Size reduction is the first step in many materials processing plants. The goal with this step is to reduce large lumps of mined materials, be it rock or mineral-bearing ores, into a conveyable size for stockpiling or further processing.
Producers have many equipment options for material size reduction, including crushers, breakers and sizers, but not all of them are suited for each application. Let’s take a look at the different equipment options for material size reduction and compare them for various applications.
What is a crusher?
A crusher is a machine that reduces material via forces of impact, compression, attrition or shear.
Compression crushers, such as Jaws, Gyratories, Cones and Roll Crushers, reduce material by squeezing or compressing it between a moving piece of steel and a stationary piece of steel
Impact crushers, such as Andreas, New Holland and MaxCap crushers, feature a spinning rotor inside a chamber. They reduce material in three ways: by contact with the spinning rotor, by contact with the breaker plates lining the walls of the crushing chamber and by contact with other particles of material that are being flung around inside the chamber.
Hammermills operate similar to impact-style crushers in that they reduce material by its contact with a spinning rotor and with breaker plates lining the walls of the crushing chamber. These machines also provide an attrition feature, grinding the material against a grate for further reduction before it is discharged.
Crushers can handle a wide range of material, from soft to extremely hard and from dry to wet, depending on the type of crusher. Jaw Crushers, Gyratory Crushers, Cone Crushers and Roll Crushers are well known for their ability to crush extremely hard materials that may be abrasive but not sticky. Impactors and Hammermills can handle soft to very hard, mildly abrasive materials that are wet or sticky.
Jaws and Gyratories are more often used as primary crushers, while Cone Crushers, known for providing a good product shape, are often used for downstream crushing to refine the product size. Roll Crushers, Impactors and Hammermills can be used in the primary and/or the subsequent crushing stages.
What is a breaker?
A breaker is a machine that reduces material by breaking it along its natural fracture lines, exploiting the natural weakness of the rock.
Types of breakers include Rotary Breakers and Feeder-Breakers. Rotary Breakers feature a rotating cylinder with internal lifters that continuously lift and drop the material to fracture it along its natural fissures. They also have the ability screen out invaluable material from the product material, in turn, rejecting the harder oversize waste rock.
Feeder-Breakers feature both a drag-chain-style Feeder and rotating pick roll in one machine. Material is dumped or loaded onto the feeder portion of the machine, which delivers the material to the rotating pick roll at the other end of the machine. The large lumps of material are broken upon their encounter with the picks.
In general, breakers are ideal for breaking material without generating excessive fines. Breakers are not suited for wet, sticky material, highly abrasive material or material other than coal that has a high fines content, such as iron ore. They are commonly used for the primary reduction of large run-of-mine lumps into smaller, more manageable lumps. Feeder-Breakers are often followed by a shaping crusher or sizer, while Rotary Breakers discharge a material that is ready for loading or washing in the coal preparation plant.
What about sizers? Where do they fit?
Sizers are small, compact machines used for material size reduction in a wide range of materials. These machines are rugged enough to handle hard rock and ores yet able to handle coal and other soft, friable materials without creating excess fines. Sizers are also able to handle wet, sticky materials that can cause material buildup in certain types of crushers, such as Jaws and Gyratories.
Sizers feature two rotating roll shaft assemblies that are equipped with breaker teeth. Material larger than the product setting, which is the space between the roll bodies, is gripped by the breaker teeth and compressed through the rolls. A breaker bar underneath the rolls helps to break up any slabby material to provide a uniform, cubical product. Undersize material passes through the rolls and is discharged out the bottom of the machine.
Because of their low profile, Sizers are ideal for underground applications, fitting into spaces with height restrictions or replacing larger crushers
Differences between crushers, breakers and sizers
Besides physical and operational differences, crushers, breakers and sizers are designed for different industries and performing different tasks. While there can be some industry overlap between the three, crushers, breakers and sizers are not always interchangeable.
For example, Rotary Breakers were designed for handling friable coal. They can accept an all-in feed and are capable of scalping out rock and refuse as well as breaking friable material into a smaller size for further processing.
Feeder-Breakers also perform well in ROM coal and other applications where the material is soft and friable. They are typically used in the primary reduction of material to provide a smaller material for secondary or tertiary sizing. Feeder-Breakers are one of the best machines for low fines generation.
Most crushers, especially compression crushers, are great for handling materials that are hard and abrasive, but not sticky. Jaw Crushers and Gyratories do not like excessive fines in the feed, so pre-screening with a Vibrating Grizzly Feeder, Wobbler Feeder or scalping screen of some sort is a must. Jaw Crushers and Gyratory Crushers tend to create fines, so they lend themselves well to applications such as gold where the valuable material is located within the rock. These two types of crushers create slabby, elongated materials, so further sizing and shaping with a secondary or even tertiary and quaternary crusher is necessary.
- Jaw Crushers can handle soft to extremely hard, abrasive materials that may be friable but are not wet or sticky.
- Gyratory Crushers can handle hard to extremely hard and abrasive materials that may be friable.
- Cone Crushers can handle soft to extremely hard materials that may be friable but are not wet or sticky.
- Roll Crushers can handle soft to extremely hard materials that may be friable but are not wet or sticky.
- Impact Crushers can handle soft to very hard materials that are wet or sticky.
- Hammermills can handle soft to very hard materials that are wet or sticky.
Sizers are great for handling clay and wet, sticky materials, such as bauxite, nickel laterites, gold oxides and iron ore, and they can handle harder rocks without creating excessive fines and without the need for pre-screening the feed (although the size of machine required may be reduced if adding a Vibrating Grizzly Feeder ahead of the Sizer in high fines applications).
While Sizers can handle much harder material than breakers, they are not always the best option for high-strength or extremely hard materials that would better be reduced by a Jaw or Gyratory. Sizers produce a uniform, cubical product and feature the smallest footprint of any of the other machines described. They are also low-fines generation machines.
Sizes are also much simpler and safer machines to work on compared to other types of primary crushers. Sizers are fitted with motorized tramming wheels to move the machine into a maintenance position, whereas maintenance for Jaws and Gyratories often takes place inside the crusher.
Which option is best?
Whether you need a crusher, breaker or sizer largely depends on the material to be crushed. Knowing the characteristics of your feed material is the first step in choosing the right equipment to perform the material size reduction.
First, what material are you processing? Is it soft or hard? Dry or wet? Is it sticky?
Other important information to consider when choosing a crusher, breaker or sizer for an application includes:
- Method of extracting the raw material
- Method of feeding the raw material to the crusher, breaker or sizer
- Desired production rate
- Desired products
From this information, you will be able to narrow down whether a crusher, breaker or sizer is the best option. You may also be able to determine what type of crusher, breaker or sizer is best suited for the job.
In the end, choosing a crusher, breaker or sizer for an application is not something to be taken lightly. Entrust a reputable equipment manufacturer who can ensure a selection that will help you meet your production goals at the most ROI.