This section discusses malleable cast iron inserts, rubber pads, composite liners, and pilfer-proof elastic fastenings.
10.6.1 MCI Inserts
Malleable cast iron inserts are directly fixed onto concrete sleepers during manufacture. MCI inserts are manufactured according to the Indian Railway Standard (IRS) specification T-32-76. These inserts are of two types.
(a) Stem-type MCI insert for use in normal pre-tension concrete sleepers. This insert is provided in concrete sleepers being manufactured in all the concrete sleeper factories in India except the one located at Allahabad. The weight of the stem-type insert is about 1.6 kg per piece.
(b) Gate-type MCI insert for use in the post-tension concrete sleepers being manufactured at Allahabad. The approximate weight of the gate-type MCI insert is 1.7 kg per piece.
10.6.2 Rubber Pads
A rubber pad (Fig. 10.24) is an integral part of an elastic fastening. It is provided between the rails and the sleepers and has the following functions.
Track Fittings and Fastenings 187
(a) It absorbs shocks.
(b) It dampens and absorbs vibrations.
(c) It resists the lateral movements of the rails.
(d) It prevents the abrasion of the bottom surface of the rail, which would otherwise come in direct contact with the sleepers.
(e) It provides electrical insulation between the rails in an electrified area.
Indian Railways uses grooved rubber pads of 4.5 mm thickness made of special
quality rubber. The grooves aid in the uniform distribution of the load on sleepers and help to limit the lateral expansion of the rubber under the pressure of dynamic loads.
The RDSO has recently designed 6-mm-thick grooved rubber pads with horns (Drg. No. RDSO/T-37) for use on 60-kg rails (Fig. 10.25). It was noticed that normal 4.5-mm-thick rubber pads (IRST-37-1982) got crushed wihtin 6-7 years and, therefore, thicker, grooved rubber pads with a service life of 15-20 years were designed particularly for use on 60-kg UIC rails. These rubber pads are still under trial.
Fig. 10.25 6-mm-thick grooved rubber pad
10.6.3 Composite Liners
The Indian Railways mostly uses nylon insulating liners. These liners, however, get crushed under the toe load exerted by Pandrol clips. To eliminate such premature failure, the following two types of composite liners have been evolved by RDSO.
(a) Composite liner with malleable cast iron and nylon components (Drg. No. RDSO/T653/1)
(b) Composite liners with MS and nylon components (Drg. No. RDSO/T-1895) These liners have been developed on the basis of the designs of the liners adopted on British Railways, which have been reported to provide trouble-free service. Composite liners have been used on Indian Railways for the last few years and are serving the railways well.
Glass-filled nylon liners
The RDSO has developed glass-filled nylon liners (Fig. 10.26) (GFN-66) of 4 mm thickness particularly for track-circuited areas and sections subject to server corrosion. These glass-filled nylon liners are considered to be technically superior to other liners because they are single piece, have a longer life, and are free from corrosion. These liners are used extensively on Indian Railways particularly with the ERC clip assembly on 60-kg and 52-kg rails and PRC sleepers.
Fig. 10.26 Glass-filled nylon liner
It has been noticed that the GFN-66 liners tend to break, particularly in yards where these liners have been fitted in the ERC clip assembly on concrete sleepers. This happens due to the rusting of the rail surface and uneven seating. To avoid breakage of GFN-66 liners, it is necessary that proper precautions be taken during initial laying to ensure that the rail surface is free from rust, etc. and that the liners are fitted evenly on the 1 in 6 sloping surface of the rail flange.
A new design of GFN-66 liners with a thickness of 6 mm (Drg. No. DSO/T-2505 Alt II) has recently been developed and is expected to be sturdier and provide a better service life.
10.6.4 Pilfer-proof Elastic Fastenings for Concrete Sleepers
The present design of elastic fastenings (Pandrol clips) is such that they can be easily removed by a single stroke of a hammer. A new type of elastic rail clip, which is pilfer-proof, has been recently developed by RDSO. A pilfer-proof elastic fastening may be defined as an elastic fastening system which is easy to fit in the assembly but is difficult to remove without damaging the system.
The design of a pilfer-proof elastic rail fastening consists of clip of almost the same design as that of the normal elastic fastening as well as a new fitting known as the pilfer-proof circlip. The circlip is a standard mechanical component manufactured according to IS specifications and is generally used for restraining the axial movements of the components mounted on shafts.