DE102011077022A1 - Bearing component, useful e.g. in electronics manufacturing, comprises coating for electrical insulation comprising silane and/or siloxane compound, metal alcoholate, polyether ether ketone and/or polytetrafluoroethylene as dispersion - Google Patents

Abstract

Bearing component comprises a coating for electrical insulation, comprising a silane and/or a siloxane compound, a metal alcoholate, polyether ether ketone (PEEK) and/or polytetrafluoroethylene (PTFE) as dispersion. An independent claim is also included for a coating method for a bearing component, comprising applying the coating on the bearing component, and subsequently sintering by pulsed magnetic induction on the component surface.

Description

The present invention relates to a coating for a bearing component having the features of the preamble of claim 1 and a corresponding coating method for a bearing component having the features of the preamble of claim 6.

Components, in particular bearing components, in which the tribological properties are of particular importance, are provided with special coatings for electrical insulation and / or for improving their tribological properties. Usually thick ceramic sprayed coatings are applied to the components for electrical insulation.

A problem with the typical thick ceramic layers is that these layers are partially limited or not at all suitable for bearing components. In particular, no coating has hitherto been known which, in addition to good electrical insulation properties, simultaneously meets the high requirements of roll-over capability - which is a prerequisite for some bearing components. In addition, the thick ceramic layers must generally be post-processed and have a relatively high mass. In addition, the ceramic layers for small bearings with inner diameters smaller than 75 mm are not suitable because they do not allow a thick insulating layer due to the low bearing tolerances or process-technical or geometric reasons can not be equipped with a ceramic spray coating.

The invention is therefore based on the object to provide a coating and a corresponding coating method for a bearing component, whereby an electrically insulating and simultaneously rollable coating can be applied to a component.

The invention solves this problem by a coating method and a corresponding coating with the features of claims 1 and 6. Further preferred embodiments of the invention can be found in the dependent claims and the associated description.

• a) Eine Silan- und/oder Siloxanverbindung,
• b) ein Metallalkoholat,
• d) PEEK und/oder PTFE als Dispersion.

To achieve the object, a bearing component with an electrical insulation is proposed according to the invention, wherein the coating comprises at least the following substances:

• a) a silane and / or siloxane compound,
• b) a metal alcoholate,
• d) PEEK and / or PTFE as a dispersion.

Furthermore, a coating method for a bearing component is proposed according to the invention for solving the object, in which a bearing component is coated with such a coating and the coating is applied to the bearing component in a first step and then sintered by pulsed magnetic induction on the component surface.

By the bearing component according to the invention or by the coating method according to the invention, it is possible to combine outstanding tribological properties with simultaneous mechanical strength and electrical insulation in one layer.

It is advantageous if the coating additionally comprises a solvent mixture of organic solvent.

Furthermore, the silane and / or siloxane compound is preferably as acyloxysilane, alkylsilane, aminosilane, bis-silyl-silane, epoxysilane, fluoroalkylsilane, glycidoxysilane, isocyanato-silane, mercapto-silane, (meth) acrylato-silane, mono-silyl-silane, Multi-silyl-silane, sulfur-containing silane, ureidosilane, vinylsilane and / or designed as a corresponding siloxane.

Preferably, the coating additionally comprises an organic polymer which has been obtained by polymerization of olefinically unsaturated monomers.

Furthermore, it is advantageous if the coating additionally comprises a surfactant, wherein the surfactant preferably comprises wetting agents and / or deaerators and / or defoamers.

In the coating method, it is advantageous if the coating is applied to the component in a first step and is then sintered by pulsed magnetic induction on the component surface. The use of pulsed magnetic induction enables the sintering of plastic particles in the millisecond and nanosecond range. The pulsed magnetic induction generates extremely steep temperature gradients that penetrate only a few microns deep into the substrate and thus do not adversely affect the base material.

In order to avoid undesirable scaling or oxidation of the applied coating or of air inclusions in the coating, the coating process is preferably carried out under protective gas or vacuum.

The coating produced by the coating method preferably has a thickness ranging from 1 to 25 μm, more preferably ranging from 1 to 10 μm lies. These relatively thin layers are well suited for components for which there are high demands on component tolerances.

