How far must the preheating be done on both sides of the weld gap?

The preheating process in thermite welding is crucial to ensure that the metal components to be joined achieve optimal temperatures before the introduction of the thermite reaction. Preheating serves several purposes: it helps to reduce thermal shock, minimizes the risk of cracking, and enhances the fluidity of the molten weld metal.

In this context, preheating must extend a significant distance on both sides of the weld gap, and a distance of about 3 feet is generally recommended. This distance ensures that the heat is effectively distributed across the materials being joined, allowing for proper fusion and a sound weld joint.

An extension of 3 feet preheating also accommodates variations in ambient conditions and helps to better align the thermal profiles of the metals involved. By adequately preheating, the welding process becomes more controlled, resulting in a stronger and more reliable weld.

Other distances mentioned might not provide sufficient preheating effects, leading to potential issues during welding, such as inadequate melting of the joint surface or increased susceptibility to defects. Thus, adhering to the 3-foot guideline promotes the integrity of the overall weld.