EP2052789A2 - Wear protection layer and method of its manufacture - Google Patents

Abstract

Wear-protection layer for frictionally stressed component or in oscillation-superimposed impact load, comprises a metal layer, preferably hard chromium layer, and a polysiloxane layer, where the polysiloxane layer is applied on the metal layer. An independent claim is included for preparing the wear-protection layer comprising (a) coating the claimed component with the metal layer and (b) applying the polysiloxane layer on the metal layer.

Description

State of the art

The invention is based on a wear protection layer for a component subject to frictional stress, comprising a metal layer, in particular a hard chrome layer, and a method for producing the wear protection layer.

For protection against wear, for example, electroplated chrome layers are used in many areas of mechanical and apparatus engineering. Thus, for example, for valve components, for example in injection valves, in particular high-pressure injection valves, hard chrome layers are known as wear protection. These are used in particular as a protective layer under impact loading.

In particular, when using the wear protection layer in auto-igniting internal combustion engines with high-pressure injection, which are generally injection pressures in the range of 1500 to 1800 bar, which can be further increased in future developments, these hard chrome layers, however, to the limits of resilience. In particular, the comparatively high coefficient of friction of hard chrome compared to steel of μ = 0.2 is increasingly negatively noticeable. This is due to a superimposed oscillating movement of the component partners, for example armature and armature nozzle or nozzle needle and nozzle body, which increases with increasing component load and thereby initiates an abrasive removal of layer particles. The released layer particles lead to accelerated damage to the protective layer system. In addition, under the high loads of injection components in the internal combustion engines, an adhesive wear, through which also layer components are broken out of the composite and thus further promote the wear of the layer. As a remedy, it is for example DE-A 197 45 811 known to store the protective layers micro- or nanoparticles with lubricating effect, for example PTFE, graphite, hexagonal boron nitride or molybdenum disulfide. The incorporation of the particles is generally carried out in microcracks in the hard chrome layer.

In a friction stress, the micro- or nanoparticles are exposed with intrinsic lubricating effect and thus act lubricating. This technique of incorporation of particles with lubricating effect is widely used in particular for nickel layers. Although the technology is described for chrome layers, it is virtually unavailable on the market. This is because the chromium plating electrolyte is generally very acidic and highly oxidizing. For this reason, organic additives are oxidatively decomposed in no time. However, the organic additives, generally surfactants, are necessary for particles to be suspended in the electrolyte and then incorporated during electrocrystallization. Without such surfactant additives, the particle incorporation is almost impossible to perform.

In addition, in thin chrome layers, for example of less than 10 microns only particles less than 1 micron can be stored in order not to weaken the supporting chromium matrix. However, especially at very low pH, smaller particles lead to increased agglomeration and to the formation of agglomerates, some of which are larger than 10 μm. This leads to a violation of the integrity of the chromium layer. Also, capsules containing lubricants and can be stored are generally much larger than 1 micron.

The likewise known melting of polytetrafluoroethylene powders on chrome layers only works on easily accessible areas. In the case of internal geometries or the coating of holes, the method can not be used or leads to very uneven layer distributions.

Disclosure of the invention Advantages of the invention

A wear protection layer designed according to the invention for a component subject to frictional stress or for vibration-overlapping impact load comprises a metal layer, in particular a hard chromium layer, wherein a layer of a polysiloxane is applied to the metal layer.

The layer of the polysiloxane applied to the metal layer improves the tendency of the metal layer to wear. For example, it is possible to use a metal layer that is not covered by another layer of polysiloxane is provided to increase the wear resistance by a factor of 4 with respect to the weight loss and by a factor of 10 with respect to the wear volume.

Under weight loss is the mass of coating material to understand, which is removed by wear from the coating. Accordingly, wear volume is understood to mean the volume of coating material which is removed by the wear. An improvement with regard to the weight removal or the wear volume means that the weight reduction or the wear volume is reduced.

In a preferred embodiment, the metal layer is designed as a hard chrome layer and has a layer thickness in the range of 2 to 20 .mu.m, preferably in the range of 5 to 15 .mu.m and in particular of about 10 microns. Furthermore, the layer of polysiloxane has a layer thickness in the range of 0.1 to 2 μm, preferably in the range of 0.2 to 0.8 μm and in particular of approximately 0.5 μm.

By applying the polysiloxane on the hard chromium layer Adhäsionsneigung the hard chrome layer is achieved by changing the chromium layer topography and achieved in the further course of wear by forming the so-called 3rd body.

