Preheat flames approximately __________ inches out of the mold risers.

The correct response indicates that the preheat flames should extend approximately 6 inches out of the mold risers. This distance is critical in thermite welding as it ensures that the surrounding area of the mold is adequately heated. Preheating helps prevent thermal shock to the mold and the material being welded, which can lead to cracking or other structural issues.

Maintaining the correct distance of the preheat flames helps in achieving an optimal temperature that facilitates effective fusion during the welding process. The preheat serves to raise the temperature of both the mold and the metal, encouraging a smoother weld and a better bond between the materials.

Additionally, ensuring that the flames are positioned at this specific distance provides a balance between enough heat to achieve the desired preheating and avoiding excessive heat that could damage the mold or distort the geometry of the weld. This technique is vital for maintaining both the quality of the weld and the integrity of the mold used in the thermite welding process.