A polyurethane elastomer rail underplate and its processing method

Abstract

This invention discloses a polyurethane elastomer rail pad and its processing method, comprising: the rail pad is integrally molded from a polyether-type polyurethane elastomer through a thermosetting process; the polyether-type polyurethane elastomer is composed of polyether polyol, isocyanate, chain extender, and functional additives; wherein the hard segment content is controlled within the range of 35%~55%, forming a microphase separation structure; while maintaining good elasticity, the hardness and load-bearing capacity of the material are significantly improved. The static stiffness of the product can reach 100kN / mm~140kN / mm, while the dynamic-to-static stiffness ratio is ≤1.4, achieving a perfect combination of high load-bearing capacity and excellent vibration reduction effect, solving the technical contradiction of traditional materials being unable to balance hardness and elasticity, and by adding ultra-high molecular weight polyethylene micropowder or polytetrafluoroethylene micropowder as wear-resistant modifiers, a synergistic reinforcing structure is formed with the polyurethane matrix, which greatly improves the wear resistance of the material, effectively extends the service life of the pad, and reduces the frequency of maintenance and replacement.

Description

Technical Field

[0001] This invention relates to the field of rail transit technology, and in particular to a polyurethane elastomer rail underplate and its processing method. Background Technology

[0002] Rail pads are important vibration damping components in railway track systems, installed between the rails and sleepers. Their main function is to buffer the high-speed impact vibrations generated when vehicles pass over the rails, protect the roadbed and sleepers from damage, and insulate the railway signaling system. Traditional rail pads are mainly made of natural or synthetic rubber, which presents the following technical problems during long-term use: First, traditional rubber pads suffer from poor mechanical property matching. Under the high-load conditions of heavy-haul railways, the pads need to possess both sufficient load-bearing capacity and good elasticity. However, while increasing the hardness of traditional rubber materials to improve load-bearing capacity, they often sacrifice elasticity, resulting in an excessively high dynamic-to-static stiffness ratio and reduced vibration damping effect. Conversely, in order to ensure good elasticity and vibration damping effect, insufficient hardness and load-bearing capacity may occur, making it difficult to achieve a balance between hardness and elasticity.

[0003] Secondly, traditional rubber track pads have limited wear resistance. Under long-term, repeated train loads, there is relative friction between the track pad and the bottom surface of the rail and the surface of the sleeper. The rubber material is prone to wear, leading to a reduction in the thickness of the track pad, changes in stiffness, and affecting the stability of the track geometry. This wear problem is particularly pronounced in curved sections and turnout areas, requiring frequent track pad replacements, increasing maintenance costs and posing safety hazards.

[0004] Meanwhile, traditional rubber pads have poor weather resistance and resistance to various media. In open-air environments, rubber materials are easily affected by ultraviolet radiation, temperature changes, rainwater, and other factors, leading to aging, hardening, and cracking, resulting in a decline in mechanical properties. Furthermore, oil stains and chemical media present along railway lines can also corrode rubber materials, accelerating their aging and failure. Especially in cold northern regions, low temperatures cause rubber materials to harden and become brittle, losing elasticity and severely impacting vibration damping effectiveness and service life.

[0005] Furthermore, traditional rubber pads have limited insulation performance, especially in humid environments where insulation resistance drops significantly, potentially affecting the normal transmission of track circuit signals. While insulation performance can be improved by adding insulating fillers, this often compromises the material's mechanical and processing properties, making it difficult to achieve a balance.

[0006] Therefore, developing a new type of rail pad that combines high load-bearing capacity, good vibration reduction effect, excellent wear resistance and weather resistance, and solving the above-mentioned technical problems of traditional rubber pads, has become an urgent technical issue to be addressed in this field. Summary of the Invention

[0007] This disclosure addresses the technical problems of traditional rubber rail pads in the prior art, such as difficulty in balancing hardness and elasticity, poor wear resistance, insufficient weather resistance, and limited insulation performance. It provides a polyurethane elastomer rail pad and its processing method. Through material formulation optimization and molding process innovation, the rail pad achieves high load-bearing capacity, excellent vibration reduction effect, wear resistance, weather resistance, and high insulation performance, meeting the usage requirements of heavy-haul railways under high load conditions.

