DE102011077021A1 - Method for producing electrically-insulated ceramic coating on piston or bearing component i.e. rolling body, of needle cage, involves applying mixture on component, and drying mixture with temperature between specific degrees Celsius - Google Patents

Abstract

The method involves applying a mixture comprising water, organic solvent, metal alcoholate i.e. organic silane, organic binding agent and metallic oxide or ceramic powder on a piston or bearing component i.e. rolling body (2), by using acid-catalyzed hydrolysis and a base-catalyzed condensation. The mixture is dried with temperature between 0 to 300 degrees Celsius. The mixture is sintered by treating with additionally pulsed microwaves by using an induction-hardening process, where the powder has average diameter that is smaller than 1 micrometer. An independent claim is also included for a piston or bearing component comprising an electrically-insulated ceramic coating.

Description

The present invention relates to a coating method for a piston or bearing component having the features of the preamble of claim 1 and a correspondingly coated piston or bearing component having the features of the preamble of claim 10.

Components, in particular piston or 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 heat input into the components associated with the coating process can be detrimental to component strength. In particular, if the temperatures in the coating process over the usual tempering temperatures of the materials are and / or temperatures are kept long, this can have an effect on the microstructure of the materials. The heat input can, for example, lead to undesirable diffusion effects or grain growth and thus, for example, worsen the results of a previously performed component hardening.

So-called sol-gel coating processes for producing electrically insulating coatings which are associated with the lowest possible heat input are known from the prior art. Such a method is for example in the document DE 10 2008 039 326 A1 described. However, there is still a need to provide for tribologically highly stressed components improved coatings with good electrical insulating and tribologically improved properties.

The invention is therefore based on the object to provide a coating method and a correspondingly coated piston or bearing component, whereby an electrically insulating and simultaneously rollable coating can be applied to a component with the lowest possible heat input.

The invention achieves this object by a coating method having the features of claim 1 and a correspondingly coated piston or bearing component having the features of claim 10.

• a) Wasser,
• b) ein organisches Lösemittel,
• c) ein Metallalkoholat,
• d) ein organisches Bindemittel sowie
• e) Metalloxid- oder Keramikpulver, wobei die das Pulver bildenden Partikel einen mittleren Durchmesser aufweisen, der im Mittel kleiner als 1 μm ist,

auf das Kolben- oder Lager-Bauteil aufgebracht wird und in einem zweiten Schritt durch eine Trocknung bei einer Temperatur zwischen 0 bis 300°C getrocknet wird.To achieve the object, a coating method for producing an electrically insulating ceramic coating on a piston or bearing component is proposed according to the invention, wherein in a first step, a substance mixture at least comprising

• a) water,
• b) an organic solvent,
• c) a metal alcoholate,
• d) an organic binder as well
• e) metal oxide or ceramic powder, wherein the particles forming the powder have an average diameter which is on average less than 1 μm,

is applied to the piston or bearing component and is dried in a second step by drying at a temperature between 0 to 300 ° C.

Preferably, the substance mixture is sintered in a third step and / or treated by an induction hardening process with additional pulsed microwaves. By the third step, the strength of the coating can be increased.

Preferably, the edge layer of the piston or bearing component is heated at least in one region and at least briefly to a temperature in a range between 850 ° and 1100 ° C. Due to the high temperatures, the coating can be cured well. In order that the occurring heat input into the component to be coated as low as possible, the described preferred pulsed induction is used. Pulsed microwave treatment preferably uses pulses in a range of 1 second to 1 picosecond.

Preferably, the materials used, for example 16MnCr5 or 100Cr6, are hardened by the induction heat treatment process.

Preferably, the piston or bearing component as a rolling bearing component, for example Rolling element, inner and / or outer ring, cage, or axial disc, executed. The coating is preferably used for electrical insulation.

Preferably, acid-catalyzed hydrolysis and base-catalyzed condensation are performed during the first step. In this case, a large excess of water and solvent is preferably provided. Preferably, an alkolic solution of the starting compound, for example tetraethoxysilane (TEOS), is prehydrolyzed by the addition of 0.01 N hydrochloric acid. The molar ratio of TEOS to water is preferably about 1 to 17. In the base-catalyzed condensation, 0.08 N NaOH is preferably used. After the base-catalyzed condensation, the mixture of substances can be applied to the component. Preferred application methods are immersion, injection, spin coating or casting processes.

The coating process preferably applies a coating of thickness 1 to 25 μm, more preferably 1 to 10 μm, to the piston or bearing component.

