Hydrothermal black oxide conversion coating process for steel components

Abstract

A hydrothermal process for coating a part containing iron is disclosed, wherein the hydrothermal process comprises placing the part containing iron into a black oxide conversion coating solution containing at least one oxidizing salt, heating the black oxide conversion coating solution to at least 20 °C and stirring 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.

Description

introduction

[0001] The technical field generally refers to processes for coating steel components with a black oxide coating and to the products manufactured using this method.

[0002] A wide variety of products, including vehicles, may contain a component that rotates or slides on bearings. Description

[0003] A number of variations of a method for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle may include the following: providing a motor vehicle part having a body with an outer surface, wherein the motor vehicle part contains iron; placing the motor vehicle part containing iron into a black oxide conversion coating solution containing at least one oxidizing salt; heating the black oxide conversion coating solution to a temperature in the range of about 20 degrees Celsius (°C) to 80 °C; and stirring or circulating the black oxide conversion coating solution for about 20 seconds to about 80 seconds without exposing the black oxide conversion coating solution to ultrasonic waves, such that the at least one oxidizing salt reacts with the iron to form a black oxide coating on the motor vehicle part.

[0004] A number of variations may include a procedure that involves cleaning the vehicle part to remove residual oil from the outer surface before placing the iron-containing automotive part into the black oxide conversion coating solution.

[0005] A number of variations may include a process in which cleaning the motor vehicle part comprises: arranging the motor vehicle part in a cleaning solution; and exposing the motor vehicle part and the cleaning solution to ultrasonic waves.

[0006] A number of variations may include a procedure that further involves rinsing the cleaning solution from the outer surface.

[0007] A number of variations may include a procedure that further comprises: rinsing the black oxide coating on the outer surface with an aqueous solution to remove the aqueous solution from it; and drying the outer surface to remove the aqueous solution from the black oxide coating.

[0008] A number of variations may include a process comprising at least one oxidizing salt, sodium metabisulfite, which is present in approximately 5 wt% to approximately 20 wt% of the black oxide conversion coating solution.

[0009] A process can include a number of variations, wherein the black oxide conversion coating solution further comprises about 3 to 15 wt% of a surfactant.

[0010] A process may include a number of variations, wherein the black oxide conversion coating solution further contains approximately 0.25 wt.% to approximately 3 wt.% citric acid.

[0011] A process can include a number of variations, with the temperature ranging from about 25 °C to about 65 °C.

[0012] A process can include a number of variations, with the temperature ranging between approximately 30 °C and approximately 60 °C.

[0013] A number of variations may include a method for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle, wherein the method comprises: providing a bearing comprising a body with an outer surface, the bearing being iron; placing the iron-bearing bearing in a black oxide conversion coating solution containing about 5 wt% to about 15 wt% sodium metabisulfite, about 3 wt% to about 15 wt% a surfactant, and about 0.25 wt% to about 3 wt% citric acid; heating the black oxide conversion coating solution to a temperature in the range of about 30°C to 60°C; and stirring or circulating the black oxide conversion coating solution for about 30 seconds to about 60 seconds, without exposing the black oxide conversion coating solution to ultrasonic waves, to form a black oxide coating on the bearing.

[0014] A system for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle may comprise a number of variations, wherein the system comprises: a tank containing a black oxide conversion coating solution, an agitator wherein at least a part of it is immersed in the black oxide conversion coating solution, a heating device wherein at least a part of it is immersed in the black oxide conversion coating solution, a robot arm and a bearing holder attached thereto, a computing device comprising an electronic processor, non-volatile storage media containing instructions that can be executed by the electronic processor to perform a functionality comprising: providing a bearing having a body with an outer surface, wherein the bearing has iron;Placing the bearing, which contains iron, into the black oxide conversion coating solution, which contains at least one oxidizing salt present in approximately 5 wt.% to approximately 20 wt.% of the black oxide conversion coating solution; heating the black oxide conversion coating solution to a temperature in the range of approximately 20 °C to 80 °C; and stirring or circulating the black oxide conversion coating solution for less than 80 seconds without exposing 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 motor vehicle part.

[0015] A system can include a number of variants, with the black oxide coating having a thickness between 2 micrometers and 4 micrometers.

[0016] A system can include a number of variants, whereby the black oxide coating is essentially free of mud cracks.

[0017] A number of variations may include a system that also involves: rinsing the black oxide coating of the outer surface with an aqueous solution to remove the aqueous solution from it; and drying the outer surface to remove the aqueous solution from the black oxide coating.

