EP3947785A1

EP3947785A1 - Pretreatment method for pretreating components prior to electroplating

Info

Publication number: EP3947785A1
Application number: EP20713239.0A
Authority: EP
Inventors: Milan Pilaski; Christoph Roland HOELZL; Tim Bergmann; Martina BUBRIN
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-03-27
Filing date: 2020-03-18
Publication date: 2022-02-09
Also published as: JP7279187B2; JP2022525782A; DE102019204225A1; US20220190562A1; CN113574210A; WO2020193307A1

Abstract

The invention relates to a pretreatment method (A) for pretreating components (10), which are each formed from at least two different materials, prior to coating. The pretreatment method (A) comprises the following steps: alkaline degreasing (1); chemical pickling (2) in a first pickling medium; anodic pickling (3) in a second pickling medium; and cathodic degreasing (4).

Description

description

title

Pretreatment process for pretreating components prior to electroplating

State of the art

The present invention relates to a pretreatment method for

Pretreatment of components, especially before a coating process. The invention also relates to a coating method for coating

Components.

It is known to use components, such as spark plug housings, which consist of two or more different materials. Such components often need to be coated due to the risk of severe corrosive attack in the area of application of the components, for example in the highly corrosive environment in a combustion chamber of an internal combustion engine. Due to the different materials, however, there are often restrictions when coating the component, in particular when it is pretreated before the actual coating. The media used for pretreatment are usually specially adapted to one of the materials and are not suitable for multi-material components.

Disclosure of the invention

The pretreatment method with the features of claim 1 offers the advantage of a pretreatment optimized for components made of two or more materials. A one-piece component is regarded as such a component, which has at least two partial areas each made of a different material. Each of the materials of the

Component both sufficiently activated, in particular with regard to a subsequent coating process, and at the same time not too strong attacked to avoid damage. An entire surface of the component can thus be produced with a particularly high quality.

According to the invention, this is achieved in that the pretreatment process comprises the following steps:

- alkaline degreasing,

- chemical pickling in a first pickling medium,

- anodic pickling in a second pickling medium, and

- cathodic degreasing. The pretreatment process enables optimal results in terms of high quality and reproducible pretreatment to be achieved. In other words, this can result in rejects in the production of the components, provided a certain quality level

The surface of the components can be kept particularly small. In particular, the pretreatment enables subsequent coating of materials, e.g. chromium-containing nickel steel, which otherwise cannot be coated.

The steps are preferably carried out one after the other in the order described above. Alternatively, it would also be possible to swap the two last-mentioned steps, that is, to carry out cathodic degreasing before anodic pickling.

It is particularly favorable if the steps take place immediately one after the other, that is to say without further possible processing steps as intermediate steps. It should be noted here that flushing, which, however, should not be viewed as a separate processing step, can advantageously take place after each of the method steps. In other words, the component is preferably rinsed between two successive method steps which affect the surface of the component.

A strongly alkaline solution with a pH greater than or equal to 12 is preferably used for alkaline degreasing. The first pickling medium is advantageously a strongly acidic medium, in particular with a pH value less than or equal to 1. A strong acid such as hydrochloric acid is particularly suitable for this. Alternatively, for example, sulfuric acid or hydrofluoric acid can be used. The pretreatment method according to the invention enables a pretreatment that is optimally tailored to components made up of several components. Not only can the individual sub-elements from which the component can be assembled, but in particular also existing ones

Weld seams that connect the sub-elements to one another are optimally pretreated. All of the surfaces of the partial areas or the weld seams are improved in terms of coatability or surface quality. The pretreatment process thus offers a particularly active pretreatment with which, or, on the surfaces

For example, oxide layers created by welding can be removed particularly well in order to obtain a perfect surface of the component. In addition, pre-treatment with consistent quality is possible.

In the pretreatment of components in large numbers, rejects can therefore be insufficient or too large, for example

pretreated / activated components are kept particularly low.