Preferably, in addition to or in place of the metal alcoholate, organically modified silanes are used. By this substitution or supplement, the ductility of the coating can be increased.

Preferably, the particles forming the powder have a mean diameter in a range between 30 to 80 nm. With particles of this size, the best results were achieved.

Preferably, a connecting layer is provided between piston or bearing component and coating. Through the bonding layer, the adhesion of the coating on the component can be improved overall. The tie layer is preferably a thin film deposited by means of a (if necessary, plasma enhanced) physical vapor deposition process.

Preferably, the organic solvent comprises alcohols, wherein the number of carbon atoms in the carbon chain of the alcohols is preferably in a range of 1 to 12. Furthermore, the alcohols preferably have 1 to 4 OH groups. It is advantageous if the organic solvent comprises a mixture of several different alcohols, all of which have the properties described.

The organic binder preferably comprises ormosils - organically modified silanes -, wherein the binder preferably comprises tetraethoxysilane,, 3-aminopropyltriethoxysilane, methyltriethoxysilane, methacryloxypropyltrimethoxysilane and / or methylcellulose.

Preferably, the metal alcoholate and / or the organic binder comprises one of the following metals: silicon, aluminum, magnesium, beryllium, boron, chromium, cerium, titanium, thorium, niobium, tungsten, yttrium and / or zirconium. Preferably, the metal oxide powder used or the ceramic powder used as a component or one or more of these metals. For example, the ceramic alumina has the constituent (binding partner) aluminum.

Preferably, the process is carried out under a protective gas atmosphere. The protective gas may contain as part of carbon dioxide, carbon monoxide, nitrogen, hydrogen or ammonia. In addition to the use of a protective gas, the use of a vacuum can also be advantageous. A preferred inert gas atmosphere comprises at least nitrogen, hydrogen and one or more noble gases.

Preferably, a sol powder is dispersed in the sol. As a result, gel layers up to 5 μm thick can be produced with a single coating cycle without cracks and uniformly thick over the entire component surface.

Furthermore, to solve the problem, a piston or bearing component is proposed with an electrically insulating ceramic coating, wherein the coating was carried out by the method according to any one of claims 1 to 9. The inventive coating method or by the piston or bearing component according to the invention, it is possible to combine outstanding tribological properties with simultaneous mechanical strength and electrical insulation in a layer without the base material is adversely affected by the temperature input during the coating. 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 cost, lower viscous lubricants with lower internal friction can be used and oil change intervals extended. In addition, rolling bearing components can also be operated under dry friction and insufficient lubrication.

The invention will be explained below with reference to preferred embodiments with reference to the accompanying figures. Showing:

1 an isometric view of two inventively coated needle cages,

2 a hydraulic support element according to the invention coated piston.

In the 1 are two needle cages 1 shown. A needle cage 1 includes a cage 3 and a plurality of rolling elements 2 , The diameter of the rolling elements 2 is greater than the thickness of the cage 3 , The rolling elements 2 are exposed to high tribological stresses. At the same time, the rolling elements should 2 have electrically insulating properties for various applications, since the current could otherwise be transmitted directly via them. For this purpose, the rolling elements were 2 coated with the coating method according to the invention.

In addition to such bearing components and piston components can be exposed to high tribological stresses. Another example is in the 2 a support element 6 shown, which is a housing 5 in which a piston 4 is arranged linearly displaceable. By a spring element 9 becomes a spring force on the piston 4 exercised, with his butt tip 7 against a drag lever 8th suppressed. In this example, the piston was 4 in the area of the piston tip 7 coated with the coating method according to the invention.

By means of the coating method according to the invention, pistons or bearing components can be provided with an electrically insulating ceramic coating without significant losses of the material properties due to the thermal influences during the coating.

For this purpose, a 1 to 10 microns thick coating is applied to the components. The components consist for example of a low-cost steel such as 16MnCr5, C45, 100Cr6, 31CrMoV9, or 80Cr2.

