Once the welded parts have cooled, reinstall them into the welding screen frame and tighten the thumb screw.
This is an Instructable that shows how to do a quick repair to a broken welding screen foot. The foot is a basic "T" that just broke apart at the weld. This "T" gets inserted into the pipe of the screen frame and gets secured with a thumb screw, so to repair it I just quickly welded it back together.
Step 1: Sandblast the broken parts
Sandblast the area on the broken parts where you plan on putting the new weld.