Bearing component made of cast iron and manufacturing process thereof
By using cast iron materials and induction hardening technology to form raceways on bearing components, combined with ADI heat treatment, the problems of unnecessary weight and material usage of bearing components are solved, resulting in lighter and more efficient bearing components, reducing material thickness requirements and creep phenomena, and improving structural strength and wear resistance.
Patent Information
- Application Number
- CN202510330733.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-03-25
- Filing Date
- 2025-03-20
- Publication Date
- 2025-09-26
AI Technical Summary
Existing bearing components are unnecessarily heavy and use more material. Furthermore, it is difficult to adjust the bearing preload and clearance during press-fit connections, which affects life and friction.
The bearing components are made of cast iron, and the raceways are formed on them through induction hardening technology, combined with austenitic-ferrite ductile iron (ADI) heat treatment to optimize material distribution and hardness, reduce overlap tolerances and creep phenomena.
This achieves lighter and more efficient bearing components, reduces material thickness requirements, avoids creep, and improves the structural strength and wear resistance of the bearing.
Smart Images
Figure CN120701663A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a bearing component according to the preamble of claim 1. The invention also relates to a process for producing a bearing component. Background Art
[0002] In many areas of application, it is desirable to make the component parts as light as possible, for example in order to save material, costs and / or energy. However, it may be the case that the material may not be able to be processed and / or constructed as ideally required. For example, it is known that in wheel bearings, forged steel hubs with integrated hardened raceways (on which the rolling elements can roll) may be used to enable the hub to rotate relative to the axis. However, forged hubs have the disadvantage that their shape and / or geometry depends on the forging method used and the forged material cannot be optimized with regard to the distribution of the loads. This leads to shapes with excess material in areas that are not subjected to the corresponding stresses, making the hub unnecessarily heavy.
[0003] Another known method for manufacturing components is casting. Casting makes it easier to produce complex shapes and / or geometries. For example, cast iron can be used. Cast iron has a lower density than forged steel, so the resulting product is generally lighter than a comparable product made from forged steel. However, cast iron does not have the hardness required to integrate raceways (for example, directly into a cast iron bearing component). Therefore, in order to, for example, cause rotation between a gear hub and an axle, in the case of a cast iron gear hub, it is necessary to use a bearing unit that is connected to the gear hub by, for example, a press fit. This has the disadvantage that the gear hub must be designed so that it can accommodate the bearing rings in an overlapping manner. This results in press seats with a high wall thickness to withstand the additional stresses caused by the press fit. This, in turn, results in the gear hub being relatively bulky and therefore heavy.
[0004] Furthermore, the overlap tolerances required for press-fitting in bearing rings that have been pressed in or pressed on can make adjustment of the bearing preload or bearing play of the bearing unit extremely difficult. However, the correct bearing play or bearing preload has a significant impact on the life and friction of the bearing.
[0005] It is therefore an object of the present invention to provide a bearing component which requires less weight and / or material than known bearing components. Summary of the Invention
[0006] This object is achieved by a bearing component according to claim 1 and a process for producing a bearing component according to claim 6 .
[0007] Next, there are solutions for a bearing component, particularly a roller bearing component, wherein the bearing component has a body forming the bearing component. The bearing component can be, in particular, a gear hub or a bearing ring. The body has at least one raceway designed to enable at least one rolling element to roll thereon. The at least one rolling element can be, for example, a ball, a cylindrical roller, a tapered roller, a pendulum roller, a needle roller, or the like.
[0008] To reduce weight and / or material requirements compared to known bearing components, the bearing component is made of cast iron and has induction-hardened raceways. The integrated, induction-hardened raceways can reduce the material thickness required due to the overlap tolerances required with press-fit (indented) bearing rings, as they are formed on the bearing component. A further advantage is that, since the raceways are integrated into the component, the described bearing rings do not experience a phenomenon known as creep, in which one indented component rotates relative to the other and which can occur with press-fits.
[0009] Cast iron is an iron-carbon alloy with a high proportion of carbon (>2%). In addition, cast iron may also include other elements such as silicon, manganese, chromium, nickel, etc.
[0010] The meaning of "inductive hardening" (also referred to as induction boundary layer hardening) is a surface hardening method in which metal components are only partially hardened in the outer layer. During surface hardening, due to the transformation of the microstructure, new material properties can be produced in the area hardened by austenitization. In the case of induction hardening, the hardened surface can become wear-resistant and / or hard, while retaining ( / preservation / maintaining) (conserved) the ductility ( / toughness) of the starting material ( / original material) in the interior of the component. In the case of induction hardening, the component is exposed to an alternating magnetic field in a very short period of time. This results in the heating of the component at the surface. This can be heated until red hot (red hot). The degree to which the heating penetrates into the component can especially depend on the frequency of the magnetic field. The higher the frequency of the magnetic field, the smaller the depth of the layer that is fully ( / completely) heated. This can be followed by quenching, for example, with water quenching.
