RUBBER COMPOSITION FOR A RAIL INTERMEDIATE LAYER

Description

[0001] The invention relates to a rubber composition for rail interlayers.

[0002] Rail pads are placed between the rail and the sleeper to either protect the sleeper and ballast bed or to reduce the noise emissions caused by moving trains.

[0003] The noise is caused by vehicles driving over the track and by the rails vibrating, with the vibrations being transmitted over long distances along the track. Noise emissions consist of low-frequency and high-frequency sound waves. Noise is believed to cause health problems if it exceeds 55 dB. A passing freight train has a maximum sound pressure level of 96 dB at 80 km / h and at a lateral distance of 7.5 m. A reduction in noise exposure of just 1 dB is perceived by many people as an improvement. A reduction of 3 dB is considered a significant improvement. A reduction of 10 dB is perceived as a 50% noise reduction.

[0004] Different types of rail pads are known from the state of the art: Firstly, there are hard paddings with high rigidity and low elasticity. Hard paddings usually have a hardness of over 90 ShA and a density of around 1 g / cm3. The rebound resilience of hard padding is around 35%. Hard paddings are usually made of thermoplastic polymers, e.g. polyester or polypropylene. Hard paddings transmit vibrations into the ballast bed with almost no dampening. Due to the high spring stiffness of the pad, the rail has little room to vibrate, so that sound transmission via the track is reduced. The shocks caused by the train passing over it are hardly dampened. The sleepers and ballast bed are therefore subjected to great stress.

[0005] To protect the sleepers and ballast bed, soft rail pads were developed. Soft rail pads have very high elasticity and low hysteresis. Soft rail pads are typically made of elastomers. They typically have a hardness of 65 to 70 ShA, a density of 1.1–1.2 g / cm³, and a rebound resilience of 50%. The elasticity of the rail pad better absorbs impacts from the moving train. This protects the sleepers and ballast bed. Since the elastic rail pad only slightly prevents the rail from vibrating, high-frequency noise emissions increase. The noise pollution is therefore significantly higher.

[0006] In general, the rail pad must exhibit good aging and weathering resistance, with particular emphasis on low water absorption and very good UV and ozone resistance. Furthermore, the spring rate should not change significantly at different temperatures, with a temperature range of approximately -25°C to approximately 50°C being particularly relevant. The rail pad should withstand the loads exerted by trains under the expected climatic conditions and be extremely durable in order to minimize maintenance requirements for a track system. In addition to low stress on the track system, noise emissions should also be reduced. Since a large number of pad pads are required for a rail line, the pad should be easy to manufacture.Furthermore, they should be compatible with existing systems to enable subsequent installation into existing track lines.

[0007] Finally, it is also necessary to ensure that abrasion or decomposition products are as environmentally friendly as possible, especially since some tracks are laid in sensitive areas, such as water protection zones. The raw materials used should therefore not be listed on the European Chemicals Act's List of Substances of Very High Concern (SVHC) and should also not appear on UNIFE's Railway Industry Substances List.

[0008] In order to meet these requirements, rail pads composed of different materials have been proposed.

[0009] DE 202012002484 U1, for example, shows rail pads with layers of different materials.

[0010] WO 2019157540 shows a rail intermediate layer comprising a foamed elastomer and cork granules.

[0011] A rail pad with a special shape is described in DE 2016 111 064 A1.

[0012] Conventional rail pads are comparatively complex to manufacture. However, the requirements for noise reduction while simultaneously dampening mechanical loads have not yet been fully met.

[0013] The object of the invention is therefore to provide a rubber composition which enables simple production of a rail intermediate layer which has good damping properties under mechanical loads and which at the same time enables noise reduction.

[0014] This object is achieved by a sulfur-crosslinkable rubber composition for a rail intermediate layer, wherein the polymeric component comprises a halogenated butyl rubber and at least one further rubber, wherein the further rubber is selected from the elastomers of the groups R or M which contain at least one double bond, wherein the halogenated butyl rubber is present in an amount of 40 to 60 phr, in particular 50 phr, wherein at least one sulfur crosslinker is present, and wherein at least one filler having a density of at least 4 g / cm 3 is present, wherein the total amount of filler having a density of at least 4 g / cm 3 is 50 to 100 phr, and wherein at least one light filler having a density of less than 4 g / cm 3 is present, wherein the light fillers have a specific surface area (BET) of at most 50 m 2 / g.

[0015] Using known crosslinking methods, this rubber composition can be used to produce a solid, single-phase material that exhibits the properties required for a rail pad. The rubber composition allows for the easy production of a material with low elastic properties and high hysteresis in the temperature range of -25 to 50 °C. The shape of the material produced by crosslinking the rubber composition can be selected according to the specific requirements, thus providing a rail pad compatible with the existing system.

[0016] A rail pad made from this rubber compound exhibits good damping properties across the entire frequency range, both in the low-frequency and high-frequency ranges, and reduces noise, thus reducing both wear on the track superstructure and noise emissions. The rubber compound enables the attenuation of shocks, vibrations, and oscillations in both the inaudible and audible ranges. Mechanical loads such as shocks, oscillations, and vibrations can therefore be dampened, and noise emissions caused by rail oscillation can be reduced.

[0017] The rubber composition therefore simultaneously dampens mechanical stress and reduces noise. Furthermore, driving noise and vibrations inside the train are reduced, thus increasing passenger comfort.

[0018] Due to the advantageous spring stiffness and damping of the rubber composition according to the invention, the load generated when a train passes over can be partially cushioned, thus protecting the sleeper and ballast bed. At the same time, vibration of the rail, which would otherwise lead to high noise emissions, is prevented, thus achieving good noise reduction.

[0019] The rubber composition according to the invention can reduce oscillations and vibrations by partially converting the kinetic energy into heat. This leads to a reduction in shocks, oscillations, and vibrations across the entire frequency range, thus achieving good damping of the mechanical stress occurring when rolling over the rail, which protects the rail and ballast bed, while simultaneously reducing rail noise, thus resulting in a reduction in noise reduction.

[0020] The rubber composition is also particularly easy to process. The fact that a single-phase mixture can be provided also allows for further processing into damping elements or rail pads without great effort. With this rubber composition, very good mechanical properties and improved noise reduction can be achieved simultaneously through simple manufacturing processes. The rubber composition thus enables the easy production of a rail pad with good damping properties for mechanical loads and good noise reduction properties.

[0021] The rubber composition achieves good damping properties and noise reduction across the entire relevant temperature range, as its elasticity is particularly constant and low in the range between -25°C and 50°C. It also offers good weather resistance.

[0022] Halogenated butyl rubber, or isobutene-isoprene rubber, is a copolymer of the following formula consisting of 95 to 99.5 wt.% isobutene (m) and 0.5 to 5 wt.% isoprene (n):

[0023] According to DIN ISO 1629:2015-3, elastomers are classified according to the composition of their main chain. Elastomers in the M group have a saturated main chain. Elastomers with an unsaturated main chain are grouped in the R group.