Furthermore, it is particularly favorable if no anodic degreasing takes place after the cathodic degreasing. This means that following the cathodic degreasing, in which the component is connected as a cathode by applying a voltage, there is no anodic degreasing in which the

Component is connected as anode by applying an opposite voltage. This avoids the surface of the component coming into contact with increased amounts of oxygen, which usually occurs during anodic degreasing. The oxygen could otherwise oxidize the surface of the component, that is, an oxide layer could be formed on it, which would be disadvantageous for possible subsequent processes, such as a coating process.

The pretreatment method is particularly suitable for pretreating components that are formed from a combination of at least two different steels in order to subsequently produce a particularly high-quality coating. In particular, stainless steels or stainless steels are usually difficult to cover with a firm coating, especially if the pretreatment process is to be suitable for "normal" steel at the same time. However, the present pretreatment process is suitable for a wide variety of steel grades and enables the component to be optimally prepared for subsequent manufacturing or machining processes. The subclaims contain preferred developments of the invention.

The second pickling medium is preferably a medium which is present in a slightly acidic to neutral range. A solution with a pH value of 4 to 8 is regarded as a medium in the slightly acidic to neutral range. The second pickling medium particularly preferably has a pH value greater than or equal to 5 and less than or equal to 6.5. The second medium preferably comprises a salt of nitric acid in order to enable a sufficiently active but not too aggressive pretreatment. Alternatively there would be one

Use of sulfuric acid salts in the second pickling medium is possible. It is also advantageous if a complexing agent is added to the second pickling medium. This enables a particularly well adapted pretreatment, which enables an effective removal of oxide layers of the component and at the same time ensures that the various materials of the component are not attacked too severely.

The anodic pickling is particularly preferably carried out under a voltage of at least 2V and a maximum of 10V. A voltage in the range from 2V to 6V, in particular 4V, is particularly advantageous. This allows a particularly targeted treatment of the surface of the component. Above all, by adjusting the voltage, the pretreatment process can be easily and effectively adapted to different materials and

Material combinations of the component are possible, with the removal of material on the surface of the component being able to be influenced in a particularly targeted manner.

Cathodic degreasing is preferably carried out in an alkaline solution. It is particularly favorable if the alkaline solution is a strongly alkaline aqueous solution of sodium hydroxide or potassium hydroxide. A solution with a pH value greater than or equal to 12 is regarded as a strongly alkaline aqueous solution. A surfactant can preferably also be added to optimize cathodic degreasing. It is also particularly advantageous if a voltage of at least 3V and a maximum of 15V, in particular from 5V to 10V, is applied to the component for cathodic degreasing. Thus, in terms of sufficient activation, there is still no to strong attack on the surface of the component optimal adaptation of the

Pre-treatment on different material combinations possible.

More preferably, the pretreatment method further comprises the step of: picking up the component.

Pickling takes place after cathodic degreasing. As a result of the pickling, in particular an alkaline solution adhering to the component is removed from the cathodic degreasing step. A weakly acidic solution is preferably used for pickling in order to neutralize the alkaline solution. The component can thus be prepared particularly well for a possible subsequent coating.

The component is particularly preferably a spark plug housing of a spark plug. The spark plug housing comprises a housing base body and a

Ground electrode. The housing base body and the ground electrode are formed from the different materials. Thus, the housing base body and the ground electrode are particularly well adapted to the respective requirements and also enable a cost-effective

Manufacture of the spark plug. The spark plug housing preferably furthermore comprises an external thread in order to enable the spark plug to be screwed into a corresponding internal thread. Furthermore, the spark plug housing advantageously has a hexagonal section or a

Polygon section to facilitate handling by means of a tool.