The polysiloxane is preferably a compound of optionally perfluorinated or partially fluorinated siloxanes.

wobei R¹, R², R³, R⁴, R⁵, R⁶ jeweils unabhängig voneinander -CF₃, -OCF₃, -O-SiR¹R²R⁵, O-Si(CF₃)₃, ein lineares oder verzweigtes C₁- bis C₁₅-Alkyl, eine Vinyl-, E-poxy-, Methacryloxy-, Amino- oder Arylverbindung, oder -O-M-OR, wobei M ein Metallatom, vorzugsweise ausgewählt aus Ti, Al und Zr, und R ein C₁- bis C₃-Alkyl oder Wasserstoff bedeuten, und
R⁷, R⁸, R⁹, R¹⁰ jeweils unabhängig voneinander Wasserstoff oder Fluor
bedeuten, wobei in den Resten R¹ bis R⁶ enthaltener Wasserstoff teilweise oder vollständig durch Fluor substituiert sein kann.The optionally perfluorinated or partially fluorinated siloxanes are preferably selected from

wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ^{6 are} each independently of one another -CF ₃ , -OCF ₃ , -O-SiR ¹ R ² R ⁵ , O-Si (CF ₃ ) ₃ , a linear or branched C ₁ - to C ₁₅ -alkyl, a vinyl, E-poxy, methacryloxy, amino or aryl compound, or -OM-OR, where M is a metal atom, preferably selected from Ti, Al and Zr, and R a C ₁ - to C ₃ alkyl or hydrogen, and
R ⁷ , R ⁸ , R ⁹ , R ^{10 are} each independently hydrogen or fluorine
mean, wherein hydrogen contained in the radicals R ¹ to R ⁶ may be partially or completely substituted by fluorine.

         CICH₂CH₂CH₂Si(OCH₃)_3,

With particular preference the siloxanes are selected from

CICH ₂ CH ₂ CH ₂ Si (OCH ₃ ) _3,

• Beschichten eines Bauteiles mit einer Metallschicht, insbesondere Hartchromschicht,
• Aufbringen einer Polysiloxanschicht auf die Metallschicht, insbesondere Hartchromschicht.

The invention further relates to a method for producing the wear protection layer, which comprises the following steps:

• Coating of a component with a metal layer, in particular hard chrome layer,
• Application of a polysiloxane layer on the metal layer, in particular hard chrome layer.

The coating of the component with the metal layer is generally carried out by a galvanic coating process. The coating process can be carried out in any manner known to those skilled in the art. Usually, a sulfuric acid chromium electrolyte with addition of dimethanesulfonic acid is used as the catalyst. For coating the component with the metal layer, the component is usually first cleaned, for example to remove fats from the surface, so that the metal layer holds firmly on the component. The purification step is generally carried out at a temperature in the range of 20 to 70 ° C for 60 to 300 seconds. After the cleaning step, a rinsing step is generally carried out with demineralized water. After rinsing, the component is first subjected to activation by electroless plating in a bath containing a metal, in particular chromium, electrolyte at a temperature of about 60 ° C for a period of about 60 s. Subsequently, the metal or chromium layer is applied by electroplating.

For the galvanic coating, the component is first roughened in a metal salt or chrome bath. This is carried out anodically at a current of 10 to 200 A / dm ² for a period of generally 30 s and at a temperature of about 60 ° C. Subsequently, the component is electroplated in the metal salt or chromium bath. This is also done anodically at a current of 10 to 200 A / dm ² for a period of 600 s at a temperature in the range of 60 ° C. For example, Ankor 1126 from Enthone GmbH is used as the chrome bath. After coating, a rinsing step is usually carried out with demineralized water at a temperature of 90.degree. Finally, the thus coated component is dried. For this purpose, the component is generally exposed to a circulating air drying at a temperature in the range of 100 ° C for a period of about 30 min.

According to the invention, the polysiloxane layer is applied to the metal or hard chrome layer in a next step. For this purpose, a siloxane dissolved in a solvent is preferably first applied by a dipping process or a spraying process.

The siloxane is preferably, as already described above, a perfluorinated or partially fluorinated siloxane.

The solvent in which the siloxane is dissolved is, for example, an alcohol, preferably selected from isopropanol, butanol, ethanol, ethylhexanol, methoxypropanol, or also, for example, acetone, ethyl acetate, xylene or water.

The ratio of siloxane to solvent is preferably in the range of 1:10 to 10: 1.

For applying the polysiloxane layer, the component is preferably cleaned in a first step and then rinsed with demineralized water. As a result, if necessary, impurities formed during application of the metal or hard chrome layer are removed.