[0024] The quantities in phr refer to 100 parts by mass of rubber. For a binary mixture, 40 phr of halogenated butyl rubber contains 60 phr of other rubber, or 60 phr of halogenated butyl rubber contains 40 phr of other rubber.

[0025] The quantities of fillers are also based on 100 parts by mass of total rubber.

[0026] Fillers are typically dispersed in the matrix. Active or reinforcing fillers alter the mechanical properties of the elastomers by binding the rubber molecules to the surface of the filler. Inactive fillers cause little or no change in the mechanical properties of the rubber.

[0027] Advantageous features are specified in the dependent claims: The rubber composition can be provided as a homogeneous blend. If the polymeric components form a substantially single-phase and homogeneous mixture, particularly both macroscopically and under the light microscope, i.e., without phase separation visible to the naked eye and / or under the light microscope, the rubber composition exhibits particularly advantageous mechanical properties, particularly with regard to its elastic-dynamic character.This is understood here to mean that the mixture is advantageously single-phase such that, after crosslinking, the rubber composition contains no elastomer particles with an average particle diameter of more than 0.5 µm, in particular more than 0.1 µm, preferably more than 0.01 µm, and / or no rubber domains with an average diameter of more than 0.5 µm, in particular more than 0.1 µm, preferably more than 0.01 µm. After crosslinking, the rubber composition preferably forms no discernible or detectable polymer particles or rubber domains at all.

[0028] The production of a rail pad is particularly simple when the rubber composition contains bromobutyl rubber as a halogenated butyl rubber. Bromobutyl rubber (BIIR) can be vulcanized particularly quickly and requires fewer vulcanization chemicals.

[0029] The other rubber is preferably halogen-free.

[0030] Polymers with a maximum glass transition temperature of -50 °C are particularly suitable as another rubber. The glass transition temperature can be measured using dynamic mechanical analysis (DMA) and derived from the shear modulus-temperature function.

[0031] Processing is particularly easy if the additional rubber is selected from a group comprising natural rubber (IR), synthetic polyisoprene (IR), or styrene-butadiene rubber (SBR), particularly with a styrene content of a maximum of 23.5 wt.%, preferably with a styrene content of 15 wt.%. This gives the material particularly good damping properties and particularly good sound reduction, especially in the low temperature range.

[0032] Natural rubber is obtained from the rubber tree and contains polyisoprene with the cis-1,4 configuration. Synthetic polyisoprene can be obtained, for example, by polymerizing 2-methyl-1,3-butadiene with a Ziegler-Natta catalyst.

[0033] The general formula is:

[0034] While natural rubber contains almost exclusively the cis-1,4 polymer, synthetic polyisoprene is a mixture of cis-1,4, trans-1,4, and 3,4 polymers, with the cis-1,4 polymer typically accounting for 90 to 98 wt.%. Polyisoprene with a higher cis-1,4 content typically has a lower glass transition temperature and better mechanical stability. The mechanical properties of natural rubber are therefore usually somewhat better than those of synthetic polyisoprene.

[0035] SBR has the following formula: where n is the number of butane-diene groups and m is the number of styrene groups. The groups are randomly distributed in the copolymer.

[0036] A rubber compound in which the other rubber component is ethylene propylene diene rubber (EPDM) is also easy to process. The damping properties and sound reduction are particularly good, especially in the low-temperature range, when EPDM is used with a polyethylene content of 45 to 55 wt.%.

[0037] EPDM has the following general formula: where m represents the number of ethylene groups, n represents the number of propylene groups and o represents the number of diene groups.

[0038] Preferably, the diene units are selected from the group of 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-cyclopentadiene, dicyclopentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 1,4-hexadiene, 1,4-cyclohexadiene, tetrahydroindene, methyl tetrahydroindene, ethylidene norbornene or 5-ethylidene-2-norbornene (ENB), 5-methylene-2-norbornene (MNB), 1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 5-isopropylidene-2-norbornene, 5-Vinyl-2-norbornene (VNB).

[0039] It is particularly advantageous if the ethylene-propylene-diene monomer rubber (EPDM) is a terpolymer of ethylene, propylene and 5-ethylidene-2-norbornene (ENB) or dicyclopentadiene (DCPD).

[0040] Processing is particularly simple when the polymer component consists exclusively of halogenated butyl rubber and the other rubber, i.e. when a binary polymer mixture is present.

[0041] The damping properties and sound reduction of the material are particularly good and particularly consistent over the temperature range of -25 °C to 50 °C when the polymer component consists exclusively of halogenated butyl rubber, especially bromobutyl rubber, and natural rubber or synthetic polyisoprene as the sole components. A binary blend of 50 phr natural rubber and 50 phr bromobutyl rubber has proven particularly advantageous.

[0042] Alternatively, good damping properties and good sound reduction are also achieved if the polymeric component consists of halogenated butyl rubber, in particular bromobutyl rubber, and styrene-butadiene rubber, in particular with a styrene content of maximum 23.5 wt.%, preferably with a styrene content of 15 wt.%, as the only components of the polymeric component.

[0043] Even if the polymeric component consists only of halogenated butyl rubber, in particular bromobutyl rubber, and EPDM, in particular with a polyethylene content of 45 to 55 wt.%, particularly good damping properties and particularly good sound reduction are achieved.

[0044] If the polymer component consists exclusively of EPDM and bromobutyl rubber, the rubber compound is particularly easy to produce, since no anti-aging or anti-ozone agents are necessary to achieve a long service life.

[0045] To avoid excessive self-heating, it may be necessary to exclude highly active reinforcing materials. Due to their surface structure, these could lead to an increase in the stress value at 100% elongation at break (according to DIN 53504: 2017-03) and poor recovery behavior. Excessive self-heating could lead to depolymerization under dynamic loading, which would destroy the material.

[0046] To avoid an increase in stress values ​​at 100% and a decrease in elongation at break, even at higher dosages, it is advantageous if the fillers are inactive. It is particularly advantageous if all fillers are inactive. Inactive fillers are those that prevent the rubber molecules from bonding to the surface of the filler and thus do not impede the flow of the rubber compound before molding.

[0047] The elasticity of the polymer component should be influenced as little as possible by the fillers. Therefore, fillers with a specific surface area (BET) of no more than 50 m² / g are particularly suitable. The specific surface area (BET) can be determined according to DIN ISO 9277:2014-01.

[0048] The same effect can be achieved if the heavy fillers have a particle size (d 50 ) of at least 1000. With a large particle size, the crosslinking of the polymers is little affected, so that the elasticity hardly changes and the fillers behave inactively with regard to crosslinking.

[0049] By adding inactive fillers, the rubber composition is easier to process because the formation of air pockets during processing can be avoided.

[0050] Furthermore, costs can be reduced by adding inactive fillers, as the fillers are usually cheaper than the polymers.