It is particularly advantageous if the ground electrode is made from a chromium-containing nickel steel. The ground electrode is particularly preferably formed from NiCr15Fe, NiCr23Fe15, or NiCr25FeAIY. This can do that

Spark plug housings can be provided with a particularly resistant ground electrode in order to meet the high requirements of high-quality, high-quality spark plugs. The spark plug housing is further preferably formed from “ordinary” steel, for example steel with the designation S235 or a material number from 1.0036 to 1.0038. The pretreatment process ensures an optimal, even finish

Preparation of the entire surface of the spark plug housing possible. The spark plug housing preferably has a welded connection by means of which the housing base body and the ground electrode are connected to one another. Oxide layers that arise on the surface of the spark plug housing as a result of the welding process when the two components are welded together can be removed easily and reliably using the pretreatment process. Thus, not only can the surfaces of both

Sub-elements of the spark plug housing, but also the weld seam connecting them, are optimally pretreated in order to provide a particularly high-quality surface of the spark plug housing, in particular with regard to subsequent methods or processes.

The invention also relates to a coating method for coating components which have been pretreated by the pretreatment method. It should be noted that the pre-treatment process can be viewed as a partial process of the coating process. The coating method further includes the step: producing the coating of the component.

In principle, any type of coating, in particular electroplating, can be carried out, such as gold plating, silver plating, zinc plating or chrome plating. However, the coating process is preferably nickel-plating. It is particularly advantageous when generating the

Coating, in particular a nickel coating, by means of a

Nickel electrolyte takes place. The nickel electrolyte advantageously has a concentration of at least 80 g / l to a maximum of 120 g / l, particularly preferably 100 g / l nickel. Due to the optimized pretreatment, a particularly high-quality and uniform coating of the

Surface can be achieved. In particular, components made of several different materials can be optimally completely covered with a coating with the slightest layer thickness fluctuations. As a result, very high qualitative requirements on the component, in particular with regard to corrosion protection, can be met. This makes it easy to maintain a degree of rust of Ri = 2 in accordance with DIN-ISO 9277 for spark plug housings, for example.

The coating method preferably further comprises the step:

- Pre-coating of the component, before the step of generating the coating. The precoating is preferably carried out by means of a low

concentrated nickel electrolytes. In particular, a thin-walled Coating of the component produced before the actual coating step in order to obtain a particularly uniform and high-quality coating directly on the surface of the component. The low-concentration nickel electrolyte particularly preferably has a concentration of at least 10 g / l and a maximum of 50 g / l, in particular 15 g / l to 25 g / l, of nickel.

Furthermore, it is particularly favorable if at least a partial area of a surface of the component is excluded from the pretreatment and / or the coating. This means that the component is partially coated in a defined manner. This is done by covering the sub-area during the pretreatment and / or the coating so that the media used in the pretreatment and / or the coating do not come into contact with the

Surface of the sub-area can come. Alternatively or additionally, the sub-area can be covered in such a way that it is protected from penetration by field lines during the pretreatment and / or the coating

Electric field is protected in the partial area, so is isolated from the electric field. Advantageously, to cover the

A cover element made of a resistant and / or electrically insulating material is used in part. The sub-area is particularly preferred during all steps of both the pretreatment process and the

Coating process covered in order to get an untreated and uncoated surface on the part area. This makes it possible to use the

To adapt the surface of the component to the most varied of requirements, for example to coated sub-areas for an optimal

Corrosion protection and also around uncoated areas for another

Treatment or processing of these uncoated areas.

At least one of the method steps of the

Pretreatment process and / or the coating process as

Frame coating carried out by means of a frame. It is particularly favorable if the component is arranged on the frame during the at least one method step. Furthermore, it is particularly advantageous if both the entire pretreatment process and the entire

Coating process is carried out by means of the frame. This enables the corresponding method steps to be carried out particularly simply and optimally adapted to the component. In addition, a particularly high quality of the coating can be achieved after coating, since several Components can each be arranged individually on a frame at fixed positions so that they do not touch each other during the process steps. This means that several people hit each other

Components, which can lead to damage to the surfaces of the components, avoided. Alternatively, it would also be possible to use at least one of the

Process steps of the pre-treatment process and / or the

Coating process to be carried out as drum coating using a drum. In this case, at least one component is arranged inside the drum during the execution of the at least one method step. A drum coating is a particularly simple and

inexpensive implementation of the pretreatment and / or the coating possible.