Due to the coating according to the invention, the dimensions and surface roughness remain virtually unchanged. The tribological properties can be improved and at the same time can also cope with the mechanical stresses. Preferably, a plastic dispersion of PEEK and metal alcoholates, a so-called. Sol-gel layer is transferred via an induction hardening in a hard layer.

The carbon layers previously used in rolling bearings have metallic elements (referred to as a-C: Me), these layers are characterized by excellent tribological properties, but they are electrically conductive due to the metallic portion. Metal-free carbon layers (for example a-C: H, a-C: H: a, ta-C: H, ta-C) have very good tribological sliding properties, but they do not withstand the mechanical stresses that occur in roller bearings.

The preferably used dispersion coating is a method in which plastic particles, an organic-inorganic hybrid compound mostly dissolved in organic solvent and / or in water, by means of a pressure coating method (or other coating method such as dipping, spraying, rolling or the like) as a very thin dispersion coating be applied to the surface area to be coated.

In the development of the plastic coating, which is preferably applied as a cloth coating, special requirements are placed on the dispersion. In particular, the sometimes low corrosion resistance of the materials to be coated (especially in the case of steels) must be taken into account in the dispersion composition, the substrate cleaning and in the heat treatment of the layer.

Further advantages, features and details of the invention will become apparent from the following description of an embodiment.

In this embodiment, a PEEK plastic layer is produced with outstanding tribological properties while high mechanical strength and electrical insulation properties.

For this purpose, a 1 to 10 .mu.m thick coating is applied to a bearing component, for example a rolling bearing made of a cost-effective steel such as 16MnCr5, C45, 100Cr6, 31CrMoV9, or 80Cr2. According to the invention, a plastic dispersion of PEEK and metal alcoholates (the sol-gel layer) is converted into a hard coating by electromagnetic induction. Electromagnetic induction systems require less space than traditional recirculating air drying systems and can be better integrated into production lines for bearing assemblies.

For preparation, the components are cleaned. In this case, it is easy to fall back on the methods customary in industrial practice, for example hot degreasing baths with surfactants and temporary corrosion protection. Despite the temporary corrosion protection, as for example with monoethanaloamine (MEA), which remains on the component after cleaning, there is no impairment of the deposited dispersion coating.

The heat is introduced, as already described, preferably by means of pulsed magnetic induction. In this case, the PEEK dispersion is baked on bearing components made of steel at a temperature which is preferably higher than the melting point of PEEK, more preferably in a range of 350 to 450 ° C, more preferably in a range between 390 to 410 ° C.

In another preferred procedure, the dispersion coating is predried by means of thermal drying using IR radiation. As a result, the lacquer becomes a still powdery organic-inorganic hybrid layer, similar to a conventional high-filled low-binder lacquer with a weak binding character to the substrate surface. This layer is then subjected to a further higher thermal drying of temperatures up to 400 ° C, whereby the powdery character is continuously lost. It begins the melting of the organic layer constituents and ultimately arises in this sintering, an optically homogeneous plastic film, which has a regularly smooth and non-porous surface.

Another possibility to produce a plastic layer is the use of aqueous hard material suspensions. Here, a hard material suspension with a microscale plastic powder is mixed in, which offers the possibility to produce hard-wearing coatings. Such abrasion-resistant coatings can be prepared, for example, by dispersing silicon dioxide (DEGUSSA, Aerosil OX50) with plastic particles (polyether ketone from Vitrex) in water. These layers can be melted directly after drying (IR drying) of the solvent and the subsequent pulsed magnetic induction of the metallic substrate become. The method makes it possible to apply high-melting plastics, such as polyether ketones, to the substrates to be coated within seconds from the powder form to form a plastic film.

For the production of the organic-inorganic hybrid polymer plastics similar starting chemicals are used, as these are also used for the sols for the deposition of oxide ceramic green sheets. In this embodiment, the plastic dispersion of PEEK and metal alcoholates (so-gel) is produced. Metal alcoholates are organic compounds in which a plurality of alcohol residues are attached to a metal ion via the oxygen atoms of an alkyl group. These are prepared by the reaction of elemental metals with alcohols with elimination of hydrogen. Suitable metal ions for a 4-valent metal, silicon, titanium or zirconium or for a 3-valent metal, aluminum, yttrium or boron in question.