[0051] Processing of the rubber composition is particularly simple when barium sulfate and / or iron oxide and / or lithopone are included as heavy fillers with a density of at least 4 g / cm³. These fillers can also be used in larger doses without causing overfilling, which manifests itself as an increase in the modulus at 100% with a simultaneous decrease in the elongation at break. A damping element made from this rubber composition therefore has particularly good sound-reducing and shock-absorbing properties. A binary polymer component consisting of 50 phr natural rubber and 50 phr bromobutyl rubber, containing barium sulfate, in particular 100 phr barium sulfate, has proven particularly advantageous.

[0052] Processing of the rubber composition is further simplified if it contains at least one lightweight filler with a density of less than 4 g / cm³. These fillers allow for particularly easy adjustment of the hardness. For rail pads, it is particularly advantageous to include lightweight fillers with a density of less than 4 g / cm³ with a total content of 20 to 60 phr, as this makes it particularly easy to achieve the desired hardness.

[0053] A rubber composition which contains carbon black, in particular carbon black N550 or N990, as a lightweight filler with a density of less than 4 g / cm 3 is particularly easy to process.

[0054] Furthermore, it is advantageous if a silica derivative, especially surface-treated silica, is included as a filler with a density of less than 4 g / cm³. According to the invention, the lightweight fillers have a specific surface area (BET) of a maximum of 50 m² / g. The specific surface area (BET) can be determined according to DIN ISO 9277:2014-01.

[0055] A composition comprising 50 phr of natural rubber and 50 phr of bromobutyl rubber, as well as 100 phr of heavy filler with a density of at least 4 g / cm 3< , in particular 100 phr of barium sulfate, and 50 phr of light fillers with a density of less than 4 g / cm 3<, wherein all fillers have a specific surface area (BET) of at most 50 m 2< / g, has proven particularly advantageous.

[0056] Further additives such as anti-aging and ozone protection may be added, which may be particularly intended if natural rubber is included in the polymeric component.

[0057] If only a small amount of plasticizer is included, the properties of the polymer component are barely altered, and the temperature dependence of the hardness is also barely altered. A material made from the rubber composition is then particularly durable, as hardening of the vulcanizate during its service life is avoided. It is therefore particularly advantageous to contain plasticizers with a content of 0 to 10 phr, especially 2.5 to 7.5 phr. For the previously described composition comprising 50 phr of bromobutyl rubber and 50 phr of natural rubber, 100 phr of heavy filler, and 50 phr of light fillers, a plasticizer content of 7.5 phr has proven particularly favorable.

[0058] To simplify and accelerate further processing and crosslinking of the rubber composition, a sulfur or sulfur donor is included as a crosslinker. This achieves particularly consistent processing results and allows for the cost-effective production of a material with good damping properties and sound reduction. The length of the sulfur network bridges and the network density can be influenced by the ratio of sulfur, sulfur donors, and accelerators, as well as the type of accelerator.

[0059] A composition comprising 50 phr of bromobutyl rubber and 50 phr of natural rubber with 100 phr of heavy filler, the composition containing a sulfur crosslinker, has proven particularly advantageous.

[0060] In order to further simplify processing and shorten the vulcanization time, at least one ultra-accelerator, in particular from the group of thiurams, preferably TBzTD (tetrabenzylthiuram disulfide), and at least one semi-ultra-accelerator, in particular from the group of thiazoles, preferably MBTS (based on dibenzothiazyl disulfide), may be included.

[0061] Additionally, at least one accelerator, particularly a delayed one, may be included, particularly from the group of sulfenamides, preferably CBS (based on N-cyclohexyl-2-benzothiazyl-sulfenamide). This allows the length of the incubation phase to be controlled particularly easily. This is particularly relevant for rubber compositions whose polymeric component contains EPDM.

[0062] Also according to the invention is a crosslinked rubber mixture made from a rubber composition described above. The material obtained by crosslinking the rubber composition exhibits particularly good damping properties under mechanical loads and particularly good sound reduction, as it exhibits a high hysteresis in a temperature range of -25°C to 50°C. A sulfur-crosslinked rubber composition is particularly suitable. The crosslinked rubber composition is preferably a single-phase compound, as the sound reduction and damping properties for mechanical impacts are particularly pronounced with a solid material.

[0063] A further objective is to provide a damping element, in particular a rail pad, that achieves good noise reduction and has shock-absorbing properties. On the one hand, the damping element is intended to absorb shocks caused by mechanical loads, particularly to protect the track superstructure. At the same time, the damping element is intended to reduce vibration of the component or rail mounted on it, since these vibrations generate sound waves that can be transmitted over long distances.

[0064] Therefore, a damping element made of a cross-linked rubber mixture described above is also in accordance with the invention. The damping element or rail pad achieves particularly good sound reduction and particularly good damping properties for mechanical loads, especially shocks, if it has a density of 1.40 to 1.65 g / cm³ and a hardness of 50 to 65 ShA (at 23°C). A rebound resilience of a maximum of 30% at 23°C is also advantageous in this context. This simultaneously achieves good sound reduction and good shock absorption. At the same time, travel noise inside a train is reduced, increasing passenger comfort.

[0065] The damping properties and noise reduction are particularly advantageous when the rubber compound is unfoamed. Noise reduction and noise reduction properties are therefore particularly good when the material of the damping element is solid, particularly with virtually no visible air pockets.

[0066] According to the invention, a rail intermediate layer is further provided, in particular as described above, with a density of 1.40 to 1.65 g / cm 3< and a hardness of 50 to 65 ShA (at 23°C), wherein the rail intermediate layer has at least two regions with different thicknesses.

[0067] The shape of a rail pad depends primarily on the rail and sleeper. For example, a UIC54 rail might require a plate with a length of approximately 160 mm and a width of 125 mm, or a UIC60 rail might require a plate with a width of 150 mm. The dimensions therefore depend on the width of the rail. The height is typically around 7 mm.

[0068] The shape can influence criteria such as spring stiffness, slip resistance, and fatigue strength. These criteria arise from the type of application and are defined in specific standards. For example, different criteria are specified for high-speed lines, lines with tight track radii, or lines with wide track radii. Using the rubber composition described above, these criteria can be met, with fine-tuning achieved by the shape of the rail pad. It has proven advantageous to provide different thicknesses in different areas.

[0069] The damping element can be provided with recesses on the top and / or bottom, in which the thickness is reduced. The spring stiffness is particularly effectively influenced if the recesses are arranged alternately on the top and bottom.

[0070] A rail pad that has grooved, particularly straight, recesses on its upper and / or lower sides in the longitudinal direction, i.e., particularly parallel to the rail path, with the rail pad having a reduced thickness in the area of ​​the recesses, achieves particularly good sound reduction and has particularly good damping properties. This reduces the mechanical loads on the sleeper and the ballast bed, while simultaneously reducing noise emissions.

