Multi-material rail pad and method for manufacturing same

Abstract

This disclosure relates to a rail pad including a pad matrix having a first material and at least one damping element at least partially encapsulated or embedded in the pad matrix. The damping element includes a second material. The second material includes at least one damping element having a damping factor tan delta greater than or equal to 0.5 in the audible frequency of 1000 Hz. Methods for producing the rail pad are also disclosed.

1 . A rail pad comprising:
 a pad matrix comprising a first material; and   at least one damping element at least partially encapsulated or embedded in the pad matrix, the damping element comprising a second material, and   wherein the second material comprises a damping factor tan delta greater than or equal to 0.5 at a frequency of 1000 Hz at room temperature.   
     
     
         2 . The rail pad according to  claim 1 , wherein the at least one damping element comprises between 10% and 90% of a total volume of the rail pad. 
     
     
         3 . The rail pad according to  claim 1 , further comprising a single damping element. 
     
     
         4 . The rail pad according to  claim 1 , further comprising a plurality of damping elements. 
     
     
         5 . The rail pad according to  claim 1 , wherein the at least one damping element comprises a polygonal or circular cross-section in at least one plane configured to form shapes of cuboids, spheres, ellipsoids, cylinders, or prisms. 
     
     
         6 . The rail pad according to  claim 1 , wherein the at least one damping element comprises a plurality of monodispersed or polydisperse particle-like units. 
     
     
         7 . The rail pad according to  claim 6 , wherein the plurality of monodispersed or polydisperse particle-like units comprise an average dimension between 50 nanometers and 1 millimeter. 
     
     
         8 . The rail pad according to  claim 1 , wherein the at least one damping element ( 2 ) comprises is configured as a sheet or film. 
     
     
         9 . The rail pad according to  claim 8 , wherein the sheet or film configuration comprises at least one corrugated surface. 
     
     
         10 . The rail pad according to  claim 1 , wherein the at least one damping element further comprises at least one of polyisobutene, crosslinked polyisobutylene (butyl rubber, IIB), polyurethane elastomers (PU), polymermodified bitumen, polar polymers, such as nitrile, hydrogenated or carboxylated nitrile rubber (NBR, HNBR, XNBR), chlorinated polyolefins (for example, polychloroprene (CR), chlorinated polyethylene or polypropylene, or chlorosulfonated polyethylene), acrylate rubbers (ACM) or epoxidized rubbers (ER), particularly where these have been modified with polar fillers and/or plasticizers or antiplasticizers, conventional vulcanized rubbers such as natural rubber (NR) or synthetic polyisoprenes (PI), polybutadiene (PBD), styrene-butadiene rubber (SBR), styrene-butadiene-styrene black copolymers (SBS), ethylene-propylene diene monomer rubber (EPDM), particularly where these contain high proportions of carbon black or silica fillers d plasticizers or antiplasticizers. 
     
     
         11 . The rail pad according to  claim 1 , wherein the pad matrix comprises at least one of crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber or natural rubber (NR), synthetic cis 1,4-polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene-5 butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene-vulcanized ethylene-propylene-diene-monomer (EPDM) blends, copolyester elastomers (COPE), or polyamide elastomers (PAE). 
     
     
         12 . The rail pad according to  claim 1 , wherein at least one of the pad matrix and at least one damping element comprises at least one of pores, cavities and voids. 
     
     
         13 . The rail pad according to  claim 12 , wherein at least one of the pores, cavities and voids are sized and distributed so that at least one of the pad matrix and the at least one damping element is configured as a close-celled or open-celled foam. 
     
     
         14 . The rail pad according to  claim 1 , further comprising one or more stiffness modifying element arranged within or onto the pad matrix, separated from the at least one damping element. 
     
     
         15 . The rail pad according to  claim 14 , wherein the one or more stiffness modifying element comprises a material configured to increase stiffness of at least a portion of the pad matrix relative to a stiffness of the pad matrix and comprising elastic moduli at least one of which is higher than the corresponding matrix modulus. 
     
     
         16 . The rail pad according to  claim 14 , wherein the one or more stiffness modifying element is configured to decrease the stiffness of at least a portion of the pad matrix relative to a stiffness of the pad matrix and comprises elastic moduli at least one of which is lower than the corresponding matrix modulus. 
     
     
         17 . The rail pad according to  claim 14 , wherein the one or more stiffness modifier(s) comprises a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms. 
     
     
         18 . The rail pad according to  claim 8 , wherein the sheet further comprises external studs or ribs or other types of profile on one or both major faces. 
     
     
         19 . The rail pad according to  claim 1 , wherein at least one of the pad matrix and the at least one damping element comprises internal gaps or holes or grooves or other types of profile. 
     
     
         20 . The rail pad according to  claim 8 , wherein the gaps or holes or grooves or other types of profile comprise a cylindrical shape with a spherical or ellipsoidal cross-section, and/or prisms with a polygonal cross-section, or grooves with a semispherical or semi-ellipsoidal or rectangular or triangular cross-section. 
     
     
         21 . The rail pad according to  claim 19 , wherein the grooves comprise rectilinear trajectories. 
     
     
         22 . The rail pad according to  claim 19 , wherein the grooves comprise regular or irregular zigzag or curvilinear trajectories. 
     
     
         23 . The rail pad according to  claim 19 , wherein the gaps or holes or grooves or other types of profile of the pad matrix and/or the at least one damping element are either filled with air or with a material different from a one used for the damping element, whose bulk modulus is lower than the bulk modulus of the damping element and/or the pad matrix. 
     
     
         24 . The rail pad according to  claim 19 , wherein said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are filled with a material whose bulk modulus is a least one order of magnitude lower than that of the respective material used for the said pad matrix and/or said at least one damping element. 
     
     
         25 . The rail pad according to  claim 19 , wherein the gaps or holes or grooves or other types of profile of said pad matrix and/or the at least one damping element are filled with an elastomeric close-celled or open-celled foam. 
     
     
         26 . A method for producing a rail pad, comprising the steps of:
 a) preparing in a preform at least one damping element comprising a material having a damping factor tan delta greater than 0.5 at a frequency of 1000 Hz at room temperature;   b) introducing in a mold a before-prepared at least one damping element; and   c) performing a multi-step molding process to at least partially encapsulate or embed the at least one damping element with a pad matrix and,   wherein the rail pad comprises a pad matrix comprising a first material and at least one damping element at least partially encapsulated or embedded in the pad matrix, the damping element comprising a second material wherein the second material of the at least one damping element comprises a damping factor tan delta greater than or equal to 0.5 at a frequency of 1000 Hz at room temperature.   
     
     
         27 . The method according to  claim 26 , further comprising the step of introducing in the mold at least one stiffening modifier before performing the multi-step molding process.