Metal alcoholates are extremely reactive, the alkoxides can react with, for example, water or organic compounds. The alcohol residues are split off. The reaction with organic compounds is used to produce sols with polymeric structures. In addition, the reaction with water should be avoided. Metal alcoholates are very easily hydrolyzed, so that even small amounts of water can lead to an uncontrolled precipitation of macromolecular metal hydroxide particles. An organic compound such as acetic acid, glycine and aminocaproic acid added to the alcoholate before hydrolysis prevents the metal alkoxide complex from being completely hydrolyzed and precipitated as a hydroxide, thus the alcoholate can be stabilized. Acetic acid-stabilized alcoholates have significantly shorter gel times than alcohol stabilized with other acids. Although the lower acidity of acetic acid in alcohol retards the hydrolysis, it accelerates the condensation so much that the overall reaction proceeds faster. These partially hydrolyzed metal alcoholates can now polymerize with each other. Chains are formed depending on the stabilization and three-dimensional networks. Water formed by the reaction can provide further hydrolysis.

In addition to metal alcoholates, preference is given to using organically modified silanes (OR MOSILs). Another silane used is 3-aminopropyltriethoxysilane, alkoxysilane, alkoxy-functional organopolysiloxanes and glycol-functional organosilicon compounds, which are known as adhesion promoters for metals, silicate glasses and oxidic materials. In addition to the simple alkoxides, such as tetraethoxyorthosilane (TEOS), network-modifying and network-forming ORMOSILs are used for sol synthesis. The TEOS is used for the generation of stable, dense oxide layers. Because of these dense oxide layers, TEOS has poor electrical conductivity and is insulating and accordingly used as a protective oxide. Since TEOS also contains silicon, the oxide layer to be applied grows linearly and very quickly.

One of the simplest network-modifying ORMOSILs is methyltriethoxysilane (MTES). In addition to the three epoxy groups, which crosslink by polycondensation, it contains a methyl group, which remains chemically inactive and thus reduces the degree of crosslinking in the gel. A typical network-forming ORMOSIL is methacryloxypropyltrimethoxysilane (MATMS). The organic crosslinking takes place here via a methacrylic group. As metals in addition to silicon and aluminum, titanium, zirconium are known and preferred, but there are also many more conceivable. An application of the method shows the further development of MTES / TEOS brine in conjunction with organically modified zirconium, wherein the sol should be adjusted to alkaline. These preferred sols have an excellent coating behavior. Even at critical points, such as component edges, the coating is characterized by lower susceptibility to cracking.

The preferred particle size distribution of a polymeric base catalyzed silica sol and a colloidal acid stabilized alumina sol ranges from 40 to 100 nm. Use of acid catalysis for the silica sol results in small and base catalysis of large particles. It has been found that in the pH range of the plastic dispersion between pH 0 and 2, under the chosen conditions, the equilibrium of the hydrolysis-condensation reactions is on the side of the hydrolysis, ie. H. it forms structures with high degree of hydrolysis and low degree of condensation. At pH values of 2 to 5, condensation is the rate-limiting step. Monomers and smaller oligomers with reactive silanol groups are present side by side. Further condensation leads to a relatively weakly branched network with small cage-like units. At comparable conditions in the alkaline pH range, the equilibrium is on the side of the condensation, i. H. after slow formation of types of hydrolysis, the condensation reaction begins immediately, forming separate highly crosslinked polysiloxane units. In the basic medium, the hydrolysis is rate-limiting. The clusters grow mainly by condensation with monomers. This results in networks with large particles and pores. In the basic catalysed sol-gel process, sodium hydroxide or ammonia are preferably used. This results in principle an analogous dependence of the reaction rate on the base strength, as in acid catalysis of the acidity.

Extensive coating experiments have shown that the structure of the condensates formed, apart from the pH of the reaction medium on the type of solvent, the type and chain length of the alkoxy function, the molar Si / water ratio, the concentrations, the temperature, the type and concentration depend on the catalyst, evaporation rates and the amount of water added.

Approaches with molar water / silicon ratios (r) of 1 to 50 are described in the literature. An increasing molar ratio r significantly accelerates the acid-catalyzed hydrolysis and leads to more SiOH groups, which facilitates the formation of cyclic structures in the sol. Also, the competing condensation reactions depend critically on the concentration of water, since at r <2 the condensation with elimination of alcohol and at r> 2, the condensation predominates with elimination of water. At high water concentration, dilution effects occur which delay the hydrolysis and condensation reactions. Viscous, spinnable sols are obtained at a preferred molar ratio of Si (OR) 4 to water of 1: 1 to about 1: 2. Further preferred are ratios of 1: 4 to 1:11, since thereby layers with low susceptibility to cracking can be produced. If the excess of water compared to TEOS further increased, result in monolithic solids, which should be avoided. In general, the same basic course of reaction results for all catalysts, but the rates change as a function of the strength and concentration of the catalyst. It was found that this effect is due to differences in the dissociation behavior and thus to the pH value.

