Crushers vs. Breakers: A Complete Guide for Choosing the…

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.

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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.

The most common types of crushers include Jaw Crushers, Gyratory Crushers, Cone Crushers, Impact Crushers, Roll Crushers and Hammermill Crushers.

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.

In particular:

• 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?

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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.

Selecting the appropriate crusher is important for every operation.

Understanding the stages of crushing and the types of crushers that best fit each stage simplifies equipment selection. Each type of crusher is different and used to achieve a certain end result.

Similarly, a certain output is expected at the end of each crushing stage for the next phase of the process. Aggregate producers who pair the correct crusher to the correct stage will be the most efficient and, in turn, the most profitable.

Crushing stages

Most aggregate producers are well acquainted with the selection of crushing equipment and know it is possible to select a piece of equipment based solely on spec sheets and gradation calculations. Still, theoretical conclusions must always be weighed against practical experience regarding the material at hand and of the operational, maintenance and economical aspects of different solutions.

Generally, material reduction is handled in stages. There are some single-crusher systems, but the most common systems involve at least two or three crushing stages.

Primary crushing. The duty of the primary crusher is, above all, to make it possible to transport material on a conveyor belt. In most aggregate crushing plants, primary crushing is carried out in a jaw crusher, although a gyratory primary crusher may be used. If material is easily crushed and not excessively abrasive, an impact breaker could also be the best choice.

The most important characteristics of a primary crusher are the capacity and the ability to accept raw material without blockages. A large primary crusher is more expensive to purchase than a smaller machine. For this reason, investment cost calculations for primary crushers are weighed against the costs of blasting raw material to a smaller size.

In most cases, trucks transport raw materials to a fixed primary. The costs of fuel, tires, maintenance and return on investment should also be considered.

A pit-portable primary crusher can be an economically sound solution in cases where the producer is crushing at the quarry face. In modern plants, it is often advantageous to use a moveable primary crusher so it can follow the movement of the face where raw material is extracted.

Intermediate (secondary) crushing. The purpose of intermediate crushing is to produce various coarser fractions or to prepare material for final crushing. If the intermediate crusher is used to make railway ballast, product quality is important.

In other cases, there are normally no quality requirements, although the product must be suitable for fine crushing. In most cases, the objective is to obtain the greatest possible reduction at the lowest possible cost.

Fine (tertiary) crushing. In this crushing stage, the quality and quantity of fine products are determined. Quality requirements can be stringent for final products, especially within the aggregate industry.

In most cases, the fine crushing and cubicization functions are combined in a single crushing stage. The selection of a crusher for tertiary crushing calls for both practical experience and theoretical know-how. This is where producers should be sure to call in an experienced applications specialist to make sure a system is properly engineered.

Crusher types

Jaw crushers. A jaw crusher is a compression type of crusher. Material is reduced by squeezing the feed material between a moving piece of steel and a stationary piece. The discharge size is controlled by the setting or the space between those two pieces of steel. The tighter the setting, the smaller the output size and the lower the throughput capacity.

As a compression crusher, jaw crushers generally produce the coarsest material because they break the rock by the natural inherent lines of weakness. Jaw crushers are an excellent primary crusher when used to prepare rock for subsequent processing stages.

Cone and gyratory crushers. These are also compression-type machines that crush material between a moving and a stationary piece of steel. The setting between the two pieces controls the output.

Although the chamber is round in shape, the moving piece of steel is not meant to rotate. Instead, a wedge is driven around to create compression on one side of the chamber and discharge opening on the opposite side. Cone crushers are used in secondary and tertiary roles as an alternative to impact crushers when shape is an important requirement, but the proportion of fines produced needs to be minimized.

Impact crushers. An impact crusher uses mass and velocity to break down feed material. First, the feed material is reduced as it enters the crusher with the rotating blow bars or hammers in the rotor. The secondary breakage occurs as the material is accelerated into the stationary aprons or breaker plates.

Impact crushers tend to be used where shape is a critical requirement and the feed material is not very abrasive. The crushing action of an impact crusher breaks a rock along natural cleavage planes, giving rise to better product quality in terms of shape.

Final thoughts

When selecting the crusher to best suit your operation, it&#;s important to understand your needs for each stage.

During the primary stage, look to get material to a size your conveyors and other processing machines can handle.

Some operations need further crushing in the secondary and tertiary crushing stages. These stages are used to better control and size the output.
Understanding how to best match the type of crusher to the right crushing stage will ensure crushing efficiency throughout your operation and overall profitability.

Gerry Mangrich is a process engineering specialist at McLanahan Corp.

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