Electrically conductive rubber composition, sealing assembly and rolling bearing
By optimizing the ratio of conductive carbon black, carbon nanotubes, and graphene in conductive rubber, a highly efficient three-dimensional conductive network is formed, which solves the problem of performance degradation of conductive rubber when the filling ratio is inappropriate, achieves a balance between conductivity and mechanical properties, and prevents electrical erosion of bearing raceways.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SCHAEFFLER TECHNOLOGIES AG & CO KG
- Filing Date
- 2025-07-09
- Publication Date
- 2026-05-29
AI Technical Summary
When the filling ratio of existing conductive rubber is not appropriate, it will lead to a decline in the performance of sealing products, especially poor conductivity and mechanical properties, and sensitivity to temperature and voltage, which will affect the sealing ability and service life of bearings.
A conductive rubber composition consisting of a uniform mixture of conductive carbon black, carbon nanotubes, and graphene is used. By optimizing the ratio of these components in the matrix rubber, a highly efficient three-dimensional conductive network is formed, ensuring low resistivity and good mechanical properties.
By balancing conductivity and mechanical properties, it can effectively prevent bearing raceway erosion caused by shaft current or charge accumulation, and improve the stability and fatigue resistance of conductive rubber compositions.
Abstract
Description
Technical Field
[0001] This invention relates to the field of rubber materials technology, and in particular to a conductive rubber composition, a sealing component, and a rolling bearing. Background Technology
[0002] Conductive rubber refers to rubber in which conductive particles or fibers are uniformly distributed. Pressure brings these particles into contact, achieving excellent conductivity. Conductive rubber has many applications in sealing products and can be manufactured through molding or extrusion processes. It exhibits good sealing capabilities against splashes of water, oil, or grease, while also providing good conductivity under certain pressure.
[0003] In the field of railway bearings, conductive sealing rubber rings are installed on bearings to prevent electrical erosion of the bearing raceways caused by shaft current or the discharge of accumulated charges. The conductive sealing ring structure of box bearings uses conductive rubber, typically NBR, HNBR, AEM, and ACM. Shaft current first enters the interior of the sealing rubber ring through the conductive rubber lip that is interference-fitted with the inner ring of the bearing, and finally flows out of the bearing through the outer sealing ring that contacts the outer ring.
[0004] Currently, the conductive materials used to fill conductive rubber are mainly carbon black and carbon nanotubes. While these materials make the rubber conductive, an inappropriate filling ratio can negatively impact the performance of the sealing product. For example, excessive conductive material can lead to excessively high rubber hardness, resulting in poor tensile strength, elongation at break, and tear strength. The rubber's compressibility decreases, leading to a reduction in the overall sealing performance and lifespan of the seal. Conversely, insufficient conductive material filling can significantly result in excessively high volume resistivity or even complete non-conductivity.
[0005] Furthermore, conductive rubber is also highly sensitive to temperature and voltage. Volume resistivity decreases with increasing temperature and voltage. This change is caused by the ratio of carbon black to carbon nanotubes incorporated into the rubber. This is because high temperature or high pressure enhances the mobility of conductive particles and fibers, making it easier for electrons to move and conduct electricity within the rubber material. When too little conductive material is incorporated, even if the conductive particles or fibers have good mobility, insufficient contact may prevent the achievement of ideal conductivity; excessive conductive material will reduce the mechanical properties of the rubber.
[0006] Therefore, it is necessary to specify the appropriate filling ratio of conductive fillers in rubber in order to obtain rubber with superior electrical conductivity and mechanical properties. Summary of the Invention
[0007] To overcome the problems existing in the related technologies, this disclosure provides a conductive rubber composition, a sealing assembly, and a rolling bearing to prevent electrical erosion of the bearing raceway caused by shaft current or accumulated charge discharge.
[0008] According to a first aspect of the present disclosure, a conductive rubber composition is provided, comprising: a matrix rubber, conductive carbon black, carbon nanotubes, and graphene, wherein the conductive carbon black, the carbon nanotubes, and the graphene are uniformly mixed into the matrix rubber, wherein the conductive carbon black is in the range of 25 to 55 parts by mass; the carbon nanotubes are in the range of 3 to 5 parts by mass; and the graphene is in the range of 2 to 7 parts by mass.
