SAG Mill - Complete Foundation Repair Service

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This work report highlights the importance of maintaining the mounting system of a grinding mill to prevent costly downtime and lost production. A poorly designed, constructed, or deteriorated foundation can significantly impact the performance of the mill and cause high vibration levels.

Alphatec Engineering carried out rehabilitation work on the mounting system of a pinion-bearing pedestal of an 8,5 m ø x 3,8 m semi-autogenous grinding mill. 

 

The Problem and Solution

 

The grinding mill in a mining operation was experiencing high vibrations due to a poorly designed and deteriorated foundation. This not only affected mill performance but also had the potential to render the mill out of action, costing millions of dollars in lost production. 

 

The solution involved removing the base frame, repairing the damaged concrete, replacing all anchor bolts and installing new ones, injecting Alphatec® 342 resin into the foundation, chock grouting new bearing pedestals with Alphatec® 170 and using Alphatec® 800 High-performance Epoxy Grout for grouting the baseplate and pinion base skid grouted. The work also involved measuring, adjusting, levelling, and aligning the components to ensure the proper functioning of the mill.




Features

Client
CupruMin SA Abrud
Final user
CupruMin Preparation Plant
Project
All Anchor Bolt Replacement, Foundation Repair, Resin Pressure Injection, Chock Grouting, Pinion Base Skid Grouting
Equipment
8,5x3,8 m SAG Mill 4 000 kW Electric Motor Pinion Gear Base Frame
Work period
April 2019
Location
Rosia Poieni, Romania

The Procedure

 

At Alphatec Engineering, our approach to foundation repair for machinery involves a thorough inspection and evaluation of the mounting system, which includes the concrete foundation, anchoring, and grout. We then identify the root causes of any problems, such as deterioration or misalignment, and employ precise repair procedures to restore the anchoring system. 

 

Inspection, Evaluation and Diagnosis 

 

The mill was installed in the 1970s and during the site investigation, and the motor and pinion shafts of the mill had a large angular misalignment, causing high vibrations in the machine. 

The drive foundation of the mill had been repaired previously using short anchor bolts replacing longer, originally installed embedded bolts. But according to GMRC, anchor bolts should be as long as possible. 

Deterioration of the mounting system, including the pinion baseframe and the pinion gear, had been severe, causing visible movement relative to the base frame. The designed anchor bolts for both the motor and pinion baseframe were heavy-duty but were only 1000 mm long, which is too short. Additionally, the tension applied to these bolts was low, leading to further problems, including broken bolts. Oil was soaking into the joint between the base and soleplates.

 

The Mounting System

 

The pinion bearing pedestal was mounted on top of the base frame, on steel chocks and was visibly moving relative to it. The foundation was substantial, with a height of 9,863 m and a total volume of around 577 m3. This gave an inertial mass of 1400 tonnes, which is adequate if properly consolidated. 

The pinion gear base frame was not grouted but instead sat on 20 mm thick steel plates embedded in the concrete. As a result, it was solely restrained by the anchor bolt tension, making it prone to sliding around the foundation top.

 

Repairs

 

The repair process involved 

  • Removing the base frame to access the anchor bolts
  • Drilling Injection holes at 8,5 m into the foundation
  • Chipping out damaged concrete
  • Replacing the anchor bolts with new ones wrapped with PE foam
  • Alphapads® were placed to take the weight of the pinion gear base frame

After this formwork was installed and sealed with ALPHATEC® 240 Epoxy putty. ALPHATEC® 342 injection resin was pumped under high pressure into the injection holes to fill any cold joints, separations, fissures, or discontinuities in the concrete. 

The components were then measured, adjusted, levelled, and aligned before the pinion gear base frame was grouted with ALPHATEC® 800 High-performance Epoxy Grout. The following day, formwork was made for the bearing pedestal, and ALPHATEC® 170 Chock grouting was mixed and poured to embed it. Finally, the Superbolt™ or multi-jack bolt tensioner (MJT) system was used to ensure proper clamping force.

 

Conclusion

 

The rehabilitation work carried out by Alphatec Engineering on the mounting system of a pinion-bearing pedestal of an 8,5 m ø x 3,8 m SAG mill highlights the importance of maintaining a well-designed and constructed foundation to prevent costly downtime and lost production. 

At Alphatec Engineering, our approach to foundation repair for machinery ensures optimal support for the machinery while minimising the risk of vibration-related damage or failure.