Method for producing a ceramic bearing component
A heat treatment step after machining, combined with optical inspection, addresses defects in ceramic bearings, enhancing quality and reducing scrap rates by repairing cracks and improving mechanical strength.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- AB SKF SKF PATENT DEPARTMENT
- Filing Date
- 2025-12-08
- Publication Date
- 2026-06-18
AI Technical Summary
Ceramic bearing components often develop defects such as cracks during machining and handling, leading to material fatigue and reduced mechanical strength, and existing inspection methods are costly, intricate, and time-consuming, with high scrap rates due to false positives.
Incorporate a heat treatment step after grinding or lapping, using methods like hot isostatic pressing, sintering, or vibratory finishing to repair or densify defects, followed by optical inspection with white and UV light to ensure quality.
Reduces the number of defective components by repairing or reducing defects, improving the quality and mechanical strength of ceramic bearings, and minimizing scrap rates through a cost-effective process.
Smart Images
Figure EP2025085939_18062026_PF_FP_ABST
Abstract
Description
[0001] 2024P00140DE
[0002] Description
[0003] Method for manufacturing a ceramic bearing component
[0004] Technical field
[0005] The present invention relates to a method for manufacturing a ceramic bearing component for a bearing, in particular for a rolling bearing, according to the preamble of claim 1.
[0006] Technical background
[0007] Defects such as cracks, star cracks, etc., often occur in ceramic bearing components, especially in ceramic ball bearing components, during the finishing and handling of such ceramic components. In general, defects in ceramic bearing components are undesirable, as they often lead to faster material fatigue during rolling contact and to reduced mechanical strength.
[0008] Detecting and subsequently rejecting these defects often requires a highly complex surface inspection process, which is typically costly, intricate, and time-consuming. False positives during testing lead to increased scrap rates and necessitate inspection methods specifically tailored to certain defect types on the surfaces of the rolled parts. For example, the surfaces of ceramic bearing components can be inspected for defects after machining using white light and / or UV light testing methods. This inspection can be performed either manually or using automated processes. Particularly thin linear defects, especially fine cracks, can only be detected using specialized dye penetrant inspection (FPI) techniques under UV light.FPI stands for Fluorescent Penetrant Inspection, which is a proven non-destructive testing method specifically designed for detecting surface defects such as cracks, pores or other imperfections. 2024P00140DE.
[0009] Irregularities are used that are difficult or impossible to detect using white light testing.
[0010] It is therefore an object of the present invention to provide a method by which it is possible to manufacture a ceramic bearing component with fewer defects or healed defects, which is also cost-effective.
[0011] Summary of the invention
[0012] This problem is solved by a method for manufacturing a ceramic bearing component for a bearing, in particular for a rolling bearing, according to claim 1.
[0013] The process for manufacturing a ceramic bearing component for a bearing, in particular a rolling bearing, comprises the following steps: a. Providing a ceramic bearing component in the form of a semi-finished product (also called "blank") and grinding the semi-finished product, or providing a finished ground ceramic component (which may have defects); b. Heat treating the ground semi-finished product or the finished ground bearing component; c. Optical inspection of the bearing component.
[0014] Finish grinding and / or lapping can be performed before or after heat treatment, as explained in more detail below. As explained above, surface damage to the bearing component can occur during machining, particularly grinding, but also lapping or finish grinding, or through handling of the bearing component during machining. This damage can take the form of any defects, such as cracks. To reduce the proportion of bearing components that must be rejected after the final surface inspection due to these defects, the method proposed here includes a heat treatment step after grinding the bearing component, i.e., heat treatment of the ground semi-finished product or the finished bearing component.Until now, such a heat treatment step was only used during the production of the bearing component blank / semi-finished product. 2024P00140DE.
[0015] However, it has been found that a heat treatment step after machining the surface of the bearing component, particularly after grinding the semi-finished product, or a heat treatment step on the finished, ground bearing component, is capable of repairing or densifying any potential defects in the ceramic bearing component. By incorporating heat treatment at this stage of the manufacturing process, the quality of the ceramic bearing component, and thus the manufacturing process itself, can be improved, and the number of defective bearing components can be reduced.
