Roller Grinding Mill Foundation Repair and Regrout

The Problem and Solution

The project involved addressing the problem of excessive vibration levels in the mills. The mills had been installed on a large built-up I-beam cruciform structure, which was then grouted into the foundation top with normal concrete.

The vibration had been caused by a poorly bonded concrete foundation that was unable to sufficiently transmit the high dynamic loading experienced by machines of this size. All this was compounded by the presence of relatively large quantities of oil to which concrete shows little resistance.

When vibration levels reached unacceptable levels, maintenance managers investigated possible solutions. One proposed solution was to completely rebuild the mill and gearbox foundation, which would take an estimated four months and entail significant expenses.

Alphatec proposed an alternative solution involving the injection of epoxy resin followed by regrouting with ALPHATEC® 800 high performance epoxy grout. The client accepted the proposal, and the Alphatec team of grouting specialists started the work on the first Raw Mill within two weeks.

The Procedure

The repair work carried out was identical in its nature and scope on both raw mills since the condition was the same.

It involved removing both drive motors and gearboxes.  All 16-mill-stand M56 grade 3.6 steel anchor bolts were checked for integrity with ultrasonic equipment by a specialist contractor. Their integrity was confirmed over the vertical straight length.

12 major injection holes were drilled at suitable locations around the foundation to a depth of 3,300mm, reaching  the middle of the lowest part of the foundation. Additional holes were drilled towards the base of the mill stand anchor bolts and also in the central area.

After inspecting the main foundation, it was found to be in good condition. The extracted cores showed that the concrete had sound crushed aggregate and a dense structure. 

However, cracks were discovered in the baseplate and support structure which were subsequently re-welded by the client. 

To address all of these issues, ALPHATEC® 800 epoxy grout was mixed and poured to the original foundation level. Before grouting, all metal surfaces that would come into contact with the grout material were meticulously ground and sanded down to ensure optimum adhesion. The entire repair work was completed within 10 days. And the subsequent vibration readings that were taken showed a reduction of approximately 50% in vibration levels, which brought them back within acceptable limits. 

In the case of the second Mill, the inner part of the baseplate was intentionally set to a level 5-10 mm below the baseplate level and then topped up by ALPHATEC® 170, a specially formulated two-component self-levelling chock grout. 

Conclusion

The success of the repair work, along with the high level of professionalism demonstrated by Alphatec personnel, led Cementir to request Alphatec to carry out the same work on the second Mill. The repair work was successful, resulting in another large reduction in vibration levels. Both mills are now operating on firm foundations, ensuring their operational continuity for many years to come.