Protective device for a cardan joint

Abstract

Protective device for a universal joint (28) with an encapsulation (34), wherein the universal joint (28) comprises two forks (30) which engage with each other via a central cross piece (32), characterized in that the universal joint (28) is completely surrounded by the encapsulation (34), wherein the space between the inner wall of the encapsulation (34) and the outer contour of the universal joint (28) is completely filled with elastic mass (22) which completely surrounds the universal joint (28).

Description

[0001] The invention relates to a protective device for a universal joint, which is used particularly in conjunction with drive and conveyor systems. Such devices serve to transmit forces and movements between shafts that are generally aligned, but may also exhibit misalignment in certain operating conditions or due to tolerances. These devices must withstand high mechanical loads as well as vibrations emanating from the motor or the screw conveyor and external influences. In practice, however, weaknesses are evident in the mechanical stability and in the protection of the sensitive components from external influences.

[0002] The present invention builds upon known technical solutions to overcome specific weaknesses and meet new requirements.

[0003] According to the prior art, for example, the applicant's DE 202017101929 is known. This describes an elastic shaft coupling and serves as a starting point for the further development of the present invention. While DE 202017101929 offers basic solutions for vibration damping and the absorption of radial and axial forces, it does not address specific problems. In particular, it lacks effective protection against dust, liquids, and mechanical damage.

[0004] With conventional, open cardan shafts, the following additional challenges arise: If the motor or shaft runs backwards accidentally or due to maintenance work, bulk material in the auger can destroy the universal joint.

[0005] Another problem arises when transporting abrasive, aggressive bulk materials or dusts such as pellets, ash, and similar substances. The abrasive dust from these materials can damage even solid steel. This advancement eliminates these problems by ensuring both comprehensive protection and increased system resilience.

[0006] Furthermore, protective devices for cardan shaft couplings are known from the prior art, such as DE 1575978 C and DE 1750129 A: German patent DE 1575978 C describes a protective device consisting of a rigid sleeve and a plastic bushing. These components are secured by a flange-groove connection and a clamping ring. While this design provides basic mechanical protection, it does not address the challenges of comprehensive protection against dust, liquids, abrasive and aggressive materials, nor does it offer the possibility of damping vibrations.

[0007] German patent DE 1750129 A relates to a protective device for cardan or ball joints, consisting of two spherical caps with a ball segment in between. This design protects the joint even during large angular movements of the shafts. However, it offers no protection against dust, liquids, or abrasive and aggressive materials, and does not allow for the compensation of radial and axial forces or the damping of vibrations.

[0008] The present invention addresses the weaknesses of the known prior art and offers a solution that includes both complete protection against external influences such as dust, liquids, and abrasive and aggressive materials, as well as significant mechanical improvements. In particular, it enables the damping of vibrations, the compensation of small radial misalignments, the correction of angular misalignments, the absorption of high axial forces, and the reduction of loads.

[0009] The invention is based on the objective of providing a protective device for a universal joint that meets precise mechanical requirements while reliably protecting the sensitive components of the universal joint from external influences. The device is designed to dampen vibrations and compensate for minor angular deviations between the shafts without impairing the mechanical stability or functionality of the system. Furthermore, its dust- and liquid-tight construction ensures comprehensive protection against abrasive, aggressive, or liquid materials. The device is also intended to be robust and durable, and to allow for easy integration into existing drive and conveyor systems.

[0010] To solve this problem, a protective device for a universal joint is provided, which, through a combination of protective and connecting elements, comprehensively protects the sensitive components of the universal joint (28) mechanically while simultaneously enabling the absorption of radial and axial forces. The design ensures a defined freedom of movement of the universal joint and offers reliable protection against external influences such as dust, liquids, and abrasive and aggressive materials.

[0011] The exact technical design of the solution is set out in claim 1. The dependent claims disclose preferred further developments and embodiments of the invention.

[0012] The following description explains the invention with reference to an exemplary embodiment illustrated in the accompanying drawings. This serves to illustrate the invention and to explain its essential features and advantages. However, this does not limit the scope of protection of the claims.