[0016] After step c., a decision is made as to whether the bearing component has defects or not. If the bearing component has no defects, the process is completed and the bearing component can be used. Alternatively, if the bearing component has defects, it can be reintroduced into the process in step a. as a finished, ground bearing component.
[0017] According to one embodiment, after grinding the semi-finished product according to step a, a fine grinding or lapping of the ground semi-finished product is carried out, as already explained above. This additional fine grinding can further improve the surface quality of the ceramic bearing component. It is also conceivable to perform several fine grinding steps, with progressively increasing grit size of the grinding material used. This allows existing cracks or surface defects to be at least partially repaired or reduced even before heat treatment. Since the heat treatment according to step b takes place after grinding, fine grinding, or lapping of the bearing component or the semi-finished product, defects or cracks that occur during the grinding, fine grinding, or lapping, or the associated handling, can be repaired or reduced by the heat treatment.
[0018] Alternatively, as explained above, the fine grinding or lapping of the ground semi-finished product can also be carried out after heat treatment.
[0019] According to another embodiment, after step b., and in particular after subsequent lapping or fine grinding, the bearing component undergoes vibratory finishing. Lapping is a manufacturing process used for the fine finishing of workpieces to achieve extremely high dimensional and geometric accuracy as well as a very smooth surface. It is a so-called loose-grain machining process in which abrasive particles are usually freely embedded in a carrier fluid (e.g., oil or paste). Vibratory finishing is a surface treatment process in which workpieces are processed in a container together with abrasive particles (so-called chips) and a usually liquid or pasty additive (compound) by mechanical relative motion. The aim of vibratory finishing is to deburr, smooth, polish, or clean workpieces.Vibratory finishing is efficient, cost-effective, and particularly suitable for processing workpieces in large quantities. Lapping and / or vibratory finishing after heat treatment further improves the surface quality of the bearing component, achieving a high surface quality of the ceramic bearing component with virtually no defects.
[0020] According to a further embodiment, the optical inspection according to step c. comprises an examination of the bearing component with white light and / or an examination with UV light. The examination using white light or UV light has the advantage that a non-destructive examination of the bearing component's surface is possible. Surface examination with white light can be used to detect surface defects such as cracks, pores, scratches, or other irregularities. The workpiece to be examined is illuminated with bright, visible light (typically daylight or artificial light), and the reflections or shadows on the surface are examined visually or with the aid of optical devices. However, the white light method is often insufficient for very fine or invisible defects, such as very fine cracks.For such requirements, supplementary methods such as FPI techniques can be used, which were specifically developed for the smallest and hard-to-see defects.
[0021] In a further embodiment of the process, the heat treatment of the ceramic bearing component according to step b. comprises hot isostatic pressing, sintering, field-assisted sintering, in particular electromagnetic field (electro-magnetic) assisted sintering, plasma sintering, gas pressure sintering and / or low-pressure sintering or a combination thereof.
[0022] Hot isostatic pressing (HIP) is a process in which a workpiece is compressed under high pressure (typically 100 to 300 MPa) and elevated temperature (often above 1000 °C). The process works as follows: A component, in this case the ceramic bearing component, is placed in a chamber filled with a gaseous medium (an elevated nitrogen partial pressure is necessary for the sintering of silicon nitride, as decomposition can otherwise occur). The pressure acts uniformly (isostatically) on the bearing component from all sides while it is heated. This causes compression and the closing of pores or the healing of defects. Heat treatment preferably takes place at a temperature of up to... 2000°C, particularly preferably from a temperature of 800°C.