[0018] A number of variations may include a system comprising at least one oxidizing salt, sodium metabisulfite, present in approximately 5 wt% to approximately 15 wt% of the black oxide conversion coating solution.

[0019] A system can include a number of variations, with the black oxide conversion coating solution still containing approximately 3 to 15 wt% of a surfactant.

[0020] A system can include a number of variations, with the black oxide conversion coating solution containing approximately 0.25 wt% to approximately 3 wt% citric acid.

[0021] A system can include a number of variations, with temperatures ranging from approximately 25 °C to approximately 65 °C.

[0022] A system can include a number of variations, with temperatures ranging from approximately 30 °C to approximately 60 °C. Brief description of the drawings

[0023] The illustrative variants are described below in conjunction with the following drawings, where identical numbers denote identical elements and where: Fig. Figure 1 is a flowchart illustrating a series of steps in a hydrothermal process for forming black oxide on a part containing iron, according to a number of variants; Fig. Figure 2 shows a bearing with a black oxide coating, which was produced in various versions using a hydrothermal process; Fig. Figure 3 shows a pair of SED-SEM images, the image on the left being a black oxide coating produced by a hydrothermal process according to a number of variants, and the image on the right being a black oxide coating produced by an ultrasonic process; Fig. Figure 4 illustrates a system for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle according to a number of variants; and Fig. Figure 5 is a schematic representation of a vehicle with an electric drive unit comprising a bearing assembly with a bearing having a black iron coating on it, which is free or substantially free of mud cracks according to a number of variants. Detailed description

[0024] The following detailed description is merely exemplary and is not intended to limit application and use. Furthermore, there is no intention to be bound by any express or implied theory set forth in the preceding introduction, the brief description of the drawings, the short summary, or the following detailed description.

[0025] A number of disclosed variants may include systems and processes for coating a part with black (iron) oxide. The part may be a ball bearing assembly for a rotating shaft of an automotive electric drive unit. The part has a body and an outer surface, the outer surface being coated with a black oxide coating consisting of an iron oxide film and iron sulfide platelets arranged on the iron oxide film. The outer surface of the part may be coated with black oxide using a hydrothermal process. The hydrothermal process can reduce the cycle time to approximately 30 to 60 seconds. The hydrothermal process does not require acid pickling or pre-etching, as is necessary in conventional alkaline salt processes.Furthermore, the hydrothermal process does not involve conventional alkaline salt black oxide conversion coating processes that use hydroxide and nitrate solutions, which require significant health and safety controls. Additionally, the hydrothermal process does not require large and costly specialized hydrostatic pathways, as are necessary with conventional ultrasonic black oxide coating processes.

[0026] Fig. Figure 1 is a flowchart illustrating a series of actions in a process according to a number of variations, where the process may include Act 22, in which a part containing iron is placed in a black oxide conversion coating solution containing 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 stirring the black oxide conversion coating solution so that the at least one ionizing salt reacts with the iron and forms black oxide on the part.

[0027] Fig. Figure 2 shows a bearing 28 with a black oxide coating 30, which is produced by a process, e.g., but not limited to, that described in Figure 2. Fig. The method shown in Figure 1, on which the black oxide coating formed on the surface of the bearing, covers the surface of the bearing 28 uniformly and is free of mud cracks or at least substantially free of mud cracks.

[0028] Fig. Figure 3 shows a pair of secondary electron detector-scanning electron microscope (SED-SEM) images. The image on the left (32) is of a black oxide coating produced by a hydrothermal process according to a number of variations, and the image on the right (34) is of a black oxide coating produced by an ultrasonic process. Both coatings were applied to or formed onto ball-bearing rolling elements. The black oxide coating produced by the hydrothermal process exhibited significantly fewer "mud cracks" (36) than the black oxide produced by the ultrasonic process. The "mud cracks" (36) are caused by internal stresses in the black oxide coating, which are generated by conventional alkaline salt or ultrasonic processes.

[0029] A number of variants may involve a hydrothermal process for coating a motor vehicle part, such as an electric drive unit bearing assembly, with iron oxide for an electric drive unit. In a number of variants, the part may be processed before Act 22 of Fig. 1. The part needs to be cleaned to remove residual oil from its outer surface. In several variations, the part can be placed in the first tank containing a cleaning solution. An ultrasonic device can be positioned in the first tank to generate ultrasonic waves that travel through the cleaning solution and strike the outer surface of the part. Afterward, the part can be removed from the first tank and rinsed in a cleaning solution by spraying or immersing a water-based solution onto the part.