[0011] The cast iron is preferably spheroidal graphite cast iron. Ductile iron (also known as SG cast iron) is an iron-carbon casting material in which the carbon is in the form of spheroidal graphite particles. It is also known as ductile cast iron. Ductile iron can advantageously have mechanical properties similar to steel.
[0012] In another preferred embodiment, the bearing component is at least partially made of austenitic-ferritic ductile iron (ADI (austempered ductile iron, austempered ductile cast iron). ADI is described in DIN EN 1564: 2012-01. ADI can be used as an alternative to cast and wrought steel in components that are subject to high stresses. Compared to ductile iron, ADI has a relatively high yield point and tensile strength ( / ultra-tensile strength) and, at the same time, high ductility, while offering the advantages of cast materials with respect to forming. The substrate for ADI is ductile iron that has undergone a specific heat treatment known as bainitization or ausferritization. In this treatment, the component is first austenitized and then quenched to a defined temperature, where it is kept isothermally at this temperature for an extended period of time while the process continues. After a specific processing time, the component is then cooled to room temperature in a controlled manner. Advantageously, ADI materials can be used in bearing components where the load distribution requires a relatively high yield point and tensile strength while requiring high ductility. This allows lighter components to be constructed with the same structural strength.
[0013] Another advantage of ADI is that it can also be induction hardened. It is possible for the primary structure of a bearing component to include ADI, and for the primary structure of the outer layer in the area of the raceway to include hardened ADI. In other words, a bearing component made of ductile iron can be partially converted to ADI, and / or the boundary layer of the ductile iron can be induction hardened. In particular, ADI is easier and less expensive to produce than forged steel.
[0014] In another aspect, a process for manufacturing a bearing component is provided. Here, the bearing component has a body forming the bearing component, wherein the body has at least one raceway designed to enable at least one rolling element to roll thereon. The process comprises the following steps:
[0015] The main body of the component is composed of cast iron bearings;
[0016] Processing the body to provide a bearing component having a defined size;
[0017] Induction hardening of the raceways;
[0018] Annealing bearing components; and
[0019] Machined hardened raceways.
[0020] The cast iron is preferably ductile iron. As already described in detail above, cast iron comprising spheroidal graphite or ductile iron is an iron-carbon casting material in which carbon is in the form of spheroidal graphite particles. Ductile iron can advantageously have mechanical properties similar to steel.
[0021] Furthermore, the machining of the hardened raceway may include, for example, turning, grinding, honing, polishing, and the like.
[0022] In another preferred embodiment, before machining the bearing component to provide the bearing component with defined dimensions, the body is heat treated to at least partially convert the cast iron into ADI. As already stated, ADI has a relatively high yield point and tensile strength, while also having high ductility and simultaneously offering the advantages of a cast material with respect to forming.
[0023] The basis for ADI is ductile iron that undergoes a specific heat treatment known as bainitizing or ausferitizing. In this process, the component is first austenitized and then quenched to a defined temperature, where it is kept isothermal for an extended period of time while the process is ongoing (isothermal transformation). After a specific processing time, the component is then cooled to room temperature in a controlled manner. Advantageously, ADI materials can be used in bearing components where the load distribution requires a relatively high yield point and tensile strength while also requiring high ductility. This freedom provided by the casting process enables the construction of lighter components with the same structural strength.
[0024] The heat treatment to form the austenitic-ferritic ductile iron is preferably carried out by induction heating. Induction heating makes it possible to treat the component only partially with heat, so that even complex geometries (for example, in the case of significant variations in wall thickness) can be treated without inherent stress problems and / or uncertainty as to whether the ADI microstructure is actually formed throughout the entire component. The exclusive treatment of the regions of the component associated with the functional layer ensures that the desired material state is present in these regions. In addition, since both austenitization and isothermal transformation are carried out by induction, bearing components made of ADI can be manufactured at much lower cost and in an environmentally friendly manner. In particular, bearing components consisting of ductile iron can be locally transformed into ADI and / or the boundary layers of the ductile iron can be additionally induction hardened.
[0025] In a further processing step, after the heat treatment for forming the ADI, the bearing component can be quenched, during which time the component is held at a defined transformation temperature. The isothermal transformation temperature can affect the resulting microstructure and, therefore, the mechanical properties of the casting or component. Lower temperatures increase the hardness and strength of the resulting material, while also reducing the residual austenite content. The defined transformation temperature is preferably below 300°C.