[0008] According to one aspect of this disclosure, a polyurethane elastomer rail underplate is provided, comprising: The track pad is integrally formed using a thermosetting process with a polyether-type polyurethane elastomer. The polyether-type polyurethane elastomer is composed of polyether polyol, isocyanate, chain extender and functional additives. The hard segment content is controlled within the range of 35% to 55%, forming a microphase separation structure.

[0009] Furthermore, the polyether polyol is polypropylene glycol or polytetrahydrofuran glycol, with a number average molecular weight of 1000-3000; the isocyanate is 4,4'-diphenylmethane diisocyanate (MDI) or carbodiimide-modified MDI; and the chain extender is 1,4-butanediol or a mixture of 1,4-butanediol and trimethylolpropane.

[0010] Furthermore, the functional additives include wear-resistant modifiers, weather-resistant modifiers, and insulation modifiers; the wear-resistant modifier is made of ultra-high molecular weight polyethylene micro powder or polytetrafluoroethylene micro powder, and the addition amount is 2% to 8% of the total mass of the system; the weather-resistant modifier is a compound system of hindered amine light stabilizers and benzotriazole ultraviolet absorbers, and the total addition amount is 0.5% to 2% of the total mass of the system; the insulation modifier is made of fumed silica or nano alumina, and the addition amount is 3% to 10% of the total mass of the system.

[0011] Furthermore, the static stiffness of the rail pad is 100kN / mm~140kN / mm, the dynamic-to-static stiffness ratio is ≤1.4, the permanent compression deformation is ≤8%, and the fatigue performance shows no cracking after 3 million load cycles.

[0012] Furthermore, the structure of the rail pad includes an upper surface, a lower surface, and a side surface.

[0013] Furthermore, the upper surface of the rail pad is provided with a raised stripe structure that contacts the rail, and the stripes are arranged in a cross array on the surface of the pad.

[0014] Furthermore, the side of the rail pad is provided with a groove structure for locking and fixing. The inner corner of the groove structure is rounded to avoid stress concentration caused by right-angled edges, thereby improving fatigue resistance and service life.

[0015] According to another aspect of this disclosure, a method for processing a polyurethane elastomer rail underplate is provided, comprising: The raw material pretreatment step involves vacuum dehydrating the polyether polyol at 100℃~120℃ for 2h~3h, controlling the moisture content to ≤0.05%; The prepolymer preparation steps involve mixing dehydrated polyether polyol and isocyanate at an NCO / OH molar ratio of 1.5 to 2.5, reacting at 70°C to 90°C for 2 to 4 hours to prepare a polyurethane prepolymer with an NCO content of 4% to 8%. The preparation steps for component A involve mixing the chain extender and functional additives uniformly at 60℃~80℃ and then degassing under vacuum. In the casting process, the prepolymer and component A are mixed evenly in a predetermined ratio and injected into a mold preheated to 90°C~110°C for compression molding. The post-vulcanization process involves vulcanizing the molded product at 100℃~120℃ for 12h~24h, and then leaving it at room temperature for more than 7 days to obtain the final product.

[0016] Furthermore, in the casting molding step, a high-pressure casting machine is used for casting, with a casting pressure of 8MPa~15MPa and a casting temperature of 70℃~90℃; the molding vulcanization time is 20min~40min and the vulcanization pressure is 5MPa~10MPa.