[0030] After cleaning the part, the iron-containing part can be placed in a black oxide conversion coating solution containing at least one oxidizing salt. The oxidizing salt may, but is not limited to, sodium metabisulfite (Na₂SO₃). In several variations, the black oxide conversion coating solution may contain sodium metabisulfite (Na₂SO₃) in an amount ranging from about 3 wt% to about 20 wt%, or within any range, and the range may include at least one endpoint or single wt% 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 conversion coating solution can be applied in quantities ranging from approximately 3 wt% to approximately 15 wt%.-% or in any range in between, and the range may contain at least one endpoint or a single wt% 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 dodecylbenzenesulfonate, or any other suitable solution, without this 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 trade name TEEPOL 610s. The black oxide conversion coating solution may contain an amount in the range of about 0.25 wt% to about 3 wt% or in any range in between, wherein the range includes at least one endpoint or single wt% of 0.5 wt%, 0.8 wt%, 1 wt%, 1.3 wt%, 1.5 wt%, 1.8 wt%.The solution may contain -%, 2 wt%, 2.3 wt%, 2.5 wt% and 2.8 wt% citric acid. The remainder of the black oxide conversion coating solution may be water.

[0031] As in Act 24 of Fig. As shown in Figure 1, the black oxide conversion coating solution can be heated to a temperature in the range of about 25 degrees Celsius (°C) to about 80 °C, including any sub-range in between, and the range can 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.

[0032] The black oxide conversion solution can be stirred or circulated in a tank for a period of approximately 10 seconds to approximately 80 seconds, or in any intermediate range, and can include at least one endpoint or a single time interval 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 process can produce an iron oxide layer of 1–4 µm on the surface of the part. The black oxide conversion coating solution can be stirred or circulated, for example, with a motorized stirrer, pump, or aerator, without exposing the solution to ultrasonic waves.

[0033] After process 26 in Fig. 1. The hydrothermal process can further include drying the outer surface of the part, including any coating formed on it, to remove any water / alcohol-based solution. In several variations, drying can be carried out using a blower, a drying oven, or a drying tunnel, employing air or nitrogen at a temperature in the range of approximately 40 °C to approximately 50 °C.

[0034] The hydrothermal process allows iron sulfide (FeS) platelets to form on the surface of the black oxide coating on the part. The black oxide coating can be applied to the entire outer surface of the bearing by stirring or circulating the black oxide conversion coating solution appropriately. The black oxide coating produced by the hydrothermal process provides corrosion protection during storage of the coated part.

[0035] The citric acid can be arranged to chemically activate the surface of the part, enabling a reaction with oxygen / hydrogen species and iron (Fe) to form iron hydroxide, Fe(OH)₂. The sodium metabisulfite can be arranged to react with the iron hydroxide, forming iron oxysulfide (FeSO₃) on the iron-containing part. The iron oxysulfide can then react with oxygen / hydrogen to create an iron oxide film (FeO, Fe₂O₃, Fe₃O₄) and iron sulfide platelets (FeS) on the iron-containing part. That is, a first portion of the iron oxysulfide reacts with oxygen to create the iron oxide film on the outer surface of the iron-containing part, and a second portion reacts with hydrogen to create the iron sulfide platelets arranged within the iron oxide film. The black oxide coating 40 is available in a range of variants with a concentration between 50 wt.% and 100 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.%.The black oxide coating 40 may contain 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, and 95 wt.% iron oxide. Additionally, the black oxide coating 40 may contain an amount in the range of 0 wt.% to approximately 50 wt.% and any subrange in between, and the range may contain at least one endpoint or single point 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 in the range of approximately 0.5 micrometers to approximately 4 micrometers or any subrange in between and have at least one endpoint or single point of thickness of 1 micrometer, 1.5 micrometers, 2 micrometers, 2.5 micrometers, 3 micrometers, or 3.5 micrometers.

[0036] Fig. Figure 4 illustrates a system for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle according to a number of variants. The system 300 can comprise a tank 330 and an agitator 302, which may include a motor 304 and a shaft connected at one end to the motor 304, as well as a propeller 308 at the other end. At least part of the agitator 302 is immersed in a black oxide conversion coating solution 310 contained in the tank 330. The system 300 can also include a heating device 312, at least part 314 of which is immersed in the black oxide conversion coating solution 310. The system 300 can include a robot arm 326, which is functionally connected to a second motor 328 and to a bearing holder 324 for holding at least one bearing 28.The agitator 302, the robot arm 326 and the heating device 312 can be connected to a device 316 which may include an electronic processor 318 and a non-volatile memory 320 with instructions 322 for carrying out the functions described here.

