Hydrothermal black oxide conversion coating process for steel components

Abstract

Disclosed is a hydrothermal method of coating a part including iron, the hydrothermal method including placing the part including iron in a black oxide conversion solution including at least one oxidizing salt, heating the black oxide conversion coating solution to at least 20° C., and agitating or circulating the black oxide conversion coating solution so that the at least one oxidizing salt reacts with the iron to form a black oxide coating on the part.

What is claimed is: 
     
         1 . A method of forming a black oxide coating on an automotive part for an electric drive unit of a vehicle, the method comprising:
 providing an automotive part comprising a body having an outer surface, the automotive part comprising iron;   placing the automotive part comprising iron in a black oxide conversion coating solution including at least one oxidizing salt;   heating the black oxide conversion coating solution to a temperature ranging from about 20° C. to 80° C.; and   agitating or circulating the black oxide conversion coating solution for about 20 seconds to about 80 seconds, without subjecting the black oxide conversion coating solution to ultrasonic waves, so that the at least one oxidizing salt reacts with the iron to form a black oxide coating on the automotive part.   
     
     
         2 . The method of  claim 1  further comprising, prior to placing the automotive part comprising iron in the black oxide conversion coating solution, cleaning the automotive part to remove residual oil from the outer surface. 
     
     
         3 . The method as set forth in  claim 2  wherein cleaning the automotive part comprises:
 disposing the automotive part in a cleaning solution; and 
 subjecting the automotive part and the cleaning solution to ultrasonic waves. 
 
     
     
         4 . The method as set forth in  claim 3  further comprising rinsing the cleaning solution from the outer surface. 
     
     
         5 . The method as set forth in  claim 1  further comprising:
 rinsing the black oxide coating on the outer surface with an aqueous solution to remove the aqueous solution therefrom; and 
 drying the outer surface to remove the aqueous solution from the black oxide coating. 
 
     
     
         6 . The method as set forth in  claim 1  wherein the at least one oxidizing salt comprises sodium metabisulfite present in about 5 weight (wt) percent (%) to about 20 wt % of the black oxide conversion coating solution. 
     
     
         7 . The method as set forth in  claim 6  wherein the black oxide conversion coating solution further comprises about 3 wt % to about 15 wt % of a surfactant. 
     
     
         8 . The method as set forth in  claim 6  wherein the black oxide conversion coating solution further comprises about 0.25 wt % to about 3 wt % citric acid. 
     
     
         9 . The method as set forth in  claim 1  wherein the temperature ranges from about 25° C. to about 65° C. 
     
     
         10 . The method as set forth in  claim 1  wherein the temperature ranges from about 30° C. to about 60° C. 
     
     
         11 . A method of forming a black oxide coating on an automotive part for an electric drive unit of a vehicle, the method comprising:
 providing a bearing comprising a body having an outer surface, the bearing comprising iron;   placing the bearing comprising iron in a black oxide conversion coating solution comprising about 5 weight (wt) percent (%) to about 15 wt % sodium metabisulfite, about 3 wt % to about 15 wt % of a surfactant, and about 0.25 wt % to about 3 wt % citric acid;   heating the black oxide conversion coating solution to a temperature ranging from about 30° C. to 60° C.; and   agitating or circulating the black oxide conversion coating solution for about 30 seconds to about 60 seconds, without subjecting the black oxide conversion coating solution to ultrasonic waves, to form a black oxide coating on the bearing.   
     
     
         12 . A system for forming a black oxide coating on an automotive part for an electric drive unit of a vehicle, the system comprising:
 a tank having a black oxide conversion coating solution, an agitator having at least of portion thereof in the black oxide conversion coating solution, a heater having at least of portion thereof in the black oxide conversion coating solution, a robot a, and arm and a bearing holder attached thereto, a computing device including an electric process, non-transitory storage media having instructions thereon executable by the electronic processor to carry out functionality comprising:   providing a bearing comprising a body having an outer surface, the bearing comprising iron;   placing the bearing comprising iron in the black oxide conversion coating solution comprising at least one oxidizing salt present in about 5 weight (wt) percent (%) to about 20 wt % of the black oxide conversion coating solution;   heating the black oxide conversion coating solution to a temperature ranging from about 20° C. to 80° C.; and   agitating or circulating the black oxide conversion coating solution for less than 80 seconds, without subjecting the black oxide conversion coating solution to ultrasonic waves, so that the at least one oxidizing salt reacts with the iron to form a black oxide coating on the automotive part.   
     
     
         13 . The system as set forth in  claim 12  wherein the black oxide coating has a thickness of between 2 microns and 4 microns. 
     
     
         14 . The system as set forth in  claim 12  wherein the black oxide coating is substantially free of mud cracks. 
     
     
         15 . The method as set forth in  claim 12  further comprising:
 rinsing the black oxide coating of the outer surface with an aqueous solution to remove the aqueous solution therefrom; and 
 drying the outer surface to remove the aqueous solution from the black oxide coating. 
 
     
     
         16 . The system as set forth in  claim 12  wherein the at least one oxidizing salt comprises sodium metabisulfite present in about 5 weight (wt) percent (%) to about 15 wt % of the black oxide conversion coating solution. 
     
     
         17 . The system as set forth in  claim 16  wherein the black oxide conversion coating solution further comprises about 3 wt % to about 15 wt % of a surfactant. 
     
     
         18 . The system as set forth in  claim 17  wherein the black oxide conversion coating solution further comprises about 0.25 wt % to about 3 wt % citric acid. 
     
     
         19 . The system as set forth in  claim 12  wherein the temperature ranges from about 25° C. to about 65° C. 
     
     
         20 . The system as set forth in  claim 12  wherein the temperature ranges from about 30° C. to about 60° C.