阅读说明：本技术 具有电镀的含镍和锌的保护层和含硅的密封层的火花塞壳体以及具有该壳体的火花塞和制造该壳体的方法 (Spark plug shell with electroplated nickel and zinc containing protective layer and silicon containing sealing layer and spark plug with shell and method for manufacturing shell ) 是由 S·努费尔 T·希尔特 于 2020-03-18 设计创作，主要内容包括：本发明涉及用于火花塞(1)的壳体(2),其具有沿着所述壳体(2)的纵轴X的钻孔,由此所述壳体(2)具有外侧(205)和内侧(204),并且其中在所述壳体(2)的外侧(205)的至少一部分上布置电镀施加的含镍和锌的保护层(210),并且在所述含镍和锌的保护层(210)上布置密封层(220),其中所述密封层(220)包含硅。(The invention relates to a housing (2) for a spark plug (1), having a bore along a longitudinal axis X of the housing (2), whereby the housing (2) has an outer side (205) and an inner side (204), and wherein an galvanically applied protective layer (210) comprising nickel and zinc is arranged on at least a part of the outer side (205) of the housing (2), and a sealing layer (220) is arranged on the protective layer (210) comprising nickel and zinc, wherein the sealing layer (220) comprises silicon.)

1. Housing (2) for a spark plug (1) having a bore along a longitudinal axis X of the housing (2), whereby the housing (2) has an outer side (205) and an inner side (204), and wherein an galvanically applied protective layer (210) comprising nickel and zinc is arranged on at least a part of the outer side (205) of the housing (2), and a sealing layer (220) is arranged on the protective layer (210) comprising nickel and zinc, characterized in that the sealing layer (220) comprises silicon.

2. A housing (2) according to claim 1, wherein the sealing layer (220) is chromium-free.

3. The housing (2) according to any one of the preceding claims, wherein the sealing layer (220) has a layer thickness A of 10 nm to 10 μm, in particular 100 nm to 1 μm.

4. The housing (2) according to any one of the preceding claims, characterized in that the nickel and zinc containing protective layer (210) has a layer thickness B of 1 μm to 30 μm on the housing (2).

5. The housing (2) according to any one of the preceding claims, characterized in that a first intermediate layer (301) is applied between the housing (2) and the nickel and zinc containing protective layer (210), and/or a second intermediate layer (302) is applied between the nickel and zinc containing protective layer (210) and the sealing layer (220), and/or a cover layer (303) is applied on the sealing layer (220).

6. A housing (2) according to claim 5, characterized in that the first intermediate layer (301) has a layer thickness C of 1 nm to 1000 nm.

7. A housing (2) according to any one of claims 5 or 6, characterized in that the second intermediate layer (302) has a layer thickness D of 1 nm to 1000 nm.

8. The housing (2) according to any one of claims 5 to 7, characterized in that the cover layer has a layer thickness (303) E of 1 nm to 2000 nm.

9. The housing (2) according to one of the preceding claims, characterized in that the nickel-and zinc-containing protective layer (210) and the sealing layer (220) are constructed over the entire outer side (205) of the housing (2), and in particular over at least a part of the inner side (204) of the housing (2), and when a first intermediate layer (301) and/or a second intermediate layer (302) and/or a covering layer (303) is present, the first intermediate layer (301) and/or the second intermediate layer (302) and/or the covering layer (303) are constructed over the entire outer side (205) of the housing (2), and in particular over at least a part of the inner side (204) of the housing (2).

10. Spark plug (1) with a housing (2) according to one of claims 1 to 9, an insulator (3) arranged in the housing (2), a center electrode (4) arranged in the insulator (3) and a ground electrode (5) arranged on the combustion chamber-side end of the housing (2), wherein the ground electrode (5) and the center electrode (4) are provided so as to jointly form an ignition gap.