[0071] The recesses allow the damping element or rail spacer to deflect or compress under load. Grooves with an isosceles trapezoidal cross-section have proven advantageous. Because the recesses run parallel to the rail direction, the displaced air can easily escape when the damping element deflects under load.

[0072] A rectangular cross-section of the grooves results in greater deflection at the beginning of loading and, at higher loads, a strongly progressive spring characteristic in the relevant range. The trapezoidal cross-section, on the other hand, results in a less progressive spring characteristic in the relevant range. The synergy between material and design is therefore particularly pronounced in this design.

[0073] Particularly good damping properties and particularly good sound reduction are achieved by a rail intermediate layer that has webs running parallel to the rail support and that are thicker than other areas of the rail intermediate layer. In particular, it is provided that lateral edge areas and / or a central area are thicker. The remaining areas, which have a smaller thickness, can be referred to as connecting areas. The rail support can advantageously be formed by the connecting areas.

[0074] A process for producing a crosslinked rubber composition as described above, in particular a damping element or a rail intermediate layer, is particularly simple and cost-effective, wherein the vulcanization takes place at 150 °C to 180 °C, in particular at 170 °C.

[0075] Production is particularly quick and easy when crosslinking is performed using the compression molding process and the residence time in the vulcanization mold is 4 to 20 minutes, especially 5 minutes. Alternatively, production can be performed using the injection molding process, with a residence time in the vulcanization mold of 2 to 8 minutes. Both methods allow for the rapid production of a material, or rather a damping element, particularly a rail pad, with high hysteresis and good damping properties, achieving good noise reduction.

[0076] The invention is illustrated by way of example with reference to the following experiments and the following drawings, without limiting the inventive concept by these explanations. Examples:

[0077] Comparative tests were carried out with different polymer components and different fillers and filler contents.

[0078] Binary mixtures of bromobutyl rubber and another rubber were produced. To produce the rubber mixture, a rolled sheet was first formed from the polymer component on a laboratory rolling mill. To ensure homogeneity, the mixture sheet was cut three times alternately from the left and right up to approximately three-quarters of the roll width at an angle of approximately 45° before the additives were added. The removed mixture was then applied to the other side, referred to below as three left and right cuts.

[0079] Stearic acid and fillers were then added, and three cuts were made on the left and right sides of the specimen. Inactive fillers were used to achieve the lowest possible stress values ​​at 100% strain and thus have little influence on hysteresis.

[0080] Then accelerator and zinc oxide were added, and three more cuts were made at the end, each on the left and right. Finally, the mixture was turned over six times and the skin removed.

[0081] Alternatively, production was also carried out in an internal mixer. For this purpose, the polymers of the polymer component were blended and mixed for 2 minutes. After the stearic acid and fillers were added, mixing was continued for another 2 minutes, and the mixer was swept. The accelerators and zinc oxide were then added, followed by another 1 minute of mixing, and the mixer was swept again. After ejection, homogenization was carried out for 2 minutes in a stock blender. The mixture sheets were removed, and the rubber composition was deposited.

[0082] To produce the test specimens, the rubber composition was crosslinked in a compression process for 5 minutes at 170°C.

[0083] Solid discs with a diameter of 42 mm and a thickness of 6 mm were used as test specimens. These showed no visible air inclusions. At least the hardness (ShA), density, and rebound resilience of the test specimens were determined.

[0084] The hardness was determined according to DIN ISO 7619 - 1 : 2012 - 02, with the values ​​measured at -30 °C, -15 °C, 23 °C, 30 °C, and 50 °C. From these values, the change in hardness from -15 °C to 30 °C was calculated.

[0085] The density was measured according to DIN ISO 1183 - 1 : 2019 - 09 using the immersion method.

[0086] The rebound resilience was measured according to DIN 53512: 2000-04, with two test specimens stacked to achieve the required thickness. The rebound resilience was measured at temperatures between -30 °C and 50 °C.

[0087] To assess the damping properties and the sound reduction, several criteria were used that reflect the requirements for good sound reduction and good shock absorption: First, a density of 1.40 to 1.65 g / cm 3 was used to achieve good structure-borne sound insulation without impairing the mechanical properties by overfilling the polymer component.

[0088] A further criterion was a rebound elasticity of up to 30% at 23 °C in order to achieve good shock absorption values.

[0089] In addition, the change in hardness from -15 °C to 30 °C was used to achieve good damping properties and good sound reduction over the entire relevant temperature range, whereby a maximum value of 6 ShA was accepted.

[0090] These criteria were derived from several test series. A simplified test was conducted, based on the decay rate measurement. A metal sleeve with an inner cone, with an outer diameter of 150 mm, a height of 120 mm, and a wall thickness of 5 to 15 mm, was used. This sleeve was positioned on a test specimen and excited by a hammer blow. The faster the sound decayed in this configuration, the better the sound reduction.

[0091] In another test, a steel ball with a diameter of 40 mm and a weight of approximately 260 g was dropped from a height of 0.5 m onto a test specimen. The more energy absorbed by the test specimen, the less the steel ball rebounded from the specimen. After impact, the bounce height and the number of bounces were measured. The lower the bounce height and the number of bounces of the steel ball after impact, the better the mechanical damping.

[0092] Example 1: Bromobutyl rubber and natural rubber as polymeric components Bromobutyl rubber was blended with natural rubber in different mixing ratios and test specimens were prepared and tested as previously described.

[0093] The glass transition temperature (T g ) of natural rubber is -70°C, while that of bromobutyl rubber is -66°C. The two rubbers are therefore particularly well suited for blending. Blends were prepared with a ratio of 100 wt.% bromobutyl rubber : 0 wt.% natural rubber in 10% increments down to a ratio of 0 wt.% bromobutyl rubber : 100 wt.% natural rubber. For Example 1, no heavy filler with a density of at least 4 g / cm 3 was added.

[0094] Despite the addition of inactive carbon black, the mixed fur was not completely smooth, so processing the mixtures was complex.

[0095] Table 1 shows that compounds with a ratio of 60:40 to 40:60 were able to meet the criteria regarding rebound resilience and change in hardness. Starting with a ratio of 60 phr of bromobutyl rubber to 40 phr of natural rubber, an acceptable, small increase in spring rate at low temperatures was observed. At a natural rubber content of more than 60 phr, sufficient damping was no longer achieved at room temperature. The best values ​​were achieved with a compound containing 50 phr of bromobutyl rubber and 50 phr of natural rubber.

[0096] However, at 1.22 g / cm 3<, sufficient density was not achieved to achieve the desired improved noise reduction.

