What is not allowed when preparing ties for a thermite weld?

When preparing ties for a thermite weld, notching is not allowed because it can weaken the structural integrity of the ties. Notching involves creating a groove or indentation, which can disrupt the flow of molten metal during the weld process, potentially leading to incomplete fusion or a weak connection. Proper preparation of ties is essential for ensuring that the weld is strong and reliable.

In contrast, cutting, removal, and spacing may be part of the necessary preparations to ensure that the material is appropriately aligned and ready for the welding process. Cutting can be essential for adjusting the size of the ties, removal may be necessary for proper alignment or to eliminate any obstructive material, and spacing ensures there is an adequate gap for the thermite reaction to occur effectively. Therefore, avoiding notching is crucial in maintaining the overall strength and effectiveness of the thermite weld.