Mill Liners: Material Selection, Design, Wear Measurement and RFQ Guide

Mill liners protect the shell of ball, SAG, AG and rod mills, but protection is only one part of their job. Liner profile, spacing, material, fastening and wear condition influence charge motion, grinding-media trajectory, pulp flow, throughput, power draw, maintenance exposure and the risk of liner or bolt failure. A material with high laboratory hardness can still perform poorly when its profile, impact duty or installation system is wrong.

This engineering guide is for mine and cement plant maintenance teams, process engineers and buyers. It explains how to define mill duty, compare metallic and non-metallic liner options, measure wear, diagnose failure and prepare a drawing-based RFQ. It does not replace the mill OEM’s design, site risk assessment, structural review or approved reline procedure. Final material, profile, thickness, fixing and replacement limit must be approved for the specific mill and operating envelope.

Start with the grinding duty, not a material name

Metso describes a mill lining as a customized wear part and notes that lining type and design affect throughput and total grinding cost. Therefore, “high manganese,” “high chrome,” “rubber” or “Cr-Mo” is not a complete specification. The supplier needs the mill geometry, speed, charge, ore, operating history and the current liner drawing before proposing a route.

Input	Information to provide	Why it changes the liner
Mill and zone	OEM/model, diameter, length, speed, shell/head/discharge position and rotation	Charge trajectory, impact and attachment differ by mill and position.
Feed and product	F80/P80, ore type, hardness/abrasiveness, moisture, clay and tramp metal	Changes abrasion, impact, packing and pulp-lifting demand.
Charge	Ball size distribution, filling, density and operating power	Controls impact energy and sliding/rolling contact.
Slurry	Solids, pH, chlorides, temperature, density and flow	Corrosion and erosion can interact with mechanical wear.
Current performance	Wear scans, mass loss, cracks, loose bolts, throughput and shutdown history	Separates material, profile, fastening and operating causes.

Functions of shell, head, grate and pulp-lifter liners

Shell liners protect the cylindrical shell and lift the charge. Feed and discharge head liners protect end plates and influence material movement. Grates control discharge apertures, while pulp lifters move slurry from the grate chamber toward the trunnion. Trunnion and trommel liners have their own flow, fit and wear requirements. A complete RFQ identifies each zone rather than calling every component a “mill liner plate.”

Profile is a process variable. Lifter height, face angle, pitch, number, wave shape, grate opening and pulp-lifter volume can change charge motion and discharge capacity. Copying a worn liner reproduces lost geometry. Use the approved new-liner drawing or a controlled reverse-engineering plan that restores original dimensions.

Material families and their selection boundaries

Material family	Potential fit	Main strength	Critical limit
Austenitic manganese steel	Zones with sufficient impact and deformation to support work hardening	Damage tolerance and work-hardening response	Low-impact abrasion may not generate the intended hardened surface; chemistry alone does not prove performance.
Cr-Mo alloy steel	Large metallic liners requiring a controlled hardness-toughness balance	Heat-treatable matrix and section-size flexibility	Grade, heat treatment, section and impact duty must be connected; excessive hardness can increase fracture risk.
High-chromium white cast iron	Severe abrasion with limited impact, depending on geometry and support	Hard chromium-rich carbides	Carbide-bearing irons are less tolerant of bending, point loading and uncontrolled bolt stress.
Ni-Hard white iron	Abrasion-dominant liners and plates under a suitable duty	Carbide/matrix wear system	Exact grade, matrix, heat treatment and impact boundary must be specified.
Rubber	Selected lower-impact zones where elasticity, weight and corrosion behavior help	Lower component mass and elastic response	Temperature, chemicals, sharp feed, impact and aging control suitability.
Composite or metal-rubber	Applications that combine structural inserts with elastomer	Can tailor mass, stiffness and wear by zone	Bonding, insert retention, fire/spark work and repair rules require supplier-specific approval.

ASTM A128/A128M covers austenitic manganese steel castings, while ASTM A532/A532M-10(2023) covers abrasion-resistant cast irons. Neither standard chooses the correct liner family for a mill. The purchase order must name the applicable grade, delivery condition, test basis and any purchaser-specific chemistry, hardness, impact or microstructure requirement.

