Cage, rolling bearing and machine tool

Abstract

The invention relates to a cage for a rolling bearing, wherein the cage is formed from a material comprising a wood-plastic composite having wood fibers and / or embedded wood flour embedded in a plastic matrix in a volume fraction of 30 vol% to 95 vol%.

Description

[0001] The present invention relates to a cage for a rolling bearing, a rolling bearing and a machine tool.

[0002] A rolling bearing may have a cage, which guides the rolling elements. The cage is typically designed to space the rolling elements apart, for example, to minimize friction and heat generation. Furthermore, the cage keeps the rolling elements at a fixed distance from each other during rolling, thus achieving even load distribution.

[0003] The state of the art in rolling bearing cages, especially for use in high-speed applications in angular contact ball bearings such as high-speed spindle bearings, includes various approaches to optimizing cage properties.

[0004] Commonly used materials for these applications include hard fabrics, which are a combination of cotton fabric and phenolic resin. While these materials are used in high-speed applications due to their strength and durability, they are not optimal in terms of environmental compatibility. The phenolic resin matrix, made from phenol and formaldehyde, is considered a concern because it is classified as a neurotoxin and cell toxin, thus posing environmental and health risks.

[0005] In addition to the classic cotton fabric-phenolic resin materials, there are developments such as hybrid fabrics and the production of cages made of different fabric types, as described, for example, in DE 10 2013 225 339 A1 and DE 10 2016 212 124 A1.

[0006] In addition, typical plastics with or without reinforcing fibers are also used for cage materials. The selection of these materials aims to optimize both the mechanical properties and reduce friction at the contact points – the guide surfaces – with the rolling elements and the outer ring rim. Among other things, approaches are also being pursued to reduce thermal expansion and moisture absorption, which are critical issues when using phenol-cotton materials.

[0007] However, the use of such hard fabrics made of phenolic resin also brings with it limitations. Among them is the limited design freedom, as the manufacturing processes for these materials are often complex and not flexible enough to respond quickly to new design requirements. Furthermore, there is a need to improve the recyclability of the cages and reduce the environmental impact resulting from the production and disposal of these materials. The natural vibration modes of rolling bearing cages and the associated damping properties continue to be a critical aspect, especially in applications where vibration and noise must be minimized.

[0008] The object of the invention is therefore to reduce or completely eliminate the disadvantages known from the prior art and to provide an improved cage for rolling bearings. Furthermore, the object of the invention is to realize an optimized rolling bearing and an optimized machine tool.

[0009] This object is achieved by a cage for a rolling bearing, wherein the cage is formed from a material comprising a wood-plastic composite having wood fibers and / or embedded wood flour embedded in a plastic matrix in a volume fraction of 30 vol% to 95 vol%.

[0010] The cage according to the invention offers the advantage that, through the use of a wood-plastic composite material with a volume fraction of 30% to 95% wood fibers or wood flour embedded in a plastic matrix, a good balance between the cage's strength and weight can be achieved. The wood content provides natural damping and can reduce vibrations and noise, resulting in smoother running of the rolling bearing. At the same time, the plastic matrix enables easy processing and shaping of the cage, resulting in cost-effective production.

[0011] Furthermore, the cage according to the invention exhibits reduced temperature and humidity expansion compared to phenol-cotton materials. Furthermore, the use of renewable raw materials such as wood and environmentally friendly thermoplastics (PP, PE) can improve the environmental compatibility and recyclability of the cage.

[0012] The use of the wood-plastic composite also creates an optimized surface of the cage-to-rib and cage-to-rolling element contact points, which can also contribute to energy savings by reducing friction.

[0013] For the purposes of this patent application, a wood-plastic composite is a material consisting of a combination of wood particles, such as fibers and / or flour, and a plastic polymer. The composite combines the advantageous properties of both components, with the wood component optimizing the material's environmental performance and the plastic matrix optimizing its shape and function.

[0014] The function of the wood-plastic composite in the invention is to create a rolling bearing cage that combines the natural texture of wood with the formability, resilience, and durability of a plastic. This material effectively contributes to reducing friction and noise while simultaneously improving the environmental footprint of the rolling bearing through the use of a partially renewable raw material.

[0015] The structure of the wood-plastic composite is characterized by the embedding of wood particles in the plastic matrix. These composites preferably contain a wood content of 30% to 95% by volume, which imparts positive properties such as stiffness and impact resistance to the composite material, derived from the wood components. The plastic matrix, made of polyethylene (PE), polypropylene (PP), and / or a bio-based plastic, provides the necessary cohesion and resistance to moisture and chemical influences.