The cleaning is usually carried out by wetting the component with a weakly alkaline cleaner. The wetting takes place, for example, by dipping or by means of a spraying technique. Commonly used weakly alkaline cleaners are, for example, commercial products containing potassium hydroxide or sodium hydroxide with added surfactant. A suitable cleaner is, for example, Slotoclean AK-FSA from Dr.-Ing. Max Schlötter GmbH & Co.KG in 1 to 2% solution. If the wetting of the component takes place by dipping, then this is preferably immersed for about 60 s at a temperature of about 70 ° C in the cleaner. So that the chrome surface of the component is loaded with hydroxyl groups, the alkalinity of the cleaner is a prerequisite. At the sites loaded with hydroxyl groups, the siloxane binds by hydroxylation reaction. Alternatively, however, a plasma activation is possible.

After cleaning, the component having a metal or a hard chrome layer is blown off. As a result, the component is dried. The blowing off takes place with inert gases, which are highly pure and oil-free. This is necessary to avoid contamination of the surfaces with oil residues. Suitable gases are, for example, high-purity and oil-free nitrogen or high-purity or oil-free air.

After blowing off, the solvent-dissolved siloxane is applied by spraying or dipping. Following the application of the siloxane, another blow-off with a high-purity and oil-free gas takes place. By blowing off with ultrapure and oil-free gas, any excess of siloxane which is formed during application is discharged from the component again. The paint surplus results, for example, when the siloxane is applied to the components or into the interior of, for example, injector valves by rinsing, dipping or spraying techniques. During application, a 5 to 50 μm thick paint film may form. If this paint film is directly crosslinked or cured, it leads to embrittlement with insufficient paint adhesion and paint stability. In order to avoid this, the paint surplus, which arises during application, is discharged from the component.

After blowing off the component with highly pure and oil-free gas, for example nitrogen or air, layer thicknesses of the siloxane coating are in the range from 0.1 to 2 μm. As an alternative to blowing off with the high-purity and oil-free gas, excess paint can also be thrown off.

Finally, the siloxane is cured to the polysiloxane layer. The curing takes place at a temperature in the range of 120 to 350 ° C for a time in the range of 15 to 60 minutes.

Brief description of the drawings

An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description.

The single FIGURE shows a representation of a nozzle body for an injection valve Embodiments of the invention

In the single figure, a nozzle body for an injection valve is shown.

A nozzle body 1 comprises a bore 3, in which an injection valve member, not shown here, is guided. With the injection valve member, an injection port 5 is closed or released. To close the injection opening 5, the injection valve member is placed in a valve seat 7.

The nozzle body is first chrome plated with a hard chrome layer. After chrome plating, cleaning is carried out in a weakly alkaline cleaner. The cleaning is generally carried out at a temperature in the range of 20 to 90 ° C for a period of 10 to 300 s. To remove the residues of the cleaner is then followed by a rinse in demineralized water for preferably 10 to 300 s. By blowing off with a high-purity and oil-free inert gas, preferably with nitrogen, the surface of the nozzle body 1 is dried residue-free. After drying the surface, a silane coating is performed. The coating is carried out, for example, with Silan H5099 or H5098 from FEW.

To coat the nozzle body 1 with silane, siloxane is diluted by means of a water or solvent mixture in the ratio of siloxane to solvent in the range from 1:10 to 10: 1. Thereafter, the nozzle body 1 for 10 to 60 s at room temperature in the Siloxane / solvent mixture dipped. Alternatively, it is also possible to wet the nozzle body 1 by spraying with the siloxane / solvent mixture. A uniform coating is achieved in this case by several successive spraying steps. After application of the solvent-siloxane mixture, the nozzle body 1 is blown off with a high-purity and oil-free inert gas. Nitrogen is particularly suitable as the gas. By blowing off excess siloxane / solvent mixture is removed. In addition, it serves for venting with simultaneous escape of the solvent.

After blowing, curing takes place by crosslinking of the polymer chains by splitting off water or alcohol groups. The mechanical properties of the resulting polysiloxane coating, ie hardness and abrasion, are dependent on the curing process. The thermal curing is generally carried out for at least 100 ° C. for at least 30 minutes. A maximum layer hardness of the polysiloxane layer is achieved at temperatures above 150 ° C.

In addition to the nozzle body 1 shown here, the layer according to the invention can also be used in any other component which is subjected to wear.

Furthermore, the coating according to the invention with a polysiloxane is also suitable for components which, instead of a hard chrome layer, have a layer of another metal or are made from this. For example, metal layers which have an oxidic surface or are coated or fabricated with insert steels which are used or blind-hardened are, for example, a 16MnCr5, a 16MnCrS5, a 18CrNi8 or a 15CrNi66 steel , Also suitable are tool steels or rolling bearing steels such as 100Cr6 or HS652 as well as nitriding steels. If nitriding steels are first oxynitrided, a subsequently applied siloxane layer adheres particularly well to this surface layer.

example

To test the coating according to the invention, wear measurements were carried out with a pin-and-disk tribometer as a model test stand. For this purpose, a coating according to the invention was applied to a round disk with a diameter of 25 mm and a thickness of 8 mm made of 100 Cr6 steel. For comparison, a disc was coated with a hard chromium layer as known in the art.

