An intermediate rubber pad for track vibration damping fasteners and its stiffness design method

Abstract

This invention discloses an intermediate rubber pad for track vibration damping fasteners and its stiffness design method. The method involves controlled pre-expansion of uncured rubber containing thermally expanding microspheres, followed by heated curing to permanently lock the cell structure. Precise stiffness design is achieved by controlling the degree of pre-expansion. This invention enables customized stiffness design. The closed-cell structure of the microspheres endows the product with excellent fatigue resistance and resilience. It solves the technical bottlenecks of cumbersome stiffness control and long-term performance degradation in existing technologies from the material's origin. A series of stiffness products can be prepared using the same formula, adapting to the refined vibration damping needs of urban rail transit.

Description

Technical Field

[0001] This invention belongs to the field of vibration reduction technology for rail transit, specifically relating to an intermediate rubber pad for rail vibration reduction fasteners, and more particularly to an intermediate rubber pad for rail vibration reduction fasteners with stiffness controlled by thermally expanded foamed microspheres and a matching stiffness design method. Background Technology

[0002] Track fasteners are core components in rail transit lines that fix the rails and bear and transmit the dynamic loads of trains. Their stiffness parameters directly determine the vibration and noise reduction performance of the track system, affecting the propagation intensity of vibrations and noise generated by train operation to the track foundation, surrounding buildings and structures, and sensitive areas. With the rapid development of urban rail transit, the number of lines passing through vibration-sensitive areas such as residential areas, hospitals, research institutes, and precision laboratories is increasing. Different sections of the same line often have different environmental sensitivities, geological conditions, and differences in bridge or tunnel structures. Fasteners with a single stiffness cannot meet the vibration reduction requirements of the entire line, which places higher engineering demands on the accuracy and adaptability of track vibration reduction technology.

[0003] The stiffness control of existing track vibration damping fasteners mostly relies on adjusting the rubber formula, changing the size of the pad structure, or replacing the rubber material with one of different hardness. This has the following technical drawbacks: First, products with different stiffnesses require separate formula design and production process adjustments, making the production process cumbersome and difficult to quickly adapt to the differentiated vibration damping requirements of different sections of the track. Second, under long-term service conditions, rubber materials are prone to creep, which leads to a gradual increase in stiffness and a weakening of resilience, directly affecting the long-term stability of the vibration damping effect.

[0004] To address the aforementioned industry pain points, there is an urgent need for an intermediate rubber pad that is suitable for rail transit scenarios, has precisely adjustable stiffness, and excellent fatigue performance, along with a corresponding design method. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an intermediate rubber pad for track vibration damping fasteners and its stiffness design method. Taking the closed-cell structure characteristics of thermally expanded foamed microspheres as the core, the invention achieves customized stiffness design through precise control of the foaming ratio. The closed-cell structure of the microspheres endows the product with excellent fatigue resistance and resilience, thus solving the technical bottlenecks of cumbersome stiffness control and long-term performance degradation in the prior art from the material source.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a stiffness design method for an intermediate rubber pad used in track vibration damping fasteners, using thermally expandable foamed microspheres as the core medium for stiffness control. By precisely controlling the foaming ratio and expansion degree of the thermally expandable foamed microspheres in the rubber composite material, the stiffness of the intermediate rubber pad can be customized. The thermally expandable foamed microspheres have a closed-cell structure, which endows the intermediate rubber pad with fatigue resistance and resilience, and can meet the long-term service requirements of track application scenarios. The method includes the following steps: S1. Mixing: Raw rubber, vulcanizing agent and unexpanded thermally expanded foamed microspheres are mixed and kneaded to obtain a uniform rubber compound. The initial volume addition ratio of the thermally expanded foamed microspheres is 3% to 8% of the total volume of the rubber compound. S2. Pre-expansion and shaping: The compounded rubber is placed in the padding mold and subjected to controlled heating treatment at a temperature lower than the activation temperature of the vulcanizing agent. By precisely controlling the proportion of thermal expansion foaming microspheres, heating temperature, and holding time, the thermal expansion foaming microspheres are controlled to expand to a predetermined degree, and an expanded and shaped padding is obtained. S3. Vulcanization molding: The temperature is raised to the vulcanization temperature, and the expanded and shaped pad is vulcanized under pressure to fully cross-link and cure the rubber, permanently locking the expansion structure of the thermally expanded foamed microspheres, and obtaining a regular pad blank. S4. Cooling and stabilizing: Cool the vulcanized pad blank to room temperature to eliminate internal thermal stress, stabilize the pad size and structure, and obtain the finished intermediate rubber pad with preset stiffness.

