Material choice balances impact toughness vs. abrasion resistance. Grate bars experience both — hammer impact from above and abrasive sliding from below:

• High manganese (Mn13, Mn13Cr2, Mn18Cr2): Standard for most applications where feed contains >80 mm particles that strike the grate directly. The impact energy work-hardens the surface to 500-650 HB. Mn bars also deform plastically under overload — they bend before breaking, giving warning. Mn18Cr2 recommended for crushers above PC800 size.
• High chrome (Cr15, Cr20): Cost 25-40% more than Mn steel but justifies the premium when material SiO2 exceeds 15%. In abrasive limestone applications, Cr20 bars achieve 2.5-3.0x longer life, reducing replacement frequency and downtime. The break-even point is approximately 6 months of operation — if Mn bars last <6 months, Cr bars are more economical after accounting for labour and downtime.
• Cr chrome limitation: Never use chrome bars in crushers that process feed containing tramp metal (rebar, drill bits, bucket teeth). Chrome is brittle under impact — a single tramp metal strike can shatter multiple bars. Use Mn steel in demolition recycling and other contaminated feed applications.
• Mixed configuration (practical solution): Install Cr15/Cr20 bars in the centre zone where material is already fine and impact is lowest, and Mn18Cr2 bars at the edges where large fragments may still impact. This hybrid setup captures the benefits of both materials at minimal cost premium.

Grate bar replacement speed directly impacts crusher availability. A systematic approach reduces 4-hour bar changes to under 90 minutes:

• Pre-assembled cassette method (fastest): Remove the entire grate bar assembly as a cassette (bars + mounting frame). Bench-assemble the replacement set with new bars and spacers in the workshop during scheduled downtime. Swap cassettes in 20-30 minutes on-site. This is standard practice for high-tonnage operations where crusher availability is critical.
• Individual bar replacement (spot repair): Replace only damaged or excessively worn bars. Use a slot-setting jig or spacer template — a piece of flat bar ground to the exact slot width. Place the jig between adjacent bars as you tighten each bolt. This guarantees consistent slot spacing and eliminates time-wasting re-adjustments. Never “eyeball” slot width — 2 mm variability reduces product quality measurably.
• Spacer design matters: Use tapered spacers (wider at bolt end, narrow at discharge end) if bars are curved or tapered. This ensures parallel slots along the entire bar length. Flat spacers work only for parallel-sided bars. Weld a small tack on each spacer to prevent rotation during assembly.
• Bolt torque sequence: Tighten a star pattern (centre outward) to 50% torque first pass, then 100% second pass. This prevents bar warping. Use Nord-Lock wedge washers under every bolt head — grate bars experience 4,000-7,000 vibration cycles per minute and standard washers loosen predictably.