PRETREATMENT METHOD FOR PRETREATING COMPONENTS PRIOR TO ELECTROPLATING

Abstract

A pretreatment method for pretreating components, which are each formed of at least two different materials, prior to a coating process. The pretreatment method includes the steps: alkaline degreasing; chemical pickling in a first pickling medium; anodic pickling in a second pickling medium; and cathodic degreasing.

Claims

1-14. (canceled)

15. A pretreatment method for pretreating a component, which is formed of at least two different materials, the method comprising the following steps: alkaline degreasing the component; chemical pickling the component in a first pickling medium; anodic pickling the component in a second pickling medium; and cathodic degreasing the component.

16. The pretreatment method as recited in claim 15, wherein the second pickling medium is in a slightly acidic to neutral range, the second pickling medium including salts of nitric acid.

17. The pretreatment method as recited in claim 16, wherein the second pickling medium includes a complexing agent.

18. The pretreatment method as recited in claim 15, wherein the anodic pickling takes place under a voltage of at least 2 V and no more than 10 V.

19. The pretreatment method as recited in claim 15, wherein the cathodic degreasing takes place in an alkaline solution.

20. The pretreatment method as recited in claim 15, further comprising: pickling the component after the cathodic degreasing.

21. The pretreatment method as recited in claim 15, wherein the component is a spark plug housing and includes a housing base body and a ground electrode, the housing base body and the ground electrode being formed of different materials.

22. The pretreatment method as recited in claim 21, wherein the ground electrode is formed of a chromium-containing nickel steel.

23. The pretreatment method as recited in claim 21, wherein the ground electrode is formed of NiCr15Fe or NiCr23Fe15 or NiCr25FeAIY.

24. The pretreatment method as recited in claim 21, wherein the spark plug housing includes a weld joint using which the housing base body and the ground electrode are joined to one another.

25. A coating method for coating a component which is formed of at least two different materials, the method comprising the following steps: pretreating the component using a pretreatment method including: alkaline degreasing the component, chemical pickling the component in a first pickling medium, anodic pickling the component in a second pickling medium, and cathodic degreasing the component; and generating a coating of the component using a nickel electrolyte.

26. The coating method as recited in claim 25, wherein the component is a spark plug housing.

27. The coating method as recited in claim 26, further comprising: precoating the component using a low-concentration nickel electrolyte, prior to the step of generating the coating.

28. The coating method as recited in claim 25, wherein at least one subarea of a surface of the component is excluded from at least one of the method steps of the pretreatment method and/or of the coating method, by covering the subarea.

29. The coating method as recited in claim 25, wherein at least one of the method steps of the pretreatment method and/or of the coating method is carried out using a rack, the component being situated at the rack during the at least one method step.

30. The coating method as recited in claim 29, wherein the rack includes an internal anode, the internal anode being situated in a through-opening of the component, while the at least one method step is being carried out.

31. A spark plug housing formed of at least two different materials, the spark plug housing being coated by: pretreating the spark plug housing using a pretreatment method including: alkaline degreasing the spark plug housing, chemical pickling the spark plug housing in a first pickling medium, anodic pickling the spark plug housing in a second pickling medium, and cathodic degreasing the spark plug housing; and generating a coating of the spark plug housing using a nickel electrolyte.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention is described hereafter based on one exemplary embodiment in connection with the figures. In the figures, functionally equivalent components are each denoted by identical reference numerals.

[0039] FIG. 1 shows a simplified schematic view of a spark plug housing in use at a spark plug, the spark plug housing having been pretreated and coated with the aid of a coating method according to one preferred exemplary embodiment of the present invention.

[0040] FIG. 2 shows a simplified schematic view of a set-up for carrying out the coating method of the spark plug housing of FIG. 1.

[0041] FIG. 3 shows a simplified schematic view of the sequence of the method steps of the coating method for pretreating and coating the spark plug housing of FIG. 1, in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0042] FIG. 1 shows a simplified schematic view of a component which was pretreated and coated with the aid of a coating method B according to one preferred exemplary embodiment of the present invention. The component is a spark plug housing 10. Spark plug housing 10 is an integral part of a spark plug 100 and includes a housing base body 11 and a ground electrode 12. Housing base body 11 is essentially concentrically designed with respect to a longitudinal axis 19 and includes a male thread 16 and a hexagonal section 20. With the aid of male thread 16, spark plug housing 10, and thus spark plug 100, may be screwed into a corresponding female thread of a cylinder head, which is not shown, of an internal combustion engine. Housing base body 11 is additionally designed to accommodate further components of spark plug 100, such as an insulator 101.

[0043] Housing base body 11 and ground electrode 12 are formed of two different materials and joined to one another with the aid of a weld joint 13. Ground electrode 12 is formed of a chromium-containing nickel steel, more precisely NiCr15Fe. Housing base body 11 is formed of ordinary steel, more precisely steel with the designation S235.

[0044] In addition, a plate 17 made up of a precious metal alloy is welded onto ground electrode 12 to withstand the particularly high stresses due to ignition sparks during the operation of spark plug 100.

[0045] To withstand the high stresses, primarily with respect to highly corrosive surroundings when spark plug 100 is used in a combustion chamber of an internal combustion engine, and to meet maximum quality standards, a coating of spark plug housing 10 in the form of a nickel coating 70 is provided. Nickel coating 70 is situated on the entire surface of spark plug housing 10, i.e., at its outer side as well as at its inner side, which is defined by a through-opening 15. It shall be noted that nickel coating 70 is not required on the entire inner side of spark plug housing 10. For example, a partial coating of the inner side or a thinner nickel coating 70 compared to the outer side is also possible. To generate nickel coating 70, spark plug housing 10 is coated with the aid of coating method B. Before the individual steps of coating method B are described in detail, initially an arrangement and handling of spark plug housing 10 for carrying out coating method B is explained with respect to FIG. 2.

