The decision depends on the wear mechanism at the liner position — specifically whether impact or abrasion dominates:

Manganese Steel (Mn13Cr2 / Mn18Cr2 / Mn22Cr2) — for HIGH IMPACT positions:

• Why it works: Mn steel is soft when installed (HB 200-250) but work-hardens to HB 400-620 under repeated impact. The harder the impact, the harder the surface becomes. This is perfect for positions where material or grinding balls strike the liner at speed.
• Where to use: Ball mill 1st compartment shell liners (60-90mm balls striking continuously), SAG mill shell liners (100-150mm balls + ore, highest impact in any mill), gyratory crusher top shell liners (large rocks dropping from feed hopper).
• Where NOT to use: Positions with only sliding abrasion and no impact — Mn steel never work-hardens and remains soft (HB 200-250), wearing 3-5x faster than properly selected alloy steel.

High Chrome Cast Iron (Cr15 / Cr20) — for LOW IMPACT, HIGH ABRASION positions:

• Why it works: High chromium content (15-22%) forms hard M7C3 carbides that resist abrasive wear from fine material sliding across the surface. No impact needed — hardness is achieved through metallurgy, not work-hardening. HRC 50-62 as-cast.
• Where to use: Ball mill 2nd compartment shell liners (small 15-30mm balls, fine material, abrasion dominant), cone crusher upper frame liners (material slides along surface, minimal direct impact).
• Where NOT to use: Any position with ball impact above 40mm diameter or drop height above 2 meters — high Cr is brittle (4-8 J/cm²) and will fracture under impact.

Alloy Steel (ZG35CrMo / ZG42CrMo) — the MIDDLE GROUND:

• Why it works: Quenched and tempered to HRC 35-48 with impact toughness of 35-60 J/cm². It bridges the gap: harder than as-cast Mn steel (before work-hardening), tougher than high Cr cast iron.
• Where to use: Mill shell liners with moderate ball impact (30-50mm balls), crusher liners with occasional rock impact but no continuous hammering.

Quick rule: If you hear impact (balls/rocks striking the liner) → Mn steel. If material just slides across → High Cr. If somewhere in between → Alloy steel.

Liner replacement is judged by remaining thickness, not failure. Unlike crushing wear parts where profile loss affects product quality, liners only need replacement before they wear through to the housing. However, premature failure has several common causes:

When to replace — the 30% rule:

• Replace when remaining thickness reaches 30% of original. Example: if original liner is 80mm thick, replace at 24mm. This leaves safety margin for uneven wear (some spots wear faster than others) and prevents the bolts from becoming exposed.
• Measure thickness at the thinnest point (typically the center of the impact zone), not at the edges. Use ultrasonic thickness gauge through the liner from the outside if the mill is running.
• If any bolt head becomes visible below the liner surface, replace immediately — exposed bolts will snap, and a loose liner section can cause catastrophic damage.

Three common causes of premature liner failure:

• Wrong material for the wear mechanism: The #1 mistake. Using Mn steel in a low-impact zone where it never work-hardens leaves a soft HB 200 liner in a zone that needs HRC 50+. Using high Cr in a high-impact zone causes fracture. A $5,000 wrong-material liner that fails in 3 months is far more expensive than a $7,000 correct-material liner that lasts 2 years.
• Loose bolts: As liners wear thinner, bolts stretch and loosen. A loose bolt allows the liner to vibrate, which accelerates bolt hole elongation, which allows more vibration — a self-reinforcing failure cycle. Check bolt torque at every planned shutdown. Use Nord-Lock washers or Belleville spring washers to maintain tension as the liner wears.
• Uneven wear due to incorrect installation: Liners must sit flush against the shell. If debris or old backing material is left between the liner and the shell, the liner bridges over high spots and cracks under impact. Always clean the shell surface completely before installing new liners. ZHILI supplies zinc-based backing compound for gap filling.

ZHILI liner replacement package: We supply complete liner sets with all bolts, washers, gaskets, and installation instructions. Bolt torque specifications are provided for each liner type. We can also arrange on-site supervision for the first liner change by a ZHILI engineer.