What maximum distance is acceptable for the flow on the rail head before welding?

In thermite welding, ensuring proper joint alignment and avoiding defects in the weld is critical for the integrity of the welded rail. The maximum acceptable distance for the flow on the rail head before welding is designated to be 2 inches. This distance serves to define the limits within which the molten metal can flow and still achieve a strong bond without compromising the quality of the weld or affecting the fit-up of the rail.

Exceeding this distance could lead to issues such as misalignment of the rail sections or an uneven weld bead, which can introduce weak points and potentially lead to failures under load. Thus, maintaining this flow distance ensures optimal heat distribution and proper fusion of the rail materials during the welding process, which is essential for achieving the necessary structural integrity.