[0007] Furthermore, the pre-expansion temperature of the controlled heating treatment in S2 is negatively correlated with time and target stiffness: the lower the target stiffness value, the larger the required proportion of thermally expanded foamed microspheres, the higher the foaming ratio, and the higher the corresponding heating temperature and the longer the heat preservation time; the higher the target stiffness value, the smaller the required proportion of thermally expanded foamed microspheres, the lower the foaming ratio, and the lower the corresponding heating temperature and the shorter the heat preservation time.

[0008] Furthermore, the controlled heating treatment parameters are set as follows: When the target stiffness value is 6kN / mm, the proportion of thermally expanded foamed microspheres is 7%-8%, the heating temperature is 120-130℃, and the treatment time is 20-30 minutes; When the target stiffness value is 12kN / mm, the proportion of thermally expanded foamed microspheres is 5%-6%, the heating temperature is 105-115℃, and the processing time is 15-20 minutes. When the target stiffness value is 18kN / mm, the proportion of thermally expanded foamed microspheres is 3%-4%, the heating temperature is 80-90℃, and the processing time is 5-10 minutes.

[0009] Furthermore, in S1, the raw rubber is natural or synthetic rubber; the initial expansion temperature of the thermally expanded foamed microspheres is ≥80℃.

[0010] Furthermore, in S3, the vulcanization process parameters are: temperature 140-150℃, pressure 1-20MPa, and vulcanization time 8-30 minutes.

[0011] An intermediate rubber pad for track vibration damping fastener is prepared by the stiffness design method described above; the intermediate rubber pad contains uniformly dispersed thermally expanded foamed microspheres with a fixed structure and expansion shape, and the stiffness is precisely controlled by the degree of pre-expansion to adjust the foaming ratio and expansion degree of the thermally expanded foamed microspheres.

[0012] Furthermore, the intermediate rubber pad is a series of products, including multiple stiffness levels of 6kN / mm, 12kN / mm, and 18kN / mm, which can adapt to the needs of different levels of track vibration reduction projects.

[0013] A track vibration damping fastener device includes the aforementioned intermediate rubber pad, which serves as the core component for stiffness adjustment. By replacing intermediate rubber pads with different stiffnesses, the overall stiffness of the fastener system can be quickly adjusted.

[0014] Compared with existing track vibration damping fastener stiffness control technology, this invention has the following outstanding advantages: Using a unified basic rubber compound formulation and vulcanization process, stiffness can be adjusted by controlling the expansion of microspheres through controlled heating, eliminating the need to design separate formulations for products with different stiffnesses, adjust process parameters, and reduce raw material loss and process debugging costs.

[0015] Closed-cell microsphere structure imparts excellent mechanical properties: thermally expandable foamed microspheres have a closed-cell structure, forming uniformly distributed independent micropores within the rubber matrix. This structure effectively disperses stress concentration under cyclic dynamic loads, significantly improving the material's fatigue resistance; simultaneously, the excellent resilience of the closed-cell structure ensures that the rubber pad maintains stable stiffness output under long-term service conditions, effectively suppressing stiffness drift caused by creep.