11. Method of manufacturing a housing (2) according to any of claims 1 to 9, having the steps of:

providing a housing (2) for a spark plug (1) having a nickel-and zinc-containing protective layer (210) which is applied to the housing (2) by means of an electroplating coating method, wherein the housing optionally has a first and/or a second intermediate layer (301, 302),

subsequently rinsing the housing (2) coated with the nickel-and zinc-containing protective layer (210) (S2),

subsequently, a step (S3) of applying a sealing layer (220) onto the nickel-and zinc-containing protective layer (210) or the second intermediate layer (302) is performed.

12. The method of manufacturing a case (2) according to claim 11, characterized in that the manufacturing method has a step (S1) of cleaning the surface of the case (2) coated with at least the nickel and zinc containing protective layer (210) before the rinsing step (S2).

13. Method for manufacturing a casing (2) according to any of claims 11 or 12, characterized in that it has a drying step (S4) after applying the sealing layer (220) onto the nickel and zinc containing protective layer (210) or onto the second intermediate layer (302), wherein possible water or solvent from applying the sealing layer is removed, in particular from the surface of the casing (2).

14. The method of manufacturing a case (2) according to claim 13, further having a polycondensation step after the drying step (S4), wherein the sealing layer (220) is cured.

15. A method of manufacturing a casing (2) according to any of claims 11 to 14, further having the step of applying a cover layer (303) onto the sealing layer (220).

16. Method of manufacturing a housing (2) according to any of claims 11 to 15, characterized in that for applying the sealing layer (220) a sol-gel method, CCVD or PVD is used as coating method.

17. Method of manufacturing a housing (2) according to any of the preceding claims 11 to 16, characterized in that for the sealing layer (220) a silane with a functionalization, in particular an alkoxysilane, an aminosilane or an acryl silane, is used.

18. Method for producing a housing (2) according to claim 17, characterized in that for the sealing layer (220) furthermore a silane without functionalization, in particular an alkyltrialkoxysilane, is used.

Prior Art

The invention relates to a housing for a spark plug according to claim 1 and a spark plug according to claim 10 having at least one such housing, and a method for producing the housing according to claim 11.

Spark plugs of today have a housing made of steel which is subject to corrosion, in particular rust, under the conditions present in the engine. For this reason, the housing of spark plugs has long been coated with a protective layer which should protect the steel housing against corrosion. Nickel-and/or zinc-containing protective layers are very widely used. Protective layers comprising nickel and zinc have higher corrosion and heat resistance than pure zinc coatings and at the same time are less costly than pure nickel coatings. However, the corrosion protection of protective layers containing nickel and zinc is reduced by defects in the protective layer. These defects may reach all the way from the surface of the nickel and zinc containing protective layer to the surface of the casing and thus act as an erosion path that corrodes the casing itself.

It is known, for example from EP 2546938 a1 and EP 2605348 a1, that this problem in nickel-containing protective layers can be minimized by applying a chromium-containing sealing layer to the nickel-containing protective layer and thus sealing the defects.

The chromium-containing sealing layer can be deposited on the housing surface, for example, from a CrVI-containing medium. Here a sealing layer with incorporated chromium 3 is formed. It may however occur that depending on the environmental conditions, the 3-valent chromium from the surface of the sealing layer that is actually bound to the surface is converted to free 6-valent chromium. The problem here is that chromium with a valence of 6 is classified as harmful to health and its use is prohibited in some countries.

Disclosure of the invention

The object of the invention is to provide a housing for a spark plug with a corrosion protection layer system which offers good corrosion protection and at the same time essentially dispenses with the use of a sealing layer containing Cr. In particular, the corrosion protection layer system should also have a heat resistance of 300 ℃.