[0026] Further advantages and advantageous embodiments are listed in the description, the drawings and the claims. In particular, the combinations of features listed in the description and the drawings are merely illustrative, and the features may also exist alone or in other combinations. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Hereinafter, the present invention will be described in detail with reference to the working examples shown in the accompanying drawings. The working examples and the combinations shown in the working examples are merely illustrative and are not intended to limit the scope of protection of the present invention. The scope of protection of the present invention is limited only by the appended claims.
[0028] The accompanying drawings show:
[0029] Figure 1 : A schematic side view of a bearing component according to a first embodiment,
[0030] Figure 2 : A schematic side view of a bearing component according to a second embodiment,
[0031] Figure 3 : a schematic side view of a portion of a bearing component according to a third embodiment, and
[0032] Figure 4 : Schematic diagram of a process for producing a bearing component according to a fourth embodiment.
[0033] Description of Reference Numerals
[0034] 1 Bearing components
[0035] 2 Main body
[0036] 4 rollers
[0037] 6ADI area DETAILED DESCRIPTION
[0038] In the following, identical or functionally equivalent elements are identified by the same reference numerals.
[0039] Figure 1 A bearing component 1 according to a first embodiment is shown. Figure 1 The bearing component 1 shown in FIG is a bearing ring for a roller bearing. The bearing component 1 includes a body 2 having at least one raceway 4 designed so that at least one rolling element (not shown) can roll thereon. The at least one rolling element can be, for example, a ball, a cylindrical roller, a tapered roller, a pendulum roller, a needle roller, or the like.
[0040] Bearing component 1 is made of cast iron. For example, bearing component 1 can be made of cast iron with a carbon content greater than 2% (>2%). Bearing component 1 is preferably made of ductile iron, where the carbon in the ductile iron is in the form of spherical graphite particles. Furthermore, raceway 4 is induction-hardened. This means that raceway 4 is formed directly on bearing component 1.
[0041] In the case of induction hardening or induction boundary layer hardening, only partial hardening occurs in the outer layer. During induction surface hardening, new material properties can be generated in the area hardened by austenitization due to microstructural transformations. In the case of induction hardening, the hardened surface can become wear-resistant and / or hard, while the ductility (toughness) of the starting material (original material) (in this case cast iron) is retained ( / preserved / maintained) in the interior of the bearing component 1. In the case of induction hardening, the component can be subjected to an alternating magnetic field for a very short period of time, which leads to heating of the bearing component 1 at its surface. The extent to which the heating penetrates into the bearing component 1 can depend in particular on the frequency of the magnetic field. The higher the frequency of the magnetic field, the smaller the depth of the layer that is fully ( / completely) heated. This is followed by quenching, for example, with water.
[0042] Figure 2 A bearing component 1 according to a second embodiment is shown. Figure 2 The bearing components 1 shown in FIG. Figure 1 The bearing component 1 shown in FIG differs in that the body 2 of the bearing component is made of ductile iron that has been transformed into ADI (Austempered Ductile Iron) at least in the region 6 below the raceway 4. ADI is an austenitic-ferritic ductile iron and is described, for example, in DIN EN 1564: 2012-01. ADI can be used as a replacement for cast and wrought steel in components that are subject to high stresses and has a relatively high yield point and tensile strength compared to ductile iron, as well as high ductility, while offering the advantages of a cast material with regard to forming.
[0043] To form the ADI, the ductile iron undergoes a specific heat treatment known as bainizing or ausferitizing. During this process, the microstructure of the bearing component 1 is first austenitized and then quenched to a defined temperature, where it is held isothermally for an extended period of time, the duration of the process. After the specified processing time, the bearing component 1 is then cooled to room temperature in a controlled manner. After the ADI has been formed in region 6 of the bearing component 1, the raceway 4 is further induction hardened.
[0044] exist Figure 2In the embodiment, ADI (austempered ductile iron) is formed in this region of the raceway 4. Of course, it is also possible, additionally or as an alternative, to form ADI in other regions of the bearing component 1. Preferably, ADI can be used in regions of the bearing component 1 that are subject to abnormal stresses.
[0045] Figure 3 A portion of a bearing component 1 according to a third embodiment is shown. Figure 3 The bearing components 1 shown in FIG. Figure 2 The bearing component 1 shown in FIG. 1 is different in that the bearing component 1 is a gear hub. Figure 3 The bearing component 1 shown in FIG. 1 has a body 2 formed from ductile iron at least partially transformed to ADI.
[0046] In addition, from Figure 3 The bearing component 1 in the form of a gear hub has two raceways 4 which are preferably induction hardened. This means that Figure 3 The bearing component 1 in the form of a gear hub can be used directly as the outer ring of a double-row bearing unit for a wheel bearing. This has the advantage that pressing a separate bearing ring into the gear hub is unnecessary, which reduces the required material thickness due to the overlap tolerances required with pressed-in (indented) bearing rings. Another advantage is that since the raceway 4 is integrated into the bearing component 1, the phenomenon known as creeping, in which the pressed-in bearing ring rotates relative to the gear hub, cannot occur.
