Agitator and Mixer Shaft Rebuilding

The challenge

A tank agitator shaft wears where it matters most. The seal area grooves under the packing or mechanical seal, the bearing journals lose their fit, and the wetted length pits where the process fluid attacks the steel. Once the seal area is worn the shaft no longer runs true, the seal leaks, and worn journals let the bearings sit loose and out of square. The plant is then looking at a new forging on a long lead time, with the mixer down and the vessel idle while it waits.

Our approach

We take the shaft into the shop and look at the worn zones before we touch it. We blast the worn seal area, the journals, and the pitted wetted length back to clean, profiled metal so the repair bonds. Then we rebuild the seal area and the journals cold with a machinable composite that we turn back to the original diameter on the lathe, so the shaft runs true through the seal and carries the bearings square. We dress the wetted length to a smooth profile and coat it against the process fluid, so the steel resists the chemistry that thinned it the first time. The shaft goes back the same shaft, repaired and protected, not replaced.

1. Assess the shaftWe inspect the seal area, the bearing journals, and the wetted length to map the wear and pitting and confirm the process fluid so the coating is keyed correctly.
2. Blast to clean metalWe grit-blast the worn zones to clean, profiled steel so both the composite and the coating bond to bare metal.
3. Rebuild cold with machinable compositeWe rebuild the seal area and the journals with a machinable composite, with no heat input to distort the shaft.
4. Machine and coatWe turn the rebuilt areas back to the original diameter on the lathe, then dress and coat the wetted length against the process fluid.
5. Return to serviceWe check the dimensions and the finish and turn the shaft back over so it runs true, carries the bearings square, and resists the chemistry that thinned it.