[0097] The amount of the components of the rubber composition is given in phr. Table 1: Test series of bromobutyl rubber with natural rubber Test mixture 1 2 3 4 5 6 7 8 9 NR (CV60) 0 10 20 30 40 50 60 80 100 BIIR (EXXON 2255) 100 90 80 70 60 50 40 20 0 Stearic acid 1 1 1 1 1 1 1 1 1 Soot (N990) 80 80 80 80 80 80 80 80 80 Thiazole accelerator (MBTS75%) 1 1 1 1 1 1 1 1 1 Thiuram accelerator (TBzTD70%) 1 1 1 1 1 1 1 1 1 Sulfur (S80) 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 Zinc Oxide Red Seal (G01) 5 5 5 5 5 5 5 5 5 190 190 190 190 190 190 190 190 190 Hardness [ShA] 50 53 53 54 55 56 56 56 57 Density [g / cm 3 ] 1,22 1,22 1,22 1,22 1,22 1,22 1,22 1,22 1,22 Rebound resilience -30°C [%] 10 9 8 8 7 6 6 6 9 Rebound resilience -15°C [%] 3 4 4 4 5 6 6 9 20 Rebound resilience 23°C [%] 8 10 12 16 20 24 29 39 57 Rebound resilience 30°C [%] 10 12 14 18 22 25 30 41 57 Rebound resilience 50°C [%] 23 25 29 32 35 40 44 51 59 Hardness [ShA] -30°C 71 68 66 63 63 63 63 62 62 Hardness [ShA]-15°C 61 62 61 61 59 59 59 59 59 Hardness [ShA] 23°C 50 53 53 54 55 56 56 56 57 Hardness [ShA] 30°C 49 52 52 53 54 56 56 56 56 Hardness [ShA] 50°C 45 49 51 51 53 54 54 54 55 Change in hardness [ShA] between -15 °C and 30 °C 12 10 9 8 5 3 3 3 3 Example 2: Rubber compositions with different fillers

[0098] Rubber compositions with different filler contents were tested. The polymeric component consisted of 50 phr natural rubber and 50 phr bromobutyl rubber.

[0099] Barium sulfate and iron oxide were used as heavy fillers with a density of at least 4 g / cm³. The iron oxide used had a density of 5.2 g / cm³, and the barium sulfate used a density of 4.4 g / cm³. Both fillers are heavy and have a particle size d50 greater than 1,000 nm, with iron oxide having an average particle size d50 of 10,000 nm and barium sulfate having an average particle size d50 of 3,000 nm. These fillers have little influence on the elasticity of the crosslinked rubber composition.

[0100] Silica and carbon black were included as lightweight fillers with a density of less than 4 g / cm³, while inactive fillers were also used to minimize their impact on the elasticity of the crosslinked rubber composition. The Neuburg Silica used is supplied by Hoffmann Mineral GmbH and is a mixture of amorphous and cryptocrystalline silica and lamellar kaolinite with the CAS No. 1020665-14-8. Various organofunctional silanes and / or paraffins are used as adhesion promoters. Bis-[3-(triethoxysilyl)]-tetrasulfane, marketed by Evonik under the name Si 69, could also be used. The Aktisil PF216 used had a specific surface area of ​​9 m² / g, while the carbon black N550 used had a specific surface area of ​​42 m² / g.

[0101] The mixtures and test specimens were manufactured and tested as described above. In addition to the material properties mentioned above, the tensile strength and elongation at break were measured according to DIN 53504: 2017-03 using a standard S2 specimen, and the tear resistance was tested according to DIN ISO 34-1: 2016-09 using a strip specimen. The results are summarized in Table 2.

[0102] Table 2 shows that test compounds 20 and 21, which did not contain heavy fillers, failed to achieve sufficient density. These test compounds exhibited the highest stress value at 100% elongation and therefore poorer recovery behavior. Test compound 10 also produced a relatively low elongation at break.

[0103] Test mixtures 25, 26 and 28, which contained heavy fillers with more than 100 phr, had an increased density of over 1.65 g / cm 3< .

[0104] Test mixtures 22, 23, 24, and 27 met all criteria. It was observed that these mixtures caused the sound to decay more quickly. At the same time, the jump height and number of jumps were reduced.

[0105] The dynamic and mechanical properties of Test Mix 24 were further investigated using dynamic mechanical analysis (DMA). For this purpose, test specimens measuring 40 mm x 7 mm x 2 mm were cut from a rail pad produced with Test Mix 24, and the storage modulus (G' in Pa) and loss modulus (G" in Pa) were determined. A "soft sample 1" made of pure EPDM, representing known soft rail pads, was used for comparison. A "hard sample 2" made of pure EVA, representing a known hard rail pad, was also investigated. The test specimens were also cut from the respective rail pads. The size of the test specimen for the hard rail pad was 40 mm x 6 mm x 2 mm, and for the soft rail pad, 40 mm x 7 mm x 2 mm.The storage modulus represents the elastic component of a material and the proportion of energy that is released after deformation upon unloading. It is also a measure of a material's stiffness. The loss modulus represents the viscous component of a material and represents the energy that is converted into heat due to internal friction during deformation. From these values, the loss compliance (1 / Pa) was calculated, which is used to determine the stiffness-independent damping behavior of materials of different stiffnesses. The higher the loss compliance, the better the damping behavior of a material.

[0106] The temperature sweep was measured between -80°C and 50°C at a heating rate of 1°C / min, a frequency of 1 Hz, a deflection of 0.5°, and a preload of 0 N. The specimen was previously cooled to -80°C at 5°C / min. The frequency sweep was measured between 0.01 Hz and 10 Hz at -25°C, 23°C, and 50°C, with a deflection of 0.5° and a preload of 0.5 N (tensile). Before testing, the measuring chamber was temperature-controlled, the specimen was clamped, and brought up to temperature within 10 minutes. Temperature deviations of <0.05°C from the target temperature at the start of the test were accepted.

[0107] The test was carried out using an Anton Paar MCR501 rheometer, measuring system: SRF12-SN19150.

[0108] Fig. 3a, 3b , 4a and 4b show results of these measurements.

[0109] The test specimen made from test compound 24 exhibited a low storage modulus and high loss compliance, with low temperature dependence. Test compound 24 demonstrated particularly good damping properties across the entire relevant temperature range.