[0013] The invention relates to a protective device for a universal joint, specifically designed for use in conveyor systems. However, it is not limited to this application and can be used wherever movements with misalignment between drive and driven shafts need to be reliably transmitted. The aim is to design the mechanical connection in such a way as to ensure both flexibility and effective protection against external influences such as dust, liquids, and abrasive and aggressive materials. Particular emphasis is placed on a robust and adaptable design characterized by high load-bearing capacity and versatile application possibilities.

[0014] Materials handling technology encompasses the transport of a wide variety of materials, each with different technical requirements depending on the application and operating conditions. These include, among others, pellets (especially wood pellets), wood chips, biomass, food products, ash, powders, granules, plastics (particularly in the recycling sector), glass, and rubber. This list is not exhaustive, as other materials are processed in practice, requiring specialized technical solutions.

[0015] The material properties create challenges during transport: The transport of these materials often presents specific problems arising from their abrasive and aggressive properties, the presence of dust and liquids, and operational stresses. Abrasive materials such as sand, glass granules, plastic waste, or wood-based bulk materials cause significant mechanical stress on conveying equipment, particularly on moving parts like shaft couplings.

[0016] Dust generated by dry materials such as powders, biomass, or pellets penetrates sensitive components, leading to malfunctions, blockages, or even corrosion. Liquids, such as those encountered in food processing or chemical applications, attack the components and significantly shorten their lifespan.

[0017] Additional stresses arise in recycling processes because materials such as plastics, rubber, or similar substances are often mixed with foreign materials like sand or soil. This leads to further wear and tear, especially in heavily stressed areas such as couplings and seals.

[0018] Another risk arises from operator error or maintenance work, particularly if the motor or drive shaft is accidentally or intentionally run in reverse. In such a case, any bulk material remaining in the auger will also be conveyed backward and can enter mechanical components such as universal joints or drive units, potentially leading to serious damage or even complete destruction of the drive unit.

[0019] Conventional approaches to protecting shaft couplings often focus on the use of enclosures, such as bushings or domes, as described earlier. These designs provide a basic barrier against external influences like dust and liquids, but their effectiveness is often limited in practice. Fine dust can still penetrate the sensitive areas of the coupling, especially in designs that are not completely sealed. Similarly, aggressive liquids, such as those encountered in the chemical industry or food processing, can significantly reduce the service life of such protective mechanisms.

[0020] Another problem with conventional encapsulations is their lack of flexibility. They are often unable to compensate for radial, axial, or angular misalignment caused by assembly inaccuracies or operational movements. These shortcomings lead to increased wear and reduced load-bearing capacity of the coupling, which in turn negatively affects the reliability and service life of the entire conveyor system.

[0021] According to the inventor, existing designs often struggle with a fundamental conflict of objectives: they can either offer protection from external influences or sufficient flexibility, but not both simultaneously in a satisfactory manner. Furthermore, many of these solutions prove vulnerable to the specific challenges of conveyor technology, particularly with abrasive materials and in high-stress applications.

[0022] Another approach known in engineering involves using filling layers or elastic materials within the coupling. Such designs provide additional sealing and dampen vibrations to some extent. However, in practice, these also exhibit weaknesses, particularly regarding the long-term stability of the materials, material wear, and the ability to completely prevent external influences.

[0023] The present invention addresses the weaknesses of conventional solutions and aims to improve the protection of coupling elements against external influences such as dust, liquids, and abrasive materials without compromising the flexibility or strength of the design. The objective is to provide a protective device that combines high resistance to external influences with reliable functionality and easy adaptability to different applications.

[0024] For this purpose, an elastic intermediate element and a protective cover are combined in such a way as to create a robust and durable construction that meets the requirements of diverse applications.

[0025] The invention is explained below with reference to an exemplary embodiment shown in the drawing. The drawing shows: Fig. Figure 1 shows a fully assembled shaft coupling 10 in overall view, Fig. 2 shows the shaft coupling of the Fig. 1 with open socket 34 Fig. Figure 3 shows an exploded view of the shaft coupling 10, in which the individual components and their connections to each other are shown schematically. Fig. Figure 4 shows a detailed view of the multi-part cardan joint 28 with elastic mass 22 and encapsulation 34.