This object is achieved by the housing for a spark plug according to the invention in that the sealing layer arranged on the protective layer containing nickel and zinc contains silicon. An advantage provided by using a silicon-containing sealing layer is that the chromium-containing sealing layer can be discarded and thus the risk of forming 6-valent chromium and leaving the sealing layer is prevented. Furthermore, silicon-based sealing layers have proven to be very heat resistant. In particular, in a test series for spark plug housings having a corrosion protection layer system made of a nickel-containing protective layer and a silicon-containing sealing layer, it can be shown that the housing still has a degree of rusting of 0 after 24 hours on the salt spray test, i.e. the housing does not show rusting sites in the region of the housing to which the corrosion protection layer is applied. Even after aging the housing at 300 ℃ for 3 hours, the housing still had a rust scale of 0 after 24 hours at the time of the salt spray test.

A housing for a spark plug has a bore along its longitudinal axis. Through this bore, the housing obtains an outer side and an inner side. A bore in the housing is typically provided for receiving an insulator having a center electrode and a connector. The housing is typically made of steel, such as carbon steel. On at least a part of the outer side, a protective layer is applied to the surface of the housing, which protective layer should protect the housing against corrosion. The protective layer is a nickel and zinc containing protective layer which is applied to the housing by means of an electroplating technique. In the electroplating technique, a housing, which serves as an anode, is immersed in an electrolytic cell containing nickel and zinc, together with an electrode, which serves as a cathode. By applying a voltage between the housing and the electrodes, a current flows from the coated electrode through the electrolyte to the housing, whereby a protective layer comprising nickel and zinc is deposited on the side of the housing facing the coated electrode. The protective layer is composed mainly of nickel and zinc. Here, the proportion of nickel in the protective layer is preferably 12 to 15 wt.%. The protective layer then has a heat resistance of up to about 500 ℃. When the nickel content is low, the heat resistance is low. At higher nickel contents, the zinc is not sufficiently stable and dezincification of the protective layer occurs under corrosion load. This means that zinc is strongly reduced in the protective layer, for example due to oxidation of zinc in the protective layer. The protective layer loses its corrosion protection effect. Iron from the coated electrode is also deposited on the shell along with nickel and zinc. The proportion of iron in the protective layer containing nickel and zinc is generally from 2 to 6% by weight. Other impurities in the nickel and zinc containing protective layer, such as sulfur and trace amounts of sodium or potassium, are possible.

The nickel-and zinc-containing protective layer on the housing serves as a corrosion protection for the cathode, i.e. the nickel-and zinc-containing protective layer is electrochemically more inert than the material of the housing and forms a barrier against moist media. The corrosion protection provided by the protective layer containing nickel and zinc depends on the layer thickness B of the protective layer containing nickel and zinc and its defect-free nature. The thicker the nickel and zinc containing protective layer, the less likely defects will extend from the surface of the nickel and zinc containing protective layer through the entire thickness of the nickel and zinc containing protective layer to the surface of the casing and thereby open up an erosion path for the corrosion process of the casing. By means of an additional sealing layer on the protective layer containing nickel and zinc, these defects are sealed off and the corrosion protection of the housing is improved.

Further advantageous embodiments are the subject of the dependent claims.

In an advantageous embodiment, it is provided that the sealing layer is free of chromium, i.e. that the sealing layer contains no intentionally added chromium and at most chromium as an technically unavoidable impurity, which is undesirably incorporated into the sealing layer, for example during the production process.

It has been found to be advantageous for the sealing layer to have a layer thickness a of not less than 10 nm and not more than 10 μm, in particular not less than 100 nm and/or not more than 1 μm. It has been shown that the sealing layer should have a layer thickness a of not less than 10 nm, in order to make the sealing layer thick enough to close defects in the nickel and zinc containing protective layer. It has furthermore been shown that, in the case of a layer thickness a of the sealing layer of more than 10 μm, no significant improvement in the above-described technical effect of the sealing layer occurs.

Additionally or alternatively, the layer thickness B of the nickel-and zinc-containing protective layer is from 1 μm to 30 μm.

In one embodiment of the invention, it is provided that a first intermediate layer is applied between the housing and the protective layer containing nickel and zinc, and/or a second intermediate layer is applied between the protective layer containing nickel and zinc and the sealing layer, and/or a cover layer is applied on the sealing layer.

