Continuous in-line processing to produce hot-dip zinc-spelter coated flat-rolled mild-steel strip

Abstract

Methods and apparatus for continuous in-line processing of flat-rolled mild steel substrate, by correlating in-line operations for surface cleansing and substrate heating in preparation for hot-dip zinc-spelter coating of flat-rolled mild steel, pneumatically controlling hot-dip zinc-spelter coating weight on each surface, selective surface solidification of said zinc-spelter coating, and in-line refined-surface-finishing of said solidified zinc-spelter, in a manner which enables in-line adjustment of mechanical-properties, and level presentation, carried out without darkening of such zinc-spelter color or detriment to said uniformly-smooth refined zinc-spelter finish; and, capable of added protective coating free of chemical-treatment of a refined-finish surface.

1 . Continuous in-line processing of flat-rolled steel substrate, providing for 
 i. substrate surface preparation for hot-dip zinc-spelter coating of flat-rolled mild steel,    ii. selective hot-dip zinc-spelter coating weight of said substrate,    iii. selective in-line solidification of said molten zinc-spelter coating,    iv. in-line refinement-surface-finishing of said solidified zinc-spelter, and    v. in-line adjustment of characteristics of said steel substrate, free of detriment to said refined zinc-spelter finish, comprising the steps of    (A) supplying flat-rolled mild steel substrate of selected thickness gauge;    (B) delivering said steel substrate as continuous-strip establishing an in-line travel path for carrying out zinc-spelter hot-dip coating operations;    (C) cleansing planar surfaces of said flat-rolled substrate by removing surface debris;    (D) heat-treating said continuous-strip substrate in-line in preparation for entry at a selected temperature into a molten hot-dip zinc-spelter coating bath;    (E) pre-selecting molten zinc-spelter composition for said hot-dip coating bath;    (F) controlling submersed travel and substantially-vertical in-line exit travel from said molten zinc-spelter coating bath;    (G) pneumatically controlling molten zinc-spelter coating weight remaining on each planar surface of the substrate while traveling substantially-vertically in-line above said molten hot-dip coating bath;    (H) solidifying said controlled coating-weight hot-dip zinc-spelter coating while traveling in-line above said bath;    (I) delivering approximately ambient-temperature zinc-spelter-coated substrate traveling in-line, in preparing for refinement-surface-finishing of said solidified zinc-spelter coating;    (J) providing elongated flapper-wiping structures with elongated flexible polymer filaments presenting an elongated exterior configuration which is symmetrically-disposed relative to an elongated centrally-located axis of rotation;    (K) arranging a plurality of said flapper-wiping structures within an at-least partially-enclosed space establishing a longitudinally-elongated in-line travel path for surface refinement of said solidified zinc-spelter coating;    (L) orienting said individual wiping structures to extend width-wise of said coated strip during said surface-refinement travel, 
 with each said flapper-wiping structure  
 (i) presenting radially-oriented elongated polymer filaments, characterized by polymeric toughness and flexibility, which filaments are arranged in contiguous-contacting-relationship both radially and along said elongated roll-dimension of said individual wiper structure,  
 (ii) presenting, when free of contact with coated substrate, a substantially-continuous cylindrical exterior configuration, in which  
 (iii) distal ends of said filaments are embedded with abrasive-particulate-grit, establishing a working surface for each said wiper-structure when said filaments are contacting zinc-spelter coated substrate;  
   (M) selecting abrasive particulate grit size for distal ends of said filaments, of each said flapper-wiper structure, as said structures are distributed longitudinally along said elongated surface-refinement travel path;    (N) refining said zinc-spelter coating on contacted substrate, by: 
 (i) powered rotational driving of each said flapper-wiper-structure, about its respective centrally-located axis of rotation,  
 (ii) positioning each said rotatably driven flapper-wiper structure, to selectively establish embedded-grit-distal-ends of wiping-filaments, in contact with solidified zinc-spelter coated surface of said substrate during said surface-finishing travel, and  
 (iii) controlling-pressure exerted by each said roller-configuration flapper-wiper structure to control wiping action force exerted by each said longitudinally-elongated working structure, providing for smoothening and producing a glare-free silvery finish for said contacted zinc-spelter surface; followed, in-line, by  
   (P) adjusting said steel substrate characteristics, by selecting from the group consisting of 
 (i) adjusting temper of said steel substrate  
 (ii) tension-leveling said steel substrate, and  
 (iii) a combination of (i) and (ii); while  
   (P) enabling liquid quenching of said finish-surface zinc-spelter coated substrate, during said selected adjusting of characteristics of said substrate, free of detriment to said refined-surface-finish of said zinc-spelter coating.    
   