[0110] Compared to Sample 1 and Sample 2, the best damping was achieved with test compound 24. Table 2: Rubber compositions with different fillers Test mixture 20 21 22 23 24 25 26 27 28 Natural rubber 50 50 50 50 50 50 50 50 50 Bromobutyl rubber 50 50 50 50 50 50 50 50 50 Iron oxide (MagniF 10) 85 170 Barium sulfate 50 80 100 120 150 Soot N550 80 20 20 20 20 20 20 Neuburg Siliceous Earth, surface-treated 100 30 30 30 30 30 30 30 (Aktisil PF 216) Mineral oil plasticizers 5 5 5 6,5 7,5 8,5 10 2,5 2,5 Stearic acid 1 1 1 1 1 1 1 1 1 Thiazole accelerator (MBTS75%) 1 1 1 1 1 1 1 1 1 Thiuram accelerator (TBzTD70%) 1 1 1 1 1 1 1 1 1 Sulfur 80% 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 Zinc oxide red seal 5 5 5 5 5 5 5 5 5 Hardness [SHA] 56 59 57 58 60 61 64 58 63 Density [g / cm 3 ] 1,22 1,33 1,4 1,5 1,6 1,7 1,76 1,58 1,9 M100 [N / mm 2 ] 2,3 2,2 1,8 1,8 1,8 1,7 2,1 1,9 1,8 M300 [N / mm 2 ] 7,6 7,3 6,4 6 5,7 5,1 5,5 5,9 5 Tensile strength [N / mm 2 ] 8,1 8,5 8,9 7,7 7,7 6,5 6,3 7,3 5,6 Elongation at break [%] 340 370 412 379 403 380 340 377 342 Tear resistance [N / mm] 6,2 6,6 6,4 6,7 6,9 6,8 6,7 5,1 5,7 Rebound resilience -40°C[%] 6 5 6 6 6 6 7 6 6 Rebound resilience -30°C[%] 6 5 6 6 6 6 7 6 6 Rebound resilience -25°C[%] 5 5 5 5 5 5 6 5 5 Rebound resilience -15°C[%] 5,5 4,5 5 5 5 5 5 5 5 Rebound resilience -10°C[%] 6 5 6 6 6 5 5 6 5 Rebound resilience 0°C[%] 9 8 9 8 8 7 8 8 7 Rebound resilience 5°C[%] 14 12 12 12 11 12 12 12 12 Rebound resilience 23°C[%] 23 20 21 21 21 19 19 22 22 Rebound resilience 30°C[%] 25 27 28 27 26 25 25 26 25 Rebound resilience 50°C[%] 42 43 44 44 44 43 41 44 43 Hardness [ShA] -15°C 59 57 60 61 62 64 67 60 66 Hardness [ShA] 23°C 56 55 57 58 60 61 64 58 63 Hardness [ShA] 30°C 56 53 56 58 59 60 63 57 62 Hardness [ShA] 50°C 54 50 55 56 58 59 62 56 61 Change between -15 and 30°C 3 4 4 3 3 4 4 3 4 Example 3: Bromobutyl rubber and EPDM as polymeric component

[0111] In another series of tests, a blend of bromobutyl rubber with EPDM was tested. Keltan 6750, an EPDM with a polypropylene content of 51%, was used. Barium sulfate, also used in Example 2, was added as a filler with a density of at least 4 g / cm³. Carbon black N550 and Aktisil PF216 were used as fillers with a density of less than 4 g / cm³.

[0112] Tensile strength and elongation at break were measured as in Example 2 according to DIN 53504: 2017-03 using standard S2 bar. Tear resistance was tested using a strip specimen according to DIN ISO 34-1: 2016. The results are summarized in Table 3.

[0113] The criteria used for these test mixtures were also a density of 1.40 g / cm 3< to 1.65 g / cm 3<, a rebound resilience at 23 °C of maximum 30% and an increase in hardness between -15 °C and 30 °C of maximum 6 ShA.

[0114] The best results were obtained for a rubber compound with a polymer component consisting of 50 phr bromobutyl rubber and 50 phr EPDM. The low-temperature properties of this blend were barely noticeably worse than those of the blend of bromobutyl rubber and natural rubber down to -25 °C. The advantage of using EPDM is that it allows for long durability even without anti-aging and anti-ozone agents, simplifying formulation and production. Table 3: Test series of bromobutyl rubber with EPDM Test mixture 30 31 32 33 34 35 36 BIIR 100 60 50 40 30 20 0 EPDM (Keltan 6750) 0 40 50 60 70 80 100 Barium sulfate 100 100 100 100 100 100 100 Soot (N550) 20 20 20 20 20 20 20 Neuburg Siliceous Earth, surface-treated (Aktisil PF216) 30 30 30 30 30 30 30 Mineral oil plasticizers 2,5 2,5 2,5 2,5 2,5 2,5 2,5 Stearic acid 1 1 1 1 1 1 1 Thiazole accelerator (MBTS75%) 1,7 1,4 1,3 1,2 1,1 1 0,8 Sulfenamide accelerator) (CBS80%) 0,3 0,4 0,4 0,5 0,6 0,7 Thiuram accelerator (TBzTD70%) 0,6 0,8 0,9 1,1 1,2 1,5 Sulfur (S80%) 0,6 1,2 1,3 1,5 1,6 1,7 2 Zinc oxide red seal 5 5 Magnesium oxide (Elastomag170) 0,2 0,1 0,1 Hardness [ShA] 51 60 61 61 62 64 72 Density [g / cm 3 ] 1,62 1,6 1,59 1,58 1,57 1,57 1,55 Rebound resilience at 23° C [%] 10 22 25 28 33 37 55 Tensile strength [N / mm 2 ] 8 9,5 9,8 10,2 10,6 11 12,2 Elongation at break 564 481 468 444 429 401 387 M100 [N / mm 2 ] 1,3 1,6 1,7 1,8 2,2 2,4 2,7 M300 [N / mm 2 ] 3,8 5 5,6 6,4 7,5 8,1 9,1 M500 [N / mm 2 ] 7,1 Tear resistance [N / mm] 9,1 6,1 4,9 4,9 4,5 4,3 3,5 Hardness [ShA] -30°C 71 70 69 69 69 71 78 Hardness [ShA] -15°C 61 65 64 64 65 67 74 Hardness [ShA] 23°C 51 60 61 61 62 64 72 Hardness [ShA] 30°C 50 59 61 61 62 64 71 Hardness [ShA] 50°C 46 57 58 59 61 63 70 Change in hardness [ShA] between -15 °C and 30 °C 11 6 3 3 3 3 3 Example 4: Interlayers with different shapes

[0115] Fig. 1 a shows an example rail interlayer in plan view Fig. 1b shows a section along the axis A -A through the intermediate layer of Fig. 1 a Fig. 2 a shows another example of a rail interlayer in plan view Fig. 2 b shows a section along the axis AA through the intermediate layer of Fig. 2a

[0116] Fig. 1a shows an exemplary rail pad 1 made of a previously described exemplary cross-linked rubber compound with the basic shape for a UIC60 rail with a 150 mm rail base width. The rail pad 1 is plate-shaped and has a thickness d of 7 mm. The length I, which runs parallel to the rail, measures 160 mm, and the width b, perpendicular to the rail, measures 150 mm. The corners have a radius of 1.5 mm.

[0117] Instead of the rail intermediate layer1 shown, damping elements for other applications could also be produced from the cross-linked rubber mixture described above.

[0118] In the illustrated embodiment, the rail spacer 1 has recesses 2 arranged alternately on the top side 3 and the bottom side 4 of the rail spacer 1. This allows for expansion of the rail spacer 1, even in the fastening area, when subjected to load. In the illustrated embodiment, the recesses 2 run in a groove-like pattern over the entire length 1 of the rail spacer 1. The edges of the recesses each have a radius of 1 m.