[0017] Furthermore, in the raw material pretreatment step, the isocyanate is preheated before use, and the preheating temperature of the isocyanate is controlled at 40°C to 60°C.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Excellent balance between hardness and elasticity: This disclosure achieves an ideal microphase separation structure by precisely controlling the hard segment content of the polyurethane elastomer within the range of 35% to 55%, significantly improving the material's hardness and load-bearing capacity while maintaining good elasticity. The product's static stiffness can reach 100kN / mm to 140kN / mm, while the dynamic-to-static stiffness ratio is ≤1.4, achieving a perfect combination of high load-bearing capacity and excellent vibration reduction effect, and solving the technical contradiction of traditional rubber materials' inability to balance hardness and elasticity. Significantly improved wear resistance: This disclosure improves the wear resistance of the material by adding ultra-high molecular weight polyethylene micro powder or polytetrafluoroethylene micro powder as wear modifier, forming a synergistic reinforcing structure with the polyurethane matrix. The wear resistance is dozens of times that of ordinary rubber materials, effectively extending the service life of the pad and reducing the frequency of maintenance and replacement. Outstanding weather resistance and resistance to various media: This disclosure uses a compound system of hindered amine light stabilizers and benzotriazole UV absorbers as weather-resistant modifiers, effectively resisting UV and thermo-oxidative aging; the polyether-type main chain structure itself has good hydrolysis resistance. The product can be used in a temperature range of -70℃ to 120℃, and after hot air aging (70℃×168h), the tensile strength retention rate is over 100%, and the elongation at break is well maintained, making it adaptable to various harsh environmental conditions; Excellent insulation performance: This disclosure significantly improves the insulation performance of the material without significantly affecting its mechanical properties by adding fumed silica or nano-alumina as an insulation modifier. The product's working resistance can reach over 10^9 Ω, far exceeding the standard requirement of 10^6 Ω, and it can maintain good insulation performance even in humid environments, ensuring reliable transmission of track circuit signals; The processing technology offers high controllability: This disclosure employs a prepolymer casting molding process, ensuring the uniformity and stability of the polyurethane elastomer's structure and properties through precise control of NCO content, reaction temperature, and time. Post-curing further enhances the crosslinking reaction, improving the material's mechanical properties and aging resistance.

[0019] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0020] The accompanying drawings are provided to better understand this solution and do not constitute a limitation of this disclosure. Wherein: Figure 1 This is a schematic diagram of the overall structure of the polyurethane elastomer rail underplate according to an exemplary embodiment of the present disclosure; Figure 2 This is a bottom view of the polyurethane elastomer rail pad in an exemplary embodiment of the present disclosure. Figure 3 According to an exemplary embodiment of this disclosure Figure 1 A magnified schematic diagram of the structure at point A; Figure 4 This is a schematic flowchart of a method for processing a polyurethane elastomer rail underplate according to an exemplary embodiment of the present disclosure.

[0021] In all the accompanying drawings, the same reference numerals denote the same technical features, as follows: 10. Main body of the rail pad; 11. Upper surface; 12. Lower surface; 13. Side; 20. Raised stripe structure; 30. Groove structure. Detailed Implementation

[0022] The exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0023] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0024] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. Example 1:

[0025] A polyurethane elastomer rail underplate, reference Figures 1 to 4 ,include: The entire structure is integrally cast from polyether-type polyurethane elastomer using a thermosetting process. The rail pad includes a main body 10 with dimensions of 190mm × 149mm × 10mm.

[0026] In this embodiment, the polyether-type polyurethane elastomer is formulated as follows: 100 parts polypropylene glycol (number average molecular weight 2000), 45 parts 4,4'-diphenylmethane diisocyanate (MDI), 8 parts 1,4-butanediol, 5 parts ultra-high molecular weight polyethylene micro powder, 0.5 parts hindered amine light stabilizer, 0.5 parts benzotriazole ultraviolet absorber, and 6 parts fumed silica. The hard segment content is controlled at approximately 45%.

