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The Reline That Was Six Weeks Late

A concentrator scheduled a SAG mill reline against a calendar date that had been used for four years. The liners came out with the shell exposed in two places, and the mill had been running with falling throughput for most of the previous quarter. Nobody had measured anything; the date had simply been copied from the previous year, and by the time the failure was visible the damage had reached the shell.

Calendar-based relining is still the norm in a surprising number of plants, and it is the single largest controllable cost in mill liner management. Liners do not wear on a calendar. They wear against tonnage, ore hardness and ball charge, and any of those three can move a reline date by months. Plants that measure instead of schedule routinely find both that they can extend campaigns safely and, more importantly, that they stop the occasional shell damage event that dominates the cost.

What to Measure and Where

The useful measurement is residual liner thickness, taken on a fixed grid, at a fixed interval. A grid of points along the mill length and around the circumference gives a wear map rather than a number, and the wear map is what tells the maintenance buyer where the mill is actually losing metal.

Five points around the circumference at each of four to six positions along the mill is a workable starting grid, and it should be recorded on the same drawing every time so that successive surveys are directly comparable. The discipline of using the same grid matters more than the precision of any individual reading, because the trend is the product.

Ultrasonic thickness measurement is the practical method for steel liners and it is quick once the grid is marked. Where access is the constraint, a mechanical probe or a simple depth gauge on the liner lifter face will do, provided the same points are used every time.

Manganese and alloy steel liner sets such as the Mn13 Mn18 Mn22 manganese steel wear parts should be baselined at installation, because a survey without an as-installed thickness is a number with no reference.

Reading the Wear Map

The wear map shows three things, and each one has a different action attached. Uniform wear across the whole mill means the campaign is behaving as designed and the reline date can be projected with confidence. Localised wear at the feed end points to feed size or distribution. Localised wear at a single circumferential position points to a liner that was not seated correctly at installation.

The third case is the one worth chasing, because it is free to fix at the next reline and it is expensive to ignore. A liner panel that is not backed correctly wears to failure in a fraction of the campaign and takes its neighbours with it, and the symptom is a single hot spot on the wear map months before anything is visible inside the mill.

Two further readings matter. Lifter height, because it is what drives the charge lift and therefore throughput, and the profile of the lifter face, because a rounded lifter moves the mill off its designed trajectory long before the plate is thin. A mill can lose throughput while the liner is still structurally sound, and that is a reline decision driven by performance rather than by wear.

Concave and bowl liner components are often changed on a different cycle from the shell plates, and a set such as the cone crusher wear parts cone liner and concave should be surveyed on its own grid so that the two cycles do not get conflated in the maintenance plan.

Turning Measurements Into a Reline Date

Once two surveys exist, the wear rate is a slope and the reline date is arithmetic. Residual thickness minus minimum safe thickness, divided by the measured wear rate per thousand tonnes, gives the remaining tonnage, and that converts to a date using the forecast throughput. The precision improves with every survey.

The minimum safe thickness is the one number the plant must decide deliberately rather than inherit. Setting it at a level that leaves genuine structural margin is what prevents shell damage, and that decision is worth more than any improvement in liner metallurgy. A conservative minimum costs a small amount of liner life and removes a category of event that costs weeks.

The planning benefit is where the money actually is. A reline date derived from measurement can be moved into a scheduled shutdown, which means the liners, the labour and the lifting equipment are all available and the outage is planned rather than reactive. Plants that make this shift typically recover more from avoided unplanned outage than from any change in liner specification.

Mainframe and frame liner components are frequently forgotten in this planning. A part such as the mainframe liner for MP series cone crushers has a long lead time relative to its wear rate, and the measurement routine is what ensures it is ordered before it is needed rather than after.

What the Measurement Routine Should Cost

Very little. A marked grid drawing, a thickness gauge or ultrasonic unit, a survey at every planned stop or at a fixed monthly interval, and one spreadsheet with the results plotted. That is the whole system, and most plants can run it with existing staff in an hour per survey.

The output is worth a great deal. Beyond the reline date itself, the wear map is the evidence base for every conversation with a liner supplier. A plant that can show a wear map, a tonnage record and an ore hardness record can hold a supplier to a documented campaign life, and a plant with none of those has an argument it will lose.

Where the mill runs a manganese liner set, confirm that the replacement specification matches the original. A high manganese steel cone liner and bowl liner set should be ordered against the grade the wear map was generated with, because changing grade changes the wear rate and invalidates the projection.

Larger components should also be surveyed on their own schedule. A casting steel concave and bowl liner for a 7ft cone crusher is expensive enough and slow enough to source that the measurement routine pays for itself on that single item.

The Takeaway

Stop relining on the calendar. Baseline at installation, survey a fixed grid at a fixed interval, plot the trend, and convert residual thickness into remaining tonnage: the reline moves into a planned shutdown, the shell stays protected, and every conversation with a supplier is backed by data instead of memory.

Post time: Oct-15-2026