Mill Liners

Grinding Mills: Ball Mill & Rod Mill Design & Parts

Common types of grinding mills include Ball Mills and Rod Mills. This includes all rotating mills with heavy grinding media loads.  This article focuses on ball and rod mills excluding SAG and AG mills. Although their concepts are very similar, they are not discussed here.

Photographs of a glass ended laboratory ball mill show action of ball mass within the mill. The action of other grinding media is similar.

As the mill revolves, lifters assist in picking up the grinding charge and elevate it to an angle at which gravity overcomes friction and centrifugal force. The charge then cascades downward, effectively grinding particles of material within the mill by continuous, repeated impact and attrition action.

Grinding Mill RPM – Rotating Speed

Grinding Mill speed is one of the factors affecting the character of the cascading charge. As shown in the illustrations, the lower the percentage of critical speed, the smoother the flow of balls from top of charge to bottom. Higher percentage of critical speed is used for impact grinding of large feed. Lower percentage of critical speed is used for attrition grinding when a fine product is desired. The graph below will be helpful in determining percentage of critical speed when internal ….Read more

SAG Mill Liner Design

SAG_LinersTo a more significant degree than in other comminution devices, SAG Mill Liner Design and Configuration can have a substantial effect mill performance. In general terms, lifter spacing and angle, grate open area and aperture size, and pulp lifter design and capacity must be considered. Each of these topics has had a considerable amount of research, and numerous case studies of evolutionary liner design have been published. Based on experience, mill-liner designs have moved toward more open-shell lifter spacing, increased pulp lifter volumetric capacity, and a grate design to facilitate maximizing both pebble-crushing circuit utilization and SAG mill capacity. As a guideline, mill throughput is maximized with shell lifters between ratios of 2.5:1 and 5.0:1. This ratio range is stated without reference to face angle; in general terms, and at equivalent spacing-to-height ratios, lifters with greater face-angle relief will have less packing problems when new. but experience higher wear rates than those with a steeper face angle. Pulp-lifter design can be a significant consideration for SAG mills, particularly for large mills. As mill sizes increases, the required volumetric capacity of the pulp lifters grows proportionally to mill volume. Since AG/SAG mill volume is ….Read more

SAG Mill Grinding Circuit Design

AG and SAG mills are now the primary unit operation for the majority of large grinding circuits, and form the basis for a variety of circuit configurations. SAG circuits are common in the industry based on:

  • High single-line capacities (leading to capital efficiency)
  • The ability to mill a broad range of ore types in various circuit configurations, with reduced numbers of unit operations (and a corresponding reduction in the complexity of maintenance planning and coordination)
  • Favourable operating costs (with contributions from reduced liner/media consumption relative to conventional circuits)

SAG Mill in Operation Buy a Small SAG Mill

Though some trepidation concerning AG or SAG circuits accompanied design studies for some lime, such circuits are now well understood, and there is a substantial body of knowledge on circuit design as well as abundant information that can be used for bench-marking of similar plants in similar applications. Because SAG mills rely both on the ore itself as grinding media (to varying degrees) and on ore-dependent unit power requirements for milling to the transfer size, throughput in SAG circuits are variable. Relative to other comminution machines in the primary role. SAG mill operation is more ….Read more

Ball Mill Liner Design

There are many different designs and styles of ball mill liners. As with grinding balls local economics and ultimately operating costs determine the best design and material to use. The initial set of liners is rarely the final design selected. Based upon individual experience, mill superintendents develop preferences for liner designs. The following is given as a guideline for the initial set of liners.

For 60 mm (2.5″) and smaller top size balls for cast metal liners use double wave liners with the number of lifters to the circle approximately 13.1 D in meters (for D in feet, divide 13.1 D by 3.3). Wave height above the liners from 1.5 to 2 times the liner thickness. estimate rubber liner lifeRubber liners of the integral molded design follow the cast metal design. If using the replaceable lifter bar design in either metal or rubber the number of lifters should be about 3.3 π D in meters (for D in feet* divide 3.3 π D by 3.3) with the lifter height above the liners about twice the liner thickness.
The use of double wave liners, particularly when using 50 mm (2″) or larger balls, may show a loss ….Read more

Gibson Roll Ball Mill

CRUSH, GRIND and CLASSIFY in a single pass!

YOU Will save time, money and labor with the Gibson combination Elliptic Roll and Ball Mill.• It is the first successful mill put on the market that will take the mine run of ore. Crush grind and classify in a single pass. • Horsepower consumption over one third less than ordinary ball mills. • Available in 12, 25, 50 and 100 tons capacity handling 4”, 6” and 8” material.Gibson Roll Ball Mill

Estimated/Approximate Steel Liner Wear Life/Rate

A mill’ steel liner wear rate and total useful operating life is a function of its hardness (mostly).  Here is a chart displaying Liner Hardness on the Brinell Scale as a function of the tonnage of ore/rock milled/processed.

Not showed here is the impact a mill’s RPM has on the liner’s wear rate.

estimate mill liner wear rate

Comminution and Energy Consumption: By National Research Council (U.S.). Committee on Comminution and Energy Consumption

Estimated/Approximate Rubber Liner Wear Life/Rate Cost

In a Ball Mill (particularly) the wear rate or wear life of Rubber depends much on the Ball Size/Diameter used in that mill.  The grinding media size which itself is much of a function of the ore/material P80 feed size into that mill.

The other primary and addition factor contributing to a mill rubber liner wear is the RPM at which you operate the mill at.

estimate rubber liner life

 

Comminution and Energy Consumption: By National Research Council (U.S.). Committee on Comminution and Energy Consumption

How a Grate Discharge Ball Mill Works

Here I try to explain how ground slurry is discharged from a grate ball mill (or SAG).  How it works is, the slurry flows across the grate as it would a screen panel.

On the other side of the grate/screens are veins like a pump impeller.  As the mill turns/rotates the slurry is “pumped” out and discharged.

Grate Discharge Ball Mill http://www.metso.com/

Discharge Grates

The natural flexibility of rubber has allowed rubber manufacturers to produce grates that are less prone to plugging than the traditional metal grate.

The main reason for this is the flexing or diaphragming action that a rubber grate is subjected to as it goes through its rotational cycle of a rotating mill.

Each time the grate enters the mill charge, the horizontal force of the load in the mill deflects the grate. This stretches the rubber and forces any large material caught in the grate opening along through the grate slot.

As the grate leaves the charge, the rubber assumes its original shape. This diaphragming action works the large particles that enter the grate through to discharge and produces a near zero blinding of grate wall. The pieces of media or ….Read more

Grinding Mill Liners

Mill_Linings http://www.metso.com/

There are basically two groups of Grinding Mill Liners. Ones with a HIGH PROFILE and those with a LOW PROFILE. The high profile liner is designed to give the media the higher lift. This type will be used in mills that are designed for primary grinding and as a result require the impact of the higher cascade.  Ball mills working as the secondary portion of a grinding circuit will utilize the lower profile liners. The reason is as lift decreases, friction increases. To function effectively they need this type of grinding action to obtain the maximum contact of their high surface area. There are two other factors that the liner design must accommodate other than the degree of lift. The TYPE of grinding media and the SIZE of the media. To do this, there have been developed different liner profiles, RIPPLE LINERS, WAVE LINERS, SINGLE STEP LINERS, DOUBLE STEP LINERS, SHIPLAP LINERS and LIFTER BARS. These are also known as a KICKER BAR LINERS. The important measurements being the WIDTH of the valleys, the HEIGHT of the lifting portion of the liner and the overall THICKNESS of the liner.

….Read more

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