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monitoring and corrective adjustments of critical flange bolts

mill bolt monitoring

Broken Bolts - Flanges

Broken flange bolts can be more than just a costly production-interruption nuisance; Long before loose bolts fail in fatigue, slight flange separation in wet mills can cause erosion as slurry begins to wash out the joint. This compromises flange integrity in the affected area which may lead to repeated failure.


Loose Bolts - Girth Gear

Improperly tightened Girth Gear-to-Head-to-Shell fasteners could result in minor flange slippage and run-out changes which can impact gear tooth integrity.


OEM's Solution

Major mill OEMs recognise that accurate flange fastener preload is paramount to joint integrity. This is why they mandate that the torquing of their mill flanges must be controlled by elongation monitoring during initial assembly. Performed by trained and qualified Technicians supporting the local torquing crew, this important procedure satisfies the OEM's warranty requirements as it ensures absolute bolt clamp load at the time of construction.


Gradual Loss of Clamp Load

Mill bolts operate in a highly dynamic environment. Bolt load loss and load migration are inevitable under such conditions. In the early years of a mill's life it's common to find up to 2-3 % of the total fastener population requiring annual re-tightening to return them to within the necessary tolerance. Regular scheduled monitoring and adjustment where necessary ensures that problems can be identified and corrected before they manifest into much more serious issues. Since the equipment used to measure fastener elongation is ultrasonic-based, skilled Technicians can also usually detect detective fasteners even when their clamp load is within tolerance.


Regular Monitoring and Corrections

With only 2 of our experienced Technicians working with a small crew of the client's mechanics, we can usually check and tune all existing mill fasteners on a typical large 3-can mill with segmented shells and heads within a single shift. The process requires extra time on mills being relined since the reline crew drives the inching/creeping frequency.


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