SHEATH FOR FIXING RAILWAY RAILS

Abstract

Sheath for fixing railway rails, with a substantially tubular sheath body comprising a crown section, an upper cylindrical shaft section, a helical section and a lower cylindrical shaft section, the helical section comprising a truncated conical outer projection, configured as an external thread that is adapted for screwing / unscrewing the sheath into a solid ground, and an inner recess, configured as an internal thread that is adapted for screwing / unscrewing a lag screw into the sheath, wherein a base surface of the outer projection of the helical section forms an angle with respect to a vertical line that is parallel to the longitudinal axis of the sheath body, wherein a value of the angle formed between the base surface of the outer projection and the vertical line increases progressively helically in the direction of screwing the sheath into the solid ground.

Description

SHEATH FOR FIXING RAILWAY RAILS TECHNICAL FIELD OF THE INVENTION The present invention relates to a sheath or wedge, of the type used in securing railway rails on a solid surface or ground, such as a sleeper or track on a concrete slab. BACKGROUND OF THE INVENTION Currently, railway rail fixing systems, for both ballasted track and slab track, comprise different elements where each of them has its particular function in ensuring the fixing and alignment of the rail, with the singularity that said fixing must absorb and transmit the vibrations and stresses that occur when the rolling stock, that is, the railway transport means, passes to the sleeper or the slab track. One of these elements are the well-known plastic sleeves or plugs used as a transition between two other elements of the railway rail fixing system, namely the lag screw and the solid ground to which the railway rail is fixed, where the material of each of them, steel and normally concrete respectively, have very different characteristics and stresses. In the calculations of these railway rail fixing systems, the transmission of stresses from the rolling stock to the different component elements involved in the fixing is usually taken into account, relegating the sheath to a secondary position as a component of said fixing without paying much attention to its interaction with the concrete in which it is installed, being a component of plastic material that has very different characteristics from those of the materials of the elements with which it must coexist, and especially the dimensional variations that the sheath suffers due to the climatic variations that it must also face during its useful life. For example, document ES 2196099 shows a plastic threaded sleeve or plug used to fix a rail to a concrete beam. This type of plug has the disadvantage of having a very thin wall, which means it transmits vibrations directly from the steel of the lag screw to the solid surface of the beam. Furthermore, the plug itself would eventually break under stress due to its inherent weakness. Additionally, because of the low Young's modulus of elasticity of the sleeve material, excessive deformation of its outer surface causes vertical displacement of the lag screw, or even its accidental removal. On the other hand, a thick-walled sheath with a high modulus of elasticity transmits considerable stress to the solid ground simply due to weathering and differential deformation between the sheath and the solid ground where it is embedded. It should be noted that the coefficient of thermal expansion of thermoplastics is approximately 10 times greater than the coefficient of thermal expansion of concrete, as considered in document ES 2571941. Similarly, a high Young's modulus in the sheath material causes the sheath's internal threads to not adapt to variations in the lag screw due to the thread tolerances between the screw and the sheath. This can lead to the sheath's internal threads breaking before the lag screw reaches its breaking point. Furthermore, it causes the sheath to transmit vibrations to the solid ground without any attenuation. Furthermore, accidental actions exceeding the operating conditions of the fastening system can lead to the breakage of component elements of the fastening system, including the sheath, for example, due to excessive tightening torques. Therefore, methods for replacing the sheath are commonly devised when necessary, for example, as shown in document ES 2621388, which addresses the replacement of the sheath on the railway track when it is damaged or requires replacement. This is essential to avoid having to undertake much more costly actions in terms of time and money. Therefore, it is necessary to design, in a simple and economical way, an alternative sheath solution for fixing railway rails that facilitates their replacement or substitution when required. DESCRIPTION OF THE INVENTION The present invention is set forth and characterized in the independent claim, while the dependent claims describe other features thereof. The object of the invention is a sheath for fixing railway rails, which is adapted to hold a lag screw for fixing a rail to a solid surface, such as a sleeper or track on a concrete