What liner materials are available for ball mills?

ATF offers mill liners in chrome-moly steel, Ni-hard, and high-chrome white iron. Chrome-moly is standard for most applications. Rubber and rubber-steel composite liners are also available for noise reduction and specific applications.

How do liner profiles affect grinding efficiency?

Liner profile determines ball trajectory and grinding action. Wave liners provide gentle lift for fine grinding, while high-lift designs are better for coarse grinding. Our engineers can optimize profiles for your specific grind requirements.

What is the typical life of mill liners?

Mill liner life varies from 6-18 months depending on material, mill size, and operating conditions. Proper liner selection and mill operation practices significantly impact wear life.

SAG Mill Grates | Pebble Ports Pulp Lifters

Key Specifications

Grate Aperture Range: 10–40 mm (circuit-dependent)
Pebble Port Size: 80–120 mm (critical-size rock removal)
Steel Hardness: 350–450 BHN (Cr-Mo), 600+ BHN (HCWI)
Open Area: 8–25% (SAG-specific, lower than ball mill)
Panel Weight: 200–1,500 kg per segment
Pulp Lifter Types: Radial, Curved, Twin-Chamber
Slot Geometry: Tapered, flared, and anti-pegging profiles
Campaign Life: 4–12 months (matched to shell liner schedule)

Grates

SAG Mill Grates: Critical Control Point for Primary Grinding

The grate discharge system is the most critical control point in SAG mill operation, directly governing throughput capacity, product size distribution, and grinding circuit efficiency. Grate aperture size—typically 10 to 40 mm for SAG mills—determines what material exits the mill: apertures that are too small restrict throughput and cause slurry pooling behind the grate, while apertures that are too large pass oversize material that recirculates through the circuit or overloads downstream ball mills and classification equipment. SAG mill grates must also withstand severe impact loading from 100–150 mm forged steel balls and large ore chunks while maintaining aperture integrity and dimensional stability throughout their service life. ATF manufactures SAG mill grate panels from chrome-moly steel at 350–450 BHN, high-chrome white iron at 600+ BHN for maximum abrasion resistance, and rubber-steel composite configurations for anti-pegging performance in applications prone to near-size particle blockage.

SAG mill discharge systems comprise multiple integrated components that must work together for efficient operation: grate panels with precisely sized apertures and optimised open area (typically 8–25% for SAG mills), pebble ports (80–120 mm openings) for removing critical-size rock that is too large for efficient grinding but too small for effective impact breakage, and pulp lifters—available in radial, curved, and twin-chamber configurations—that transport classified slurry from behind the grate face to the discharge trunnion. The design interaction between these components significantly affects mill performance: pulp lifter capacity must match the slurry generation rate to prevent back-flow, and pebble port positioning must avoid interfering with grate panel structural integrity. ATF engineers complete grate systems as integrated assemblies, using 3D CAD modelling to verify all interface dimensions and flow paths, ensuring each component is optimised for your specific circuit requirements, ore characteristics, and throughput targets.

Custom Apertures

Pebble Port Systems

Integrated Pulp Lifters

SAG mill pebble-ported grate panels manufactured by ATF

Pebble-ported grate panels with optimised aperture distribution for SAG mill discharge and pebble circuit control

Key Features of ATF SAG Mill Grate Systems

Optimized Aperture Sizing

Grate apertures from 10-40mm designed for your target product size and circuit requirements.

Pebble Port Integration

Pebble port (critical rock) systems to remove oversize material for pebble crushing circuits.

Pulp Lifter Design

Radial and curved pulp lifter designs for efficient slurry transport at high throughput rates.

Impact-Resistant Materials

Heavy-duty chrome-moly and rubber-steel composite options to survive SAG mill impact conditions.

Anti-Pegging Features

Tapered slots and anti-pegging designs to prevent near-size particle plugging.

Large Open Area

Maximized open area designs for high throughput capacity in primary grinding circuits.

Material Options for SAG Mill Grates

SAG mill grate material must resist impact from balls and ore while maintaining aperture geometry. Rubber-steel composites offer anti-pegging benefits in suitable applications.

Discharge Grates, Pebble Ports and Pulp Lifters for SAG Mills — Material comparison showing hardness ratings, applications, and performance characteristics
Material	Hardness	Application	Notes
Chrome-Moly Steel	350-450 BHN	Standard SAG mill grate panels	Good impact resistance, maintains aperture integrity
High-Chrome White Iron	600+ BHN	Grate panels in specific applications	Maximum wear resistance, some impact limitations
Rubber-Steel Composite	Steel: 400 BHN, Rubber: 65 Shore A	Anti-pegging requirements, corrosive slurries	Rubber flexibility reduces plugging
Polyurethane Composite	85-95 Shore A	Abrasive-corrosive conditions	Wear and corrosion resistant

Chrome-Moly Steel

Hardness:350-450 BHN

Application:Standard SAG mill grate panels

Notes:Good impact resistance, maintains aperture integrity

High-Chrome White Iron

Hardness:600+ BHN

Application:Grate panels in specific applications

Notes:Maximum wear resistance, some impact limitations

Rubber-Steel Composite

Hardness:Steel: 400 BHN, Rubber: 65 Shore A

Application:Anti-pegging requirements, corrosive slurries

Notes:Rubber flexibility reduces plugging

Polyurethane Composite

Hardness:85-95 Shore A

Application:Abrasive-corrosive conditions

Notes:Wear and corrosion resistant

Note: SAG mill grate aperture sizing significantly affects circuit performance. Consult ATF for recommendations based on your specific circuit requirements.