[0023] Sintering is a thermal process in which powdered materials are heated so that the particles densify without completely melting. Field-assisted sintering accelerates the actual sintering process by applying an electric or magnetic field. This promotes the diffusion process during sintering. Plasma sintering is a special form of field-assisted sintering in which a pulsed electric current is passed directly through the material. The material is pressed between two dies. A pulsed current generates heat and plasma discharges between the particles, which accelerate the diffusion process. The entire process takes only a few minutes. Advantages of this heat treatment therefore include very fast processing, homogeneous material properties, and lower energy consumption compared to conventional sintering.
[0024] Spark Plasma Sintering (SPS) can also be used. This is a rapid sintering process that uses pulsed electric current and pressure to densify powder at lower temperatures. The process comprises four main phases: gas removal / vacuum generation, pressure application, resistance heating, and cooling. SPS enables rapid densification while preserving nanostructures, resulting in improved material properties.
[0025] In gas pressure sintering (GPS), sintering is combined with gas pressure (up to ~10 MPa). The workpiece or bearing component is heated in a chamber under pressure (often with inert gases such as nitrogen). The gas pressure exerts pressure on the material and promotes the sintering of the particles. The gas pressure is also applied to suppress / prevent the decomposition of silicon nitride and further reduces porosity and defects. 2024P00140DE
[0026] To further improve the healing or densification process during heat treatment according to step b., the process can be further refined by adding agents for densifying and / or healing defects in the ceramic bearing component during heat treatment. Suitable healing or densification agents include adhesives, glass, slips, or combinations thereof. Infiltration materials are also conceivable. Polymers and metal infiltrates are suitable for infiltration. Polymers such as epoxy resins or polyurethanes can be used. These are particularly suitable for low mechanical loads or as temporary repairs. Molten metals such as aluminum, copper, silicon, etc., can be used as metal infiltrates. These reduce porosity and increase mechanical strength. Ceramic glazes can also be used.In this process, a thin layer of glass is applied to the surface and then fired at high temperatures. This can seal defects, improve the corrosion resistance of the bearing component, and smooth the surface. The use of ceramic slurries is also conceivable. These are suspensions of ceramic particles that penetrate defects and, after drying and sintering, fill them. They can be used for complex geometries and to repair microcracks. The use of oxides or metal oxides such as silicon dioxide or aluminum oxide in liquid or powder form can also be employed to fill defects.
[0027] Advantageously, during the heat treatment according to step b., a light- and / or heat-induced self-curing agent is added as an agent for sealing and / or healing defects in a bearing component. Preferably, this is a multi-component resin and / or adhesive. Light-induced self-curing agents usually contain photoinitiators that are activated by UV or visible light and cause polymerization or curing of the agent. Examples include UV-curing resins, especially epoxy or acrylic resins, which are cured by UV light, and UV-curing varnishes, usually transparent or colored coatings that close defects and produce a smooth surface.
[0028] Heat-induced self-curing agents utilize thermal energy to trigger chemical reactions such as polymerization or solidification. Examples of heat-induced self-curing agents include thermosetting resins, particularly epoxy or phenolic resins, which cure at temperatures up to 200 °C, and ceramic suspensions, especially slurries (ceramic suspensions) with heat-activated binders. The suspension is preferably cured at elevated temperatures, resulting in a dense, pore-free structure. Hybrid materials that combine light and heat curing mechanisms are also conceivable. Examples include dual-curing adhesives, which contain both photoinitiators (for UV curing) and thermal catalysts (for heat curing).
[0029] According to a further embodiment, the method provides that the provision of the ceramic bearing component in the form of a semi-finished product ("blank") according to step a. comprises the production and provision of the ceramic blank component, i.e., the semi-finished product. Advantageously, the production of the ceramic bearing component includes debinding, gas pressure sintering, and / or HIP (heat-in-place injection). During debinding, organic materials, especially paraffins and additives, are usually removed from the workpiece. Paraffins are often used as binders or additives in the production of ceramic components because they facilitate the shaping and pressing of the ceramic material. Debinding typically takes place before the sintering process to prevent the paraffin from burning during heating and negatively affecting the ceramic, particularly by causing cracking.Furthermore, the production of the ceramic bearing component can include cold pressing of ceramic granules. This step is preferably carried out as a manufacturing step prior to the debinding, gas pressure sintering (GPS), and heat injection molding (HIP) steps described above. The ceramic powder used is particularly advantageously obtained by milling silicon nitride (Si3N4) with sintering additives followed by spray granulation.
