution for

• electrolytically tinplating elongated continuous-strip flat-rolled steel substrate, while traveling substantially-horizontally in the direction of its length through such plating solution;
• with
• a bottom planar surface confronting, and being tinplated, from tin-anode-bar means which are submerged in such plating solution,
• a top planar surface confronting, and being tinplated, from a separate tin pellet anode means which is suspended in such plating solution above such top planar surface, and in which
• such plating solution:
• (i) has a pH of about 3.5,
• (ii) is substantially free of iron ions resulting from dissolution of surface iron from such steel substrate,
• (iii)is substantially free of additive induced ferrocyanide precipitant resulting from plating solution dissolution of surface iron from such steel substrate during halogen-bath electrolytic tinplating operations.

Method for construction and assembly of separate-anode means and support structure for use in a horizontally-oriented electrolytic tinplating line for continuous-strip flat-rolled steel substrate traveling horizontally, in the direction of its length, so as to present a top surface and a bottom surface during travel through a plurality of horizontally-oriented plating cells containing acidic stannous-ions plating solution, comprising the steps of:

• A. fabricating an elongated support structure for top-surface plating means, in which such support structure, includes
• (i) a framework lined with heavy-gauge open-mesh woven-wire, presenting:
• (ii) elongated sidewall means, end wall means, and bottom wall means for support of tin pellets, while maintaining
• (iii)an accessible upper opening;
• B. electrically insulating such woven-wire support structure;
• C. assembling an elongated electrically-conductive interior liner for fitting within, and contiguous to, an interior periphery of such electrically-insulated woven-wire support structure defined by such side wall means, endwall means and bottom wall means of such support structure, with such liner
• (i) providing for and establishing an elongated electrically-conductive power-input chamber, extending from one longitudinal end of such liner, for holding tin pellets forming a top surface anode means,
• (ii) providing for and establishing an elongated electrically-conductive basket portion located at the remaining longitudinal end of such elongated liner, for holding tin pellets forming a second-anode, with
• (iii)such elongated basket portion extending across, and confronting, the full width of such top surface of such horizontally-oriented travel strip;
• D. providing solution-porous cloth-like material for internally circumscribing such basket portion within such elongated electrically-conductive liner,
• E. supporting such separate-anode means and tin anode pellets internally of and in electrical contact with such elongated conductive liner,
• F. establishing plating current in such tin pellets, with such cloth-like material
• permitting free access of plating solution and migration of stannous ions resulting from dissolution of such tin pellets,
• G. tinplating such steel substrate top surface from tin pellets within such solution-porous material by
• (i) submersing at least a portion of such tin pellets in plating solution of such entry cell, while
• (ii) preventing solid particulate tin from passing through the solution-porous material lining such basket portion so as to avoid contact of solid particulate with such strip.