The frame particularly preferably has an inner anode. The inner anode is preferably arranged in a through opening of the component while the at least one method step is being carried out. As a result, a breathing space of the component defined by the passage opening can also be coated in a simple and reliable manner.

The inner anode is preferably formed from a chemically resistant material. The inner anode is particularly preferably formed from platinum-coated titanium.

This guarantees a high level of resistance in order to reliably achieve a high quality of the coating over the long term.

The invention thus preferably also leads to a method for producing nickel-plated spark plug housings, comprising the steps:

- Providing a spark plug housing with a ground electrode which is formed from at least two different materials, a ground electrode of the spark plug housing being formed from a nickel steel containing chromium,

- Pretreatment of the spark plug housing with the pretreatment process, in particular all surfaces of the spark plug housing,

- Preferably pre-nickel plating of the spark plug housing, and

- Nickel plating of the spark plug housing. Furthermore, the invention leads to a component which by means of the

coating process described was coated. The component is preferably a spark plug housing of a spark plug. One through that A component coated with a coating process thus has a particularly long-lasting and high-quality coating which can reliably withstand the high loads, for example in a corrosive environment in an internal combustion engine. The pre-treatment process and the subsequent coating process result in an optimal, high-quality coating of both the housing base body, the

Ground electrode, as well as the weld seam possible.

Brief description of the drawings

In the following, the invention is illustrated in FIG

Connection with the figures described. In the figures, functionally identical components are each identified by the same reference symbols. It shows:

FIG. 1 shows a simplified schematic view of a spark plug housing in use on a spark plug, the spark plug housing having been pretreated and coated by means of a coating process according to a preferred exemplary embodiment of the invention,

Figure 2 is a simplified schematic view of a structure for

Carrying out the coating process for the spark plug housing of FIG. 1, and

Figure 3 is a simplified schematic view of the sequence of

Process steps of the coating process for pretreating and coating the spark plug housing of FIG. 1. Preferred embodiment of the invention

FIG. 1 shows a simplified schematic view of a component which, by means of a coating method B according to a preferred

Embodiment of the invention was pretreated and coated. The component is a spark plug housing 10. The spark plug housing 10 is part of a spark plug 100 and comprises a housing base body 11 and a ground electrode 12. The housing base body 11 is essentially concentric to a longitudinal axis 19 and has an external thread 16 and a hexagonal section 20. Using the

External thread 16 can be screwed into the spark plug housing 10 and thus the spark plug 100 into a corresponding internal thread of a cylinder head (not shown) of an internal combustion engine. The housing base body 11 is also designed to accommodate further components of the spark plug 100, such as an insulator 101, for example.

Housing base body 11 and ground electrode 12 are made of two

formed from different materials and connected to one another by means of a welded joint 13. The ground electrode 12 is formed from a nickel steel containing chromium, more precisely NiCr15Fe. The housing base body 11 is made of simple steel, more precisely steel with the designation S235.

A plate 17 made of a noble metal alloy is also welded to the ground electrode 12 in order to withstand the particularly high loads caused by

Withstand ignition sparks during operation of the spark plug 100.

In order to withstand the high loads, especially with regard to a highly corrosive environment in the application of the spark plug 100 in a combustion chamber of an internal combustion engine, and to ensure the highest quality

To meet standards, a coating of the spark plug housing 10 in the form of a nickel coating 70 is provided. The nickel coating 70 is located on the entire surface of the spark plug housing 10, that is to say on its outside and also on its inside, which is defined by a through opening 15. It should be noted that the nickel coating 70 is not required on the entire inside of the spark plug housing 10. For example, a partial coating of the inside or a thinner nickel coating 70 compared to the outside is also possible. To produce the nickel coating 70, the spark plug housing 10 is by means of

Coating method B coated. Before a detailed description of the individual steps of the coating process B takes place, an arrangement and handling of the spark plug housing 10 for carrying out the coating process B will first be explained with reference to FIG.

