JP7741038B2 - Fastening springs used in rail fastening structures - Google Patents

Description

The present invention relates to a fastening spring used in a rail fastening structure for fastening rails to tie plates attached to track slabs or sleepers.

When fastening rails, such as railway rails, to track slabs or sleepers, a rail fastening structure is used in which the rails are held in place by metal components such as leaf springs. Various such rail fastening structures are known, including the rail fastening device described in Patent Document 1.

In other words, the rail fastening device described in Patent Document 1 fixes a tie plate to the roadbed side, and holds the rail by pressing from above with a leaf spring fixed to this tie plate. In this case, the end face of the leaf spring is positioned parallel to the longitudinal direction of the rail, and this end face presses directly against the upper surface of the rail bottom.

JP 2018-123480 A

The tie plates and leaf springs used in conventional rail fastening devices are made of metal, and to prevent corrosion and ensure electrical insulation, insulating plates are inserted and the leaf springs are surface-treated. Furthermore, there is a need to improve the electrical insulation performance mentioned above in order to prevent transportation disruptions caused by ground faults in the return current, which are caused by the electrical insulation between the rail and rail fastening device.

However, conventional rail fastening devices have the problem that because the tie plates and leaf springs are made of metal, short circuits can occur due to damage to the surface treatment of the leaf springs, such as thinning, breakage, or detachment of the leaf springs, making it difficult to completely prevent the occurrence of the above-mentioned transportation disruptions.

In addition, if the surface treatment of tie plates or leaf springs is damaged, the rails may break due to corrosion or electrolytic corrosion caused by those parts, so there is a demand to reduce the risk of such rail breakage to as close to zero as possible.

The present invention was made in consideration of the above problems, and aims to provide a fastening spring for use in rail fastening structures that uses a non-metallic material that has excellent electrical insulation and corrosion resistance and can reduce weight.

The fastening spring according to the present invention is a fastening spring for fastening a rail to a tie plate formed of a non-metallic material, the fastening spring being formed of a non-metallic material, having a through hole through which a bolt inserted into the tie plate can be inserted , the fastening spring being curved so as to be convex upward in the width direction, the through hole being formed as an elongated hole that is long in the width direction, and in a vertical cross section, the diameter of the through hole narrows vertically from top to bottom .

Furthermore, in the fastening spring according to the present invention, it is preferable that the non-metallic material be carbon fiber reinforced plastic.

Furthermore, in the fastening spring according to the present invention, it is preferable that the fastening spring has an arc-shaped end at the widthwise end.

Furthermore, in the fastening spring according to the present invention, it is preferable that the fastening spring is formed by winding a carbon fiber reinforced plastic sheet in the width direction, thereby laminating the carbon fiber reinforced plastic.

The above summary of the invention does not list all of the necessary features of the present invention, and subcombinations of these features may also constitute inventions.

The rail fastening structure of the present invention uses tie plates and fastening springs made of non-metallic materials, resulting in a rail fastening structure with excellent electrical insulation and corrosion resistance. Furthermore, because these components are made of non-metallic materials, it is possible to reduce weight.

1 is a perspective view showing an overview of a rail fastening structure according to an embodiment of the present invention; 1A and 1B are six-view diagrams and a cross-sectional diagram of a fastening spring used in a rail fastening structure according to an embodiment of the present invention. 1 is a diagram showing a rail fastening structure according to an embodiment of the present invention, viewed from the rail extension direction; 10 shows measurement results of fastening spring stress of the rail fastening structure according to the present embodiment. 6 is a graph showing the results of a temperature characteristic test of a fastening spring of the rail fastening structure according to the present embodiment. 6 is a graph showing a load-displacement curve during a tip spring characteristic test of a fastening spring of the rail fastening structure according to the present embodiment.

Below, preferred embodiments for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the inventions described in the claims, and not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.

Figure 1 is a perspective view showing an overview of a rail fastening structure according to an embodiment of the present invention, Figure 2 is a six-sided view and a cross-sectional view of a fastening spring used in the rail fastening structure according to an embodiment of the present invention, Figure 3 is a view of the rail fastening structure according to an embodiment of the present invention seen from the rail extension direction, Figure 4 is a measurement result of the fastening spring stress of the rail fastening structure according to this embodiment, Figure 5 is a graph showing the temperature characteristic test results of the fastening spring of the rail fastening structure according to this embodiment, and Figure 6 is a graph showing the load-displacement curve during a tip spring characteristic test of the fastening spring of the rail fastening structure according to this embodiment.