[0016] This invention applies the precise expansion control technology of thermally expanded foamed microspheres with closed-cell structures to the field of intermediate rubber pads for track vibration damping fasteners. It specifically addresses the industry pain point of differentiated vibration damping in different sections of rail transit lines. The product's weather resistance, mechanical properties, and fatigue performance are all suitable for the long-term service requirements of tracks. Leveraging the structural advantages of closed-cell microspheres, it also possesses excellent resilience and creep resistance, making it highly feasible for industrial production and of great engineering application value. Areas not detailed in this invention represent existing commonly used technologies. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to embodiments and specific implementation methods: Example

[0018] Raw material preparation and mixing: Chloroprene rubber (CR) is selected as the rubber matrix. A vulcanizing agent is added according to the conventional rubber formulation. The vulcanizing agent is zinc oxide and / or magnesium oxide, accelerator, antioxidant, reinforcing carbon black and conventional additives. Unexpanded thermally expanded foamed microspheres with an initial expansion temperature of about 80°C are added. Their closed-cell structure will give the product excellent fatigue resistance and resilience in subsequent processes. The amount of microspheres added accounts for 5% of the total volume of the compound. All raw materials are put into an internal mixer and mixed at 70-80°C until the rubber compound is uniform and free of particles, so as to obtain a compound with uniform properties.

[0019] In-mold expansion and vulcanization molding: The mixed rubber is placed directly into the fastener padding mold, and the expansion and shaping and vulcanization are completed sequentially on a flat vulcanizing machine by controlling the process parameters in stages. The process parameters are as follows: Low stiffness pad (target stiffness 6kN / mm): First, it is heat-treated at 125℃ and normal pressure for 25 minutes to allow the thermal expansion microspheres to fully expand and increase the internal porosity of the pad; then, it is pressurized to 15MPa, heated to 145℃, and held at temperature and pressure for 20 minutes to carry out vulcanization crosslinking, so that the rubber is fully cured and a regular pad blank is formed. Medium stiffness cushion layer (target stiffness 12kN / mm): First, heat treatment at 110℃ and normal pressure for 18 minutes to allow the microspheres to expand moderately and balance the density and porosity of the cushion layer; then pressurize to 15MPa, heat to 145℃, and hold for 20 minutes for vulcanization crosslinking. High-rigidity cushioning layer (target stiffness 18kN / mm): First, it is stabilized by heat treatment at 90℃ and normal pressure for 5 minutes, during which the microspheres expand slightly and the cushioning layer maintains high density; then, it is pressurized to 15MPa, heated to 145℃, and kept at temperature and pressure for 20 minutes for vulcanization crosslinking.

[0020] Cooling and stabilization: The pad blank is placed in a room temperature (23±2℃) environment and allowed to cool naturally for more than 24 hours to completely eliminate the internal thermal stress of the pad, so that the size and microsphere structure are completely stable, and the finished intermediate rubber pads with different preset stiffness are obtained.

[0021] Performance testing: Mechanical property tests were conducted on the three types of stiffness intermediate rubber pads produced in batches. The results showed that: The measured average stiffness of the low-stiffness pad is 6.1 kN / mm, and the standard deviation of stiffness for products of the same specification is ±1.2 kN / mm. The measured average stiffness of the medium-stiffness cushion layer is 12.2 kN / mm, and the standard deviation of stiffness for products of the same specification is ±1.3 kN / mm. The measured average stiffness of the high-stiffness cushion layer is 17.9 kN / mm, and the standard deviation of stiffness for products of the same specification is ±1.1 kN / mm.

[0022] Fatigue performance testing: A 3 million-cycle cyclic load test was conducted according to relevant standards for rail transit fastener systems. The results showed: The stiffness variation rate of the three stiffness pads is 5%~7%, which meets the industry standard requirements; the pads have no cracks or permanent deformation, and the closed-cell microsphere structure remains intact, verifying the product's excellent fatigue resistance. Test results show that the intermediate rubber pad prepared by this invention has high stiffness accuracy and excellent product consistency. With the structural characteristics of closed-cell foamed microspheres, it has both excellent fatigue resistance and rebound characteristics, which fully meets the long-term service requirements of rail transit vibration damping fasteners under complex working conditions.