[0030] Further advantages and advantageous embodiments are specified in the description, the drawings, and the claims. In particular, the combinations of features specified in the description and the drawings are purely exemplary, so that the features may also exist individually or in different combinations.
[0031] Brief character description
[0032] The invention will now be described in more detail with reference to exemplary embodiments illustrated in the drawings. The exemplary embodiments and the combinations shown in the exemplary embodiments are purely illustrative and are not intended to define the scope of protection of the invention. This is defined solely by the appended claims.
[0033] They show:
[0034] Fig. 1: a schematic representation of a prior art method for producing a ceramic bearing component, and Fig. 2: an embodiment of the method for producing a ceramic bearing component in a schematic representation.
[0035] Detailed description of the invention
[0036] In the following, identical or functionally equivalent elements are marked with the same reference symbols.
[0037] Fig. 1 shows a schematic representation of a prior art process for manufacturing a ceramic bearing component 1. First, in step S9, a semi-finished product or bearing component blank 1a is produced. The production of the ceramic bearing component blank or semi-finished product ("blank") in step S9 initially comprises providing silicon nitride 3, which may contain sintering additives. This is ground in a first step, S10, until the desired grain size is reached, and then further refined by spray granulation, Si 1. To bring the ceramic granules (according to process SI 1) into the desired shape, cold pressing S12 takes place, in which the ceramic granules 3 are pressed into spherical bearing components 1 according to step SI 1. These spherical bearing components 1 obtained in this way are then debound, step S13.freed from any residues, sintered under gas pressure (S14) and hot-isostatically pressed in step S15 HIP.
[0038] The bearing component semi-finished product la obtained from manufacturing step S9 is subsequently refined in a finishing step. First, the ceramic bearing component blank la is prepared (Sl) and roughly ground (S2) to remove initial imperfections. This rough grinding (S2) is followed by fine grinding (S5) and lapping / ground-in (S6) to further refine the surface. After surface finishing, it is optically inspected (S4). This is done using methods known from the prior art, for example, with a 2024P00140DE.
[0039] White light examination S7 followed by a UV light examination S8. If the ceramic bearing component 1 meets the requirements of the optical examinations S4, production is complete. Otherwise, it is rejected.
[0040] Fig. 2 shows an embodiment of the inventive method for manufacturing a ceramic bearing component, also in a schematic representation. In principle, the same manufacturing steps can be carried out to produce S9 a ceramic bearing component blank 1a. However, the hot isostatic pressing (HIP) step S15 can be omitted. Therefore, it is optional in the embodiment shown here according to Fig. 2. It is also possible to use previously manufactured, used, or defective ceramic bearing components 1b in the preparation step S1, as is also explained below.
[0041] The inventive method for manufacturing a ceramic bearing component 1 differs from the prior art method essentially by an additional step in the final processing of the ceramic bearing component (semi-finished product 1a or defective bearing component 1b). If a semi-finished product 1a is to be further processed, it is first coarsely ground after manufacturing (S9), step 2. Crucially, the ground bearing component 1b or the ground semi-finished product 1a undergoes heat treatment (step 3) before further processing. Optionally, fine grinding or lapping (S5) can be carried out before or after step 3.
[0042] The heat treatment S3 of the semi-finished product 1a or the ceramic bearing component 1b can include HIP (hot isostatic pressing), sintering (GPS), field-assisted sintering, in particular electromagnetic field-assisted sintering, plasma sintering, SPS (gas pressure sintering), and / or low-pressure sintering, or a combination thereof. This heat treatment S3 ensures that defects, such as cracks, which occurred during the grinding process S2 and optionally S5, or through general handling, are immediately repaired or reduced (e.g., in number or dimensions).