Further experimental results regarding the shrinkage behavior of both preferred gels during sintering show that acid catalysis of the silica sols leads to rapid and base catalysis to time-retarded shrinkages. The combination of network-forming and network-modifying ORMOSILs and pure metal alcoholates in the polymer dispersions makes it possible to produce very different hybrid layers. These layers according to the invention are distinguished by novel properties, since a mixture of inorganic metal oxide bridges and organic bonds via hydrocarbon chains in a plastic matrix is present at the molecular level. The chemical composition of these hybrid layers, the layer deposition conditions and the heat treatment parameters such as heating rate, temperature, holding time have an influence on the layer properties.

By the method according to the invention, layers with a thickness of 5 to 150 μm can be produced. As already described, the preferred layer thicknesses are in a range between 1 to 25 μm or 1 to 10 μm. Thinner plastic layers have - in addition to the advantages described above - a higher crosslinking stability and less prone to chipping or peeling.

By means of the described layer structure according to the invention of plastic layers with embedded metal oxides, it is possible to combine the outstanding tribological properties with mechanical strength and electrical insulation, resulting in the advantages already described. Since the coating can be used without reworking due to the high mechanical strength and the small layer thickness, any reworking costs are eliminated. The excellent tribological properties mean that lower-priced, lower viscosity lubricants with lower internal friction can be used and oil change intervals can be delayed. In addition, rolling bearing components can also be operated under dry friction and lack of lubrication, since the PTFE dispersion preferably used acts as a dry lubricant. Instead of PTFE, similar equivalent dry lubricants with low coefficients of friction can be used, the core of the invention is not affected.

In addition to the abovementioned α-C: H: Me layers, the layers also have an equally good thermal stability of about 350 to 380 ° C., which results in a marked field of application. The possibility resulting from the invention of using hydraulic oil, diesel fuel, water and even gasoline as a lubricant opens up completely new areas of application in the food industry, productronics, drive technology as well as hydraulic and other media-lubricated applications.

Claims (10)

Bearing component with a coating for electrical insulation, characterized in that the coating comprises at least the following substances: a) a silane and / or siloxane compound, b) a metal alkoxide, c) PEEK and / or PTFE as a dispersion. Bearing component according to claim 1, characterized in that the coating additionally comprises a solvent mixture of organic solvent. Bearing component according to one of the preceding claims, characterized in that the silane and / or siloxane compound as acyloxysilane, alkylsilane, aminosilane, bis-silyl-silane, epoxysilane, fluoroalkylsilane, glycidoxysilane, isocyanato-silane, mercapto-silane, (meth) acrylato Silane, mono-silyl-silane, multi-silyl-silane, sulfur-containing silane, ureidosilane, vinylsilane and / or is designed as a corresponding siloxane. Bearing component according to one of the preceding claims, characterized in that the coating additionally comprises an organic polymer which has been obtained by polymerization of olefinically unsaturated monomers. Bearing component according to one of the preceding claims, characterized in that the coating additionally comprises a surfactant, wherein the surfactant wetting agent and / or deaerator and / or defoamer comprises. Coating method for a bearing component, characterized in that the bearing component is coated with a coating according to one of claims 1 to 5, and the coating is applied in a first step on the bearing component and is then sintered by pulsed magnetic induction on the component surface. Coating method according to claim 6, characterized in that the process is carried out under a protective gas atmosphere or vacuum. Coating method according to one of claims 6 or 7, characterized in that the coating produced has a thickness which lies in a range between 1 to 25 □ m. Coating method according to one of claims 6 or 7, characterized in that the coating produced has a thickness which lies in a range between 1 and 10 μm. Coating method according to one of claims 6 to 9, characterized in that a 1 to 10 □m thick coating on a rolling bearing component of a 16MnCr5, C45, 100Cr6, 31CrMoV9, or 80Cr2 steel is applied.