As shown in Figure 1, the rail fastening structure 1 according to this embodiment is attached to track slabs and sleepers positioned on the roadbed (not shown). The rail fastening structure 1 according to this embodiment includes a tie plate 10 made of glass fiber reinforced thermoplastic (FRTP), a non-metallic material, attached to the track slabs and sleepers; a rail 2 placed on the tie plate 10 via a rail height adjustment pad 3 and a track pad 4; a fastening spring 20 that holds the lower part of the rail 2 from above; and a fastening bolt 33, fastening nut 32, and insulating washer 31 that secure the fastening spring 20.

As shown in Figure 2, the fastening spring 20 is a member that is curved so that it is convex upward in the width direction, and is made of non-metallic materials such as glass fiber reinforced plastic (GFRP) or carbon fiber reinforced plastic (CFRP), for example, epoxy resin mixed with carbon. Carbon fiber reinforced plastic has a particularly high Young's modulus and lower electrical conductivity than metals, making it suitable for use in the rail fastening structure 1 according to this embodiment.

A through-hole 21 extending vertically is formed in the center of the fastening spring 20. The through-hole 21 is formed as an elongated hole that is long in the width direction and is formed so that its diameter decreases from top to bottom.

The widthwise ends of the fastening spring 20 have arc-shaped ends. The fastening spring 20 is constructed by winding a carbon fiber reinforced plastic sheet in the widthwise direction, with reinforcing fibers laminated on the cross section, and winding the carbon fiber reinforced plastic sheet in the widthwise direction makes it possible to form the arc-shaped ends. Furthermore, to improve electrical insulation and wear resistance, a glass fiber reinforced plastic layer may be formed on the outer layer of the carbon fiber reinforced plastic of the fastening spring 20.

As shown in Figure 3, the rail fastening structure 1 according to this embodiment is configured as follows: the tie plate 10 is fixed to the roadbed (not shown), and the rail 2 is held in place by the fastening spring 20 pressing from above with the fastening bolts 33 and fastening nuts 32. At this time, the arc end 22 on the base end of the fastening spring 20 is engaged with the engaging portion 12 so that it can rotate freely around the laying direction of the rail 2, allowing the arc end on the other end to be attached with adjustable height.

In addition, the through hole 21 of the fastening spring 20 is formed so that its diameter decreases from top to bottom, preventing interference between the fastening bolt 33 and the through hole 21 caused by rotation of the arc end on the other end as described above, and ensuring that the elastic force of the fastening spring 20 is applied to the rail 2.

In addition, because the tie plate 10 of the rail fastening structure 1 according to this embodiment is made of a non-metallic material, it is possible to eliminate the insulating plate that is interposed between the tie plate and the roadbed, which is used in conventional rail fastening structures.

Next, with reference to Figure 4, the performance test results of the rail fastening structure 1 according to this embodiment will be explained. The performance test was conducted under static and dynamic bidirectional load testing in accordance with the "Railway Structure Design Standards and Commentary: Track Structures" (hereinafter referred to as the "Track Standards"). The load testing assumed application to JIS 60 kg rails, conventional lines (fastening interval 625 mm), and tracks with a curve radius of 600 m or more, and the design action A load and B load were determined under a design axle load of 150 kN. Measurements were taken at positions I near one fixing bolt hole on the back of the tie plate, II near the other fixing bolt hole, and III and IV near one longitudinal end of the rail engagement groove on the top surface of the tie plate.

As shown in Figure 4, the maximum stress generated in the fastening spring 20 of the rail fastening structure 1 according to this embodiment during loading was 57.1 MPa, which was confirmed to be sufficiently small compared to the tensile strength of carbon fiber reinforced plastic, which is 638 MPa.

The dynamic loading test was carried out under the same conditions as the static loading test, with the target number of repetitions set at ^106. After ¹⁰⁶ loading cycles, no loosening of the fastening bolts or fastening nuts occurred, and no external abnormalities were found.

As such, the results of the static loading test and dynamic loading test confirmed that the rail fastening structure 1 according to this embodiment is safe in terms of fatigue fracture.

Next, an electrical insulation resistance test was conducted in accordance with the track standard on the rail fastening structure 1 according to this embodiment. The electrical insulation resistance test measured electrical insulation resistance values under three conditions: no spraying (dry condition), spraying of tap water (rainfall condition), and spraying of 0.1% salt water (polluted condition). The results of the electrical insulation resistance test showed that the electrical insulation resistance value exceeded the design reference value of 1.6 kΩ specified in the track standard in all conditions, and was more than 20 times that of conventional rail fastening structures, even in the polluted condition test condition. This confirmed that the rail fastening structure 1 according to this embodiment has sufficiently high electrical insulation properties compared to conventional rail fastening structures.