The advantage obtained by the first intermediate layer is that the protective layer containing nickel and zinc adheres better to the housing. The first intermediate layer serves as an adhesive bonding layer and may be composed of, for example, impact copper or nickel.

The advantage obtained by the second intermediate layer is that the silicon-containing sealing layer adheres better to the nickel-and zinc-containing protective layer and reduces the thermal stress between the layers. The second intermediate layer serves as an adhesive tie layer, and may contain, for example, at least one of the following elements: nickel, copper, chromium, zinc or titanium.

The capping layer on the silicon-containing sealing layer serves to protect the sealing layer from mechanical damage and may, for example, contain at least one of the following elements: nickel, copper, zinc, chromium or titanium.

Additionally or alternatively, the first intermediate layer has a layer thickness C of 1 nm to 1000 nm, and/or the second intermediate layer has a layer thickness D of 1 nm to 1000 nm, and/or the cover layer has a layer thickness E of 1 nm to 2000 nm. Advantageously, the layer thicknesses of the intermediate layer and the cover layer are significantly smaller than those of the protective layer containing nickel and zinc, so that internal stresses in the intermediate layer and the cover layer are prevented. Due to internal stresses in the layer, adhesive bonding defects may occur or detachment of the layer from another layer, for example a protective or sealing layer containing nickel and zinc, may occur.

The advantageous effect of the corrosion protection layer system with the protective layer and the sealing layer comprising nickel and zinc and the optional first intermediate layer and/or the optional second intermediate layer and/or the optional cover layer is achieved in particular when the protective layer and the sealing layer comprising nickel and zinc and the optional first intermediate layer and/or the second intermediate layer and/or the cover layer are constructed over the entire outer side of the housing. And the corrosion protection layer system is also formed, in particular, additionally on at least a part of the inside of the housing. It is particularly advantageous if the nickel-and zinc-containing protective and sealing layers and the optional first intermediate layer and/or the optional second intermediate layer and/or the optional cover layer are formed over the entire surface of the housing. The more the surface of the housing is covered by the corrosion protection layer system, the less exposed surface of the housing is susceptible to corrosion processes.

The invention also relates to a spark plug having a housing according to the invention, an insulator arranged in the housing, a center electrode arranged in the insulator, and a ground electrode arranged at the combustion chamber-side end of the housing, wherein the ground electrode and the center electrode are provided for jointly forming an ignition gap.

The invention further relates to a method for producing a housing according to the invention. The production method comprises the following steps:

providing a housing for a spark plug, which has a nickel-and zinc-containing protective layer applied to the housing by means of an electroplating coating method, wherein the housing optionally has a first and/or a second intermediate layer,

subsequent rinsing of the casing coated with at least the nickel and zinc containing protective layer,

a step of applying a sealing layer onto the protective layer or the second intermediate layer comprising nickel and zinc is subsequently carried out.

Optionally, the manufacturing method may further include a cleaning step, before the rinsing step, in which the surface of the case coated with at least the nickel and zinc-containing protective layer is cleaned. The cleaning step serves to clean the surface of the housing and of the protective layer containing nickel and zinc or of the optional second intermediate layer to remove, for example, particles, dirt and passivating agents, and in particular to carry out hydrolysis or activation of the surface for binding the silane solution.

In the rinsing step, the cleaning agent or its residue is removed from the casing coated with at least the nickel and zinc containing protective layer. Alternatively, when the cleaning step itself is dispensed with, coarse dirt, for example dust, is also washed off in the rinsing step.

In the sealing layer applying step, the sealing layer is applied at least to the protective layer or the second intermediate layer containing nickel and zinc.