Chemistry, microstructure and heat treatment

Chemical composition provides the alloy system; it does not fully describe the delivered liner. Carbon, manganese, chromium, molybdenum, nickel, silicon and residuals interact with section size, solidification and heat treatment. In white iron, carbide type, volume and distribution work with the matrix. In alloy steel, hardenability and tempering determine the hardness-toughness balance. In manganese steel, solution treatment and carbide control matter before service work hardening begins.

Control	What to specify	Evidence	Common error
Chemistry	Standard/grade, edition, all limits and product-analysis rule	Heat analysis linked to liner marking	Ordering only a chromium or manganese percentage.
Heat treatment	Required condition, furnace control and cooling route	Traceable furnace chart and load record	Accepting “heat treated” without a defined condition.
Hardness	Method, scale, location, surface preparation and range	Mapped readings with calibrated equipment	Comparing HRC and HB values without valid conversion or location.
Microstructure	Only when technically justified: matrix, carbides, retained phases and sampling	Report with preparation method and reference criteria	Applying one micrograph limit to unrelated section thicknesses.
Mechanical tests	Tensile/impact requirement, specimen type, orientation and representation	Test report connected to heat/lot	Assuming a separate coupon reproduces every local liner section.

Liner profile, charge motion and DEM limits

Lifter geometry should create the charge motion required by the comminution duty without excessive direct impact on liners or the shell. Mill speed, filling, ball size, liner wear and ore condition change the trajectory. Discrete-element modelling can compare concepts, but its results depend on calibration inputs and assumptions. It is a decision tool, not proof of guaranteed throughput or wear life.

Profile changes require process and mechanical review. Raising lifters can increase lifting until trajectories become damaging; reducing spacing can alter packing and available volume. Grate and pulp-lifter changes may relieve or create discharge limitations. Record the design revision and do not mix incompatible profiles in one row unless the approved design requires it.

Fastening, backing and joint control

A liner system fails when the load path is incomplete. Bolts, nuts, washers, seals, backing, shell condition, hole geometry and liner seating work together. A high-strength bolt cannot compensate for poor contact or an incorrect grip. Tightening values depend on fastener property, lubricant, coating, joint stiffness and the approved preload method.

Interface	Check before installation	Failure evidence
Liner-to-shell	Clean contact, backing condition, curvature, high spots and foreign material	Polished rocking areas, fretting, broken backing or shell marks.
Bolt hole and head seat	Drawing dimensions, alignment, head form, contact and edge distance	One-sided seating, hole battering, bent bolts or head cracking.
Threaded assembly	Property class, thread, nut/washer, lubricant and tool procedure	Thread stripping, nut movement, fatigue beach marks or inconsistent elongation.
Seal	Correct material, orientation and compression	Slurry leakage, cut seals, corrosion or washout around the hole.
Panel joints	Approved gap/overlap and installation sequence	Peening, trapped material, local chipping or liner migration.

For a deeper fastening review, use the mill liner bolt selection and failure guide. The mill must be isolated before inspection or tightening; work must follow the OEM and site energy-control procedure.

Wear measurement and replacement decisions

Metso states that regular wear follow-ups provide profile data needed to improve lining design and plan maintenance. Establish a repeatable baseline at installation and measure the same locations, datums and mill hours at each inspection. Manual thickness readings, templates, weight, photogrammetry or 3D scans can be used when their accuracy and safety are controlled.

Do not decide replacement from average thickness alone. Minimum remaining wall, bolt-hole proximity, cracks, local washout, loose panels, deformation and the ability to complete the next operating interval all matter. The OEM or authorized engineer should define limits. Measurement never justifies personnel entering an inadequately isolated mill.

Failure modes and evidence-based diagnosis

Observation	Possible contributors	Evidence to collect
Premature abrasive loss	Ore change, wrong material/matrix, low hardness, unfavorable profile or slurry corrosion	Feed data, wear map, chemistry, hardness, metallography and operating trends.
Cracked or broken liner	Impact, casting defect, excessive hardness, thin section, poor seating or bolt loading	Fracture location, photos before removal, NDT, fracture surface, heat and installation record.
Loose liner or bolt	Preload loss, joint settlement, wrong fastener, leakage, backing failure or hole mismatch	Torque/preload record, nut position, thread condition, liner contact and bolt fracture analysis.
Uneven row wear	Feed distribution, mixed profiles, charge motion, liner orientation or installation error	Position-coded scan, row map, rotation, operating conditions and drawing revision.
Grate plugging or discharge restriction	Aperture/profile, pebble size, slurry, worn lifters or process change	Throughput, pool indicators, grate map, pebble distribution and pulp-lifter inspection.