slab. The sheath includes a substantially tubular sheath body which, in the direction of screwing of the sheath into the solid surface, comprises a crown section, an upper cylindrical shaft section, a helical section, and a lower cylindrical shaft section. For its part, the helical section comprises a truncated conical outer projection, configured as an external thread that is adapted to screw / unscrew the sheath into the solid ground, and an inner recess, configured as an internal thread that is adapted to screw / unscrew the lag screw into the sheath. Additionally, a base surface of the outer projection of the helical section forms an angle with respect to a vertical line parallel to a longitudinal axis of the sheath body. The value of this angle, formed between the base surface of the outer projection and the vertical line, increases progressively along the helical direction of the coil, preferably along the entire length of the helical section. For example, from a minimum angle of approximately 90° to 95°, corresponding to the beginning of the helical section following the upper cylindrical shank section, to a maximum angle of approximately 130° to 145°, corresponding to the end of the helical section before the lower cylindrical shank section. In any case, the ratio between the minimum and maximum angle values ​​is preferably between 0.1 and 0.67. This allows for easier screwing and unscrewing of the duct in solid ground, whether it's a sleeper or a track on a concrete slab. As is known, at greater depths, the transmission of forces becomes more radial, and thanks to the specific configuration of the external protrusion, which acts as an external thread on the helical section, this radial force transmission is more easily overcome, facilitating both screwing and unscrewing of the duct in solid ground. Similarly, when using the sheath, that is, when it is screwed to the solid ground as part of the railway rail fixing system, the particular configuration given to the outer projection in the form of an external thread of its helical section also allows reducing the concentration in the transmission of loads to the concrete, thus decreasing the possibility of the appearance of cracks or fissures in the concrete produced by said loads. BRIEF DESCRIPTION OF THE FIGURES This descriptive report is complemented by a set of figures, illustrative of the preferred example, and never limiting the invention. Figure 1 represents a front view of the sheath for fixing railway rails. Figure 2 represents an enlarged detail of Figure 1, showing the crown and upper cylindrical shaft sections of the sheath body. Figure 3 represents a front cross-section view of the sheath in Figure 1 rotated 90° about its longitudinal axis, adopting a horizontal arrangement. Figure 4 represents an enlarged cross-section detail of Figure 3, showing the crown and upper cylindrical shaft sections of the sheath body. Figure 5 represents an enlarged cross-section detail of Figure 3, showing part of the helical section and the lower cylindrical shaft section of the sheath body. Figure 6 represents a front view of the sheath in Figure 1, which schematically shows the behavior of load transmission to the concrete along its helical section. DETAILED EXPLANATION OF THE INVENTION The present invention is a sheath for fixing railway rails, of the type adapted to contain a lag screw for fixing a rail to a solid ground, such as a sleeper or track on a concrete slab. As shown in Figures 1 and 3, the sheath includes a substantially tubular sheath body (1), preferably with a total length between 25 and 35 mm less than the length of the lag screw (not shown in the figures) to be installed in the sheath for fixing to the solid ground (not shown in the figures). Said sheath body (1) is preferably made of a thermoplastic material, for example, and not limited to polyoxymethylene (POM), polyamide (PA), polyvinyl chloride (PVC), polybutylene terephthalate (PBT), polyetheretherketone (PEEK), polyetheretherketone (PEKK), and polypropylene (PP). In any case, with a modulus of elasticity of between approximately 3,000 MPa and approximately 5,000 MPa, under temperature conditions of between approximately 20°C and approximately 25°C, and humidity less than 0.2%. Thus, using the sleeve prevents the formation of fissures or cracks in the concrete of the solid floor due to climatic variations, and increases the lifespan of the optimal tightening torque of the lag screw. Furthermore, in the event of failure of the fastener, damage to the concrete is avoided by creating a ductile fracture that usually causes the lag screw to break before the sleeve. Where, in a coiling direction (e) of the sheath in the solid ground, the sheath body (1) comprises a crown section (1.1), followed by an upper cylindrical shaft section (1.2), followed by a helical section (1.3) and, finally, followed by a lower cylindrical shaft section (1.4) as a sheath tip. It is preferred that the crown section (1.1) be adapted to accommodate a mounting tool (not shown in the figures) for attaching the sheath to the solid ground. As shown in Figure 4, the crown section (1.1) could comprise an inner