[0009] In some embodiments, the conductive carbon black is in the range of 25 to 35 parts by weight.
[0010] In some embodiments, the graphene is in the range of 2 to 4 parts by mass.
[0011] In some embodiments, the matrix rubber is one or a combination of two or more of polyacrylate rubber, ethylene-acrylate rubber, hydrogenated nitrile rubber, and nitrile rubber.
[0012] In some embodiments, the conductive rubber composition is cured by hot pressing and vulcanization.
[0013] In some embodiments, the conductive carbon black has a spherical structure.
[0014] In some embodiments, the carbon nanotubes are single-walled nanotubes or multi-walled carbon nanotubes.
[0015] In some embodiments, the graphene has a sheet-like structure.
[0016] According to a second aspect of the present disclosure, a sealing assembly is provided, comprising: a skeleton; and a sealing body made of the conductive rubber composition described in the first aspect, the conductive rubber composition being attached to the surface of the skeleton by a vulcanization process.
[0017] According to a third aspect of the present disclosure, a rolling bearing is provided, comprising: an inner ring; an outer ring; and a sealing assembly as described in the second aspect, wherein the skeleton is interference-fitted with the outer ring, and the sealing body is dynamically sealingly abutting against the inner ring.
[0018] The technical solutions provided by the embodiments of this disclosure may include the following beneficial effects: by optimizing the ratio of conductive fillers in the conductive rubber composition to balance conductivity and mechanical properties, a highly efficient three-dimensional conductive network is formed, ensuring low resistivity and enabling static electricity to be released continuously, quickly, and in a timely manner. Especially when applied to rolling bearings, it can prevent electrical erosion of the bearing raceway caused by shaft current or accumulated charge discharge. Detailed Implementation
[0019] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.
[0020] To solve the above-mentioned technical problems, this disclosure provides a conductive rubber composition comprising at least: a matrix rubber, conductive carbon black, carbon nanotubes and graphene, wherein the conductive carbon black, carbon nanotubes and graphene are uniformly mixed into the matrix rubber.
[0021] The base rubber serves as an elastic matrix, providing flexibility and mechanical strength. The base rubber can be selected from one or more combinations of polyacrylate rubber (ACM), ethylene-acrylate rubber (AEM), hydrogenated nitrile butadiene rubber (HNBR), and nitrile butadiene rubber (NBR). Among these, polyacrylate rubber (ACM) exhibits good high-temperature resistance and oil resistance. Ethylene-acrylate rubber (AEM) demonstrates excellent heat aging resistance. Hydrogenated nitrile butadiene rubber (HNBR) possesses high strength and excellent oil and corrosion resistance. Nitrile butadiene rubber (NBR) is characterized by low cost and excellent overall performance.
[0022] The above selection of base rubber is just an example. Only one type of base rubber can be selected, or two or more base rubbers can be mixed and used. Other types of base rubber can be selected according to different working conditions (such as high temperature and oily environment). For example, other base rubbers such as isoprene rubber (IR) and carboxyl-terminated nitrile butadiene rubber (CTBN) can also be selected. These will not be listed in detail here.
[0023] Conductive carbon black is the main conductive filler. Preferably, the conductive carbon black can be acetylene black, which is obtained by acetylene cracking and has high crystallinity, high conductivity and high purity. Acetylene black has extremely low resistivity.
[0024] Conductive carbon black typically has a spherical structure with a particle size distribution of 20–100 nm. Spherical carbon black is easy to disperse, reduces agglomeration, and improves the conductivity uniformity of conductive rubber compositions. When conductive carbon black forms a complementary conductive network with conductive fillers such as fibrous carbon nanotubes and sheet graphene, it can provide a basic conductive pathway or conductive network.
[0025] In one exemplary embodiment, the conductive carbon black is added in parts per hundreds of rubber (phr), which is the number of parts added per 100 parts (by weight) of the base rubber. The mass range of conductive carbon black is 25 to 55 parts, meaning that when the base rubber is 100 parts, 25 to 55 parts of conductive carbon black are added. This range of conductive carbon black ensures the mechanical strength and abrasion resistance of the final conductive rubber composition.