[0027] By precisely controlling the hard segment content and microphase separation structure, the polyurethane elastomer in this embodiment maintains good elasticity while exhibiting high hardness and load-bearing capacity. The hard segments primarily provide hardness and strength, while the soft segments provide elasticity and toughness. The two are separated by microphase to form a balanced system with both robust and tough mechanical properties.

[0028] The structure of the rail pad includes an upper surface 11, a lower surface 12, and a side surface 13.

[0029] The upper surface 11 of the rail pad is provided with a raised stripe structure 20 that contacts the bottom surface of the rail. The stripes are arranged in a cross array on the surface of the pad. This multi-point contact force structure increases the contact area and improves the load-bearing capacity. It also enhances the vibration reduction effect through the elastic deformation of the stripes, while reducing the actual contact area with the bottom surface of the rail and reducing wear.

[0030] The side of the rail pad is provided with a groove structure 30 for locking and fixing. The inner corner of the groove structure is rounded to avoid stress concentration caused by right angle edges, thereby improving the fatigue resistance and service life of the pad.

[0031] The performance test results of the polyurethane elastomer rail pad prepared in this embodiment are as follows: static stiffness 125 kN / mm, dynamic-to-static stiffness ratio 1.36, compression set 6.2%, no cracking observed after 3 million load cycles, tensile strength 17 MPa, elongation at break 457%, and working resistance 4.9 × 10⁻⁶ kN / mm². The Ω value meets and exceeds all standard requirements. After hot air aging (70℃×168h), the tensile strength is 17.4MPa, the elongation at break is 403%, and the aging resistance is excellent. Example 2:

[0032] This embodiment provides a method for processing a polyurethane elastomer rail underplate, referencing... Figure 4 The flowchart shown illustrates that the method includes the following steps: Step S1, Raw Material Pretreatment. Polypropylene glycol (number average molecular weight 2000) is added to the reactor and dehydrated under vacuum at 110℃ for 2.5 hours, controlling the moisture content to ≤0.05%. 4,4'-diphenylmethane diisocyanate (MDI) is preheated and melted at 50℃, then filtered for later use. Controlling the moisture content of the raw materials is crucial for ensuring a controllable polyurethane reaction; excessive moisture will react with the isocyanate to generate bubbles, affecting product performance.

[0033] Step S2, prepolymer preparation. Dehydrated polypropylene glycol is added to a reactor, heated to 80°C, and then preheated MDI is slowly added at an NCO / OH molar ratio of 2.0. The mixture is stirred and reacted for 3 hours under nitrogen protection to prepare a polyurethane prepolymer with an NCO content of approximately 6%. During the reaction, the NCO content is measured periodically; the reaction is stopped once the predetermined value is reached, and the temperature is lowered to 60°C for later use. The prepolymer method allows for better control of the reaction process and product performance.

[0034] Step S3, Preparation of Component A. 1,4-Butanediol, ultra-high molecular weight polyethylene micropowder, hindered amine light stabilizer, benzotriazole UV absorber, and fumed silica are added to a mixing vessel according to the formula ratio. The mixture is stirred at high speed at 70°C until homogeneous, then vacuum degassed for 30 minutes to remove any incorporated air bubbles. Uniform dispersion of functional additives is a crucial step in ensuring the overall performance of the product.

[0035] Step S4, Casting. The prepolymer and component A are mixed uniformly using a high-pressure casting machine at a predetermined ratio (OH / NCO molar ratio of 0.95) under a casting pressure of 10 MPa and a casting temperature of 80°C. The uniformly mixed material is then rapidly poured into a steel mold preheated to 100°C. The mold is closed and pressurized to 8 MPa, and the molding is carried out for 30 minutes. Precise control of the casting parameters ensures sufficient material flow and filling of the mold, avoiding air bubbles or insufficient resin.