Preferably, the sealing layer is a silicon-containing sealing layer, wherein the silicon-containing sealing layer is formed by silanizing the surface of the case coated with at least the nickel and zinc-containing protective layer. Silanization is the chemical bonding of silane compounds to surfaces. The bonding is carried out by a condensation reaction between the hydrolysable groups of the silane used and the chemical groups on the surface. The silanes used for silanization generally have the general formula R_mSiX_nWherein R represents an organofunctional group and X represents a hydrolyzable group, and m and n represent the number of organofunctional groups and hydrolyzable groups.

In an advantageous embodiment, the method has at least one drying step, in which water or solvent is removed from the surface of the coated and sealed housing. In this case, for example, the silane compound has already started crosslinking. Further, the manufacturing method may further include a polycondensation step of curing the sealing layer. Upon curing of the silane compound, the crosslinking of the silane compound is ended and the crosslinking solidifies, so that a strong and robust sealing layer is formed.

Additionally or alternatively, the manufacturing method may also have the step of applying a cover layer onto the sealing layer. Thereby protecting the sealing layer from mechanical damage.

In the preferred silylation, for example, polycondensation of a silane compound coupled to the surface of the second intermediate layer or the surface of the nickel and zinc-containing protective layer of the case with each other, or polycondensation of a silane compound coupled to the surface of the second intermediate layer or the surface of the nickel and zinc-containing protective layer of the case with an uncoupled silane compound may be included.

In principle, it is also possible to incorporate other silicone compounds, such as silicone oils (e.g. diorganopolysiloxanes), into the silane compound network formed by polycondensation.

In an advantageous embodiment of the production method, a sol-gel process, CCVD or PVD is used as a coating method for applying the sealing layer.

In the sol-gel process, the shell is placed in a silane solution. During the silanization process, the silanes accumulate on the surface of the housing coated with at least the nickel-and zinc-containing protective layer and there begin to crosslink with one another and form a sealing layer.

In the CCVD process (combustion chemical vapor deposition), also known as flame coating, a starting compound, here a silane, is added to the combustion gas, which is suitable for producing the desired layer. The flame is moved over the substrate to be coated, here the housing coated with a protective layer containing nickel and zinc, at a small distance. Due to the high combustion energy, the starting compounds form very reactive species which are strongly bound to the substrate surface. The substrate itself is less thermally loaded because it is only briefly in contact with the flame.

In the PVD process (physical vapor deposition), the material to be deposited, in this case silane, is present in solid form in the coating chamber. The material is evaporated by bombardment with a laser beam, ions, electrodes or an electric arc discharge. The evaporated material moves through the coating chamber onto the component to be coated, here the housing which is coated with at least the nickel-and zinc-containing protective layer, where it condenses and thus forms a protective layer.

It has been found to be advantageous to use silanes with functionalization, in particular alkoxysilanes, aminosilanes or acrylosilanes, for producing the silicon-containing sealing layer. In addition, silanes without functionalization, in particular alkyltrialkoxysilanes, can also be used for the silane-containing sealing layer. Partially or perfluorinated siloxanes can only be used to a limited extent, since the layers formed therefrom do not have a heat resistance of up to 300 ℃.

Further features, application possibilities and advantages of the invention emerge from the following description of an embodiment of the invention shown in the figures of the drawings.

Drawings

FIG. 1 shows an example of an anticorrosion layer system according to the invention on a housing

FIG. 2 shows another example of an anticorrosion layer system according to the invention on a housing

FIG. 3 shows one example of a spark plug having a housing according to the present invention

Fig. 4 shows an exemplary method for producing a housing according to the invention.

Description of the embodiments

Fig. 1 shows an example of a corrosion protection layer system according to the invention, which is composed of a nickel-and zinc-containing protective layer 210 and a silicon-containing sealing layer 220. A protective layer 210 containing nickel and zinc is applied on the surface of the housing 2. A silicon-containing sealing layer 220 is in turn applied over the nickel and zinc-containing protective layer 210.

