DE102020131772A1 - Bearing component, method for its production, and roller bearing or plain bearing - Google Patents

Abstract

The invention relates to a bearing component (1) and a method for its production, having a metallic base body (2) which at least partially has an electrically insulating coating (4) comprising a ceramic layer (6) with pores (8) and a plastic (10) for filling the pores (8) and coating the ceramic layer (6), the ceramic layer (6) being formed to contain at least 99% by weight aluminum silicate. The invention further relates to a rolling bearing or plain bearing comprising at least one bearing component (1) of this type.

Description

The invention relates to a bearing component having a metallic base body which at least partially has an electrically insulating coating comprising a ceramic layer with pores and a plastic for filling the pores and coating the ceramic layer. The invention further relates to a method for producing the bearing component and a roller bearing or plain bearing comprising at least one such bearing component.

Such bearing components and their manufacture and use in electrically insulating bearings are from WO 2014174382 A1 known.

the JP 2016-014413 A2 discloses rolling bearings having an insulating ceramic layer formed by thermal spraying to prevent electrolytic corrosion.

Electrically insulated roller bearings are increasingly being used in today's electric motors. Some of these can no longer adequately insulate the high-frequency currents that arise when modern frequency converters are used. The insufficient electrical insulation leads to electroerosion, i.e. the removal of material. This leads to a significant increase in friction and/or premature bearing failure.

Despite the use of electrically insulating roller bearings to interrupt the circuit, damage caused by electrical erosion has increased steadily in recent years. In some cases, damage occurs even after a low mileage (from 300,000 km). Compared to the target mileage of 1.5 million km, defects can be observed after just 20% of the planned mileage. The pulse width modulated (PWM) frequency converters can be cited as the main cause. These work with very high switching frequencies (approx. 3-12 kHz), which can lead to voltage increases of up to 8-10 kV/µs. These voltage pulses of the PWM output voltage of the frequency converter induce parasitic currents in the motor shafts. A response spectrum with high voltage amplitudes in the high frequency range is excited by the short voltage pulses. These voltage amplitudes can be up to 1 kV, with the frequency spectrum ranging from a few kHz to the MHz range. These high-frequency currents cause electrical erosion.

The electrically insulating coatings known from the prior art, comprising ceramic layers mostly made of aluminum oxide or aluminum oxide and an addition of titanium dioxide, reach their physical limits with regard to the insulating behavior in the case of high-frequency circular currents.

It is the object of the invention to provide an electrically insulating coating for bearing components which is improved in this regard and thus to enable improved insulation on bearings.

The object is achieved for a bearing component, having a metallic base body which at least partially has an electrically insulating coating comprising a ceramic layer with pores and a plastic for filling the pores and coating the ceramic layer, in that the ceramic layer contains at least 99% by weight Aluminum silicate containing mullite is formed. High electrical insulation values are thus achieved.

The aim was to increase the impedance Z (alternating current resistance) even at higher frequencies f in order to achieve a lower current flow through a bearing due to the higher resistance, in order to minimize electrical erosion. The impedance of an electrically insulating coating is determined from the ohmic resistance R (usually > 50 MΩ in practice) and the capacitance C of the coating and. The frequency-dependent impedance Z decreases both with increasing frequency f and with increasing capacitance C. Today's bearings with thermally sprayed electrical insulation layers only have an impedance Z of approx. 1.5 MΩ at a frequency of f=50 Hz, which corresponds to only a fraction of the DC resistance. Currents with frequencies of several kHz pass the bearings almost unhindered and thus lead to increased electrical erosion.

In order to maintain the electrical insulation effect even at higher frequencies, the capacitance C has to be reduced. With the same material, this could be achieved by increasing the layer thickness. Halving the capacitance would roughly mean doubling the layer thickness. However, this increases the production costs of the coating considerably. In addition, due to the thicker layers, replacing already installed bearings might no longer be possible due to the changed diameter, which would make a successful market launch of such a solution almost impossible.

For the reasons mentioned, the capacity C was reduced by a combination of material and process technology. On the physical level, the material-dependent relative dielectric constant (permittivity) εr of the insulating layer determines the capacitance C of the coating. The lower the permittivity εr, the lower the capacitance C.