[0036] Step S5, post-curing treatment. Remove the molded pad from the mold and place it in an oven at 110℃ for 16 hours to allow the cross-linking reaction to proceed fully, improving the cross-linking network structure of the polyurethane and enhancing the material's mechanical properties and aging resistance. After post-curing, allow the product to stand at room temperature for at least 7 days to ensure its properties are fully stable; this is the final product.

[0037] The processing method in this embodiment ensures the uniformity and stability of the internal quality of the polyurethane elastomer rail pads by precisely controlling various process parameters, achieving a product qualification rate of over 98%. The prepared products possess excellent mechanical properties, vibration damping properties, wear resistance, weather resistance, and insulation properties, fully meeting the usage requirements of heavy-haul railways under high-load conditions. Example 3:

[0038] The embodiments provide specific implementation schemes for high-strength polyurethane elastomer rail pads suitable for heavy-haul railways. Compared with Embodiment 1, the main differences lie in the formulation composition and structural parameters to adapt to heavier load conditions.

[0039] In this embodiment, the polyether-type polyurethane elastomer is formulated as follows: 80 parts of polytetrahydrofuran diol (number average molecular weight 1000), 20 parts of polypropylene triol (number average molecular weight 3000), 55 parts of carbodiimide-modified MDI, 10 parts of a mixed chain extender of 1,4-butanediol and trimethylolpropane (mass ratio 7:3), 6 parts of polytetrafluoroethylene micropowder, 0.8 parts of hindered amine light stabilizer, 0.7 parts of benzotriazole ultraviolet absorber, and 8 parts of nano-alumina. The hard segment content is controlled at approximately 52%.

[0040] The performance test results of the high-strength polyurethane elastomer rail pad prepared in this embodiment are as follows: static stiffness 138 kN / mm, dynamic-to-static stiffness ratio 1.32, compression set 5.8%, tensile strength 18.5 MPa, elongation at break 435%, and working resistance 6.2 × 10⁻⁶ kN / mm². Ω. No cracks were observed after 3 million load cycles, demonstrating excellent fatigue performance.

[0041] Actual line testing showed that the product in this embodiment, when used on the Shijiazhuang-Taiyuan heavy-haul railway, had a service life that was more than three times longer than that of ordinary rubber pads, significantly reduced maintenance costs, and demonstrated excellent vibration reduction and insulation performance.

[0042] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved. This embodiment does not impose any limitations on these steps.

[0043] It should be understood that the terms "system," "device," "unit," and / or "module" used in this embodiment are a method of distinguishing different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they can be replaced by other expressions.

[0044] This embodiment uses a flowchart to illustrate the operations performed by the system according to this embodiment. It should be understood that the preceding or following operations are not necessarily performed precisely in sequence. Instead, each step can be processed in reverse order or simultaneously. Furthermore, other operations can be added to these processes, or one or more steps can be removed from them.

[0045] As shown in this embodiment, unless the context explicitly indicates an exception, words such as "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0046] The definitions used in this embodiment, such as the terms "having," "may have," "comprising," or "may include," indicate the presence of corresponding functions, operations, elements, etc., in this embodiment, but do not limit the presence of one or more other functions, operations, elements, etc. Furthermore, it should be understood that the terms "comprising" or "having," as used herein, indicate the presence of features, numbers, steps, operations, elements, components, or combinations thereof described in the specification, without excluding the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof.

[0047] In this embodiment, the definitions of "A or B", "at least one of A and / or B" or "one or more of A and / or B" as used herein include any and all combinations of the words listed therewith. For example, "A or B", "at least one of A and / or B" or "one or more of A and / or B" means (1) including at least one A, (2) including at least one B, or (3) including both at least one A and at least one B.

[0048] The definitions of "first" and "second" in this embodiment, and the descriptions of "first" and "second" appearing in this embodiment, are only for illustration and to distinguish the objects being described. They do not indicate any order and do not represent a special limitation on the number of devices in this embodiment, nor do they constitute any limitation on this embodiment. For example, the first element can be referred to as the second element without departing from the scope of this disclosure, and similarly, the second element can be referred to as the first element.