[0047] Figure 4 A schematic diagram of a process for manufacturing a bearing component 1 is shown. In a first step S1, a body 2 is cast from cast iron, in particular from ductile iron. Subsequently, in a following step S2, the body 2 is machined to provide a bearing component 1 with defined dimensions. Thereafter, in a step S3, at least one raceway 4 is induction hardened. To complete the bearing component 1, the bearing component 1 is then annealed in a step S4. Subsequently, in a step S5, final machining of the hardened raceways is performed. Final machining may include, for example, turning, grinding, honing, polishing, etc.
[0048] If the bearing component 1 is made of ductile iron, a step S6 of heat treating the body 2 to at least partially transform the ductile iron into ADI may optionally be provided before processing the bearing component in step S2.
[0049] The heat treatment for forming the ADI is preferably accomplished by induction heating. In particular, induction heating allows for the thermal treatment of only portions of the bearing component 1. This allows even complex geometries (e.g., with significant variations in wall thickness) to be treated without inherent stress problems and / or uncertainty regarding whether the ADI microstructure has actually formed throughout the entire component. Exclusive treatment of the component regions associated with the functional layer ensures that the desired material state is present in these regions.
[0050] Furthermore, in another optional processing step S7, after the heat treatment for forming ADI in step S6, the bearing component 1 can be quenched, during which the bearing component 1 is maintained at a defined transformation temperature. The isothermal transformation temperature may affect the resulting microstructure and, therefore, the mechanical properties of the casting or component. The lower the temperature, the higher the hardness and strength of the resulting material, and the lower the residual austenite content. The defined transformation temperature is preferably below 300°C.
[0051] In summary, a bearing component 1 can be provided that requires less weight and / or material than known bearing components. Thanks to the integrated, induction-hardened raceways, the material thickness required due to the overlap tolerances required in press-fit bearing rings can be reduced, as the raceways are formed on the bearing component. A further advantage is that, since the raceways are integrated into the component, the phenomenon known as creep, in which one of the press-fit components rotates relative to the other and which can occur in press-fits, does not occur in the depicted bearing rings. Advantageously, the microstructure of the bearing component can be at least partially converted to ADI in areas where the load distribution requires a relatively high yield point and tensile strength, while also exhibiting high ductility. This freedom offered by the casting process enables the construction of lighter components with the same structural strength.
Claims
1. A bearing component (1), in particular a bearing component for a roller bearing, wherein: The bearing component (1) has a body (2) forming the bearing component, wherein the body (2) has at least one raceway (4), and the at least one raceway (4) is designed so that at least one rolling element can roll on the at least one raceway (4), characterized in that the bearing component is made of cast iron and has at least one induction-hardened raceway (4).
2. The bearing component (1) according to claim 1, characterized in that The cast iron is ductile iron.
3. The bearing component (1) according to claim 1 or 2, characterized in that: The bearing components are at least partially made of austenitic-ferritic ductile iron.
4. The bearing component (1) according to claim 3, characterized in that In the region of the at least one raceway (4), the bearing component is made of austenitic-ferritic ductile iron.
5. Bearing component (1) according to any one of the preceding claims, characterized in that The bearing component (1) is a gear hub and / or a bearing ring.
6. A process for manufacturing a bearing component (1), wherein: The bearing component (1) has a body (2) forming the bearing component (1), wherein the body (2) has at least one raceway (4), and the at least one raceway (4) is designed so that at least one rolling element can roll on the at least one raceway (4), wherein the process comprises the following steps: Casting the main body (2) of the bearing component (1) from cast iron (S1); machining the main body (2) to provide the bearing component (1) with defined dimensions (S2); Induction hardening (S3) of the at least one raceway (4); Annealing the bearing component (1) (S4); and The hardened raceway (4) is machined (S5).
7. The process according to claim 6, characterized in that The cast iron is ductile iron.
8. The process according to claim 7, characterized in that Before machining the main body (2) to provide the bearing component (1) having predetermined dimensions (S2), the main body (2) is heat treated (S6) to at least partially transform the cast iron into austenitic-ferritic ductile iron.
9. The process according to claim 8, characterized in that The heat treatment (S6) for forming austenitic-ferritic ductile iron is achieved by induction heating.
10. The process according to claim 8 or 9, characterized in that In a further processing step after the heat treatment (S6), the austenitic-ferritic ductile iron is formed by quenching (S7) the bearing component (1), wherein during the quenching (S7), the bearing component (1) is kept at a defined transformation temperature.
11. The process according to claim 10, characterized in that The defined transition temperature is below 300°C.