Do not select a harder alloy before identifying the dominant mechanism. A crack can start from design, manufacture, installation or operation. Preserve fracture surfaces from grinding and weather, retain part identity and document the as-found condition.

Installation and reline safety boundary

Relining involves massive components, suspended loads, stored energy, restricted access and tools inside a confined machine. OSHA 29 CFR 1910.147 establishes hazardous-energy control requirements for covered U.S. general-industry maintenance. The site must apply its jurisdiction, OEM procedure, lift plan, isolation verification and confined-space rules. This article is not a work instruction.

• Verify electrical, hydraulic, pneumatic, gravitational and rotational isolation.
• Use engineered lifting points and approved tools; never infer capacity from appearance.
• Control liner orientation, sequence and temporary stability.
• Keep personnel outside line-of-fire and crush zones.
• Record each installed part, position, fastener lot and tightening evidence.
• Complete the approved post-startup inspection or retightening plan.

Inspection and quality-document package

Define visual, dimensional, chemistry, hardness, NDT and traceability requirements before production. Radiography or ultrasonic examination is not automatically suitable for every geometry or alloy; specify method, zones, stage and acceptance criteria. Magnetic-particle testing applies only where material condition permits it. Liquid penetrant testing identifies surface-opening discontinuities but requires a written acceptance standard.

A practical dossier can include approved drawing, material certificate, heat-treatment chart, hardness map, dimensional report, NDT reports, repair/deviation records, part marking, packing list and release certificate. The document type and language should be agreed in the purchase order.

Controlled trial and performance comparison

When changing material or profile, define a controlled trial. Mark liner positions, capture new dimensions and mass, keep operating data, measure at fixed intervals and record removal condition. Compare wear rate, not only calendar life. Throughput, ore, charge, mill hours and maintenance practice must be considered before attributing an outcome to the liner.

A successful trial applies to the documented duty. It does not justify a universal percentage-life, energy-saving or cost guarantee. Changes to profile that affect grinding performance require process-engineering approval even if the material itself looks satisfactory.

Mill liner RFQ checklist

1. Mill OEM/model, diameter, length, speed, power, rotation and liner zone.
2. Approved new-liner drawing, 3D model if available and revision priority.
3. Current material/grade, heat treatment, hardness and certificate.
4. Feed, product, ore, charge, slurry and operating data.
5. Position-coded wear scans, failure photos and achieved mill hours/tonnage.
6. Required material standard, chemistry, hardness, impact or microstructure criteria.
7. Profile, dimensions, tolerances, machining, minimum wall and mass limits.
8. Bolt, nut, washer, seal, backing and tightening/interface requirements.
9. NDT zones, methods, acceptance and required quality documents.
10. Quantity by position, spares, marking, packaging, destination and shutdown date.

Related EB Castworld product and technical pages

Review grinding mill liners, chrome-molybdenum mill liners and ball mill liners. Compare rubber and manganese steel liners, then use the mining wear-casting RFQ guide. General quality assurance and factory capability pages do not replace part-specific approval.

Send drawings and operating evidence

Use the contact page to send the drawing, position list, service data, wear measurements, material/inspection requirements, quantity and destination. Final material, geometry, fixing and installation method must follow customer-approved documents.

References and engineering boundary

• Metso, Mill Liners.
• Metso, Mill Liner Wear and Performance Monitoring.
• ASTM A128/A128M, Austenitic Manganese Steel Castings.
• ASTM A532/A532M-10(2023), Abrasion-Resistant Cast Irons.
• OSHA 29 CFR 1910.147, Control of Hazardous Energy.

Boundary: Mill performance, structural integrity, replacement criteria, lifting and installation remain the responsibility of the mill owner, OEM and authorized engineers. No service-life, throughput, energy or savings result is guaranteed without a controlled application and evidence.