   
       2 . The process of  claim 1 , further including 
 (Q) selecting axial-length and axial orientation of said longitudinally-elongated cylindrical-roll-configuration flapper-wiper structures, so as to extend across strip width and beyond each respective lateral-edge of said elongated strip, during said surface-finishing in-line travel; while    (R) providing for rotating each cylindrical-roll wiper structure about its respective centrally-located longitudinal axis, 
 (i) contacting zinc-spelter coated surface across full width of said strip with a selected force, during said surface-finishing travel,  
 (ii) selectively establishing the number of flapper-wiping-structures operating during said surface-refining travel, and  
 (iii) increasing the number of flapper-wiping structures during said surface-refining travel with increasing surface-refining in-line travel speed for said zinc-spelter coated mild-steel substrate.  
   
   
   
       3 . The process of  claim 2 , further including 
 (S) selecting particle size of embedded grit contiguous to distal ends of said radially-oriented flapper wiping filaments, while 
 (i) correlating location of said selected grit rotatable flapper-wiper structures along said travel path for surface-refinement, by:  
 (ii) establishing larger particulate-size embedded grit for more aggressive wiping by filaments of a flapper-wiping-structure as located for first contacting said zinc-spelter coated substrate during in-line surface-finishing travel, and  
 (iii) establishing smaller particulate-size embedded grit and less-aggressive wiping, by said structures at locations subsequent to said entrance location during said surface-refining travel.  
   
   
   
       4 . The process of  claim 1 , in which a selected adjustment of steel substrate temper is carried-out, by 
 limiting percentage elongation of said steel substrate to be within a range from less than about 0.5% and extending to about 3.0%.    
   
   
       5 . The process of  claim 4 , further including 
 (T) applying a protective coating to a refined-zinc-spelter finish-surface, by    selecting said protective coating from the group consisting of 
 (i) paint,  
 (ii) organic lacquer, and  
 (iii) a thermoplastic polymeric formulation; including  
   (U) applying said protective coating by selecting from the group consisting of 
 (i) both said zinc-spelter refined-surfaces of said substrate, and  
 (ii) solely a single zinc-spelter refined surface of said substrate.  
   
   
   
       6 . Hot-dip zinc-spelter coated flat-rolled mild-steel substrate with refined-surface-finish having 
 a uniformly-smooth zinc-spelter finish surface produced in accordance with the process of  claim 1 .    
   
   
       7 . Hot-dip zinc-spelter coated flat-rolled mild-steel substrate, with refined-surface-finish, having 
 a uniformly smooth zinc-spelter finish surface produced in accordance with the process of  claim 3 .    
   
   
       8 . Hot-dip zinc-spelter refined-surface-finish flat-rolled mild-steel substrate, having 
 an added protective coating produced in accordance with  claim 5 .    
   
   
       9 . Continuous in-line production apparatus for correlating coating and substrate processing of 
 (i) hot-dip zinc-spelter coated flat-rolled mild steel substrate, with    (ii) refined-finish-surface of solidified zinc-spelter, and    (iii) subsequent in-line adjustment of characteristics of said steel substrate, free of detriment to said refined-surface-finish zinc-spelter coating, comprising    (A) means supplying coils of flat-rolled mild steel substrate of selected thickness gauge for hot-dip zinc-spelter coating;    (B) continuous-line means for forming continuous-strip from said coils for in-line travel;    (C) means for preparing said continuous-strip steel substrate for hot-dip zinc-spelter coating, including: 
 (i) cleansing means for planar surfaces of said flat-rolled steel substrate to remove manufacturing debris, and  
 (ii) means for removing surface iron oxide;  
   (D) temperature-controlled molten zinc-spelter hot-dip coating-bath means for immersion of said cleansed strip and in-line travel;    (E) means for delivering said strip from said coating-bath means, with adhering molten zinc-spelter, for substantially-vertical upwardly-directed in-line travel;    (F) pneumatic means, located along said substantially-vertical in-line travel path, for controlling molten-spelter coating weight on each surface of said steel substrate,    (G) means for controlling solidification characteristics of said molten zinc-spelter coating, selected from the group consisting of: 
 (i) means for minimizing spangle formation during solidification of said coating,  
 (ii) heating means for alloying said zinc-spelter with iron of said mild steel substrate during solidification of said coating, and  
 (iii) in-line means for cooling-solidification of said controlled-coating weight molten zinc-spelter and substrate;  
   (H) in-line means for refinement-surface-finishing of said solidified zinc-spelter, including 
 (i) a plurality of longitudinally-elongated rotatably-mounted flapper-wiper-structures sequentially mounted in-line for surface-finishing travel with said coated strip, with each such wiper structure  
 (ii) defining a longitudinally-elongated external cylindrical-roll-configuration, which is symmetrical with a central axis of rotation for said configuration,  
 (iii) an inner longitudinally-elongated rigid core means, which is symmetrical with said axis of rotation, with  
 (iv) flapper-wiper elongated flexible filaments contiguously-located longitudinally and radially of said cylindrical-configuration, extending radially from each said core means, with 
 (a) distal-end portions of said filaments ladened with embedded grit of selected particulate size and hardness,  
 (b) located for wiping contact with coated zinc-spelter; and  
 