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OEM Compatibility

ATF manufactures complete grate systems for all SAG mill makes with correct mounting and interface configurations.

Metso Outotec

All SAG mill sizes

FLSmidth

All SAG mill sizes

ThyssenKrupp

All SAG mill sizes

CITIC

All SAG mill sizes

Custom Mills

Any SAG mill configuration

FAQ

Grates FAQs

Find answers to common questions about grates materials, selection, maintenance, and ordering. Can't find what you're looking for?

Contact Our Team

What grate aperture size should I use?

Optimal aperture size depends on the target product P80, downstream ball mill or classification equipment capacity, grinding media size, and ore characteristics. The primary constraint is that apertures must be smaller than the smallest grinding ball to prevent media discharge—for a SAG mill using 100 mm balls as the minimum, grate apertures should not exceed approximately 80 mm, with most SAG mills operating in the 10–40 mm range depending on circuit configuration. Single-stage SAG circuits requiring fine product typically use smaller apertures (10–20 mm), while SAG-ball mill circuits can use larger apertures (25–40 mm) since the downstream ball mill provides additional size reduction. Grate open area (8–25% for SAG mills, lower than ball mills due to impact loading requirements) also affects throughput: increasing open area improves discharge capacity but reduces structural strength. ATF engineers evaluate your complete circuit flowsheet, including downstream equipment constraints, to recommend the optimal aperture size and open area configuration.

What is a pebble port and why is it important?

Pebble ports are larger openings, typically 80–120 mm in diameter, incorporated into the SAG mill grate system to allow critical-size rock to exit the mill for external pebble crushing. Critical-size material—generally 25–75 mm in SAG mill circuits—is too large for efficient grinding by the ball charge but too small to be effectively broken by impact from the cataracting charge, causing it to accumulate in the mill and reduce grinding efficiency. As critical-size rock builds up, it displaces active grinding charge, increases mill power draw without productive breakage, and can cause throughput to drop dramatically. Pebble ports discharge this problematic size fraction to a dedicated pebble crusher (typically a cone crusher), which reduces it to a size that can be efficiently ground when returned to the SAG mill or sent to a downstream ball mill. ATF designs pebble port systems with optimised size, number, and positioning to maximise critical-size rock removal without compromising grate structural integrity.

How do pulp lifters affect mill throughput?

Pulp lifters are responsible for transporting ground slurry from behind the grate panels to the discharge trunnion, and their capacity directly limits mill throughput. If pulp lifters cannot move slurry fast enough, material accumulates behind the grate—a condition known as slurry pooling—which reduces the effective grinding volume, dampens charge impact energy, and increases power draw without productive grinding. Radial pulp lifters (straight vanes) are simpler but may allow slurry back-flow during a portion of each revolution; curved pulp lifters mitigate this by directing flow more efficiently. Twin-chamber (or "scroll") designs further reduce back-flow losses and are preferred for high-throughput applications. Worn pulp lifters with reduced vane height lose transport capacity progressively, and their condition should be assessed during every grate inspection. ATF designs pulp lifter systems matched to your mill speed, slurry density and flow rate, ensuring that discharge capacity exceeds the mill grinding rate under all normal operating conditions.

What causes grate plugging and how is it prevented?

Grate plugging (pegging or blinding) occurs when near-size particles wedge into grate apertures, progressively blocking the discharge face and restricting mill throughput. The primary cause is an aperture size too close to the median particle size in the grinding product, but plugging can also result from processing clay-rich or sticky ores, surges in fine material generation, corrosion products building up on slot walls, and physical damage that deforms aperture geometry. Prevention strategies include specifying tapered or flared slot profiles that widen from the grinding face toward the discharge side (allowing particles to pass through rather than wedge), selecting rubber-steel composite grate panels whose inherent flexibility dislodges stuck particles during mill rotation, increasing aperture size by 2–5 mm while managing downstream sizing requirements, and maintaining consistent feed size distribution to avoid surges of near-size material. ATF anti-pegging grate designs combine optimised slot geometry with appropriate material selection to minimise plugging frequency and extend intervals between grate cleaning.

Technical content reviewed by ATF Engineering Team | Metallurgical specifications verified against ASTM/ISO standards

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SAG Mill Grates | Pebble Ports Pulp Lifters | ATF