The nickel and zinc containing protective layer 210 has a layer thickness B. The layer thickness is measured perpendicular to the surface of the housing. Since the nickel-and zinc-containing protective layer 210 is applied to the housing 2 by means of electroplating techniques, the layer thickness B of the nickel-and zinc-containing protective layer 210 can be different at different locations of the housing 2. For example, the housing 2 may not have a nickel and zinc containing protective layer 210 or only partially have a nickel and zinc containing protective layer 210 on its inner side 204. Preferably, the housing 2 has a protective layer 210 comprising nickel and zinc on its entire outer side 205.

The silicon-containing sealing layer 220 has a layer thickness a. In the case of a silicon-containing sealing layer 220 applied by means of an immersion bath in a silane solution, a very uniform layer thickness a of the silicon-containing sealing layer 220 is generally obtained. In particular, silicon-containing encapsulant layer 220 may be configured over the entire surface of enclosure 2, as well as in locations of enclosure 2 where nickel and zinc-containing overcoat layer 210 is not present, such as in the region of interior side 204 of enclosure 2.

Fig. 2 shows another example of a corrosion protection layer system according to the invention, which is composed of a nickel-and zinc-containing protective layer 210 and a silicon-containing sealing layer 220 as well as a first intermediate layer 301 and a second intermediate layer 302 and a cover layer 303. A first intermediate layer 301 is applied on the surface of the housing 2. To which in turn a protective layer 210 comprising nickel and zinc is applied. A second interlayer 302 is disposed between the nickel and zinc-containing protective layer 210 and the silicon-containing sealing layer 220. A cap layer 303 is in turn applied over the silicon-containing sealing layer 220.

The nickel and zinc containing protective layer 210 has a layer thickness B. The first intermediate layer 301 has a layer thickness C and the second intermediate layer 302 has a layer thickness D. The layer thickness is measured perpendicular to the housing surface. When the nickel-and zinc-containing protective layer 210 is applied to the housing 2 by means of an electroplating technique, the layer thickness B of the nickel-and zinc-containing protective layer 210 can be different at different locations of the housing 2. For example, the housing 2 may not have a nickel and zinc containing protective layer 210 or only partially have a nickel and zinc containing protective layer 210 on its inner side 204.

The silicon-containing sealing layer 220 has a layer thickness a. In the case of a silicon-containing sealing layer 220 applied by means of an immersion bath in a silane solution, a very uniform layer thickness a of the silicon-containing sealing layer 220 is generally obtained. In particular, silicon-containing encapsulant layer 220 may be configured over the entire surface of enclosure 2, as well as in locations of enclosure 2 where nickel and zinc-containing overcoat layer 210 is not present, such as in the region of interior side 204 of enclosure 2. The capping layer 303 has a layer thickness E.

In a further embodiment of the housing 2 with the corrosion protection layer system according to the invention, the corrosion protection layer system can also have, in addition to the protective layer 210 and the sealing layer 220 containing nickel and zinc, only the cover layer 303, or only the first or second intermediate layer 301, 302, or a combination of the cover layer 303 and the first or second intermediate layer 301, 302.

Fig. 3 shows the spark plug 1 in a half-cut view. The spark plug 1 includes a housing 2. An insulator 3 is inserted into the housing 2. The housing 2 and the insulator 3 each have a bore along their longitudinal axis X. Through which the housing 2 has an outer side 205 and an inner side 204. The longitudinal axis of the shell 2, the longitudinal axis of the insulator 3 and the longitudinal axis of the spark plug 1 coincide. The center electrode 4 is inserted into the insulator 3. Furthermore, the connecting bolt 8 extends into the insulator 3. A coupling nut 9 is arranged on the coupling screw 8, by means of which the spark plug 1 can be brought into electrical contact with a voltage source, not shown here. The coupling nut 9 forms the end of the spark plug 1 facing away from the combustion chamber.