 (v) means for controlling wiping force exerted by contact of said distal ends of said flexible filaments, by controlling contact thereof during surface-refining travel of said zinc-spelter coated surface, by: 
 (a) selective size of said abrasive particulate grit as embedded contiguous to such distal end portions of said filaments, for contacting said zinc-spelter coated surface,  
 (b) selective rate of rotating longitudinally-elongated wiping structures, and  
 (c) means for controlling contact of said embedded grit distal-end portions, which extend across full-strip width and beyond each lateral-edge during said surface finishing in-line travel, by controlling movement of said cylindrical-configuration flapper wiper structures toward and away from said zinc-coated substrate, to change the force exerted by said wiping contact;  
 
   (I) means for rotatably driving said flapper-wiper means with embedded abrasive-grit contiguous to said distal ends of said filaments contacting said zinc-spelter coating so as to produce a uniformly-smooth surface during said surface-finishing in-line contact, and    (J) means located in-line, subsequent to said refined-surface-finishing means, for adjusting characteristics of said mild-steel substrate, by selection from the group consisting of 
 (i) changing mechanical-properties by limited elongation of said coated substrate,  
 (ii) tension-leveling of said coated substrate, and  
 (iii) combinations of (i) and (ii); in which 
 (a) elongation of said coated substrate, if any, is limited to a range of length of less than 0.5% and extending to about 3.0%.  
 
   
   
   
       10 . The apparatus of  claim 9 , in which 
 (i) said means for cleansing planar surfaces to remove manufacturing debris include heated caustic solution, from which    (ii) solid particulate is removed from said solution during said cleansing; and    (iii) means for removing surface oxide comprise heated-reducing gas located within a confined passageway leading into said hot-dip zinc-spelter coating bath,    (iv) pneumatic means provided for controlling zinc-spelter coating weight, on each respective mild-steel substrate surface, selected from group consisting of 
 (a) uniform zinc-spelter coating weight on each surface, and  
 (b) a differential zinc-spelter coating weight on each surface.  
   
   
   
       11 . The apparatus of  claim 10 , in which 
 said uniform zinc-spelter coating weight for each surface is selected in the range of about four to about nine ounces per square foot, total for both surfaces.    
   
   
       12 . The apparatus of  claim 10 , in which 
 said differential zinc-spelter coating weight is selected to comprise 
 about point two (0.2) ounces per square foot on one surface, and  
 about point seven (0.7) ounces per square foot on the remaining surface.  
   
   
   
       13 . The apparatus of  claim 9 , in which 
 said hot-dip zinc-spelter bath is selected from the group consisting of    (i) about point five (0.5) to about one point two (1.2) percent aluminum with the balance substantially pure zinc,    (ii) about forty to about sixty percent aluminum with the balance substantially pure zinc, and    (iii) about five percent aluminum and misch-metal contents, with the balance substantially pure zinc.    
   
   
       14 . The apparatus of  claim 13 , including 
 (a) selecting a zinc-spelter metal with about point five (0.5) to about point one point two (1.2) percent aluminum, and further including    (b) means for heating said substrate and coating to alloy said zinc-spelter with iron of said steel substrate.    
   
   
       15 . The apparatus of  claim 9 , including 
 (O) means for delivering refined-surface-finish of said zinc-spelter coated steel strip, free of chemical treatment so as to enable direct application of a protective coating selected from the group consisting of 
 (i) paint,  
 (ii) organic lacquer, and  
 (iii) a thermoplastic polymeric formulation.