[0119] Fig. 1 bshows that in the embodiment shown, the recesses 2 are 3 mm deep, so that the rail intermediate layer 1 has a thickness da of 4 mm in the region of the recesses 2. The shape of the recesses 2 is isosceles trapezoidal in cross-section, wherein they each have a width ba of 4 mm on the top side 3 and on the bottom side 4 of the rail intermediate layer 1 and are arranged so as to converge towards the interior of the rail intermediate layer 1 and have a width bi of 2 mm on their inside. The distance ao or au between two recesses 2 that are arranged on the same side is 22 mm, so that the center point of a recess 2 on the top side 3 is 22 mm from the center point of the adjacent recess 2 on the top side 3.In the embodiment shown, a distance aa of 11 mm is provided between a section through the center of a recess 2 on the upper side 3 and the center of a recess 2 on the lower side 4.

[0120] The Fig. 1 a and Fig. 1 b The rail intermediate layer 1 shown from test mixture 24 achieved a value of about 200 kN / mm in the spring stiffness measurement based on EN 13146 - 9 : 2011 - 12.

[0121] Fig. 2a shows an alternative rail pad 1. The rail pad 1 also has a length I of 160 mm. The central zone 5 of the longitudinal extension, which serves for fastening, has a smaller width B than the edge zones 6 of the longitudinal extension. In the illustrated embodiment, the central zone 5 has a length L of 114 mm, and the edge zones 6 are each 23 mm long. In the illustrated embodiment, the central zone 5 has a width B of 146 mm, and the edge zones 6 have a width B r of 160 mm. With these dimensions, the rail pad 1 can also be retrofitted into an existing track section.

[0122] The in Fig. 2 a The rail intermediate layer 1 shown also has recesses 2 which are formed over the entire longitudinal extent of the rail intermediate layer 1.

[0123] Fig. 2 b shows that the course, shape and distance of the recesses 2 already Fig. 1bdescribed properties. The recesses 2 thus form webs and delimit different areas from one another along the width B of the rail intermediate layer 1.

[0124] In the illustrated embodiment, the rail intermediate layer 1 has edge regions 8 with increased thickness D r , and the central region 9 also has a greater thickness D m than the connecting regions 7 arranged between the edge regions 8 and the central region 9, which have a thickness D v . In the illustrated embodiment, the edge regions 8 each have a width B r of 30 mm, the connecting regions 7 each have a width B v of 30 mm, and the central region 9 has a width B m of 40 mm.

[0125] In the illustrated embodiment, the thickness D r of the edge regions 8 and the thickness D m of the central region 9 are each 9 mm. The thickness D v of the connecting region is 7 mm in the illustrated embodiment. The thicknesses D r , D v , D m are each specified from the top side 3 to the bottom side 4 in an area without a recess 2. In the area of ​​the recesses 2, the thicknesses D r , D v , D m are thus each reduced.

[0126] Due to the areas 7, 8, 9, which have a different thickness D v , D r , D m, the spring stiffness can be particularly easily adapted to the required values, which can vary depending on the area of ​​application, for example light rail and heavy rail applications.

[0127] The increase in thickness can also be carried out only in sections, for example only in the edge zones 6, and not over the entire longitudinal extent of the rail intermediate layer 1. The shape of the recesses can also be adapted to the relevant specifications.

[0128] The spring rates of rail pads 1 with different shapes were investigated. For this purpose, the Fig. 2aThe thicknesses D r and D m of the rail pad 1 shown were changed. The rail pad 1 was made from test compound 24, which has a hardness of 60 ShA at 23 °C. The spring rate was determined using a universal testing machine in accordance with EN 13 146 - 9 : 2011 - 12. For this purpose, force distribution plates with a length of 210 mm and a width of 125 mm or 150 mm were used, depending on the type of rail pad being tested, since the load distribution plates must be exactly as wide as the rail pad. P400 abrasive cloth was also used on the top and bottom, with two setting cycles being carried out between 18 and 85 kN and the measurement being taken between 18 and 68 kN during the third cycle. It was therefore first loaded from 0 to 85 kN, then unloaded to 18 kN, loaded again to 85 kN and unloaded again to 18 kN.The test specimen was then loaded again to 85 kN, with the spring deflection measured between 18 and 68 kN to determine the spring rate. The feed rate was force-controlled at 120 + / - 10 kN / min. While the standard recommends four independent displacement sensors, the universal testing machine used measures the displacement via the crosshead travel. The crosshead is the moving part of the machine that exerts pressure on the specimens via the specimen holders.

[0129] The results for the different forms are summarized in Table 4. Table 4: Spring rates of rail pads with different shapes Attempt Shape of the rail pad Spring rate [kN / mm] Contour 1 Uniform thickness D of 7 mm 198 Contour 2 Edge areas with a thickness D r of 7.5 mm 175 Contour 3 Edge areas with a thickness D r of 8.0 mm 149 Contour 4 Edge areas with a thickness D r of 8.5 mm 144 Contour 5 Edge areas with a thickness D r of 9.0 mm 131 Contour 6 Edge areas with a thickness D r of 9.0 mm, central area with a thickness D m of 8.0 mm 123 Contour 7 Edge areas with a thickness D r of 9.0 mm, central area with a thickness D m of 9.0 mm 121 Contour 8 Edge areas with a thickness D r of 9.5 mm, central area with a thickness D m of 9.0 mm 102

[0130] In addition, the tests described above were conducted to assess sound reduction and mechanical damping. The rail pad shown demonstrated good sound absorption and rapid energy absorption upon impact with the steel ball.

[0131] Further testing was conducted using rail pads 1 with Contour 1 from test compound 24. For this purpose, the airborne noise emissions and the pass-by noise were investigated on a test track in which rail pads 1 were installed. The airborne noise emissions were measured according to EN ISO 3095:2013.

[0132] The tests were conducted on a straight line on three consecutive track sections approximately 200 m long, each with a similar superstructure except for the rail pads tested. The test rail pad was installed on track section 3. At the same time, a hard rail pad was tested as reference rail pad 1 on track section 1, and a soft rail pad was tested as reference rail pad 2 on track section 2.

[0133] Reference pad 1 had a spring stiffness of 700 kN / mm. Reference pad 2 had a spring stiffness of 100 kN / mm.

[0134] The first measurements were taken at the beginning of December. At that time, reference track pads 2 were also installed in track section 3. Subsequently, track section 3 was converted to test track pads. A second measurement was taken at the beginning of March under comparable ambient conditions to those in December. Since the average deviations in the pass-by levels between the first measurement in December and the second measurement in March were less than 0.5 dB, it can be assumed that the ambient conditions were comparable overall with regard to the vehicles, track, and weather.

[0135] A third measurement took place at the end of June during high summer temperatures.