At high frequencies, this results in a relationship between the impedance Z and the permittivity εr of Z proportional to 1/εr. At frequencies relevant in practice, the higher impedance Z helps to avoid premature damage, which significantly reduces the service life of a bearing. In addition, for a bearing designed for 1.5 million kilometers, a 33% reduction in permittivity εr can mean an increase in service life of 500,000 km. Since electroerosion only occurs above a certain limiting current and the lowering of the permittivity εr can result in the current falling below the limiting current, this is a conservative estimate. The real potentials in terms of mileage are rated even higher by using a bearing component according to the invention.

Compared to aluminum oxide, the aluminum silicate used for the ceramic layer containing mullite, in particular corundum, was able to significantly improve the electrical insulation, based on the material-specific parameter of the relative permittivity εr. Mullite (3 Al ₂ O ₃ .2 SiO ₂ ) is the only thermodynamically stable phase in the Al ₂ O ₃ .SiO ₂ system. Aluminum silicate containing mullite and in particular also corundum shows significantly increased impedances compared to reference layers made of aluminum oxide. The permittivity εr of Al ₂ O ₃ is around 8.5, while the permittivity εr of aluminum silicate Al ₂ O ₃ +SiO ₂ is already around 7.2.

It has proven to be advantageous if the ceramic layer is formed containing an aluminum silicate with a proportion of Al ₂ O ₃ in the range from 70 to 80% by weight and SiO ₂ in the range from 20 to 30% by weight. It is particularly preferred if the ceramic layer is formed containing an aluminum silicate with a proportion of Al ₂ O ₃ of 77% by weight and of SiO ₂ of 23% by weight.

In particular, it is preferred if the ceramic layer is predominantly formed from mullite. It has proven useful if the ceramic layer is predominantly made of mullite and also has corundum.

The ceramic layer can also contain <1% by weight of TiO ₂ in order to color the ceramic layer. Alternatively, coloring can be achieved if the ceramic layer is designed to contain 0.1 to 3% by weight of Cr ₂ O ₃ .

The ceramic layer is formed in particular by means of thermal spraying. A proportion of pores of up to 30% by volume, in particular in the range from 5 to 9% by volume, forms in the ceramic layer. Both closed porosity and open porosity can be present. Pores in the area of the surface of the ceramic layer that are accessible from there are sealed with plastic.

The plastic is in particular an electrically insulating plastic. In a preferred embodiment, the plastic is formed by at least one substance from the group consisting of a resin, siloxane, polyester, and acrylic.

A layer thickness D of the electrically insulating coating is preferably 0.05 to 2.0 mm. The lower limit of the layer thickness D is due to the requirement for a minimum electrical insulation capacity and the upper limit due to the installation dimensions for the bearing component.

It has proven useful if the bearing component according to the invention is formed by a bearing ring of a roller bearing or a plain bearing.

• • Reinigen des metallischen Grundkörpers;
• • Ausbilden der Keramikschicht auf dem metallischen Grundkörper mittels thermischen Spritzens;
• • Aufbringen des Kunststoffs auf die Keramikschicht, so dass deren (zugängliche) Poren verfüllt und die Keramikschicht beschichtet wird; und
• • Aushärten des Kunststoffs.

A method for forming the bearing component according to the invention with the following steps has proven itself:

• • cleaning of the metal body;
• • forming the ceramic layer on the metallic base body by means of thermal spraying;
• • Application of the plastic to the ceramic layer so that its (accessible) pores are filled and the ceramic layer is coated; and
• • Hardening of the plastic.

The use of an aluminum silicate powder with an Al ₂ O ₃ content in the range from 70 to 80% by weight and an SiO ₂ content in the range from 20 to 30% by weight is preferred. The ceramic layer formed by means of thermal spikes from an aluminum silicate composed in this way shows high impedance values. It is particularly preferred if the ceramic layer is formed containing an aluminum silicate with a proportion of Al ₂ O ₃ of 77% by weight and of SiO ₂ of 23% by weight.

