HYDROTHERMAL BLACK OXIDE CONVERSION COATING PROCESS FOR STEEL COMPONENTS

Description

INTRODUCTION

The technical field generally relates to methods of coating steel components with a black oxide coating and products made thereby.

A variety of products, including vehicles, may have a component that rotates or slides along bearings.

SUMMARY

A number of variations may include a method of forming a black oxide coating on an automotive part for an electric drive unit of a vehicle, the method including: providing an automotive part including a body having an outer surface, the automotive part including iron; placing the automotive part including 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 degrees Celsius (° 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.

A number of variations may include a method further including, prior to placing the automotive part including iron in the black oxide conversion coating solution, cleaning the automotive part to remove residual oil from the outer surface.

A number of variations may include a method wherein cleaning the automotive part includes: disposing the automotive part in a cleaning solution; and subjecting the automotive part and the cleaning solution to ultrasonic waves.

A number of variations may include a method further including rinsing the cleaning solution from the outer surface.

A number of variations may include a method further including: 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.

A number of variations may include a method wherein the at least one oxidizing salt includes sodium metabisulfite present in about 5 weight (wt) percent (%) to about 20 wt % of the black oxide conversion coating solution.

A number of variations may include a method wherein the black oxide conversion coating solution further includes about 3 wt % to about 15 wt % of a surfactant.

A number of variations may include a method wherein the black oxide conversion coating solution further includes about 0.25 wt % to about 3 wt % citric acid.

A number of variations may include a method wherein the temperature ranges from about 25° C. to about 65° C.

A number of variations may include a method wherein the temperature ranges from about 30° C. to about 60° C.

A number of variations may include a method of forming a black oxide coating on an automotive part for an electric drive unit of a vehicle, the method including: providing a bearing including a body having an outer surface, the bearing including iron; placing the bearing including iron in a black oxide conversion coating solution including 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.

A number of variations may include a system for forming a black oxide coating on an automotive part for an electric drive unit of a vehicle, the system including: 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 including: providing a bearing including a body having an outer surface, the bearing including iron; placing the bearing including iron in the black oxide conversion coating solution including 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.

A number of variations may include a system wherein the black oxide coating has a thickness of between 2 microns and 4 microns.

A number of variations may include a system wherein the black oxide coating is substantially free of mud cracks.

A number of variations may include a system further including: 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.

A number of variations may include a system wherein the at least one oxidizing salt includes sodium metabisulfite present in about 5 weight (wt) percent (%) to about 15 wt % of the black oxide conversion coating solution.

A number of variations may include a system wherein the black oxide conversion coating solution further includes about 3 wt % to about 15 wt % of a surfactant.

A number of variations may include a system wherein the black oxide conversion coating solution further includes about 0.25 wt % to about 3 wt % citric acid.

A number of variations may include a system wherein the temperature ranges from about 25° C. to about 65° C.

A number of variations may include a system wherein the temperature ranges from about 30° C. to about 60° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The illustrative variations will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1 is a flow chart illustrating a number of steps in a hydrothermal method of forming black oxide on a part including iron according to a number of variations;

FIG. 2 is an illustration of a bearing having a black oxide coating formed thereon by a hydrothermal method according to a number of variations;

FIG. 3 illustrates a pair of SED-SEM images wherein the image on the left of the illustration is a black oxide coating produced by a hydrothermal method according to a number of variations and the image on the right of the illustration is a black oxide coating produced using an ultrasonic method;

FIG. 4 illustrates a system for forming a black oxide coating on an automotive part for an electric drive unit of a vehicle according to a number of variations; and

FIG. 5 is a schematic illustration of a vehicle having an electric drive unit including a bearing assembly having bearing with a black iron coating thereon that is free or substantially free of mud cracks according to a number of variations.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding introduction, brief description of the drawings, brief summary or the following detailed description.

A number of variations disclosed may include systems and methods of coating a part with black (iron) oxide. The part may be a ball bearing assembly for a rotating shaft of an electric drive unit of an automobile. The part comprises a body and an outer surface wherein the outer surface may be coated with a black oxide coating comprising an iron oxide film and iron sulfide platelets disposed on the iron oxide film. The outer surface of the part may be coated with black oxide using a hydrothermal method. The hydrothermal method may reduce cycle time to between about 30 to 60 seconds. The hydrothermal method does not require acid pickling or pre-etching that are required with conventional alkaline salt processes. Furthermore, the hydrothermal method does not include conventional alkaline salt black oxide conversion coating processes that use hydroxide and nitrate solutions which require significant health and safety controls. Furthermore, the hydrothermal method does not require large and costly specialized hydrostatic paths required by conventional ultrasonic black oxide coating methods.

