Design
of Tongue Rails
A tongue rail may be either
straight or curved. Straight tongue rails have the advantage that they are
easily manufactured and can be used for right-hand as well as left-hand
turnouts. However, get jolted trains while negotiating with straight tongue
rails turnouts because of the abrupt change in the alignment. Straight tongue
rails are normally used for 1 in 8.5 and 1 in 12 turnouts on Indian Railways.
Curved tongue rails are shaped
according to the curvature of the turnout from the toe to the heel of the
switch. Curved tongue rails allow for smooth turning of trains, but can only be
used for the specific curvature for which they are designed. Curved switches
are normally used for 1 in 16 and 1 in 20 IRS (Indian Railway Standard)
turnouts on Indian Railways. Recently Indian Railways has also started laying 1
in 8.5 and 1 in 12 turnouts with curved switches on important lines.
Length of Tongue Rails
The length of a tongue rail from
heel to toe varies with the gauge and angle of the switch. The longer the
length of the tongue rail, the smoother the entry to the switch because of the
smaller angle the switch rail would make with the fixed heel divergence. The
longer length of the tongue rail, however, occupies too much layout space in
station yards where a number of turnouts have to be laid in limited space. The
length of the tongue rail should be more than the rigid wheel base of a
four-wheeled wagon to preclude the possibility of derailment in case the points
move from their position when a train is running on the switch. Table 14.3
gives the standard lengths of switches (tongue rails) for BG and MG tracks.
Table
14.3 Length of tongue
rail
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