[0037] Fig.Figure 5 is a schematic representation of a vehicle 400, which may include at least one front wheel 402 functionally connected to at least one front axle 404. The vehicle 400 may include at least one rear wheel 406 functionally connected to at least one rear axle 426. A steering interface 408 may be equipped with a steering shaft 410. The steering shaft 410 may be equipped with a steering rack 412, which may be connected to the at least one front wheel 402. The vehicle 400 may include an electric drive unit 414 for driving the vehicle 400. A front drive shaft 416 may be equipped with the at least one front axle 404 and with the electric drive unit 414. The front drive shaft 416 may be supported by a first bearing arrangement 420 with at least one bearing 28.A rear drive shaft 422 can be connected to the at least one rear axle 426 and the electric drive unit 414. The rear drive shaft 422 can be supported by a second bearing arrangement 424, which includes at least one bearing 28. A power source 428, which can be an electric battery, can be connected to the electric drive unit 414 to supply it with power. The at least one bearing 28 can have a black iron coating that is free or substantially free of mud cracks. The at least one bearing 28 can be coated with the black iron coating, which is free or substantially free of mud cracks, by a method described herein.

[0038] Although at least one variant has been presented in the preceding detailed description, it should be understood that a large number of variants exist. It should also be noted that the variation or variations are merely examples and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the preceding detailed description is intended to provide the person skilled in the art with practical guidance for implementing the variant(s) presented. It is understood that various modifications to the function and arrangement of the elements can be made without departing from the scope of the disclosure as set out in the appended claims and their statutory equivalents.

Claims

[1] Method for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle, wherein the method comprises: Providing a motor vehicle part having a body with an outer surface, wherein the motor vehicle part contains iron; Placing the motor vehicle part containing iron in a black oxide conversion coating solution containing at least one oxidizing salt; Heating the black oxide conversion coating solution to a temperature in the range of approximately 20 °C to 80 °C; and Stirring or circulating the black oxide conversion coating solution for approximately 20 seconds to approximately 80 seconds, without exposing 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 motor vehicle part. [2] Method according to claim 1, further comprising, prior to placing the motor vehicle part which contains iron into the black oxide conversion coating solution, cleaning the motor vehicle part to remove residual oil from the outer surface. [3] Method according to claim 2, wherein the cleaning of the motor vehicle part comprises: Arranging the motor vehicle part in a cleaning solution; and Exposure of the motor vehicle part and the cleaning solution to ultrasonic waves. [4] Method according to claim 3, further comprising rinsing the cleaning solution from the outer surface. [5] Method according to claim 1, further comprising: Rinsing the black oxide coating on the outer surface with an aqueous solution to remove the aqueous solution from it; and Dry the outer surface to remove the aqueous solution from the black oxide coating. [6] Method according to claim 1, wherein the at least one oxidizing salt comprises sodium metabisulfite, which is present in about 5 wt% to about 20 wt% of the black oxide conversion coating solution. [7] Method according to claim 6, wherein the black oxide conversion coating solution further comprises about 3 wt.% to about 15 wt.% of a surfactant. [8] Method according to claim 6, wherein the black oxide conversion coating solution further comprises about 0.25 wt.% to about 3 wt.% citric acid. [9] Method according to claim 1, wherein the temperature is in the range of about 30 °C to about 60 °C. [10] System for forming a black oxide coating on a motor vehicle part for an electric drive unit of a vehicle, the system comprising: a tank containing a black oxide conversion coating solution, a stirrer wherein at least part of it is immersed in the black oxide conversion coating solution, a heater wherein at least part of it is immersed in the black oxide conversion coating solution, a robot arm and a storage holder attached thereto, a computing device comprising an electronic processor and non-volatile storage media containing instructions that can be executed by the electronic processor to perform functionality comprising: Providing a bearing having a body with an outer surface, wherein the bearing contains iron; Placing the bearing, which contains iron, in the black oxide conversion coating solution, which contains at least one oxidizing salt present in approximately 5 wt.% to approximately 20 wt.% of the black oxide conversion coating solution; Heating the black oxide conversion coating solution to a temperature in the range of approximately 20 °C to 80 °C; and Stirring or circulating the black oxide conversion coating solution for less than 80 seconds without exposing 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 motor vehicle part.

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