The wear path was 250 m with a wear force of 10 N. The wear radius was 6 mm. As a counter body, a tungsten carbide ball with a diameter of 6 mm was used. The test was carried out at room temperature and a relative humidity of 24 to 30%.

From a mass determination of the coated disks before and after the wear test, the mass loss caused by fretting was determined. In addition, the profile of the friction track was determined by means of confocal white light microscopy using a μ-surf device from Nanofocus. With the geometric wear radius, the wear volume could be calculated.

The comparison of the frictional wear results of the hard chrome plating, as known in the prior art, to the polysiloxane layer modified hard chrome plating shows that the application of the polysiloxane layer reduces the mass loss by at least 70% and the wear volume reduced by at least 90%.

Claims (15)

Wear protection layer for a frictionally stressed component or vibration superimposed impact load, comprising a metal layer, in particular hard chrome layer, characterized in that a layer of a polysiloxane is applied to the metal layer. Wear protection layer according to claim 1, characterized in that the metal layer is a hard chrome layer. Wear protection layer according to claim 1 or 2, characterized in that the metal layer is a layer of a hardened steel or a nitriding steel. Wear protection layer according to one of claims 1 to 3, characterized in that the metal layer has a layer thickness in the range of 2 to 20 microns and the layer of polysiloxane has a layer thickness in the range of 0.1 to 2 microns. Wear protection layer according to one of the preceding claims, characterized in that the polysiloxane is composed of perfluorinated and / or partially fluorinated siloxanes. Wear protection layer according to claim 5, characterized in that the perfluorinated or partially fluorinated siloxanes are selected from

wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ^{6 are} each independently of one another -CF ₃ , -OCF ₃ , -O-SiR ¹ R ² R ⁵ , O-Si (CF ₃ ) ₃ , a linear or branched C ₁ - to C ₁₅ -alkyl, a vinyl, E-poxy, methacryloxy, amino or aryl compound, or -OM-OR, where M is a metal atom, preferably selected from Ti, Al and Zr, and R a C ₁ - to C ₃ alkyl or hydrogen, and
R ⁷ , R ⁸ , R ⁹ , R ^{10 are} each independently hydrogen or fluorine
mean, wherein hydrogen contained in the radicals R ¹ to R ⁶ may be partially or completely substituted by fluorine. Process for the preparation of a wear protection layer according to one of Claims 1 to 6, comprising the following steps: Coating a component with a metal layer, in particular a hard chrome layer, - Applying a polysiloxane on the metal layer, in particular hard chrome layer. A method according to claim 7, characterized in that the coating of the component with the metal layer, in particular hard chrome layer is carried out by a galvanic coating method. A method according to claim 8, characterized in that a sulfuric acid chromium electrolyte is used for the galvanic coating process, which further contains a catalyst solution. A method according to any one of claims 7 to 9, characterized in that for applying the polysiloxane on the metal layer, first, a dissolved in a solvent siloxane is applied by a dipping process or spraying process. A method according to claim 10, characterized in that the solvent is selected from isopropanol, butanol, ethanol, ethylhexanol, methoxypropanol, acetone, ethyl acetate, xylene or water. A method according to claim 10 or 11, characterized in that the siloxane is a fluorinated or partially fluorinated siloxane selected from

wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ^{6 are} each independently of one another -CF ₃ , -OCF ₃ , -O-SiR ¹ R ² R ⁵ , O-Si (CF ₃ ) ₃ , a linear or branched C ₁ - to C ₁₅ -alkyl, a vinyl, E-poxy, methacryloxy, amino or aryl compound, or -OM-OR, where M is a metal atom, preferably selected from Ti, Al and Zr, and R a C ₁ - to C ₃ alkyl or hydrogen, and
R ⁷ , R ⁸ , R ⁹ , R ^{10 are} each independently hydrogen or fluorine
mean, wherein hydrogen contained in the radicals R ¹ to R ⁶ may be partially or completely substituted by fluorine. A method according to any one of claims 10 to 12, characterized in that the component is heat-treated after the application of the polysiloxane by the dipping process or spraying process. A method according to claim 13, characterized in that the heat treatment is carried out at a temperature in the range of 120 to 350 ° C. Use of the wear protection layer according to one of claims 1 to 6 as a coating for valve components in injection valves for internal combustion engines.

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