[0049] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A polyurethane elastomer rail underplate, characterized in that, include: The track pad is integrally formed using polyether-type polyurethane elastomer through a thermosetting process. The polyether-type polyurethane elastomer is composed of polyether polyol, isocyanate, chain extender and functional additives; wherein the hard segment content is controlled in the range of 35% to 55%, forming a microphase separation structure.

2. The polyurethane elastomer rail underplate as described in claim 1, characterized in that, The polyether polyol is polypropylene glycol or polytetrahydrofuran glycol, with a number average molecular weight of 1000-3000; the isocyanate is 4,4'-diphenylmethane diisocyanate (MDI) or carbodiimide-modified MDI; the chain extender is 1,4-butanediol or a mixture of 1,4-butanediol and trimethylolpropane.

3. The polyurethane elastomer rail underplate as described in claim 1, characterized in that, The functional additives include wear-resistant modifiers, weather-resistant modifiers, and insulation modifiers; the wear-resistant modifier is made of ultra-high molecular weight polyethylene micro powder or polytetrafluoroethylene micro powder, and the addition amount is 2% to 8% of the total mass of the system; the weather-resistant modifier is a compound system of hindered amine light stabilizers and benzotriazole ultraviolet absorbers, and the total addition amount is 0.5% to 2% of the total mass of the system; the insulation modifier is made of fumed silica or nano alumina, and the addition amount is 3% to 10% of the total mass of the system.

4. The polyurethane elastomer rail underplate as described in claim 1, characterized in that, The static stiffness of the rail pad is 100kN / mm~140kN / mm, the dynamic-to-static stiffness ratio is ≤1.4, the permanent compression deformation is ≤8%, and the fatigue performance shows no cracking after 3 million load cycles.

5. The polyurethane elastomer rail pad as described in claim 1, characterized in that, The structure of the track pad includes an upper surface, a lower surface, and a side surface.

6. The polyurethane elastomer rail underplate as described in claim 5, characterized in that, The upper surface of the rail pad is provided with a raised stripe structure that contacts the rail, and the stripes are arranged in a cross array on the surface of the pad.

7. The polyurethane elastomer rail underplate as described in claim 5, characterized in that, The side of the rail pad is provided with a groove structure for locking and fixing. The inner corner of the groove structure is rounded to avoid stress concentration caused by right-angle edges, thereby improving fatigue resistance and service life.

8. A method for processing a polyurethane elastomer rail underplate, characterized in that, include: The raw material pretreatment step involves vacuum dehydrating the polyether polyol at 100℃~120℃ for 2h~3h, controlling the moisture content to ≤0.05%; The prepolymer preparation steps involve mixing dehydrated polyether polyol and isocyanate at an NCO / OH molar ratio of 1.5 to 2.5, reacting at 70°C to 90°C for 2 to 4 hours to prepare a polyurethane prepolymer with an NCO content of 4% to 8%. The preparation steps for component A involve mixing the chain extender and functional additives uniformly at 60℃~80℃ and then degassing under vacuum. In the casting process, the prepolymer and component A are mixed evenly in a predetermined ratio and injected into a mold preheated to 90°C~110°C for compression molding. The post-vulcanization process involves vulcanizing the molded product at 100℃~120℃ for 12h~24h, and then leaving it at room temperature for more than 7 days to obtain the final product.

9. The processing method as described in claim 8, characterized in that, In the casting process, a high-pressure casting machine is used for casting, with a casting pressure of 8MPa~15MPa and a casting temperature of 70℃~90℃; the molding and vulcanization time is 20min~40min and the vulcanization pressure is 5MPa~10MPa.

10. The processing method as described in claim 8, characterized in that, In the raw material pretreatment step, the isocyanate is preheated before use, and the preheating temperature of the isocyanate is controlled at 40℃~60℃.

Images