FIG. 1 is a flow chart illustrating a number of acts in a method according to a number of variations, wherein the method may include act 22 including placing a part including iron in a black oxide conversion coating solution including at least one ionizing salt. Act 24 may include heating the black oxide conversion coating solution to at least 30 degrees Celsius (° C.). Act 26 may include agitating the black oxide conversion solution so that the at least one ionizing salt reacts with the iron to form black oxide on the part.

FIG. 2 is an illustration of a bearing 28 having a black oxide coating 30 formed thereon by a method, for example but not limited to the method illustrated in FIG. 1. The black oxide coating formed on the surface of the bearing uniformly covers the surface of the bearing 28 and is free of mud cracks or at least substantially free of mud cracks.

FIG. 3 illustrates a pair of secondary electron detector-scanning electron microscope (SED-SEM) images wherein the image on the left 32 of the illustration is a black oxide coating produced by a hydrothermal method according to a number of variations and the image on the right 34 of the illustration is a black oxide coating produced using an ultrasonic method. Both coatings were applied to or formed on ball bearing rolling elements. The black oxide coating produced by the hydrothermal method contained significantly less “mud cracking” 36 than the black oxide produced by the ultrasonic method. The mud cracking 36 or “mud cracks” 36 is/are formed due to internal stresses in the black oxide coating produced by conventional alkaline salt or ultrasonic methods.

A number of variations may include a hydrothermal method of coating an automotive part, such as an electric drive unit bearing assembly, with iron oxide for an electric drive unit. In a number of variations, prior to act 22 of FIG. 1, the part may be cleaned to remove residual oil from an outer surface of the part. In a number of variations, the part may be placed in the first tank including a cleaning solution. An ultrasonic device may be positioned in the first tank and may generate ultrasonic waves that travel through the cleaning solution and impact the outer surface of the part. Thereafter, the part may be moved from the first tank and rinsed in a cleaning solution by spraying a water-based solution on the part or by submerging the part in a water-based solution.

After cleaning the part, the part including iron may be placed in a black oxide conversion coating solution including at least one oxidizing salt. The oxidizing salt may include, but not limited to, sodium metabisulfite (Na2SO3). In a number of variations, the black oxide conversion coating solution may include sodium metabisulfite (Na2SO3) an amount ranging from about 3 weight (wt) percent (%) to about 20 wt %, or any range, and the range may include at least one endpoint, or any single weight percent, of 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 10 wt %, 12 wt %, 14 wt %, 16 wt %, 17 wt %, 18 wt %, or 19 wt % sodium metabisulfite (Na2SO3). The black oxide coating conversion solution may include an amount ranging from about 3 wt % to about 15 wt %, or any range therebetween, and the range may include at least one endpoint, or any single weight percent, of 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13 wt %, and 14 wt % surfactant. The surfactant may be a liquid detergent comprising a chlorosulfonated hydrocarbon, sodium dodecyl benzene sulfonates, or any other suitable solution without departing from the spirit or scope of the present disclosure. In a number of variations, the surfactant may include a surfactant commercially available under the tradename TEEPOL 610s. The black oxide coating conversion solution may include an amount ranging from about between 0.25 wt % to about 3 wt %, or any range there between, and the range may include at least one endpoint, or single weight percent, of 0.5 wt %, 0.8 wt %, 1 wt %, 1.3 wt %, 1.5 wt %, 1.8 wt %, 2 wt %, 2.3 wt %, 2.5 wt %, and 2.8 wt % citric acid. The balance of the black oxide coating conversion solution may be water.

As illustrated by act 24 of FIG. 1, the black oxide conversion coating solution may be heated to a temperature ranging from about 25 degrees Celsius (° C.) to about 80° C., including any sub range therebetween, and the range may include at least one endpoint temperature, or any single temperature, of 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., or 80° C.

The black oxide conversion solution may be agitated or circulated, in for example a tank, for a time ranging from about 10 seconds to about 80 seconds, or any sub range therebetween, and may include at least one time endpoint, or a single time, of 15 seconds, 20 seconds, 25 seconds, 30 seconds, 35 seconds, 40 seconds, 45 seconds, 50 seconds, 60 seconds, 70 seconds, or 75 seconds. The black oxide conversion coating method may produce 1-4 μm of iron oxide coating on the surface of the part. The black oxide conversion solution may be agitated or circulated, for example, using a motorized stirrer, pump, or bubbler but without subjecting the solution to ultrasonic waves.