[0046] As is apparent from FIG. 2, ground electrode 12, in the illustrated uncoated state, extends away from housing base body 11 in a straight manner, i.e., in parallel to longitudinal axis 19. A bending into the shape illustrated in FIG. 1 takes place subsequently to coating method B. As a result of coating method B according to the present invention, a particularly high-quality and resistant nickel coating 70 is generated. It also withstands the subsequent bending without damage, for example without the coating flaking.

[0047] Furthermore, a subarea 14 of ground electrode 12 is covered before and while coating method B described hereafter is carried out. The covering effectuates a shielding of subarea 14 with respect to field lines of an electrical field during the coating. In this way, subarea 14 is excluded from coating method B and preserves its untreated and uncoated surface.

[0048] To facilitate a handling of spark plug housing 10 while coating method B is being carried out, a coating rack 50 is provided, as is apparent in FIG. 2. Coating rack 50 encompasses ground electrode 12 to achieve the covering and to hold spark plug housing 10. Moreover, an electrical contacting of spark plug housing 10 occurs. Furthermore, coating rack 50 includes a mandrel-shaped internal anode 51, which is insertable into a through-opening 15 of spark plug housing 10. Internal anode 51 and coating rack 50 are electrically insulated with respect to one another. Multiple spark plug housings 10 may be situated at coating rack 50 to enable a simultaneous coating of multiple spark plug housings 10. For the sake of clarity and vividness, however, only a single spark plug housing 10 is shown in FIG. 2.

[0049] Due to coating rack 50, a defined positioning of spark plug housing 10 is easily possible, to avoid a free movement of spark plug housing 10, and thus a possible striking against other spark plug housing 10. Moreover, a handling during coating method B is easily possible. For this purpose, coating rack 50, including the entire spark plug housing 10, may be immersed in a corresponding medium 21. In the process, medium 21 is situated in each case in an open receptacle 20. Furthermore, an electrode 22 is immersed in medium 21 inside receptacle 20. Depending on the method step, electrode 22 may be used as an anode or a cathode or neutrally. It shall be noted that all of the method steps of coating method B described hereafter are carried out as a dipping process. In this way, FIG. 2 may be regarded as being representative of all method steps, a different medium 21 being used for each of the method steps.

[0050] The execution of coating method B is described hereafter with reference to FIG. 3. During coating method B, spark plug housing 10 consecutively undergoes the steps: [0051] alkaline degreasing 1 in a highly alkaline solution; [0052] chemical pickling 2 in a highly acidic first pickling medium; [0053] anodic pickling 3 in a slightly acidic second pickling medium; [0054] cathodic degreasing 4 in an alkaline solution; [0055] pickling 5 in a weakly acidic solution; [0056] precoating 6 in a low-concentration nickel electrolyte; and [0057] generating the coating 7 in a nickel electrolyte.

[0058] Steps 1 through 5 of coating method B are to be regarded as pretreatment method A.

[0059] After each of method steps 1 through 7, spark plug housing 10 is removed from corresponding medium 21. To remove residues of medium 21 adhering to the surface of spark plug housing 10 after the removal, a rinsing 8 of spark plug housing 10 takes place after each of method steps 1 through 7.

[0060] In the steps alkaline degreasing 1, anodic pickling 3, cathodic degreasing 4, precoating 6, and generating the coating 7, it is necessary to introduce current into spark plug housing 10 to operate spark plug housing 10 either as an anode or as a cathode. For this purpose, a first power supply unit 25A is provided (see FIG. 2). Spark plug housing 10 is connected to power supply unit 25A via coating rack 50. Furthermore, power supply unit 25A is connected to electrode 22 to also introduce a current. Furthermore, a second power supply unit 25B is provided, which is active during the step of generating the coating 7. In the process, a current is introduced into internal anode 51 by second power supply unit 25B, to also generate a nickel coating 70 at the inner side of spark plug housing 10.

[0061] As a result of coating method B, it is possible to achieve optimal results with respect to a high-quality and reproducible coating of spark plug housing 10. In this way, very high quality requirements with regard to spark plug housings 10, in particular, with respect to a corrosion protection, may be met, to manufacture particularly durable spark plugs 100.

[0062] Primarily as a result of pretreatment method A, a coating method B which is optimally adapted to the different properties of the different materials of which spark plug housing 10 is formed is made possible. As a result of pretreatment method A ideally matched to spark plug housing 10, which is formed of two different materials, it is thus possible to achieve a particularly high-quality and uniform nickel coating 70 of exterior areas and interior areas of spark plug housing 10. In the process, not only the individual subelements, i.e., housing base body 11 and ground electrode 12, of which spark plug housing 10 may be made up, but, in particular, also weld joint 13, which joins the two subelements to one another, are optimally pretreated. Pretreatment method A thus offers a particularly active pretreatment by which oxide layers present on the surface, which, in particular, resulted from the welding, may be removed particularly well to obtain a flawless surface of spark plug housing 10 prior to the actual generation of the coating 7. In this way, spark plug housings 10 may be coated with consistent quality with a nickel coating 70 by coating method B.