[0026] In optional embodiments, the mass fraction of conductive carbon black can be 25, 30, 35, 40, 45, 50, or 55, or any combination of the above values, or a range covering any of the above values. Preferably, the mass fraction range of conductive carbon black is 25 to 35 parts. This range of conductive carbon black ensures conductivity while avoiding excessive conductive carbon black that could cause rubber to become brittle or difficult to process. The synergistic effect of conductive carbon black with carbon nanotubes and graphene results in a more uniform conductive network, more stable resistivity, and better conductivity.
[0027] In other alternative embodiments, conductivity and manufacturing cost can be balanced, and other conductive carbon blacks such as furnace black can also be selected, which will not be listed in detail here.
[0028] Carbon nanotubes are a type of fibrous conductive filler. The carbon nanotubes can be one or a combination of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or double-walled carbon nanotubes (DWCNTs).
[0029] Carbon nanotubes are fibrous, thus having a high aspect ratio. When carbon nanotubes are applied to conductive rubber, they have good dispersion in the matrix rubber and easily form a conductive network in conductive rubber. A good conductive network can be formed with a low filling amount, which can significantly improve the tensile strength, tear resistance and abrasion resistance of conductive rubber compositions.
[0030] In one exemplary embodiment, the mass fraction of carbon nanotubes ranges from 3 to 5 parts, meaning that when the base rubber is 100 parts, 3 to 5 parts of carbon nanotubes are added. In alternative embodiments, the mass fraction of carbon nanotubes can be 3, 3.5, 4, 4.5, or 5, or any combination of the above values, or a mass fraction range covering any of the above values.
[0031] In optional embodiments, the graphene has a sheet-like structure and can be single-layer graphene, double-layer graphene, or even few-layer or multi-layer graphene. The graphene can be graphene oxide, hydrogenated graphene, fluorinated graphene, etc., which will not be listed in detail here.
[0032] Graphene with a sheet-like structure has a high specific surface area and a two-dimensional structure. The high specific surface area can enhance the conductivity of conductive rubber compositions, optimize the conductive pathway, improve the electrostatic dissipation efficiency, and enhance the antistatic stability.
[0033] In one exemplary embodiment, the mass fraction of graphene ranges from 2 to 7 parts. That is, when the base rubber is 100 parts, 2 to 7 parts of graphene are added. In optional embodiments, the mass fraction of graphene can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, or 7, or any combination of the above values, or a mass fraction range covering any of the above values. Preferably, the mass fraction of graphene ranges from 2 to 4 parts.
[0034] In some other embodiments, the graphene may also be in bulk form.
[0035] As can be seen from the above, the synergistic effect of conductive carbon black (25-55 parts by weight), carbon nanotubes (3-5 parts by weight), and graphene (2-7 parts by weight) reduces the agglomeration of conductive fillers, ensures uniform distribution of the conductive network, and improves the conductivity stability and fatigue resistance of the conductive rubber composition.
[0036] In some embodiments, other fillers may be added to the conductive rubber composition, such as vulcanizing agents and auxiliaries, conductive additives, anti-aging additives, and softeners, etc., which are not listed in detail here. In this invention, only the effects of the addition ratio (parts by mass) of conductive carbon black, carbon nanotubes, and graphene on the conductive and mechanical properties of the conductive rubber composition are described in detail.
[0037] To more clearly illustrate the performance effects of the above-mentioned conductive fillers (conductive carbon black, carbon nanotubes, graphene) at different addition amounts, the following table and specific examples show the performance changes of the conductive rubber composition.
[0038] Table 1
[0039] Ingredients / serving Example 1-1 Examples 1-2 Examples 1-3 Comparative Example Matrix rubber 70 60 50 100 Conductive carbon black 30 40 50 0 carbon nanotubes 3.5 4 4.5 0 Vulcanizing agents and auxiliaries 2.5 2.4 3.0 4.6 Conductive additives 2.5 3 3.5 0 Anti-aging additives 3.5 3.2 3.1 5.1 softener 2.5 2.6 3.2 3.5
[0040] Table 2
[0041] Inspection items Example 1-1 Examples 1-2 Examples 1-3 Comparative Example Tensile strength (MPa) 14.4 15.8 17.5 8.3 Elongation (%) 335 288 267 418 Compression set (%) 50 39 28 65 Surface resistivity Ωcm 2.8 2.2 1.9 Not up to standard
[0042] As shown in Tables 1 and 2 above, the higher the mass fraction of conductive carbon black, the greater the tensile strength, but the lower the elongation and resistivity. Similarly, the higher the mass fraction of carbon nanotubes, the lower the compression set and resistivity. However, the conductive rubber compositions formed by these conductive fillers within this mass fraction range exhibit significantly higher tensile strength, elongation, compression set, and surface resistivity than the matrix rubber without conductive carbon black and carbon nanotubes, meeting the relevant international or national testing standards.
