What is the minimum preheat time for rail greater than or equal to 129 lbs with ¼" head loss?

The minimum preheat time for rail that is greater than or equal to 129 lbs with a ¼" head loss is determined based on the requirements for maintaining the quality and integrity of the thermite weld. Preheating is a critical step in ensuring that the rail reaches the appropriate temperature to allow for effective welding.

A preheat time of 6 minutes is established as adequate to raise the temperature of the rail sufficiently, preventing the rapid cooling associated with the welding process. This preheating helps in minimizing the risk of cracking and ensures that the weld bonds properly to the rail.

In this context, the preheat time is specifically designed to account for the mass and the thermal characteristics of the rail, which is why the requirement is set at 6 minutes for rails of this weight range and specified head loss. It reflects a balance between efficient welding practices and the need to achieve a strong, durable joint.