wall (1.11) adapted to fit snugly into the mounting tool. For example, this inner wall (1.11) could be shaped like a triangular ring. Additionally, as shown in Figure 2, the crown section (1.1) of the sheath body (1) may comprise a truncated conical outer wall (1.12), with a first outer diameter (D1) that decreases in the threading direction (e). For its part, as shown in figure 5, the helical section (1.3) could also have a truncated conical outer shape with a second outer diameter (D2) that decreases in the direction of twisting (e). Preferably, the first outer diameter (D1) of the truncated conical outer wall (1.12) of the crown section (1.1) is larger than the second outer diameter (D2) of the truncated conical outer shape of the helical section (1.3). This facilitates the extraction of the sheath from the solid ground. On the other hand, as shown in Figure 1, the helical section (1.3) of the sheath body (1) comprises a truncated conical external projection (1.31), configured as an external thread (1.311) adapted for screwing / unscrewing the sheath into the solid ground. Likewise, as shown in Figure 3, the helical section (1.3) also comprises an internal recess (1.32), configured as an internal thread (1.321) adapted for screwing / unscrewing the lag screw into the sheath. Preferably, the external thread (1.311) and the internal thread (1.321) of the helical section (1.3) share the same thread pitch (P), which corresponds to the thread pitch of the lag screw. Additionally, it is preferred that the internal thread (1.321) of the helical section (1.3) share the same thread type as the lag screw, for example, selected from the group consisting of triangular thread, round thread and trapezoidal thread; or any other type of thread used in lag screws. On the other hand, as shown in Figure 1, the outer projection (1.31) of the helical section (1.3) is formed by a base surface (1.312) and a side wall (1.313). The base surface (1.312) forms an angle with respect to a vertical reference line that is parallel to a longitudinal axis (L) of the sheath body (1). Where, a value of the angle (Ο1, Ο2) formed between the base surface (1.312) of the outer projection (1.31) and the vertical line increases progressively helically in the winding direction (e). Preferably, the ratio between a minimum angle value (β1) and a maximum angle value (β2) is between 0.1 and 0.67. The minimum angle value (β1) corresponds to the beginning of the helical section (1.3) following the upper cylindrical cane section (1.2), and the maximum angle value (β2) corresponds to the end of the helical section (1.3) before the lower cylindrical cane section (1.4). For example, the minimum angle value (β1) is between approximately 90° and approximately 95°, and the maximum angle value (β2) is between approximately 130° and approximately 145°. In any case, thanks to the particular configuration given to the outer projection (1.31) as an external thread (1.311) of the helical section (1.3), both the threading and unscrewing of the sheath in the solid ground is facilitated and, in addition, as shown in figure 6, in use of the sheath, the concentration in the transmission of loads to the concrete is also reduced, thus decreasing the possibility of the appearance of cracks or fissures in the concrete produced by said loads. Additionally, as shown in Figure 5, it is preferred that the helical section (1.3) comprise an upper rupture zone thickness (S1) substantially equal to a lower rupture zone thickness (S2). In any case, a minimum thickness of said upper rupture zone (S1) and of said lower rupture zone (S2) is between approximately 3 mm and approximately 3.5 mm. As shown in Figure 2, the upper cylindrical shaft section (1.2) may include, as anti-rotation means, at least one external rib (1.21), preferably at least two, arranged parallel to the longitudinal axis (L) of the sheath body (1). Preferably, the external rib (1.21) projects from the outer surface of the upper cylindrical shaft section (1.2) by at least 1.5 mm. Where, a first lateral wall (1.211) of the outer rib (1.21), which is positioned towards the direction of screwing of the sheath into the solid ground, is arranged at an angle with respect to a second straight lateral wall (1.212) of said outer rib (1.21), the latter being positioned towards the direction of unscrewing of the sheath. Thus, in replacement operations, for example, due to breakage of the original sheath, the new sheath that replaces it can screw into the solid ground to the position of the original sheath, maintaining its anti-rotation function. Likewise, as shown in Figures 3 and 4, it is preferred that the inner cylindrical surface (1.22) of the upper cylindrical shaft section (1.2) be smooth, i.e., without including internal protrusions, so that the upper cylindrical shaft section (1.2) is adapted to facilitate the insertion of the lag screw into the sheath body (1). For its part, as shown in figure 5, it is preferred that the lower cylindrical cane section (1.4) be formed by a hollow cylindrical wall, so that any water that may infiltrate into the inside of the sheath body (1) can be evacuated to the outside.