Adjusting the spraying parameters to reduce the amorphous components in the ceramic layer also leads to an improvement in the electrical insulation properties of the ceramic layer. In this case, the formation of an amorphous portion is presumed based on the SiO ₂ portion. In order to achieve such a reduction in amorphous components, a reduction in the temperature of the sprayed particles is preferably set. For this purpose, a process gas of argon is preferably used in thermal spraying, with the argon being added at most to 5 standard liters per minute of hydrogen are. The amorphous parts of the ceramic layer are reduced in a targeted manner and their crystalline parts are increased. In addition to the selected composition comprising mullite, the crystalline fractions increase the electrical insulating capacity of the ceramic layer

Thermally sprayed aluminum silicate is pure white in color with scattered black dots. It has therefore proven useful to add a small amount of TiO ₂ , in particular in the range of <1% by weight, to the aluminum silicate in order to obtain a greyish hue in the ceramic layer. It could be determined that such a TiO ₂ additive has no significant influence on the impedance of the ceramic layer. Alternatively, coloring can be achieved if the ceramic layer is formed to contain 0.1 to 3% by weight of Cr ₂ O ₃ .

A rolling bearing or plain bearing comprising at least one single or multi-part bearing inner ring and one single or multi-part bearing outer ring has proven itself, in which a part of the bearing inner ring has a first surface forming a bearing inner diameter and/or a part of the bearing outer ring has a bearing outer diameter forming second surface is formed by a bearing component according to the invention.

In particular, the electrically insulating coating forms at least the first surface and/or the second surface. Optionally, the electrically insulating coating also covers at least one adjacent end face of the one-part or multi-part bearing inner ring and/or the one-part or multi-part bearing outer ring. As a result, the respective bearing ring is electrically insulated from a connection component, such as a shaft, an axle, a housing and the like, to which the bearing ring is connected at the point of use of the bearing.

Cylindrical roller bearings, needle bearings, tapered roller bearings, ball bearings, spherical roller bearings, angular contact ball bearings and the like have proven themselves as roller bearings. Self-lubricating plain bearings, hydrodynamic plain bearings or hydrostatic plain bearings can be used as plain bearings.

• 1 ein Lagerbauteil in Form eines Lagerringes mit elektrisch isolierender Beschichtung;
• 2 einen Schnitt durch ein Lagerbauteil in Form eines Lagerringes mit elektrisch isolierender Beschichtung in dreidimensionaler Darstellung;
• 3 einen Schnitt durch den Lagerring gemäß 2;
• 4 ein Wälzlager mit einem Lagerbauteil; und
• 5 ein Gleitlager mit einem Lagerbauteil;

the 1 until 5 are intended to exemplify the invention. So shows:

• 1 a bearing component in the form of a bearing ring with an electrically insulating coating;
• 2 a section through a bearing component in the form of a bearing ring with an electrically insulating coating in a three-dimensional representation;
• 3 according to a section through the bearing ring 2 ;
• 4 a rolling bearing with a bearing component; and
• 5 a sliding bearing with a bearing component;

1 shows a bearing component 1 in the form of a bearing ring 3 with an electrically insulating coating 4 on a metallic base body 2. The bearing ring 3 is here in the form of a bearing outer ring 3b having a second surface 8 forming a bearing outer diameter. The electrically insulating coating 4 forms the second surface 8 here.

2 shows a section through a bearing component 1 'in the form of a bearing outer ring 3b with an electrically insulating coating 4 in a three-dimensional representation. The electrically insulating coating 4 comprises a ceramic layer 6 with pores on the metallic base body 2 and an electrically insulating plastic 10 that seals the pores and covers the ceramic layer 6 Coating 4 is formed. The electrically insulating coating 4 also extends here to the end faces 5 of the outer bearing ring 3b which adjoin the bearing outer diameter on both sides.

3 shows a detail of a section through the outer bearing ring 3b according to FIG 2 . Shown is the metallic base body 2 and the coating 4 arranged thereon, which forms both the second surface 8 and thus the outer diameter of the bearing and extends to the adjacent end face 5 . The electrically insulating coating 4 has a layer thickness D in the range from 0.05 to 2 mm.

