Method for anodizing metallic alloys, particularly for heat exchangers made of aluminum alloys and the like for condensing boilers

Abstract

A method for anodizing metallic alloys, particularly for heat exchangers made of aluminum alloys and the like for condensing boilers, comprising a step of immersing at least one heat exchanger or the like made of a metallic alloy in a bath of an electrolytic solution functionally associated with a source of electric current through the heat exchanger, the anodizing method then providing for a step of anodizing the heat exchanger immersed in the bath, so as to anodize at least the outer surfaces of the heat exchanger, the method comprising a step of pumping the electrolytic solution into the heat exchanger immersed in the bath for the forced circulation of the electrolytic solution in the internal passage channels of the heat exchanger so as to anodize the inner surfaces of the heat exchanger.

1 . A method for anodizing metallic alloys, particularly for heat exchangers made of aluminum alloys and the like, for condensing boilers, comprising:
 a step of immersing in a bath of an electrolytic solution at a preset temperature at least one heat exchanger or the like made of a metallic alloy, said bath being functionally associated with a flow of electric current through the heat exchanger that hangs from the frame within said electrolytic solution,   a step of anodizing said at least one heat exchanger immersed in said bath, with retention of said at least one heat exchanger for a preset retention time, circulating electric current starting from a substantially nil initial value to a preset value with a preset rising ramp of said value to anodize at least the outer surfaces of said at least one heat exchanger, the method further comprising a step of pumping said electrolytic solution into said at least one heat exchanger immersed in said bath, performed during said anodizing step for the forced circulation of said electrolytic solution in the internal passage channels of said at least one heat exchanger to anodize the inner surfaces of said at least one heat exchanger.   
     
     
         2 . The anodizing method according to  claim 1 , wherein said electrolytic solution is an aqueous solution of sulfuric acid with a concentration preferably equal to 180 g/l. 
     
     
         3 . The anodizing method according to  claim 1 , wherein said electrolytic solution in said bath is at a preset temperature preferably equal to −4° C. 
     
     
         4 . The anodizing method according to  claim 1 , wherein in said anodizing step the retention time of said at least one heat exchanger in said bath is preferably equal to 45 minutes. 
     
     
         5 . The anodizing method according to  claim 1 , wherein in said anodizing step the preset value of electric current through the heat exchanger is preferably equal to 4 amps for each square decimeter of exchanger surface, with a preset rising ramp of said preset value of preferably 10 minutes. 
     
     
         6 . The anodizing method according to  claim 1 , comprising a step of degreasing said at least one heat exchanger in an aqueous solution with solvents for metals at a temperature preferably comprised between 50° C. and 60° C., said degreasing step being performed prior to said immersion step. 
     
     
         7 . The anodizing method according to  claim 6 , comprising a first step of rinsing with running water for a time preferably equal to 2 minutes said at least one heat exchanger degreased in said degreasing step, said first rinsing step being performed between said degreasing step and said immersion step. 
     
     
         8 . The anodizing method according to  claim 7 , comprising a second step of rinsing with running water for a time preferably equal to 5 minutes said at least one heat exchanger anodized in said anodizing step, said second rinsing step being performed after said anodizing step. 
     
     
         9 . The anodizing method according to  claim 8 , comprising a third step of rinsing with demineralized water for a time preferably equal to 5 minutes said at least one heat exchanger rinsed in said second rinsing step, said third rinsing step being performed after said second rinsing step. 
     
     
         10 . The anodizing method according to  claim 1 , comprising a step of drying, with forced air at a temperature preferably equal to 40° C., said at least one heat exchanger. 
     
     
         11 . An apparatus for processes for anodizing metallic alloys, particularly for heat exchangers made of aluminum alloys and the like, for condensing boilers, comprising a tank which contains an electrolytic solution, comprising means for pumping said electrolytic solution contained in said tank which can be connected functionally to at least one heat exchanger connected to a source of electric current through the frame immersed in said tank which contains said electrolytic solution by means of a recirculation system for the forced circulation of said electrolytic solution in the internal passage channels of said at least one heat exchanger for anodizing the inner surfaces of said at least one heat exchanger. 
     
     
         12 . The apparatus according to  claim 11 , wherein said recirculation system comprises at least one delivery tube for each internal passage channel formed by said at least one heat exchanger, which is functionally connected to said pumping means and can be connected functionally to said internal passage channel. 
     
     
         13 . An aluminum alloy heat exchanger for condensing boilers and the like, comprising an outer coating of aluminum oxide with a thickness comprised between 20 and 40 micrometers deposited on its inner surfaces. 
     
     
         14 . The heat exchanger according to  claim 13 , comprising an outer coating of aluminum oxide with a thickness comprised between 35 micrometers and 40 micrometers deposited on its outer surfaces.