As can be seen in FIG. 2, the ground electrode 12 extends in

uncoated state shown straight from the housing base body 11 away, that is parallel to the longitudinal axis 19. Bending into the shape shown in FIG. 1 takes place after the coating process B. The coating process B according to the invention produces a particularly high-quality and durable nickel coating 70. This also withstands the subsequent bending without damage, for example without it peeling off.

Furthermore, a partial area 14 of the ground electrode 12 is covered before and during the execution of the coating method B described below. The cover shields the sub-area 14 from field lines of an electric field during the coating. The sub-area 14 is thus used by the coating method B.

excluded and retains its untreated and uncoated surface.

In order to facilitate the handling of the spark plug housing 10 when carrying out the coating method B, a coating frame 50 is provided, as can be seen in FIG. The coating frame 50 engages around the ground electrode 12 in order to achieve the cover and to hold the spark plug housing 10. In addition, electrical contacting of the spark plug housing 10 takes place via it. Furthermore, the coating frame 50 comprises a mandrel-shaped inner anode 51 which is inserted into a through opening 15 of the

Spark plug housing 10 is insertable. The inner anode 51 and the

Coating frames 50 are electrically insulated from one another. To the

A plurality of spark plug housings 10 can be arranged in the coating frame 50 in order to enable a plurality of spark plug housings 10 to be coated at the same time. For the sake of clarity and

However, only a single spark plug housing 10 is shown in FIG. 2 for clarity.

By means of the coating frame 50, a defined positioning of the spark plug housing 10 is easily possible in order to avoid free movement of the spark plug housing 10 and thus a possible collision with other spark plug housings 10. In addition, handling during the coating process B is easy. For this purpose, the coating frame 50 with the entire spark plug housing 10 can be immersed in a corresponding medium 21. The medium 21 is located in each case in an open container 20. Within the container 20, an electrode 22 is also immersed in the medium 21. The electrode 22 can be used as an anode or as a cathode or neutral, depending on the method step. It should be noted that all of the following

described process steps of the coating process B as

Dipping process can be carried out. Thus, Figure 2 can be seen as representative of all process steps, with each of the

Method steps another medium 21 is used.

The implementation of the coating process B is described below with reference to FIG. In the coating method B, the spark plug housing 10 runs through the following steps in succession:

- alkaline degreasing 1 in a strongly alkaline solution,

- chemical pickling 2 in a strongly acidic first pickling medium,

- anodic pickling 3 in a slightly acidic second pickling medium,

- cathodic degreasing 4 in an alkaline solution,

- pickling 5 in a weakly acidic solution,

- precoating 6 in a low concentration nickel electrolyte, and

- Production of the coating 7 in a nickel electrolyte.

Steps 1 through 5 of Coating Process B are included as that

Consider pre-treatment method A.

After each of the method steps 1 to 7, the spark plug housing 10 is removed from the corresponding medium 21. In order to remove residues of the medium 21 adhering to the surface of the spark plug housing 10 after removal, the spark plug housing 10 is rinsed 8 after each of the method steps 1 to 7.

In the steps of alkaline degreasing 1, anodic pickling 3, cathodic degreasing 4, precoating 6 and generating the coating 7, a current must be introduced into the spark plug housing 10 in order to switch the spark plug housing 10 either as an anode or as a cathode . A first power supply device 25 is provided for this purpose (see FIG. 2). About the coating frame 50, the spark plug housing 10 is with the

Power supply device 25 connected. Furthermore, the

Power supply device 25 connected to the electrode 22 in order to also be used in this initiate a current. There is also a second

Power supply device 25B is provided, which in the step of

Generating the coating 7 is active. In doing so, second

Power supply device 25B introduced a current into the inner anode 51 in order to produce a nickel coating 70 on the inside of the spark plug housing 10 as well.