[0043] Elongation refers to the percentage of maximum length extension that the conductive rubber composition can achieve upon tensile fracture. Tensile strength refers to the maximum stress that the conductive rubber composition can withstand before tensile fracture. Compression set refers to the degree to which the conductive rubber composition cannot return to its original shape after prolonged compression, reflecting its elastic durability.
[0044] In an optional embodiment, the conductive rubber composition is prepared through processes such as hot-press curing and vulcanization molding. The hot-press curing process ensures that fillers such as conductive graphite, carbon nanotubes, and graphene are uniformly dispersed within the matrix rubber, preventing damage to the conductive network in the conductive rubber composition. Furthermore, the vulcanization molding process can increase the crosslinking density of the conductive rubber, enhancing the mechanical strength and durability of the conductive rubber composition.
[0045] Based on the same inventive concept, this disclosure provides a sealing assembly including a skeleton and a sealing body. The skeleton is typically made of a metal material, while the sealing body is made of the aforementioned conductive rubber composition, which is attached to the surface of the skeleton through a vulcanization process. The conductive rubber sealing body prevents static electricity buildup and avoids electrolytic corrosion, while the vulcanization process ensures a tight bond between the rubber and the skeleton, improving sealing performance and durability.
[0046] Based on the same inventive concept, this disclosure also provides a rolling bearing, comprising: an inner ring, an outer ring, and a sealing assembly located radially between the inner and outer rings. The skeleton of the sealing assembly is interference-fitted with the outer ring, while the sealing body dynamically seals against the inner ring. When the sealing assembly having the above-described conductive rubber composition is applied to a rolling bearing, the conductive rubber composition made from conductive fillers within the above-described mass fraction range is less prone to conductivity degradation due to mechanical deformation or environmental factors during long-term use, thus persistently preventing shaft current and charge accumulation and extending the life of the rolling bearing.
[0047] It is understood that in this disclosure, "multiple" refers to two or more, and other quantifiers are similar. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. The singular forms "a," "the," and "the" are also intended to include the plural forms unless the context clearly indicates otherwise.
[0048] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following scope of claims.
[0049] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.
Claims
1. A conductive rubber composition, characterized in that, Include: The matrix rubber, conductive carbon black, carbon nanotubes, and graphene are uniformly mixed into the matrix rubber. The conductive carbon black has a mass fraction of 25 to 55 parts; the carbon nanotubes have a mass fraction of 3 to 5 parts; and the graphene has a mass fraction of 2 to 7 parts.
2. The conductive rubber composition according to claim 1, characterized in that, The conductive carbon black has a mass fraction range of 25 to 35 parts.
3. The conductive rubber composition according to claim 1, characterized in that, The mass fraction of the graphene ranges from 2 to 4 parts.
4. The conductive rubber composition according to claim 1, characterized in that, The base rubber is one or a combination of two or more of polyacrylate rubber, ethylene-acrylate rubber, hydrogenated nitrile rubber, and nitrile rubber.
5. The conductive rubber composition according to claim 1, characterized in that, The conductive rubber composition is cured by hot pressing and vulcanization.
6. The conductive rubber composition according to claim 1, characterized in that, The conductive carbon black has a spherical structure.
7. The conductive rubber composition according to claim 1, characterized in that, The carbon nanotubes are single-walled nanotubes or multi-walled carbon nanotubes.
8. The conductive rubber composition according to claim 1, characterized in that, The graphene has a sheet-like structure.
9. A sealing assembly, characterized in that, include: skeleton; The sealing body is made of the conductive rubber composition according to any one of claims 1-8, said conductive rubber composition being attached to the surface of the skeleton by a vulcanization process.
10. A rolling bearing, characterized in that, include: Inner circle; Outer ring; as well as The sealing assembly as described in claim 9, wherein the skeleton is interference-fitted with the outer ring, and the sealing body is dynamically sealingly abutting against the inner ring.