[0016] The composition of the wood-plastic composite is selected to optimize the mechanical strength of the cage for the requirements of rolling bearings. The composite is preferably processed using processes such as extrusion, injection molding, or compression molding, which enables precise and reproducible production of rolling bearing cages with complex geometries.

[0017] Preferably, the wood particles have a homogeneous distribution in the plastic matrix.

[0018] The manufacture of a cage according to the invention from a wood-plastic composite material can be carried out using various processing techniques, each of which offers specific advantages and is suitable for mass production as well as for the manufacture of complex or individually shaped components.

[0019] For example, it is conceivable to produce a cage according to the invention by extrusion. In this process, wood fibers and thermoplastic polymers are first mixed and plasticized by heating. The plasticized mass is then continuously pressed through a die that defines the desired shape of the cage. Shaping occurs under pressure and heat, with the material being conveyed by a screw in the extruder. After leaving the die, the extruded strand passes through a cooling section to cure. Extrusion enables efficient and cost-effective production, particularly of cages with consistent cross-sections.

[0020] It would also be possible to produce a cage according to the invention by injection molding. During injection molding, the wood-plastic composite is first melted and then injected in a liquid state into a mold (injection mold). Under pressure, the material fills all the cavities of the mold. After a cooling process, which causes the material to solidify, the finished cage is removed from the mold. This process is particularly suitable for complex geometries and enables very short cycle times and high reproducibility.

[0021] Furthermore, it would be possible to form a cage according to the invention using rotational molding (rotomolding). Rotational molding is a process in which the material to be molded is placed into a hollow mold, which is simultaneously rotated around two perpendicular axes. The mold is heated, causing the material inside to melt and adhere evenly to the mold wall due to centrifugal force. After cooling, the molded cage can be removed. This process is particularly suitable for large-volume or hollow parts, as it allows for a relatively uniform wall thickness without weld seams.

[0022] Furthermore, it is also fundamentally possible to form a cage according to the invention using pressing techniques. In these pressing techniques, the wood-plastic composite is placed in a mold and formed into a cage using heat and pressure. This can be done using hot pressing or cold pressing, whereby the material is preheated or pressed at room temperature. These pressing processes are characterized by high material utilization and effective fusion of the components, resulting in products with high density and strength.

[0023] Furthermore, it is possible to form a cage according to the invention using a thermoforming process. During thermoforming, a previously extruded or rolled thermoplastic semi-finished product (e.g., a sheet) is heated until it becomes malleable. The soft material is then pressed to the contours of a mold using a vacuum or compressed air to assume the desired shape. After forming and cooling, the material retains its new shape. This process is particularly suitable for large and flat parts and offers possibilities for designing fine surface details and structures.

[0024] Depending on the process chosen, the physical properties of the finished cage made of wood-plastic composites can be influenced, for example, by the orientation of the wood fibers or by the choice of specific additives. The selection of the appropriate manufacturing process depends on the requirements of the final product as well as economic and production-related considerations.

[0025] The wood-plastic composite preferably has wood fibers and / or embedded wood flour embedded in its plastic matrix in a volume fraction of 40 vol% to 90 vol%, more preferably of 50 vol% to 90 vol%.

[0026] According to an advantageous embodiment of the invention, the plastic matrix can comprise polypropylene (PP) and / or polyethylene (PE). Advantageously, the invention can also be further developed such that the resilience and chemical resistance of the cage material is improved by using polypropylene (PP) and / or polyethylene (PE) in the plastic matrix. These two materials are known for their good chemical resistance, which makes the cage less susceptible to lubricants and other chemicals, thus contributing to a longer service life of the rolling bearing.

[0027] According to a further preferred development of the invention, the plastic matrix can also comprise bio-based plastics in addition to polypropylene (PP) and / or polyethylene (PE). This combination of features offers the additional advantage of making the cage a more environmentally friendly alternative. The use of bio-based plastics in the matrix gives the cage an improved ecological footprint and underscores the commitment to sustainable production and materials management.

[0028] For the purposes of this patent application, a bio-based plastic is a plastic material that is preferably obtained from renewable raw materials and thus has an organic origin. This includes materials that are made entirely or in significant proportions from biological substrates such as vegetable oils, starch, cellulose, or proteins. These plastics may be biodegradable, but are not required to be.

[0029] The function of a bio-based plastic in a wood-plastic composite is to provide a binding agent for the wood fibers or wood flour, improving the dimensional stability and mechanical properties of the composite material. The bio-based plastic gives the composite the flexibility and strength required for processing and application in a rolling bearing cage.

