Choosing Wear Resistant Steel Plate for Ball Mills

Why One Material Does Not Cover the Whole Mill

Mining equipment such as ball mills operates in an environment of severe abrasion, heavy impact and corrosive conditions. Different components of the same machine therefore have different requirements for abrasion resistance, impact resistance and yield strength.

Specifying a single grade across the shell, the liners and the supporting crushing equipment either overpays on the parts that see little wear or under specifies the parts that fail first. The practical approach is to split the machine into its structural parts and select against the duty each one carries.

• Shell carries structural load and impact
• Liners take direct contact with grinding media and ore
• Crusher and loader wear parts see abrasive and impact loading at the same time
• Corrosive wet grinding conditions change the answer again

Ball Mill Shell High Strength Low Alloy Steel

The shell is the main structural body of the mill. It must withstand the massive weight and impact forces of the steel balls and the ore, so it needs sufficient strength and rigidity rather than surface hardness.

High strength low alloy steel is the recommended material. The shell plate thickness is typically required to be greater than or equal to 15 mm so that the equipment does not deform during long term operation. On a gold exploration mill this is the specification to fix first, because every internal fitting is set out from it.

• Recommended material high strength low alloy HSLA steel
• Shell plate thickness greater than or equal to 15 mm
• Requirement is strength and rigidity not surface hardness
• Thickness protects against deformation over long term operation

Liners in High Manganese Steel Mn13

Liners are in direct contact with the grinding media and the ore, which makes them the most severely worn components in the mill. High manganese steel such as Mn13 was the first generation wear resistant material and it typically contains 12 to 14 percent manganese.

Its defining property is work hardening. Under severe impact the surface hardness increases significantly, so the liner builds its own hard skin in service. That makes it the right choice where high pressure and strong impact loads dominate, which on most mills means the coarse end of the circuit under heavy ball charge.

• Manganese content typically 12 to 14 percent
• Exceptional impact resistance and work hardening behavior
• Surface hardness rises significantly under severe impact
• First choice where the impact load is extremely high

Liners in High Chromium Cast Iron

High chromium cast iron offers extremely high wear resistance, more than twice that of high manganese steel, and excellent abrasive wear resistance. The trade is toughness, which is relatively lower than high manganese steel.

It is widely used in large ball mills and as the liner material for the coarse grinding chambers of medium and small ball mills. Where the failure mode you actually see is abrasion rather than cracking, this is the material that extends the interval between liner changes.

• Wear resistance more than twice that of high manganese steel
• Excellent resistance to abrasive wear
• Relatively lower toughness than high manganese steel
• Used in large ball mills and coarse grinding chambers of medium and small mills

Liners in Wear Resistant Rubber

Wear resistant rubber is the newer generation of liner material. It has outstanding elasticity, fatigue resistance and shock absorbing properties, and it is light, which helps reduce the overall energy consumption of the mill.

Its limits are clear: poor impact resistance and no heat resistance. That confines it to fine grinding chambers and wet grinding environments, where the impact energy is low and the benefit of reduced mass and noise is real.

• Outstanding elasticity fatigue resistance and shock absorption
• Lightweight which helps reduce equipment energy consumption
• Poor impact resistance and not heat resistant
• Suitable for fine grinding chambers and wet grinding

Quenched and Tempered Wear Plate for Supporting Equipment

Supporting equipment in gold exploration such as crushers, excavators and loaders is normally built with quenched and tempered wear resistant steel plate for the wear prone parts, including bucket plates, crusher liners and jaw plates.

NM360 and WNM400 are mid to high level quenched and tempered wear plates with high yield and tensile strength, suited to wear parts in mining and construction machinery. NM450, NM500 and NM600 belong to the high hardness series, where the number represents the nominal Brinell hardness grade. The higher the hardness the stronger the wear resistance, so NM500 and NM600 go on the extreme duty parts such as jaw plates for large jaw crushers and concaves for cone crushers.

• NM360 and WNM400 mid to high level quenched and tempered wear plate
• NM450 NM500 and NM600 high hardness wear resistant series
• Grade number represents the nominal Brinell hardness grade
• NM500 and NM600 used for large jaw crusher jaw plates and cone crusher concaves
• Typical parts bucket plates crusher liners and jaw plates

Summary Recommendation for a Gold Exploration Mill

For a ball mill built for gold exploration, use high strength low alloy steel with a thickness of 15 mm or more for the shell. Then select the liner by the dominant failure mode rather than by a single house standard.

If the impact load is extremely high, high manganese steel Mn13 is the first choice. If the main problem is severe abrasion during coarse grinding, high chromium cast iron is recommended. For wet fine grinding, wear resistant rubber liners can be considered.

• Shell HSLA steel 15 mm or thicker
• Extreme impact liner high manganese steel Mn13
• Coarse grinding abrasion liner high chromium cast iron
• Wet fine grinding liner wear resistant rubber
• Crusher and loader wear parts quenched and tempered NM360 to NM600