Screw dowel for fastening rails

Abstract

Screw dowel for concreting into a railway sleeper or ballastless track and frictionally connecting to a sleeper screw, containing a threaded portion (14) with external thread flights (18) arranged on the outside of the screw dowel (10) and with internal thread flights (19) arranged on the inside of the screw dowel; and an upper subportion (16) without external thread that is situated close to the dowel opening (26) in the installed state; the screw dowel containing two constituent parts made of different materials, namely a basic body made of plastic and a cylindrical ring (20) made of a steel material and mounted with a form fit and/or force fit.

Description

FIELD OF THE INVENTION[0001]The invention relates to a screw anchor for the concrete attachment in a railroad tie or non-ballasted track according to the preamble of claim 1. Moreover, the invention relates to a railroad tie or non-ballasted track with at least one screw anchor according to the invention.PRIOR ART AND PROBLEM[0002]Screw anchors for the concrete attachment in a railroad tie are used in railway engineering for connecting rail to tie. In this arrangement, the rail attachment is connected to the tie by means of rail screws. The screw anchors are often made of plastic and can be cast into a concrete tie or a non-ballasted track during manufacture. One reason that the anchors are often made of plastic is because the rail screw must be electrically insulated from the tie and because plastic is a cheap flexible material which is simple to process and use.[0003]A disadvantage resulting from this is that the screw anchors made of plastic often have different mechanical and ph...

AI Technical Summary

Benefits of technology

[0013]A further preferred embodiment consists in the coefficient of thermal expansion of the steel material of the cylindrical ring being at least 10 times less than that of the plastic material of the base body, which it surrounds. This has the advantage that when there are temperature fluctuations the steel ring expands only a little relative to the plastic, and the ring can thus fulfill its function to a particular degree, namely to prevent the expansion of the plastic material even at high temperatures; the linear coefficient of thermal expansion of the material of the cylindrical ring is preferably less than 3·10−5 l/K.

[0014]A further preferred embodiment consists in the coefficient of thermal expansion of the steel material being approximately equivalent to that of the concrete of the tie. In this arrangement, it has an advantageous effect that concrete and steel are then very similar in terms of their coefficient of thermal expansion and thus no stresses occur between these two materials when there are temperature fluctuations.

[0015]Furthermore, a screw anchor is preferred in which the steel material is characterized by a modulus of elasticity high enough and a hardness great enough that the cylindrical ring attached to the anchor is not expanded or only negligibly expanded by the expanding plastic of the base body when heated within the temperature range which occurs during normal use. Due to this high strength of the steel, pressure stresses between anchor and surrounding concrete are thus prevented....

Problems solved by technology

A disadvantage resulting from this is that the screw anchors made of plastic often have different mechanical and physical properties from the surrounding material.

This can lead to disadvantages, particularly in concrete tie manufacture but also in later operation, as an anchor initially in form-fit contact with the concrete expands more than the surrounding concrete when the temperature rises so that pressure is exerted on the concrete.

Cracks and fissures can occur around the anchor or radia...

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