[0030] The construction of a bio-based plastic involves polymer structures resulting from the polymerization of monomers derived directly from biological sources. Preference is given to plastics produced in compliance with ecological and sustainable principles. This may include the cultivation of raw materials sustainably and without negative impacts on food production. Furthermore, the processing of the raw materials into polymers can be carried out in a way that minimizes energy consumption and CO2 emissions, reducing environmental impact.

[0031] The composition of the bio-based plastic can be selected to provide the desired physical and chemical properties to meet the requirements of the rolling bearing cage. These include, for example, heat resistance, mechanical strength, and chemical resistance. By selecting a suitable bio-based plastic and its proportion in the plastic matrix, the cage's behavior under load can be precisely tailored to the requirements of the rolling bearing.

[0032] Furthermore, according to a similarly advantageous embodiment of the invention, it can be provided that the wood fibers and / or the wood flour are made of hardwoods. The use of hardwoods for the wood fibers or the wood flour enables improved wear resistance and mechanical stability of the cage. Hardwood is generally more resistant to mechanical stress, which contributes to an extended service life of the rolling bearing and reduces maintenance requirements.

[0033] For the purposes of this patent application, hardwood is the wood of deciduous trees, which, due to its density and structure, has greater strength and durability than softwood, the wood of coniferous trees.

[0034] The function of hardwood in a wood-plastic composite is to increase the mechanical strength and rigidity of the composite material. The use of hardwood fibers or hardwood flour in the plastic matrix improves structural integrity and allows the cage for a rolling bearing to withstand higher loads without losing its shape or breaking.

[0035] The structure of hardwood includes a complex microscopic structure of cellulose fibers surrounded by a network of lignin and hemicelluloses. This combination gives hardwood its characteristic hardness and durability. Hardwoods also exhibit lower porosity, which leads to lower moisture absorption and thus ensures dimensional stability under varying environmental conditions.

[0036] The composition of the hardwood in the composite can be designed to aid processability during cage manufacturing while achieving the desired final product properties. Hardwoods such as oak, beech, or maple are preferred because they offer good resistance to mechanical abrasion and are generally readily available and cost-effective. By incorporating hardwood in finely ground form or as short fibers, it can be effectively blended with the plastic matrix to form a uniformly distributed and strength-enhancing composite.

[0037] A preferred cage development therefore uses a wood-plastic composite consisting of hardwood fibers and environmentally friendly thermoplastic binders such as polypropylene (PP) or polyethylene (PE), as well as components made of bio-based plastics. This approach closes the gap between environmentally friendly solutions and the demanding technical requirements of high-speed rolling bearing cages, thus representing a decisive advance in sustainable and resource-efficient bearing solutions.

[0038] According to another particularly preferred embodiment of the invention, the cage can be formed in one piece, in particular monolithically. A cage formed in one piece, in particular monolithically, has the advantage of eliminating joints, which leads to increased structural integrity and stability. This can simplify manufacturing, increase reliability, and shorten the tolerance chain, which in turn improves the precision of the rolling bearing.

[0039] Furthermore, the invention can also be further developed such that the cage has wood fibers and / or wood flour embedded in the plastic matrix at least at its contact points with the rolling elements and / or at its contact point with an inner ring rim and / or outer ring rim. By deliberately enriching the plastic matrix with wood fibers or wood flour at the contact points with the rolling elements and the inner and outer ring rims, the tribological properties are optimized. This leads to reduced friction and wear, which lowers energy consumption and increases the efficiency of the rolling bearing.

[0040] In a likewise preferred embodiment of the invention, the cage can also be made entirely of a wood-plastic composite. The use of a cage made entirely of a wood-plastic composite offers the advantage of a homogeneous material distribution and the associated uniform properties. This facilitates quality control and consistency during production and can positively influence the acoustic properties of the rolling bearing, for example, by reducing operating noise.

[0041] The object of the invention is further achieved by a rolling bearing comprising a cage according to any one of claims 1-7. By integrating a cage made of wood-plastic composite into a rolling bearing, the aforementioned advantages are directly transferred to the rolling bearing. This can lead to improved performance, reduced energy consumption, and an extension of the rolling bearing's service life.

[0042] A rolling bearing can be single-row or multi-row. Preferably, the rolling bearing is configured as a ball bearing.

[0043] The rolling bearing preferably has an inner ring. The inner ring can be made of a metallic and / or ceramic material. It is generally conceivable for the inner ring to be constructed in one or more parts, particularly in two parts.

[0044] The rolling bearing preferably further comprises an outer ring. The outer ring can be made of a metallic and / or ceramic material. It is generally conceivable for the outer ring to be constructed in one or more parts, particularly in two parts.

