Method for producing a sleeper for use in the railway track superstructure

Abstract

The invention relates to a method which enables sleepers to be produced for the railway track superstructure having optimised performance characteristics, in a reliable and cost-effective manner. The method according to the invention provides the following production steps: a) providing a mixture 10-60 % mass of which consists of a granulate of a plastic, which is deformable by applying heat, and the remainder of which consists of a sand having a bulk density of 1.4-2.0 g/cm.sup.3; b) heating the mixture to a temperature of 150-200 C.; c) pouring the mixture into a press mould reproducing the sleeper; d) pressing the mixture in the mould at a pressing pressure measured in the mixture of 1-5 MPa over a pressing period of up to 60 minutes; and e) removing the sleeper from the mould.

Claims

1. A method for producing a sleeper for use in the railway track superstructure, comprising: a) Mixing a granulate of a plastic, which is deformable by applying heat, with a sand having a bulk density of 1.4-2.0 g/cm.sup.3, wherein 10-60% mass of a resulting mixture consists of the granulate of a plastic and the remainder of the mixture consists of the sand, the plastic granulate comprises a polypropylene or a polyethylene or a mixture of a polypropylene and a polyethylene; b) heating the mixture to a temperature of 150-200 C.; c) pouring the mixture into a press mould reproducing the sleeper; d) pressing the mixture in the mould at a pressing pressure measured in the mixture of 1-5 MPa over a pressing period of up to 60 minutes and e) removing the sleeper from the mould.

2. The method according to claim 1, wherein the mass provided in production step a) contains 20-40% mass of the granulate of a plastic.

3. The method according to claim 1, wherein the bulk density of the sand provided in production step a) amounts to at least 1.6 g/cm.sup.3.

4. The method according to claim 1, wherein the pressing period is at least 5 minutes.

5. The method according to claim 1, wherein the temperature which the mixture is heated to in production step b) is at least 160 C.

6. The method according to claim 1, wherein the plastic granulate consists of a polypropylene granulate (PP granulate) or a polyethylene granulate (PE granulate).

7. The method according to claim 1, wherein the plastic granulate is mixed from a PP granulate and a PE granulate.

8. The method according to claim 7, wherein 40-60% mass of the plastic granulate consists of PP granulate and the remainder consists of PE granulate.

9. The method according to claim 1, wherein the melt flow index MFI/190/2.16 of the plastic or of the plastics of which the plastic granulate consists is less than 10 in each case.

10. The method according to claim 1, wherein the sand is heated to a temperature of 150-230 C. before it is mixed with the plastic granulate.

11. The method according to claim 1, wherein the temperature of the press mould is on average 100-140 C. when being filled with the plastic granulate-sand mixture.

12. The method according to claim 1, wherein the sand consists of grains having an average grain size of 0.6-6 mm.

13. The method according to claim 12, wherein the grains of the sand have a grain size of 0.8-1.6 mm.

14. The method according to claim 1, wherein the sand has a hardness of 5-8 determined according to Mohs.

15. The method according to claim 1, wherein the sand is crushed sand.

Description

(1) The invention is explained in more detail below by means of an exemplary embodiment.

(2) A crushed quartz sand was provided for producing a sleeper, formed in a conventional way in a rectangularly elongated manner, for a ballast bed superstructure. The bulk density of the sand was approximately 1.9 g/cm.sup.3 with a hardness of 7 determined according to Mohs and an average grain size of the sand grains of 1.0-1.6 mm.

(3) Equally, a plastic granulate was provided which consisted of a mixture of PP plastic granules and HDPE plastic granules. The PP plastic granules and the HDPE plastic granules were contained in a ratio of 1:1 in the mixture. The melt flow index of the PP plastic granulate determined at 190 C. and with a load of 2.16 kg was 8, whereas in the case of the HDPE plastic granulate it was 3. The plastic granulate was also present as granulate.

(4) Before being mixed with the plastic granulate the sand was heated to 220 C. by means of a heating cartridge immersed in it and heated by a heated oil. The temperature of the plastic granulate, on the other hand, corresponded to room temperature.

(5) The hot sand was then mixed with the plastic granulate. The metering of the sand and the plastic granulate was effected such that the obtained sand-plastic mixture consisted of 30% mass of plastic granulate (15% mass of PP plastic granulate and 15% mass of HDPE plastic granulate respectively) and the rest of sand. In the course of mixing, the plastic granulate was heated and the hot sand was correspondingly cooled, so that the obtained sand-plastic mixture had a pressing temperature of 170 C. At this temperature, the plastic granulate was already fully fused.

(6) The sand-plastic mixture brought to the correct temperature in this way was filled into a mould of a pressing tool, the temperature of which was held at at least 120 C.

(7) Then, the sand-plastic mixture was held in the mould for a period of, for example, 30 minutes under a pressure of 3.6 MPa. In this way, the mould was uniformly filled with the sand-plastic mixture, so that the details of the sleeper specified by the mould were reproduced perfectly and intensive bonding of the sand to the plastic surrounding it occurred.

(8) After the end of the moulding time, the mould was opened and the sleeper obtained was cooled down to a demoulding temperature of 60 C., at which the sleeper was finally removed from the mould.

(9) The sleeper obtained had such a high break resistance that it could reliably absorb the loads occurring in practical use in an enduring manner.

(10) At the same time, the pull-out resistances, i.e. the forces required to pull the anchoring of a rail fastening out of the sleeper, have proved to be considerably greater than the minimum value stipulated for this purpose in practice.

(11) Equally, in tests with conventional sleeper screws tightening torques were obtained which were considerably above 60 kN, for example 70 kN and more.