• a) Wasser,
• b) ein organisches Lösemittel,
• c) ein Metallalkoholat,
• d) ein organisches Bindemittel sowie
• e) Metalloxid- oder Keramikpulver, wobei die das Pulver bildenden Partikel einen mittleren Durchmesser aufweisen, der im Mittel kleiner als 1 μm ist,

auf das Kolben- oder Lager-Bauteil aufgebracht wird und in einem zweiten Schritt durch eine Trocknung bei einer Temperatur zwischen 0 bis 300°C getrocknet wird.In the coating process, in a first step, a substance mixture is at least comprising

• a) water,
• b) an organic solvent,
• c) a metal alcoholate,
• d) an organic binder as well
• e) metal oxide or ceramic powder, wherein the particles forming the powder have an average diameter which is on average less than 1 μm,

is applied to the piston or bearing component and is dried in a second step by drying at a temperature between 0 to 300 ° C.

With the help of the so-called sol-gel process, the various starting materials for the ceramic material are brought into a liquid form from the outset. It is, for example, a true chemical solution that transforms into a sol, or directly to a sol, a colloidal solution consisting of liquids containing very small finely divided substances.

To prepare for the coating process, 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 in monoethanalamine (MEA), which remains on the component after cleaning, there is no impairment of the deposited dispersion coating.

Low surface roughness has a positive effect on the morphology of the layer produced, as the defect density increases with surface roughness. Possibly. existing growth errors increase with the layer thickness, therefore a homogeneous surface with a low roughness is conducive to achieving a high layer thickness.

One way to create a sol-gel coating is the use of aqueous suspensions. Here, a suspension with nanoscale powder is produced, which offers the possibility to produce layers with thicknesses of several micrometers in a coating step. For example, suspensions may be prepared by dispersing boron nitride, boron carbide, tungsten carbide, aluminum titanate, aluminum nitride, silicon carbide, silicon nitride, and flame-hydrolysed silica (eg, DEGUSSA, Aerosil OX50) in water or mixtures of organic solvents. In this way, layer thicknesses of 1 to 25 microns can be achieved. The layers can be sintered directly after drying the solvent by induction hardening.

In order to prevent the formation of cracks, some of the alcoholates used are replaced by organically modified silanes (ORMOSILs). 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, so 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, the already mentioned organically modified silanes (ORMOSILs) are also preferably used. Other silanes used are 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. During sintering, the ethyl group is split off and a ceramic layer is formed with pure silicon dioxide.

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 particle diameter of a colloidal, acid-stabilized alumina sol is about 30 to 80 nm, which is significantly lower than that of a base-catalyzed sol. The use of acid catalysis for the silica sol leads to small and base catalysis to 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, i. 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 condensation, i. 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.

Experiments have been carried out with molar water / silicon ratios (r) of 1 to 50. 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 hang critically depends 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. Ceramic layers can be prepared for both mechanical and functional requirements. The chemical composition of the sol, the layer deposition conditions and the heat treatment parameters, such as heating rate, temperature, holding time, have an influence on the coating properties.

LIST OF REFERENCE NUMBERS

1

 needle cage

2

 rolling elements

3

 Cage

4

 piston

5

 casing

6

 Abstütztelement

7

 plunger tip

8th

 cam follower

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008039326 A1 [0005]

Claims (10)

Coating method for producing an electrically insulating ceramic coating on a piston or bearing component, characterized in that in a first step, a mixture comprising at least a) water, b) an organic solvent, c) a metal alcoholate, d) an organic binder and e) metal oxide or ceramic powder, wherein the particles forming the powder have an average diameter which is on average less than 1 micron, is applied to the piston or bearing component and in a second step by drying at a temperature between 0th is dried to 300 ° C. Coating method according to claim 1, characterized in that the substance mixture is sintered in a third step. Coating method according to claim 1, characterized in that the substance mixture is treated in a third step by an induction hardening process with additionally pulsed microwaves. Coating method according to one of the preceding claims, characterized in that the edge layer of the piston or bearing component is heated at least in a range and at least briefly to a temperature in a range between 850 ° and 1100 ° C. Coating process according to one of the preceding claims, characterized in that an acid-catalyzed hydrolysis and a base-catalyzed condensation are carried out during the first step. Coating method according to one of the preceding claims, characterized in that the coating method, a 1 to 25 .mu.m, preferably 1 to 10 .mu.m, thick coating is applied to the piston or bearing component. Coating process according to one of the preceding claims, characterized in that organically modified silanes are used in addition to or in place of the metal alcoholate Coating method according to one of the preceding claims, characterized in that the particles forming the powder have an average diameter in a range between 30 to 80 nm. Coating method according to one of the preceding claims, characterized in that a connecting layer is provided between piston or bearing component and coating. Piston or bearing component with an electrically insulating ceramic coating, characterized in that the coating was carried out by the method according to one of claims 1 to 9.

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