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 fourwheeled 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

Gauge

Length of tongue rail

and type

1 in 8.5

1 in 12

1 in 12

1 in 16

1 in 20

straight

straight

curved

curved

curved

(mm)

(mm)

(mm)

(mm)

(mm)

BG (90 R)

4725

6400

7730

9750

1,1150

MG (75 R)

4116*

5485*

6700

7420

* These dimensions hold good for NG tracks also.

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