[0023] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for designing the stiffness of an intermediate rubber pad for track vibration damping fasteners, characterized in that, Using thermally expandable foamed microspheres as the core medium for stiffness control, the foaming ratio and expansion degree of the thermally expandable foamed microspheres in the rubber composite material are precisely controlled to achieve customized design of the stiffness of the intermediate rubber pad; the thermally expandable foamed microspheres have a closed-cell structure, which gives the intermediate rubber pad fatigue resistance and resilience, and can meet the long-term service requirements of track application scenarios. The method includes the following steps: S1. Mixing: Raw rubber, vulcanizing agent and unexpanded thermally expanded foamed microspheres are mixed and kneaded to obtain a uniform rubber compound. The initial volume addition ratio of the thermally expanded foamed microspheres is 3% to 8% of the total volume of the rubber compound. S2. Pre-expansion and shaping: The compounded rubber is subjected to controlled heating treatment at a temperature lower than the activation temperature of the vulcanizing agent. By precisely controlling the proportion of thermally expanded foaming microspheres, heating temperature, and holding time, the thermally expanded foaming microspheres are controlled to expand to a predetermined degree, thus obtaining an expanded and shaped padding layer. S3. Vulcanization molding: The temperature is raised to the vulcanization temperature, and the expanded and shaped pad is vulcanized under pressure to fully cross-link and cure the rubber, permanently locking the expansion structure of the thermally expanded foamed microspheres, and obtaining a regular pad blank. S4. Cooling and stabilizing: Cool the vulcanized pad blank to room temperature to eliminate internal thermal stress, stabilize the pad size and structure, and obtain the finished intermediate rubber pad with preset stiffness.

2. The stiffness design method according to claim 1, characterized in that, The pre-expansion temperature of the controlled heating treatment in S2 is negatively correlated with time and target stiffness: the lower the target stiffness value, the larger the required proportion of thermally expanded foamed microspheres, the higher the foaming ratio, and the higher the corresponding heating temperature and the longer the heat preservation time; the higher the target stiffness value, the smaller the required proportion of thermally expanded foamed microspheres, the lower the foaming ratio, and the lower the corresponding heating temperature and the shorter the heat preservation time.

3. The stiffness design method according to claim 2, characterized in that, The controlled heating treatment parameters are set as follows: When the target stiffness value is 6kN / mm, the proportion of thermally expanded foamed microspheres is 7%-8%, the heating temperature is 120-130℃, and the treatment time is 20-30 minutes; When the target stiffness value is 12kN / mm, the proportion of thermally expanded foamed microspheres is 5%-6%, the heating temperature is 105-115℃, and the processing time is 15-20 minutes. When the target stiffness value is 18kN / mm, the proportion of thermally expanded foamed microspheres is 3%-4%, the heating temperature is 80-90℃, and the processing time is 5-10 minutes.

4. The stiffness design method according to claim 1, characterized in that, In S1, the raw rubber is natural or synthetic rubber; the initial expansion temperature of the thermally expanded foamed microspheres is ≥80℃.

5. The stiffness design method according to claim 1, characterized in that, In S3, the vulcanization process parameters are: temperature 140-150℃, pressure 1-20MPa, and vulcanization time 8-30 minutes.

6. A middle rubber pad for track vibration damping fasteners, characterized in that, It is prepared by the stiffness design method according to any one of claims 1-5; the rubber matrix of the intermediate rubber pad is uniformly dispersed with thermally expanded foamed microspheres that are expanded and shaped and have a fixed structure, and the stiffness is precisely controlled by the degree of pre-expansion to adjust the foaming ratio and expansion degree of the thermally expanded foamed microspheres.

7. The intermediate rubber pad according to claim 6, characterized in that, The intermediate rubber pad is a series of products, including multiple stiffness levels of 6kN / mm, 12kN / mm, and 18kN / mm, which can adapt to the needs of different levels of track vibration reduction projects.

8. A track vibration damping fastener device, characterized in that, It includes the intermediate rubber pad as described in claim 6 or 7, and uses the intermediate rubber pad as the core component for stiffness adjustment. By replacing intermediate rubber pads with different stiffnesses, the overall stiffness of the fastening system can be quickly adjusted.