[0026] Fig. Figure 1 shows an application example of a shaft coupling 10 according to the invention in an overall view. The illustration demonstrates the use of the shaft coupling 10 in conjunction with a screw conveyor 12. A shaft 14 of the screw conveyor is connected via an encapsulated universal joint 28, which is Fig. 4 is shown in more detail, connected to a drive shaft 16 of a motor not shown in detail.

[0027] Fig. Figure 2 shows a fully assembled shaft coupling 10 with the bushing 34 open. This illustration provides insight into the internal structure of a universal joint 28 and the arrangement of the connecting elements. The shaft 14 of the screw conveyor 12 and a drive shaft 16 of the motor are connected via the universal joint 28, which is protected from external influences by the encapsulation. This design not only ensures the mechanical transmission of forces but also provides protection against dust, liquids, and abrasive materials.

[0028] Fig. Figure 3 shows an exploded view of the shaft coupling 10, in which the individual components and their connections to each other are schematically represented. This illustration clarifies the arrangement and function of the components, in particular the coupling between the drive and driven sides by the cardan joint 28.

[0029] First, the drive shaft 16 is connected to a drive flange 20. The drive flange 20 is coupled to the output flange 24 of the universal joint 28 by means of fastening elements 36. The universal joint 28 forms the central component of the shaft coupling, as it compensates for the movements between the shafts. It is rigidly connected to the screw conveyor shaft 14 via the universal joint flange 26 and the fastening elements 36.

[0030] As previously described, in the illustrated embodiment, an encapsulation 34 is firmly connected to the screw conveyor shaft 14, for example by a welded construction. Alternatively, the connection can also be made by a screw connection. This connection ensures a complete seal and provides reliable protection for the universal joint 28 against the ingress of dust, liquids, and abrasive materials.

[0031] Furthermore, the universal joint 28 is completely surrounded by an elastic mass 22, which is designed as a silicone elastomer filling. In addition to sealing, the elastic mass 22 provides effective vibration damping and protects the moving parts of the universal joint from mechanical stress and external influences.

[0032] In an alternative embodiment to the previously described rigid, one-sided connection of the encapsulation 34 to the screw conveyor shaft 14, the encapsulation 34 could be designed independently of the screw conveyor shaft 14. Instead of a direct connection, the encapsulation could be fixed to another stable component of the structure, for example by means of screw connections, clamping devices, or elastic bearings.

[0033] This alternative design offers the advantage of greater flexibility during assembly and simultaneously facilitates maintenance without compromising the protective function of the encapsulation 34. Furthermore, it ensures that the encapsulation 34 provides reliable protection even under varying operating requirements. A design in which the encapsulation 34 has no rigid connection to the left or right side would also be conceivable, thereby creating additional degrees of freedom.

[0034] The elastic mass 22 is designed as a silicone elastomer filling. This material is characterized by high flexibility and dimensional stability, as it can withstand tensile and compressive loads without losing its original shape. Its main functions include sealing, vibration damping, and resistance to external influences. (See exploded view in...) Fig. Figure 3 shows mass 22 schematically.

[0035] The compound 22 completely fills the space within the encapsulation 34 and protects the universal joint 28 from the ingress of dust, liquids, and abrasive materials. At the same time, it absorbs mechanical vibrations, thus reducing the stress on the coupling elements. Thanks to its chemical and thermal resistance, the compound retains its protective and damping function even under extreme conditions, such as high temperatures or contact with aggressive media. These properties enable the elastic compound 22 to completely encapsulate the universal joint 28, ensuring both comprehensive protection and the joint's mobility to guarantee optimal function of the shaft coupling 10.

[0036] In combination with the encapsulation 34, the elastic compound 22 provides a dual protective effect. While the encapsulation 34 serves as an outer barrier, the compound 22 provides a seal and protects the universal joint 28 from mechanical stresses and from the ingress of even the finest particles or gases. These features ensure long-term and reliable operation of the universal joint, even in environments with high levels of dust, moisture, or aggressive media.