[0043] In general, the process can therefore be used for ground semi-finished products (1a) or finished but defective bearing components (1b). 2024P00140DE
[0044] After heat treatment S3, the ceramic bearing component is lapped S6 or vibratory finished (not shown here), and an optical inspection S4 of the surface of the ceramic bearing component 1 is performed. This optical inspection S4 can also be divided into a white light inspection S7 followed by a UV light inspection S8. Other optical inspection methods are also conceivable, in particular FPI or other sequences, depending on the desired surface quality. If the ceramic bearing component passes the optical inspection S4, the final processing is complete.
[0045] If ceramic bearing component 1 meets the quality requirements, it can be reused. If it does not meet the quality requirements, the bearing component can be rejected as bearing component 1b or reintroduced into the final processing process, starting with the provision of ceramic bearing component 1b (step S1). In this case, steps S2 and S5 can be skipped, and the process can proceed directly to heat treatment in step S3.
[0046] In summary, the invention discloses a method for manufacturing a ceramic bearing component, particularly for a rolling bearing, with which any existing defects in the ceramic bearing component can be repaired, corrected, or compacted. This improves the quality of the ceramic bearing component and reduces the number of defective bearing components that are rejected.
[0047] 2024P00140DE
[0048] Reference symbol list
[0049] 1 finished bearing component la ground semi-finished product
[0050] 1b Finished bearing component with defects
[0051] 3 Raw materials, raw material powder, additives
[0052] 51 Provision of the semi-finished product or stock component
[0053] 52 Coarse Sanding
[0054] 53 Heat treatment
[0055] 54. Optical inspection, surface testing
[0056] 55 Fine grinding or lapping
[0057] 56 lapping and / or finishing grinding
[0058] 57 White light inspection
[0059] 58 FPI Inspection
[0060] 59 Production of the semi-finished product
[0061] 510 Ground
[0062] 511 Spray granulation
[0063] 512 cold presses
[0064] 513 Debinding
[0065] 514 Sintering
[0066] 515 HIP
Claims
2024P00140DE Patent claims Method for manufacturing a ceramic bearing component 1. Method for manufacturing a ceramic bearing component (1) for a bearing, in particular a rolling bearing, comprising the steps of: a. providing (S1) a ceramic semi-finished product (1a) and grinding the semi-finished product (1a) or providing (S1) a finished ground ceramic bearing component (1b), b. heat-treating (S3) the ground semi-finished product (1a) or the finished ground bearing component (1b) to manufacture the bearing component (1), and c. optical inspection (S4) of the bearing component (1).
2. Method according to claim 1, characterized in that fine grinding (S5) is carried out before or after heat treatment (S3).
3. Method according to claim 1 or 2, characterized in that after heat treatment (S3) lapping (S6) and / or vibratory finishing of the bearing component (1) is carried out.
4. Method according to one of claims 1 to 3, characterized in that the optical inspection (S4) comprises an examination with white light (S7) and / or an examination with UV light (S8).
5. Method according to one of the preceding claims, characterized in that the heat treatment (S3) comprises hot isostatic pressing, sintering, field-assisted sintering, in particular electromagnetic field-assisted sintering, plasma sintering, gas pressure sintering and / or low-pressure sintering or a combination thereof. 2024P00140DE 6. Method according to one of the preceding claims, characterized in that a means for densifying and / or healing defects of the semi-finished product (1a) or the bearing component (1b) is added during the heat treatment (S3).
7. Method according to claim 6, characterized in that a light- and / or heat-induced self-curing agent is added as a means for densifying and / or healing defects.
8. Method according to one of the preceding claims, characterized in that the heat treatment (S3) is carried out at a temperature of up to 2000°C, in particular from a temperature of 800°C.
9. Method according to one of the preceding claims, characterized in that the provision (S1) of the ceramic semi-finished product (1a) comprises a production (S9) of the ceramic semi-finished product (1a).
10. Ceramic bearing component (1) obtained according to the method according to any one of claims 1 to 9.