Rail Temperature and its Measurement
Rail temperature is the temperature
of the rail as recorded by a rail thermometer at the site. In Northern India,
the maximum rail temperature in summer is about 20 o C above the maximum ambient
temperature and the minimum rail temperature is about 2 o C to 3 o C below the
minimum ambient temperature.
on Indian Railways has been geographically divided into four rail temperature
zones as per the following criteria:
I 40 o C to 50 o C
II 51 o C to 60 o C
III 61 o C to 70 o C
IV 71 o C to 76 o C
The mean annual rail temperature
(tm) is the average of the maximum and minimum rail
temperatures during the year. The value of tm, therefore,
depends upon the range of temperature. The maximum and minimum rail
temperatures for one year should be recorded in order to determine the mean
annual rail temperature, although a record of five years is preferable.
Rail thermometers are used for
measuring the rail temperature. The different types of thermometers available
on Indian Railways are the following.
(b) Dial type
commonly used amongst these is the embedded-type thermometer (Fig. 17.4). This
type of thermometer consists of an ordinary thermometer inserted into a cavity
in a piece of rail head. The cavity is filled with mercury and sealed. The rail
piece containing the thermometer is exposed to the same conditions as the rails
in the track. The temperature recorded by the thermometer at that time is the
rail temperature. It takes about 25-30 min. to record the rail temperature.