Claims

1. A sheath for fixing railway rails, adapted to contain a lag screw for fixing a rail to a solid surface such as a sleeper or track on a concrete slab, with a substantially tubular sheath body (1) which, in a screwing direction (e) of the sheath into the solid surface, comprises a crown section (1.1), an upper cylindrical shaft section (1.2), a helical section (1.3), and a lower cylindrical shaft section (1.4), wherein the helical section (1.3) comprises: - a frustoconical external projection (1.31), configured as an external thread (1.311) adapted for screwing / unscrewing the sheath into the solid surface, and - an internal recess (1.32), configured as an internal thread (1.321) adapted for screwing / unscrewing the lag screw into the sheath, wherein, a base surface (1.312) of the outer projection (1.31) of the helical section (1.3) forms an angle with respect to a vertical line parallel to a longitudinal axis (L) of the sheath body (1), characterized in that a value of the angle (Ο1, Ο2) formed between the base surface (1.312) of the outer projection (1.31) and the vertical line increases progressively helically in the winding direction (e).

2. Sheath according to claim 1, wherein the ratio between a minimum value of the angle (Ο1) and a maximum value of the angle (Ο2) is between 0.1 and 0.

67.

3. Sheath according to claim 2, wherein the minimum value of the angle (Ο1) is between approximately 90° and approximately 95°.

4. Sheath according to claim 2, wherein the maximum value of the angle (Ο2) is between approximately 130° and approximately 145°. 5.- Sheath according to claim 1, wherein the sheath body (1) is made of a thermoplastic material with a modulus of elasticity of between approximately 3,000 MPa and approximately 5.000 MPa, under temperature conditions between approximately 20°C and approximately 25°C, and humidity less than 0.2%.

6. Sheath according to claim 1, wherein the external thread (1.311) and the internal thread (1.321) of the helical section (1.3) share the same thread pitch (P) corresponding to a thread pitch of the lag screw.

7. Sheath according to claim 1, wherein the internal thread (1.321) of the helical section (1.3) shares the same thread type as the lag screw, selected from the group consisting of triangular thread, round thread, and trapezoidal thread.

8. Sheath according to claim 1, wherein the crown section (1.1) is adapted to accommodate a tool for mounting the sheath to the solid ground.

9. Sheath according to claim 8, wherein the crown section (1.1) comprises an inner wall (1.11) adapted to fit snugly into the mounting tool.

10. Sheath according to claim 9, wherein the inner wall (1.11) is shaped like a triangular ring. 11.- Sheath according to claim 1, wherein the crown section (1.1) comprises a truncated conical outer wall (1.12) with a first outer diameter (D1) that decreases in the threading direction (e). 12.- Sheath according to claim 1, wherein the helical section (1.3) has a truncated conical outer shape with a second outer diameter (D2) that decreases in the threading direction (e). 13.- Sheath according to claims 11 and 12, wherein the first outer diameter (D1) of the outer wall (1.12) of the crown section (1.1) is larger than the second outer diameter (D2) of the helical section (1.3). 14.- Sheath according to claim 1, wherein the upper cylindrical shaft section (1.2) comprises at least one outer rib (1.21) arranged parallel to the longitudinal axis (L) of the sheath body (1), wherein, a first side wall (1.211) of the outer rib (1.21) is arranged in an inclined manner with respect to a second straight side wall (1.212) of the outer rib (1.21). 15.- Sheath according to claim 1, wherein the helical section (1.3) comprises an upper break zone thickness (S1) substantially equal to a lower break zone thickness (S2), wherein a minimum thickness of said upper break zone (S1) and of said lower break zone (S2) is between approximately 3 mm and approximately 3.5 mm.

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