[0037] Elastomers are dimensionally stable yet elastically deformable plastics that return to their original shape after being subjected to stress. They are characterized in particular by their ability to be significantly deformed under force and to regain their original shape after the force is removed. Key properties of elastomers include their high flexibility, characterized by their extensibility and elasticity, their resistance to wear, heat, and chemical influences, and their excellent damping properties, which effectively absorb vibrations and shocks.

[0038] Examples of elastomers include styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), fluoropolymer rubber (FKM), butadiene rubber (BR), and ethylene propylene diene monomer rubber (EPDM). Silicone elastomers stand out from other elastomers due to their chemical structure, as they do not contain purely organic compounds. This property gives them exceptionally high chemical and thermal resistance. They remain flexible and resilient even at extreme temperatures, making them ideal for demanding applications, especially those involving contact with aggressive media or thermal stress.

[0039] Fig. Figure 4 shows a detailed view of the multi-part cardan joint 28 with elastic mass 22 and encapsulation 34. In contrast to Fig. 3, which shows the device in an exploded view, illustrates Fig. 4 the construction in its assembled state.

[0040] The universal joint 28 consists of forks 30 that interlock via a central cross piece 32. On both sides of the universal joint 28, the forks 30 are provided with connecting parts that establish the connection to the flanges 24 and 26.

[0041] These flanges serve to connect the moving parts of the cardan joint 28 to the adjacent components of the drive train.

[0042] The cardan joint 28 is connected on one side via the flange 24 to the drive flange 20, which is attached to the drive shaft 16, and on the other side via the flange 26 to the enclosure 34. The fastening elements 36 secure both the drive flange 22 and the enclosure 34 in the corresponding threads 18 of the flanges 24 and 26.

[0043] In the closed state, the elastic compound 22 is introduced into the encapsulation 34 through an opening 38. The compound completely fills the cavity, conforms precisely to the geometries of the components, and then hardens. This ensures that the universal joint 28 is completely surrounded by the elastic compound 22, guaranteeing a permanent seal and comprehensive protection against external influences such as dust, liquids, and abrasive materials. After filling, the opening 38 can be closed by a sealing device.

[0044] A defined gap can be provided between the encapsulation (34) and the drive flange (20). This gap allows the shaft coupling (10) to compensate for a small angular misalignment relative to the motor shaft (16). The maximum compensable angular misalignment depends on the width of the gap. The degree of compensable angular misalignment depends on the gap width and the overall length of the coupling. For example, a gap of approximately 5 mm with a typical coupling length of 300 mm can allow compensation of up to 1°.

[0045] The angular offset α depends directly on the gap width s and the length L of the relevant components. The basic formula for small angles is: tan(α)≈S / L

[0046] Assuming a length of 300 mm and a gap of 5 mm, this results in an angular offset of approximately 1 degree.

[0047] This design avoids stresses within the coupling and ensures low-friction transmission of the rotary motion.

[0048] In addition to injection through the opening 38, alternative methods for introducing the elastic mass 22 can also be used: • Insertion of prefabricated elastomer parts: The elastic compound 22 can be inserted into the open encapsulation 34 by inserting prefabricated elastomer parts, such as elastomer rings. An alternative would be two elastomer half-shells. Alternatively, plates or blocks can also be used. After insertion, the compound hardens, conforms to the geometries of the surrounding components, and ensures a complete seal. This method does not require a special injection system and allows for simple and cost-effective handling. • Manual injection of the compound: Another option is to manually inject the elastic compound using a grease gun (e.g., a silicone gun) or a similar device. This method offers particular advantages during maintenance or repair work, as it can be used flexibly and precisely. • Pouring the compound: The elastic compound 22 can be poured in liquid or semi-liquid form before the final closing of the encapsulation 34. The compound then distributes itself evenly by gravity and subsequently hardens. This method is particularly suitable for designs where the geometry of the components promotes an even distribution. • Alternative design for flexible encapsulation: If the encapsulation 34 is not rigidly connected on both sides, but rather designed as a flexible sleeve, two removable plates can be positioned on the components 24 and 26 on the left and right. The encapsulation is then filled through the opening 38. The elastic compound 22 can either be injected or introduced using the alternative methods described above. This design enables a precise seal while simultaneously offering the flexibility to meet different operating requirements.

