What Are the Signs My Mill Needs Repair or Relining?
In any mining or mineral processing plant, the grinding mill is the heart of the circuit. When it runs well, you hit your production targets, control your particle size and keep costs predictable. When it doesn’t, the entire plant feels it.
Waiting for a major breakdown before scheduling repairs or relining is a costly mistake. The good news: your mill usually “talks” to you long before something fails. In this blog, SAMCAW Field Services highlights the key warning signs that your mill needs repair or relining – so you can plan your shutdowns instead of reacting to emergencies.
Why Early Mill Maintenance Matters
Unplanned mill failures don’t just damage equipment – they impact:
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Production – lost tonnes per hour and missed targets
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Costs – emergency call-outs, rush parts, extended downtime
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Safety – higher risk of accidents when something fails catastrophically
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Asset life – running with worn liners or components accelerates wear on the shell, trunnions and drive system
By watching for early warning signs and acting in time, you can schedule repairs or relines during planned shutdowns, reduce risk and protect the long-term health of your mill.
1. Drop in Throughput or Changes in Grind Size
One of the first signs that something is wrong is often found in your production data.
Common indicators include:
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Lower throughput or reduced tonnes per hour with no obvious change in ore feed
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Coarser product size leaving the mill or increased recirculating load to the mill
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Inconsistent grind – fluctuating particle size even when feed and operating conditions seem stable
These symptoms may point to:
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Worn lifter bars and liners no longer lifting the charge effectively
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Incorrect liner profile after years of wear
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Slurry or discharge problems caused by worn grates or pulp lifters
If your mill has slowly “lost performance” over time, it’s often a sign that a reline or internal repair is overdue.
2. Visual Signs of Liner Wear and Damage
Whenever the mill is down and safe to enter, visual inspections are critical. Obvious visual signs that your mill needs relining include:
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Thinning liners with minimal remaining wear allowance
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Exposed shell plating where liner material has worn through
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Broken, loose or missing lifter bars
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Cracked or deformed liners – especially around bolt holes and high-impact zones
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Liner bolts backed off, loose or leaking
If you can see liner steel “knife-edged” or worn dangerously thin, you’re already pushing the limits. At this stage a planned reline should be prioritised before the next production cycle.
3. Unusual Noise, Vibration or Temperature Changes
Operators and maintenance teams often notice changes in the way a mill “sounds” or behaves long before a failure.
Red flags include:
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Louder operation or a change in mill noise – from a steady rumble to sharp knocking or metal-on-metal sounds
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Increased vibration in the mill, bearings, gearbox or foundation
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Hot bearings: track bearing temperatures in real time during operation.
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Grinding or scraping noises that suggest contact between the shell and rotating parts
These symptoms can indicate:
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Loose or failed liner bolts
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Misalignment or damage in trunnion bearings
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Shell distortion or movement
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Critical wear in journals, gears or pinions
Ignoring abnormal noise or vibration can turn a repair job into a serious structural or mechanical failure.
4. Leaks, Spillage and Process Upsets Around the Mill
The area around the mill often tells its own story. Warning signs include:
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Slurry leaks around the trunnion seals at the feed or discharge back ends.
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Uncontrolled spillage from launders, chutes or trommels
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Liner fragments or excessive scrap steel found in the trommel or downstream equipment
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Frequent blockages in the discharge end or transfer chutes
These issues typically point to:
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Worn rubber or steel components at the feed and discharge
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Damaged or misaligned trunnion liners and seals
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Incorrectly installed liners causing flow restrictions
While small leaks and spillage might seem manageable at first, they usually get worse – and can be a clear sign that internal components need attention.
5. More Frequent Unplanned Stoppages or Repairs
A rising number of “small” breakdowns is often a symptom of a bigger underlying problem. Examples:
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Regular unplanned stops for liner bolt tightening
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Repeated issues with trunnion seals or bearings
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Shorter and shorter intervals between mill-related breakdowns
When your maintenance history shows that the mill is becoming unreliable, it’s time to step back and assess liner condition, critical components and the overall repair strategy. A planned reline and structural assessment is often cheaper than constantly fighting fire.
6. How Often Should a Mill Be Relined?
There is no one-size-fits-all answer – relining intervals depend on:
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Ore hardness and abrasiveness
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Liner materials and design
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Operating hours and loading
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Mill speed and charge volume
However, best practice is to base relining decisions on measured condition, not just calendar time. That means:
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Regularly checking liner thickness and wear patterns
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Recording inspection data after every planned shutdown
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Tracking trends in performance, power draw and vibration
When inspections show that liners are near their minimum safe thickness – or performance has dropped noticeably – it’s time to schedule the next reline.
7. How SAMCAW Field Services Helps You Stay Ahead of Problems
SAMCAW Field Services specialises in grinding mill repairs and relining for mining operations across South Africa and beyond. Our team helps you spot and address mill issues early through:
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On-site mill inspections and condition assessments
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Detailed liner wear reports and recommendations
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Planned mill relines delivered safely and efficiently
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Structural and mechanical repairs on shells, trunnions and drive components
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Shutdown planning support to minimise downtime and keep production on track
Whether you run ball mills, SAG mills or other grinding equipment, our goal is the same: keep your mill running safely, reliably and at peak performance.
When to Call SAMCAW Field Services
If you are seeing any of the following, it’s time to talk to a specialist:
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Consistent drop in throughput or coarser grind
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Changes in mill noise, vibration or temperature
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Visible liner damage, thinning or loose bolts
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Rising leaks, spillage and unplanned stoppages
The earlier you act, the more options you have – and the less it costs.
Ready to assess the condition of your mill?
Contact SAMCAW Field Services to schedule a grinding mill inspection or to plan your next repair or relining shutdown. Our experienced team will help you turn warning signs into action, protect your assets and keep your plant performing at its best.
