How many inches should the preheat flames extend out of the mold risers?

In thermite welding, the preheating process is critical for ensuring that the materials being welded reach the necessary temperature for proper fusion and that the weld is of high quality. The correct distance for the flames to extend out of the mold risers is typically about six inches. This distance allows for adequate heat distribution while also ensuring that the material around the weld area is sufficiently warmed to prevent thermal shock and allow for a strong bond between the weld metal and the base material.

Maintaining this six-inch flame extension helps to create a suitable environment for the molten thermite to flow and fill the joint properly, which is essential for achieving the intended strength and integrity of the weld. Choosing a different distance could lead to insufficient heating or overheating, which can compromise the overall quality of the weld joint.