[0045] The rolling elements of a rolling bearing are shaped like a ball or roller. They roll along the raceways of the rolling bearing and are responsible for transferring the force acting on a radial rolling bearing, for example, from the outer ring to the inner ring and vice versa. Roller-shaped rolling elements can be selected, for example, from the group of symmetrical spherical rollers, asymmetrical spherical rollers, cylindrical rollers, needle rollers, and / or tapered rollers.

[0046] The rolling elements are guided in the cage and spaced apart from each other. The cage can be constructed in one piece or in multiple pieces.

[0047] The rolling elements can roll within the rolling bearing, particularly on the inner raceway of the inner ring. For this purpose, the surface of the inner raceway can advantageously be designed to be abrasion-resistant, for example, by means of an appropriate surface treatment process and / or by applying an appropriate additional material layer.

[0048] The inner ring raceway can be flat or profiled. A profiled design of the inner ring raceway can, for example, serve to guide the rolling elements on the inner ring raceway. A flat design of the inner ring raceway, on the other hand, can, for example, allow a certain degree of axial displacement of the rolling elements on the inner ring raceway.

[0049] The rolling elements can roll within the rolling bearing, particularly on the outer ring raceway of the outer ring. For this purpose, the surface of the outer ring raceway can advantageously be designed to be abrasion-resistant, for example, by means of an appropriate surface treatment process and / or by applying an appropriate additional material layer.

[0050] The outer ring raceway can be flat or profiled. A profiled outer ring raceway can, for example, serve to guide the rolling elements on the outer ring raceway. A flat outer ring raceway, on the other hand, can allow a certain degree of axial displacement of the rolling elements on the outer ring raceway.

[0051] A rolling bearing can have a seal to prevent lubricant from escaping from the rolling bearing or dirt or moisture from entering the rolling bearing. For this purpose, the seals used can be provided with one or more sealing lips that can bear against a component of the rolling bearing. These are designed in such a way that, on the one hand, they seal the bearing for as long as possible over its entire service life, while on the other hand, the friction caused by the seal in contact is not too high. It is particularly preferred for the seal to be formed from an elastic, particularly preferably rubber-elastic material. The elastic material can preferably consist entirely or partially of an elastomer, whereby the elastomers are again preferably selected from the group of vulcanizates of natural rubber and silicone rubber.

[0052] According to a further preferred embodiment of the subject matter of the invention, the rolling bearing can be configured for rotational speeds greater than 10,000 rpm. The rolling bearing is configured for use at high rotational speeds above 10,000 rpm and is characterized by a cage adapted to the specific requirements of these operating conditions, such as increased heat generation and dynamic load changes. This requires materials and designs that ensure high strength and stability even at high speeds.

[0053] Finally, the invention can also be advantageously implemented in a machine tool comprising a spindle rotatably mounted by means of a rolling bearing, characterized in that the rolling bearing is designed according to one of claims 8-9. The use of such a rolling bearing in a machine tool contributes to increasing the precision and reliability of the spindle bearing. This is particularly relevant for high-speed applications that place high demands on the dimensional accuracy and surface finish of workpieces. The positive properties of the cage, such as low friction and reduced wear, result in improved performance and service life of the machine.

[0054] The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] DE 10 2013 225 339 A1

[0005] DE 10 2016 212 124 A1

[0005]

Claims

[1] Cage for a rolling bearing, characterized by that the cage is formed from a material comprising a wood-plastic composite having wood fibers and / or embedded wood flour embedded in a plastic matrix in a volume fraction of 30 vol% to 95 vol%. [2] Cage according to claim 1, characterized by that the plastic matrix comprises polypropylene (PP) and / or polyethylene (PE). [3] Cage according to claim 2, characterized by that the plastic matrix includes biologically based plastics in addition to polypropylene (PP) and / or polyethylene (PE). [4] Cage according to one of the preceding claims, characterized by that the wood fibers and / or wood flour are made from hardwoods. [5] Cage according to one of the preceding claims, characterized by that the cage is formed in one piece, in particular monolithically. [6] Cage according to one of the preceding claims, characterized bythat the cage has wood fibers and / or embedded wood flour embedded in the plastic matrix at least at its contact points with the rolling elements and / or at its contact point with an inner ring rim and / or outer ring rim. [7] Cage according to one of the preceding claims, characterized by that the cage is made entirely of a wood-plastic composite. [8] Rolling bearings, characterized by that the rolling bearing comprises a cage according to one of the preceding claims. [9] Rolling bearing according to claim 8, characterized by that the rolling bearing is configured for speeds greater than 10,000 rpm. [10] Machine tool comprising a spindle which is rotatably mounted by means of a rolling bearing, characterized by that the rolling bearing is designed according to one of claims 8-9.