Classification of Crossing According to Manufacturing Process: Built up crossings, Weldable Crossing and Cast Manganese Steel Crossing (CMS Crossing) ~ MECHTECH GURU

Classification of Crossing According to Manufacturing Process: Built up crossings, Weldable Crossing and Cast Manganese Steel Crossing (CMS Crossing)

Classification of Crossing According to Manufacturing Process

Built up crossings

Crossings consist of point and splice rails, wing rails, and check rails suitably held together. The assembly is made out of rails normally used for track. The point and splice rails form the vee of the crossing and to avoid the junction of these components at the nose, which would obviously be a weakness, the splice rail is housed in a notch in the point rail. The point and the splice rails are held together by turned bolts where the point and splice rails diverge they are held in their relative position with the distance blocks and bolts. Wing rails which are provided on either side of the vee and rigidly held to the vee at the requisite distance, with distance blocks and bolts, which is 44 mm for BG and 41 mm for MG. Early damage to the nose of the crossing is prevented by planning up to 6 mm from the top of the rail at the nose and running out the cut in about 90 mm along the vee. The lowering of nose compels wing rail to support the wheels as the pass over the narrow section at the nose. Wings have flared ends. Check rails which are made from ordinary rail pieces are held to the running rail with distance blocks and bolts.

Built up crossings
Built up crossings

Weldable Crossing

Welded crossings are now introduced on IR recently.. These crossings are built up by welding suitably machined rail pieces and in some cases enclosing a piece of high strength wear resistant steel bar between the running rails. The latter type, manufacture according to the patented process of M/s. Henry Boot of U.K., is planned for trial on Indian Railways. These crossings with less of loose parts and made out of tougher steel, are expected to give much longer service life in track.

Cast Manganese Steel Crossing (CMS Crossing)

Built up or fabricated crossing has a large number of separate units to which attention must be paid during service. The vee formed by the point and splice rails is weakened by heavy machining of the head and foot. 

To afford better resistance to wear and reduce the cost of maintenance and frequent renewals, cast manganese steel solid crossings have been evolved. Other advantages of cast manganese steel solid crossings when compared to common fabricated crossings are as follows:

1. Fabricated crossings demand higher maintenance labour to keep the bolts and fastenings tight.

2. When the looseness develops in them, high rail stresses are set up.

3. They lack vertical stiffness.

4. The change of section points in the assembly of rails are stress raising features, which are compatible with the best engineering practice.

5. CMS crossings are particularly useful in continuous welding of rails through points and crossing as they do not need any special strengthening so necessary for fabricated crossings.

Technologies have been developed for butt welding of CMS crossing with the plain line rails by interposing a compatible transition piece of alloy steel. 

This technology patented by M/s. Voest- Alpine of Austria, is being obtained for Indian Railways for use on high speed heavy density routes. 

CMS crossings are costlier but they [more than] repay for their initial investment in their longer life.

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