The mill was a 13' diameter by 29' ball mill with a damaged feed end head/trunnion casting. A structural crack had developed in the ligaments between the liner bolt holes in the inner most liner bolt circle near the transition radius to the bearing journal. This crack ran from liner bolt hole to liner bolt hole for approximately 180 degrees. Extensive FEA modeling of this and other mill heads have shown that the highest stress area is on the outside surface near the transition radius from the conical head to the trunnion diameter. The repair consisted of several stages, the first being the installation of Metalocks and Metalacing along the crack. These will stabilize and seal the crack. The next stage was an external reinforcing collar manufactured to fit onto the outside radius of the mill head to weld on reinforcing plates the outer surface. Lastly reinforcement plates were installed and welded to the collar. After the repair was completed “load cell” bolts were installed to replace broken socket head bolts. This was done to investigate repeated failed components in this area. It was discovered that the bolt shanks were not being uniformly tensioned when tightened to the desired torque. To correct this problem spherical washers and longer bolts were used accommodate the spot face on the collar.
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