Between the central electrode 4 and the connecting bolt 8, a resistive element 7, also referred to as CCM (ceramic composite material), is present in the insulator 3. The resistance element 7 electrically conductively connects the center electrode 4 to the connecting bolt 8. The resistor element 7 is, for example, designed as a layer system made of a first contact CCM 72a, a resistor CCM 71 and a second contact CCM 72 b. The layers of the resistance element 7 differ in their material composition and the resulting resistance. The first contact CCM 72a and the second contact CCM 72b may have different resistances or the same resistance. The resistive element 7 may also comprise only one resistive CCM layer or a plurality of different resistive CCM layers with different material compositions and resistances.

The insulator 3 rests with a shoulder against a housing seat formed on the inside of the housing. In order to seal the air gap between the inside of the housing and the insulator 3, an inner seal 10 is arranged between the insulator shoulder and the housing seat, which inner seal is plastically deformed when the insulator 3 is clamped in the housing 2 and thereby seals the air gap.

A ground electrode 5 is arranged on the housing 2 in an electrically conductive manner on its combustion chamber-side end face. The ground electrode 5 and the center electrode 4 are arranged relative to each other such that an ignition gap is formed therebetween, in which an ignition spark is generated.

The housing 2 has a lever. On this rod are configured a polygonal portion 21, a constricted recess and a thread 22. The thread 22 is used to screw the spark plug 1 into an internal combustion engine. An external sealing element 6 is arranged between the thread 22 and the polygonal portion 21. In this embodiment, the outer sealing element 6 is designed as a folded seal.

The housing 2 is made of steel, for example carbon steel. On the housing 2, in particular on its outside, a protective layer 210 containing nickel and zinc is applied. The nickel and zinc containing protective layer 210 has a layer thickness B, wherein B is preferably not less than 1 μm and not more than 30 μm. The nickel and zinc containing protective layer 210 serves as passive corrosion protection. A silicon-containing sealing layer 220 is also applied over the nickel and zinc-containing protective layer 210. The silicon-containing sealing layer 220 has a layer thickness a, where a is preferably not less than 10 nm and not more than 1000 nm.

Fig. 4 schematically shows a part of an exemplary flow of a method of manufacturing a housing 2 according to the invention:

in a first optional step S1, the casing 2 (which was previously coated with at least the nickel and zinc containing protective layer 210 and optionally with one or two intermediate layers by means of electroplating techniques) and its surface are cleaned. For this purpose, the housing 2 coated with at least the nickel-and zinc-containing protective layer 210 is placed in a bath with a strongly alkaline cleaning agent and additionally irradiated with ultrasound for about 5 minutes in the bath. The optional cleaning step serves on the one hand to remove particles, dirt and passivating agent which hinder the application of the sealing layer 220 and on the other hand to hydrolyze or activate the surface on which the sealing layer 220 should be applied, thereby giving the sealing layer 220 a good bonding potential. Optionally, before optional cleaning, the housing 2 may also have a first intermediate layer 301 and/or a second intermediate layer 302 in addition to the nickel-and zinc-containing protective layer 210.

In a second step S2, the cleaned housing 2 is rinsed, for example with deionized water, in order to remove possible residues of cleaning agent.

In a third step S3, a sealing layer 220 is applied. Here, application can be carried out, for example, by silanization of the coated housing 2. Here, the housing 2 is immersed in or sprayed with a silane solution. In this step, the silane binds to the hydrolyzed surface of the shell 2 and begins to crosslink, thereby creating the sealing layer 220.

In an optional fourth step S4, drying of the casing 2 and curing of the sealing layer 220 is performed. Here, after silanization, the housing 2 is left for about 15 minutes, for example, in a drying oven at about 130 ℃. Here, possible residual water or residual solvent, for example from the bath, is removed from sealing layer 220. At the same time, the crosslinking of the silanes with each other is ended, whereby the sealing layer 220 is cured. The drying step is particularly advantageous, since the crosslinking of the silanes with one another is thereby assisted and accelerated.

In the final step S5 shown here, the shell 2 is allowed to cool, and then it is passed on for further processing, such as applying a cover layer 303 to the silicon-containing sealing layer 220 or assembling the spark plug 1.