[0136] The pass-by noise levels of the trains operating there were measured over a period of several hours. Among them was often a three-car low-floor commuter train of the RABe 525 "NINA 3T." A passenger train of the "EWIII" type with an Re 465 locomotive and six standard III coaches was also recorded. At least four pass-bys at the same speed were used for the average. Of the passing freight trains, two freight trains with a similar speed and a length of over 200 meters were selected for the calculation. The resulting measurement results were then averaged.

[0137] On track section 3, a significant noise reduction was observed due to the test intermediate layer compared to the reference intermediate layer 2, with the difference being 2.9 to 3.0 dB for passenger trains, 2.0 to 3.0 dB for local trains and 4.1 dB for freight trains.

[0138] A noise reduction was also measurable on track section 1 due to the test intermediate layer compared to the reference intermediate layer 1, with a difference of 1.8 dB for passenger trains, 2.2 dB for local trains and 1.6 dB for freight trains.

[0139] The results are summarized in Table 5: Table 5: Airborne noise emissions of various rail pads Section 3 Section 2 Section 1 Reference measurement Comparison intermediate layer 2 (soft) Reference intermediate layer 1 (hard) 7.5m 7.5m 7.5m Period Vehicles Number - Averaging LpAeq,Tp LpAeq,Tp LpAeq,Tp dB(A) dB(A) dB(A) 12_2019 passenger train 6 82.2 82.0 80.9 12_2019 Local train 4 79.3 79.5 79.2 Test measurement Test interlayer Comparison intermediate layer 2 (soft) Reference intermediate layer 1 (hard) 03_2020 passenger train 6 79.4 82.4 81.1 03_2020 Local train 4 77.3 80.3 79.5 06_2020 freight train 2 87.9 92.0 89.5 diff passenger train 2.9 -0.4 -0.2 diff Local train 2.0 -0.8 -0.3 Results Difference to the test intermediate layer passenger train 0.0 + 3.0 + 1.8 Difference to the test intermediate layer Local train 0.0 + 3.0 + 2.2 Difference to the test intermediate layer freight train 0,0 + 4.1 + 1.6

[0140] The rail pad 1 shown can thus achieve good noise reduction and at the same time cushion the mechanical vibrations, so that the sleeper and ballast or the track superstructure are protected.

Claims

1. Sulfur-cross-linkable rubber composition for a rail pad, wherein the polymeric component comprises a halogenated butyl rubber and at least one further rubber selected from the elastomers of the R or M groups, which contain at least one double bond, wherein the halogenated butyl rubber with 40 to 60 phr, in particular with 50 phr is contained, wherein at least one sulfur cross-linking agent iscontained, and wherein at least one heavy filler with a density of at least 4 g / cm3 is contained, wherein the total amount of heavy filler with a density of at least 4 g / cm3 is 50 to 100 phr, and wherein at least one light filler with a density of less than 4 g / cm3is contained, wherein the light fillers have a specific surface area (BET) of at most 50 m2 / g.

2. Sulfur-cross-linkable rubber composition according to claim 1, wherein the halogenated butyl rubber is bromobutyl rubber.

3. Sulfur-cross-linkable rubber composition according to claim 1 or 2, wherein the further rubber is selected from a group comprising natural rubber, synthetic polyisoprene or styrene-butadiene rubber, in particular with a styrene content of at most 23.5%, preferably with a styrene content of 15%.

4. Sulfur-cross-linkable rubber composition according to claim 1 or 2, wherein the further rubber is EPDM, in particular EPDM with a polyethylene content of 45 to 55%.

5. Sulfur-cross-linkable rubber composition according to any one of claims 1 to 4, wherein the polymeric component consists exclusively of the halogenated butyl rubber and the further rubber.

6. Sulfur-cross-linkable rubber composition according to claim 5, wherein the polymeric component consists exclusively of halogenated butyl rubber and natural rubber, or wherein the polymeric component consists exclusively of halogenated butyl rubber and synthetic polyisoprene, or wherein the polymeric component consists exclusively of halogenated butyl rubber and styrene-butadiene rubber with a styrene content of at most 23.5%, in particular a styrene content of 15%, or wherein the polymeric component consists exclusively of halogenated butyl rubber and EPDM with a polyethylene content of 45 to 55%.

7. Sulfur-cross-linkable rubber composition according to any one of claims 1 to 6, wherein inactive fillers are contained, wherein in particular it is provided that only inactive fillers are contained.

8. Sulfur-cross-linkable rubber composition according to any one of claims 1 to 7, wherein the heavy filler with a density of at least 4 g / cm3 has a specific surface area (BET) of at most 50 m2 / g, wherein it is provided in particular that all fillers have a specific surface area (BET) of at most 50 m2 / g.

9. Sulfur-cross-linkable rubber composition according to any one of claims 1 to 8, wherein barium sulfate and / or iron oxide and / or lithopone is contained as a heavy filler with a density of at least 4 g / cm3.

10. Sulfur-cross-linkable rubber composition according to any one of claims 1 to 9, wherein light fillers with a density of less than 4 g / cm3 are contained in a total amount of 20 to 60 phr.

11. Sulfur-cross-linkable rubber composition according to claim 10, wherein a carbon black, in particular carbon black N550 and / or N990, is contained as a light filler with a density of less than 4 g / cm3.

12. Sulfur-cross-linkable rubber composition according to any one of claims 10 or 11, wherein a silica derivative, in particular a surface-treated silica, is contained as a light filler, with a density of less than 4 g / cm3, wherein it is preferably provided that the silica-derivative has a specific surface area of at most 50 m2 / g.

13. Sulfur-cross-linkable rubber composition according to any one of claims 1 to 12, wherein plasticizer, in particular mineral oil plasticizer is contained in an amount of 0 to 10 phr, in particular 2.5 to 7.5 phr.

14. Sulfur-cross-linked rubber mixture according to any one of claims 1 to 13.

15. Damping element, in particular rail pad, made from a cross-linked rubber mixture according to claim 14, wherein it is preferably provided that the damping element has a density of 1.40 to 1.65 g / cm3 and a hardness of 50 to 65 ShA (at 23°C).

16. Rail pad according to claim 15, wherein the rail pad has at least two areas of different thicknesses, wherein it is provided in particular that the rail pad has on its top side and / or on its underside groove-like recesses extending parallel to the rail support, wherein the thickness of the rail pad is reduced in the region of the recess.

17. Rail pad according to any one of claims 15 or 16, wherein the rail pad has webs extending parallel to the rail support with a thickness which is increased in comparison to the remaining rail pad, wherein it is provided in particular that lateral edge regions and / or a central region is provided with an increased thickness.

18. Method for producing a cross-linked rubber composition according to claim 15 or a damping element, in particular a rail pad, according to any one of claims 15 to 17, wherein the vulcanization occurs at 150°C to 180°C, in particular at 170°C, wherein it is preferably provided that the production occurs in the compression method and the dwelling time in the vulcanization mold is 4 to 20 min, in particular 5 min, or wherein it is preferably provided that the production occurs in the injection molding method and the dwelling time in the vulcanization mold is 2 to 8 min.