[0049] In this preferred embodiment, the encapsulation (34) is designed such that it has no rigid connection to the screw conveyor shaft (14) or the drive shaft (16). Instead, the encapsulation (34) is held in position by the elastic mass (22). This design allows for a certain degree of flexibility in the encapsulation (34) and reduces mechanical stresses that could arise from slight misalignments between the shafts.

[0050] Alternative design for systems with angles or curvatures: If the structure has a curve or angle, this requires appropriately adapted encapsulation. Suitable options include elastic materials such as rubber or flexible designs, for example, made of rubber or fabric tubing.

[0051] The encapsulation can be designed to compensate for a defined angle between the connected shafts. Such compensation is advantageous for angles up to 5 degrees, in exceptional cases up to 10 degrees, and in special cases up to 20 degrees to accommodate applications with slightly misaligned shafts. Even in this configuration, the elastic compound ensures a complete seal and provides reliable protection for the moving parts.

[0052] Since the elastic mass in this design is subjected to both compressive and tensile loads, this construction requires the use of highly elastic elastomers. These special materials are characterized by exceptional flexibility and resilience, enabling them to compensate for repeated deformations caused by movement and vibration without material fatigue.

[0053] It should be noted that this alternative version is not shown in the figures. Reference symbol list 10 Elastic shaft coupling 12 screw conveyors 14 Shaft of the screw conveyor 16 Motor shaft 18 screw threads 20 drive flange 22 Elastomer filling 24 Output flange 26 Cardan flange ring 28 Cardan joint 30 forks 32 Cross piece 34 socket / encapsulation 36 screws 38 Filling opening QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 202017101929

[0003] DE 1575978 C

[0006] DE 1750129 A [0006, 0007]

Claims

Protective device for a universal joint (28) with an encapsulation (34), wherein the universal joint (28) comprises two forks (30) which engage with each other via a central cross piece (32), characterized in that the universal joint (28) is completely surrounded by the encapsulation (34), wherein the space between the inner wall of the encapsulation (34) and the outer contour of the universal joint (28) is completely filled with elastic mass (22) which completely surrounds the universal joint (28). Device according to claim 1, characterized in that the encapsulation (34) for receiving the elastic mass (22) has an opening (38) which can be closed by a closure device. Device according to claim 1, characterized in that the elastic mass (22) consists of prefabricated elastomer parts which are designed as elastomer rings, plates or blocks and completely fill the cavity within the encapsulation (34). Device according to claim 1 or 2, characterized in that the encapsulation (34) has an opening (38) designed for the manual insertion of the elastic mass (22) using a grease gun or a similar device. Device according to claims 1 to 4, characterized in that the elastic mass (22) in combination with the encapsulation (34) ensures a dustproof and liquid-tight seal of the cardan joint (28). Device according to one of the preceding claims, characterized in that the encapsulation is in a curved design which compensates for an angle of up to 10 degrees, preferably up to 5 degrees, between the connected shafts. Device according to claim 6, characterized in that the encapsulation consists of an elastic material, in particular rubber, a fabric tube or a combination of these materials. Device according to one of the preceding claims, characterized in that the encapsulation (34) has no fixed connection to the screw conveyor shaft (14) or to the drive shaft (16) and is held in a defined position by the elastic mass (22). Device according to one of the preceding claims, characterized in that the cardan joint (28) is coupled on one side to the drive shaft (16) and on the opposite side to the screw conveyor shaft (14), so that a force-fit and form-fit torque transmission takes place between the drive and the conveying system. Device according to one of the preceding claims, characterized in that a gap between the encapsulation (34) and the drive flange (20) allows a small angular offset of the shaft coupling (10) relative to the motor shaft (16), wherein the degree of angular offset depends on the gap width.

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