4 shows a roller bearing 11 with a bearing component 1 in the form of a bearing outer ring 3b and also a bearing inner ring 3a. The electrically insulating coating 4 covers the circumference of the bearing outer ring 3b and thus forms the second surface 8 . Between the bearing inner ring 3a and the bearing outer ring 3b, rolling elements 9 are arranged, which can be guided in a cage or can be present without a cage in a full complement arrangement.

5 shows a sliding bearing 12 with a bearing outer ring 3b and a two-part bearing inner ring 3a ₁ , 3a ₂ . A sleeve-shaped part of the bearing inner ring 3a ₂ has the electrically insulating coating 4 and forms the bearing component 1 here. The electrically insulating coating 4 forms the first surface 7 and the bearing inner diameter.

the 1 until 5 serve only to illustrate the position of an electrically insulating coating 4 on a bearing component 1, with the form and function of the respective bearing being freely selectable here.

Reference List

1, 1'

bearing component

2

body

3

bearing ring

3a1, 3a2

bearing inner ring

3b

bearing outer ring

4

coating

5

face

6

ceramic layer

7

first surface

8th

second surface

9

rolling elements

10

plastic

11

roller bearing

12

bearings

D

layer thickness

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was 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.

Patent Literature Cited

• WO 2014174382 A1 [0002]
• JP 2016014413 A2 [0003]

Claims (10)

Bearing component (1), having a metallic base body (2) which at least partially has an electrically insulating coating (4) comprising a ceramic layer (6) with pores and a plastic (10) for filling the pores and coating the ceramic layer (6), characterized in that the ceramic layer (6) is formed containing at least 99% by weight aluminum silicate containing mullite. Bearing component (1) after claim 1 , characterized in that the pores in the ceramic layer (6) have a proportion of up to 30% by volume, in particular in the range from 5 to 9% by volume. Bearing component (1) after claim 1 or 2 , characterized in that the ceramic layer (6) also contains <1 wt .-% TiO ₂ or 0.1 to 3 wt .-% Cr ₂ O ₃ . Bearing component (1) according to one of Claims 1 until 3 , characterized in that a layer thickness (D) of the electrically insulating coating (4) is 0.05 to 2.0 mm. Bearing component (1) according to one of Claims 1 until 4 , characterized in that the ceramic layer (6) is formed containing an aluminum silicate with a proportion of Al ₂ O ₃ in the range from 70 to 80% by weight and SiO ₂ in the range from 20 to 30% by weight. Bearing component (1) according to one of Claims 1 until 5 , characterized in that the plastic (10) is an electrically insulating plastic (10), in particular by at least one substance from the group consisting of a resin, siloxane, polyester, acrylic is formed. Bearing component (1) according to one of Claims 1 until 6 , characterized in that the bearing component (1) is formed by a bearing ring (3) of a roller bearing (11) or a plain bearing (12). Method for forming a bearing component (1) according to one of Claims 1 until 7 , with the following steps: • cleaning of the metallic base body (2); • forming the ceramic layer (6) on the metallic base body (2) by means of thermal spraying; • Application of the plastic (10) to the ceramic layer (6) so that the pores are filled and the ceramic layer (6) is coated; and • hardening of the plastic (10). Rolling bearing (11) or plain bearing (12) comprising at least one single or multi-part bearing inner ring (3a ₁ , 3a ₂ ) and a single or multi-part bearing outer ring (3b), characterized in that part of the bearing inner ring (3a ₂ ) having a , a first surface (7) forming a bearing inner diameter and/or a part of the bearing outer ring (3b) having a second surface (8) forming a bearing outer diameter by a bearing component (1) according to one of Claims 1 until 7 is formed. Roller bearing (11) or plain bearing (12) according to claim 9 , characterized in that the electrically insulating coating (4) forms at least the first surface (7) and/or the second surface (8), optionally also at least one adjoining end face (5) of the one-part or multi-part bearing inner ring (3a ₁ , 3a ₂ ) and/or the one-piece or multi-piece bearing outer ring (3b).

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