Toe Load Measurement in Railway

Toe Load:

Toe load in railway engineering is the continuous downward force exerted by an Elastic Rail Clip (ERC) onto the rail's foot, holding the rail securely to the sleeper (like concrete sleepers), ensuring track stability, rigidity, and resistance to rail creep (longitudinal movement). It's a critical measurement for track maintenance, as reduced toe load indicates worn components (clips, pads, liners) and a potentially loose fastening system.

Importance of Toe Load Measurement: 

Measuring toe load helps determine if the ERCs are effectively holding the rail. Loss of toe load can indicate wear on the rubber pad or liner, or issues with the ERC itself, potentially compromising the track's stability. Toe Load Measuring Devices (TLMDs): Devices like the Electronic Toe Load Measuring Device are used to measure toe load. These devices typically engage with the ERC's toe and measure the force required to lift it, providing a reading of the toe load. Toe load is typically measured using a Toe Load Measuring Device (TLMD), which can be either mechanical or electronic. 

 1. Mechanical toe load measuring device:

This device consists of a pre-calibrated helical spring, a pointer, a lever arrangement with a link hanger, and a steel tong for gripping the ERC. The device is placed with one leg on the rail head and the other two on the sleeper. The steel tong is engaged with the toe of the ERC. A rotating handle is turned to compress the spring and lift the toe of the ERC until a gap is created between the toe and the rail foot or liner. A feeler gauge is used to confirm this lifting point. The displacement indicated by the pointer on a graduated scale, multiplied by the spring constant, gives the toe load in kilograms. Testing Frequency: Toe load measurements are typically taken periodically, with a frequency determined by factors like traffic volume and corrosion potential. For example, in the Indian Railways, toe load measurements are often taken every four years or after passage of 200 GMT of traffic, whichever is earlier. In corrosion prone area, the initial testing of ERC is to be done after two years or passage of 100 GMT, whichever is earlier. If 20% or more of sample size records toe load below 600 kg, both frequency of inspection and sample size are to be doubled. Sample Size – Toe load of elastic rail clip should be measured on 1% of ERCs randomly on every 100 sleepers (all 4 ERCs to be measured on one sleeper). 

 Operation:

• Place the device with one leg resting on the rail top and the other two legs resting on the sleeper surface. 
• Adjust horizontally the base plate by means of the nut of levelling leg. 
• Turn the handle continuously till air gap is created between rail flange/top of liner and toe of clip. Introduce a filler gauge of 0.1 mm thickness in the air gap created between the toe of the clip and the rail flange / top surface of liner . Operation…..
• The handle is then turned anticlockwise so that the filler gauge comes under a normal pressure. Turn the handle again clockwise and simultaneously pull out the filler gauge. The filler gauge when moves indicates the lifting of toe of clip. 
• At this stage note down the reading on the graduated scale which when multiplied by the spring constant gives the toe load exerted by clip on the rail foot

2. Electronic Toe Load Measuring Device :

An Electronic Toe Load Measuring Device is a specialized instrument for railway maintenance, using electronic sensors (like load cells) to precisely measure the clamping force (toe load in kg) of Elastic Rail Clips (ERCs) directly in the field, providing digital readings for accurate track upkeep, ensuring rail stability, and replacing older mechanical methods for faster, more reliable data.

How it Works (General Principle):

• The device's tong engages the toe of the elastic rail clip.
• A load cell or hydraulic sensor measures the force applied or released as the clip is manipulated.
• This force is converted into an electronic signal and displayed as the toe load (in kg).