Next, we will explain the results of the performance confirmation test of the fastening spring 20. The performance confirmation test involved testing the temperature characteristics and spring characteristics of the fastening spring 20.

(Temperature characteristics)
Resin-based materials such as CFRP change their mechanical strength and other properties depending on the ambient temperature, softening at high temperatures and becoming brittle at low temperatures. On the other hand, the ambient temperature range in which the fastening spring 20 is used is expected to be between -20°C and 60°C, so the temperature characteristics of the tensile strength, tensile modulus, and flexural strength and flexural modulus, which are indicators of mechanical strength in this temperature range, were obtained.

As shown in Figure 5, the results of the temperature property test showed that the tensile strength of CFRP was 638 MPa at room temperature of 23°C, but tended to decrease at lower temperatures, with a minimum of 527 MPa at -20°C (a 17% reduction). Meanwhile, the flexural strength was 462 MPa at room temperature of 23°C, but tended to decrease at higher temperatures, with a minimum of 439 MPa at 60°C (a 5% reduction). Thus, it was confirmed that the mechanical strength of CFRP is relatively little affected by temperature dependency.

(spring characteristics)
The tip spring characteristic test for the fastening spring 20 was performed by fastening the rail with a jig simulating the seating surface shape of the tie plate 10 as shown in Figure 3 and applying a load to the rail at a test speed of 1 mm/min. The rail was positioned so that the seating surface was 8 mm, 18 mm, and 24 mm lower than the jig's fastening spring seating surface to evaluate the effect on tip spring characteristics of changes in the fastening spring's position that are expected when adjusting the rail height during installation. The bolts were manually tightened to avoid applying axial force. In this test, a load range of 4 kN to 12 kN was repeatedly applied, and the tip spring constant was calculated from the displacement and load in the third load range of 4 kN to 12 kN. The relationship between load and displacement during the spring characteristic test is shown in Figure 6. As shown in Figure 6, the load-displacement curve for the fastening spring 20 exhibited hysteresis in the load range of 0 kN to 12 kN.

The measurement results of the tip spring characteristic test are shown in Table 1 below. The tip spring constant (calculated range 4 to 8 kN) was 8.0 MN/m at a rail position of 8 mm and 7.6 MN/m at 24 mm. As such, it was confirmed that the curved fastening spring 20 is less affected by changes in posture and can provide a stable fastening force that is not dependent on rail height.

As such, the rail fastening structure 1 according to this embodiment has tie plates 10 and fastening springs 20 made of non-metallic materials, which improves the electrical insulation between the rail and the support body, thereby reducing the risk of transportation disruptions such as return current ground faults caused by this electrical insulation.

In addition, the rail fastening structure 1 according to this embodiment uses a tie plate 10 made of a non-metallic material, making it possible to reduce the weight compared to conventional tie plates.

In addition, the rail fastening structure according to the present embodiment has been described above in terms of a case in which the tie plate 10 is made of short glass fiber reinforced thermoplastic plastic and the fastening spring 20 is made of carbon fiber reinforced plastic, but the non-metallic materials are not limited to these, and various conventionally known non-metallic materials may also be used. It is clear from the claims that such modified or improved forms are also within the technical scope of the present invention.

1 Rail fastening structure, 2 Rail, 3 Height adjustment pad, 4 Track pad, 10 Tie plate, 20 Fastening spring, 21 Through hole, 22 Arc end, 31 Insulating washer, 32 Fastening nut, 33 Fastening bolt.

Claims (4)

A fastening spring for fastening a rail to a tie plate made of a non-metallic material,
The fastening spring is made of a non-metallic material;
the fastening spring has a through hole through which the bolt inserted in the tie plate can be inserted , and is curved so as to be convex upward along the width direction ,
The fastening spring is characterized in that the through hole is formed as a long hole that is long in the width direction and has a diameter that decreases vertically from top to bottom in a vertical cross section . The fastening spring according to claim 1 ,
The fastening spring is characterized in that the non-metallic material is carbon fiber reinforced plastic. The fastening spring according to claim 2 ,
The fastening spring is characterized in that the widthwise end portion has an arc-shaped end. The fastening spring according to claim 3 ,
The fastening spring is characterized in that the carbon fiber reinforced plastic is laminated by winding a carbon fiber reinforced plastic sheet in the width direction.