The coating process B enables optimal results with regard to a high quality and reproducible coating of

Spark plug housings 10 can be achieved. This makes it possible to meet very high qualitative requirements for the spark plug housings 10, in particular with regard to corrosion protection, in order to produce particularly long-lasting spark plugs 100.

Above all, the pretreatment process A enables a coating process B that is optimally adapted to the various properties of the different materials from which the spark plug housing 10 is formed. By being ideally matched to the spark plug housing 10, which is formed from two different materials

Pretreatment method A can thus achieve a particularly high-quality and uniform nickel coating 70 of the outer areas and inner areas of the spark plug housing 10. Not only are the individual sub-elements, i.e. housing base body 11 and earth electrode 12, from which the spark plug housing 10 can be composed, but also, in particular, the welded connection 13, which connects the two sub-elements, optimally pretreated. The pretreatment method A thus offers a particularly active pretreatment with which on the

Oxide layers that are present on the surface, in particular those produced by welding, can be removed particularly well in order to obtain a perfect surface of the spark plug housing 10 before the actual production of the coating 7. As a result, the coating method B allows spark plug housings 10 of consistent quality with a

Nickel plating 70 can be coated.

Claims

Expectations

1. Pretreatment method for pretreating components (10) which are each formed from at least two different materials, comprising the steps:

- alkaline degreasing (1),

- chemical pickling (2) in a first pickling medium,

- anodic pickling (3) in a second pickling medium, and

- cathodic degreasing (4).

2. Pretreatment method according to claim 1, wherein the second pickling medium is in a slightly acidic to neutral range, and wherein the second

Pickling medium in particular salts of nitric acid, and preferably a complexing agent.

3. Pretreatment method according to one of the preceding claims, wherein the anodic pickling (3) takes place under a voltage of at least 2V and a maximum of 10V.

4. Pretreatment method according to one of the preceding claims, wherein the cathodic degreasing (4) takes place in an alkaline solution.

5. Pretreatment method according to one of the preceding claims, further comprising the step:

- Pickling (5) of the component (10) after the cathodic degreasing (4).

6. Pretreatment method according to one of the preceding claims, wherein the component (10) is a spark plug housing and comprises a housing base body (11) and a ground electrode (12), and wherein the housing base body (11) and the ground electrode (12) ) are made of different materials.

7. Pretreatment method according to claim 6, wherein the ground electrode (12) is formed from a chromium-containing nickel steel, in particular from NiCr15Fe or NiCr23Fe15 or NiCr25FeAIY.

8. pretreatment method according to one of claims 6 or 7, wherein the

The spark plug housing (10) has a welded connection (13) by means of which the housing base body (10) and the ground electrode (12) are connected to one another.

9. Coating method for coating components (10), in particular for coating spark plug housings, which are each formed from at least two different materials, comprising the steps:

- Pretreatment of the component (10) with a pretreatment method (A) according to one of the preceding claims, and

- Production of the coating (7) of the component (10), in particular by means of a nickel electrolyte.

10. The coating method of claim 9, further comprising the step of:

- Pre-coating (6) of the component (10), in particular by means of a low-concentration nickel electrolyte, before the step of producing the

Coating (7).

11. Coating method according to one of claims 9 or 10, wherein at least a portion (14) of a surface of the component (10) of at least one of the method steps of the pretreatment method (A) and / or the

Coating process (B) is excluded, in particular by

Covering the partial area (14).

12. Coating method according to one of the preceding claims, wherein at least one of the method steps of the pretreatment method (A) and / or the coating method (B) is carried out by means of a frame (50), and in particular the component (10) on the frame (50) is arranged during the at least one method step.

13. The coating method of claim 12, wherein the frame (50) has a

Having inner anode (51), and wherein the inner anode (51) in particular in a The passage opening (15) of the component (10) is arranged while the at least one method step is being carried out.

14. Component, in particular spark plug housing, coated by means of a coating method (B) according to one of claims 9 to 13.