Gyratory liner wear measurement requires specialised techniques because the liners are too large for simple bore gauges and the cost of premature or late replacement is measured in hundreds of thousands of dollars:

• Mantle wear pattern — “bathtub curve” in the lower third: The mantle wears most aggressively in the lower 20-30% of its height — the zone where material exits the crushing chamber at maximum velocity and pressure. A characteristic concave wear profile develops (hence the name “concave” for the stationary liner). This zone wears 5-8x faster than the upper mantle, which primarily guides material into the crushing zone. The danger: when the lower mantle wears thin, the crushing gap widens (OSS — Open Side Setting — increases), and product size grows. A 10 mm increase in OSS reduces product quality from P80 150 mm to P80 180 mm — causing problems for downstream SAG mills. Detection: laser profile scanning of the mantle every 500 hours — the scanner maps the entire surface profile in 3D and compares to the original CAD model. Replace when the thinnest point in the lower third reaches 25% of original casting thickness.
• Concave wear pattern — asymmetric and row-dependent: Lower concave rows wear 3-5x faster than upper rows. Additionally, wear is rarely symmetric around the circumference — the side receiving the bulk of feed from the dump pocket or feed conveyor wears 1.5-2x faster. This creates an oval crushing chamber where CSS varies 10-20 mm around the circumference. Detection: (a) laser scan concave rows individually every 500 hours; (b) measure the radial gap between mantle and concaves at 8 positions (every 45 degrees) around the crusher — maximum CSS variation should be <15% of mean CSS; (c) monitor mainshaft position sensor — a trend toward lower mainshaft position with the same hydraulic pressure indicates concaves are wearing and the shaft must descend further to maintain CSS. Replace any concave row when minimum thickness reaches 20-25% of original.
• Mantle-to-concave interaction wear — the “wedging effect”: When the mantle wears thinner in the lower zone while upper concaves remain thick, the crushing chamber shape changes — the narrowest point shifts upward from the discharge. This creates a wedging effect where material packs rather than flows, increasing power draw 10-15% and reducing throughput. The crusher “boggs” — it struggles to accept feed because the effective feed opening has reduced. Detection: throughput drops >10% with no change in feed characteristics, while power draw remains high or increases. This indicates the mantle and concaves are worn in a mismatched pattern — replace the mantle first (lower zone wear is usually the cause). After mantle replacement, if throughput recovers, the concaves were acceptable; if not, replace the lower concave row next.
• Economic replacement threshold — the $/ton optimisation: Gyratory liners have a distinct economic life different from their physical life. Liners should be replaced when the cost of lost production from an unscheduled shutdown (liner punch-through) exceeds the cost of remaining liner life. At $50,000-100,000 per hour of crusher downtime for a 60-110, a liner with 10% remaining life (worth $15,000 in liner value) that risks a punch-through (costing $500,000+ in downtime + damage) should be replaced early. The economic replacement threshold is typically when liners reach 20-25% of original thickness — not because they cannot physically run thinner, but because the risk-reward ratio of running thinner flips sharply negative.

Gyratory liner installation is a major industrial lifting operation. A single 60-110 mantle weighs more than a fully loaded city bus. Installation errors at this scale are measured in millions of dollars of damage:

• Lifting and handling (safety-critical, step 1): Every gyratory mantle and concave casting has cast-in lifting lugs designed for the specific centre of gravity. Never use improvised lifting points — a 14,000 kg mantle that rotates 5 degrees during a lift becomes uncontrollable. Use a crane with minimum 2x the part weight capacity and a 4-point lifting beam that distributes load evenly across all lifting lugs. Lift 10 cm first and hold for 30 seconds to verify stability before continuing. The lifting area must be cleared of all personnel — a dropped 14,000 kg mantle is unsurvivable within 15 metres due to the crater-and-spall effect. Concave rows are lifted individually using a special concave-handling beam that grips the concave at 3-4 points around its circumference — never use chain slings that can mark or dent the machined seating surface.
• Mantle installation (step 2 — precision seating): The mantle seats on the mainshaft head — a machined spherical or conical surface with an interference or tight-clearance fit. Procedure: (a) Clean the mainshaft head to bare metal — any rust, scale, or old epoxy prevents proper seating. A 0.5 mm particle under a 14,000 kg mantle creates a 2-3 mm misalignment at the crushing surface due to the 2:1 leverage of the mantle height. (b) Apply epoxy backing compound evenly to both the shaft head and mantle inner surface — 200-500 litres for a 60-110 mantle. The compound must be mixed in small batches (20-30 kg each) to prevent premature curing before all compound is placed. (c) Lower the mantle using the crane, guide it onto the shaft head, and immediately tighten the mantle nut to 50,000-80,000 Nm using a hydraulic torque wrench. The nut must be tightened within 20-30 minutes of epoxy placement at ambient temperature — faster in hot conditions. (d) Allow the epoxy to cure for 12-24 hours (follow manufacturer’s temperature-time chart). Do not rush curing with external heat — uneven curing creates hard skin over uncured core, which will collapse under load.
• Concave installation (step 3 — row-by-row stacking): Concaves are installed row by row, starting from the bottom row. Procedure: (a) Clean each concave seat in the top shell to bare metal. (b) Apply a thin, even layer of epoxy to the seat. (c) Lower the concave row using the concave-handling beam, position it, and tighten all bolts to 50% torque in a cross pattern, then 100% torque. (d) Verify the concave is centred by measuring the radial gap between the concave inner surface and a centred plumb line from the spider — gap must be within ±2 mm around the circumference. (e) Install the next row upward, repeating the procedure. Critical: concave rows must be installed in the correct order (bottom upward) and each row must be fully tightened and verified centred before the next row is placed — a misaligned row cannot be corrected once the row above is installed. (f) After all rows are installed, run a laser scan of the complete concave assembly to verify concentricity with the mainshaft centreline — maximum radial deviation <3 mm.
• First-hour operation (step 4 — verification): (a) Run the crusher empty at minimum speed for 30 minutes — listen for knocking, scraping, or unusual vibration. (b) Run at full speed empty for 30 minutes — monitor bearing temperatures (must stay <70 C), mainshaft position sensor, and vibration levels (<7 mm/s RMS). (c) Feed material at 25% design rate for 1 hour, then 50% for 1 hour, then 75% for 1 hour, then 100%. (d) After 8 hours at full load, stop and re-check mantle nut torque — expect 5-10% relaxation as the epoxy fully beds in. (e) Run a laser scan of both mantle and concaves — this becomes the baseline for future wear measurements. The baseline scan after 8 hours of operation (after bedding-in wear) is the true zero-hour reference — not the as-installed scan.