After act 26 in FIG. 1, the hydrothermal method may further include drying the outer surface of the part including the coating formed thereon to remove any water-based/alcohol-based solution therefrom. In a number of variations, the drying may be accomplished using a blower, a drying cabinet, or a drying tunnel using air or nitrogen at a temperature ranging from about 40° C. to about 50° C.

The hydrothermal method may produce iron sulfide (FeS) platelets on the surface of the black oxide coating on the part. The black oxide coating may be applied to the entire outer surface of the bearing by using the appropriate amount of agitation or circulation of the black oxide conversion coating solution. The black oxide coating produced by the hydrothermal method produces corrosion protection during storage of the part coated therewith.

The citric acid may be arranged to chemically activate the surface of the part and to allow for the reaction with oxygen/hydrogen species and iron (Fe) forming iron hydroxide, Fe(OH)2. The sodium metabisulfite may be arranged to react with the iron hydroxide generating iron oxysulfide (FeSO3) on the part including iron. The iron oxysulfide may react with oxygen/hydrogen species to produce an iron oxide (FeO, Fe2O3, Fe3O4) film and iron sulfide (FeS) platelets on the part including iron. That is to say that a first portion of the iron oxysulfide reacts with oxygen to produce the iron oxide film on the outer surface of the part including iron, and a second portion of the iron oxysulfide reacts with hydrogen to produce the iron sulfide platelets disposed in the iron oxide film. In a number of variations, the black oxide coating 40 may comprise between 50 wt % and 100 wt %, 55 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, and 95 wt % iron oxide. Additionally, the black oxide coating 40 may include an amount ranging from 0 wt % to about 50 wt %, and any sub range therebetween, and the range may include at least one endpoint weight, or a single weight, of 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, or 45 wt % iron sulfide. Furthermore, the black oxide coating may have a thickness ranging from about 0.5 micron to about 4 microns, or any sub range therebetween and may have at least one endpoint, or a single thickness, of 1 micron, 1.5 micron, 2 microns, 2.5 microns, 3 microns, or 3.5 microns.

FIG. 4 illustrates a system for forming a black oxide coating on an automotive part for an electric drive unit of a vehicle according to a number of variations. The system 300 may include a tank 330 and an agitator 302, which may include a motor 304 and a shaft connected to the motor 304 at one end and a propeller 308 at another end. Wherein at least a portion of the agitator 302 is submerged in a black oxide conversion coating solution 310 contained in the tank 330. The system 300 may also include a heater 312 having at least a portion 314 submerged in the black oxide conversion coating solution 310. The system 300 may include a robotic arm 326 operatively connected to a second motor 328 and to a bearing holder 324 for holding at least one bearing 28. The agitator 302, robotic arm 326 and the heater 312 may be connected to a computing device 316, which may include an electronic processor 318, non-transitory memory 320 having instructions 322 thereon to carry out any of the functionalities described herein.

FIG. 5 is a schematic illustration of a vehicle 400, which may include at least one front wheel 402 operatively connected to at least one front axle 404. The vehicle 400 may include at least one rear wheel 406 operatively connected to at least one rear axle 426. A steering interface 408 may be operatively connected to a steering shaft 410. The steering shaft 410 may be operatively connected to a steering rack 412 which may be operatively connected to the at least one front wheel 402. The vehicle 400 may include an electric drive unit 414 for propelling the vehicle 400. A front drive shaft 416 may be operatively connected to the at least one front axle 404 and to the electric drive unit 414. The front drive shaft 416 may be supported by a first bearing assembly 420 including at least one bearing 28. A rear drive shaft 422 may be operatively connected to the at least one rear axle 426 and to the electric drive unit 414. The rear drive shaft 422 may be supported by a second bearing assembly 424 including at least one bearing 28. A power source 428, which may be an electric battery, may be operative connected to the electric drive unit 414 to supply power thereto. The at least one bearing 28 may have a black iron coating thereon that is free or substantially free of mud cracks. The least one bearing 28 may be coated with the black iron coating thereon that is free or substantially free of mud cracks by a method as described herein.

While at least one variation has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the variation or variations are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the illustrative variation or variations. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.