Everything You Need to Know About Rock Crushers

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Do you need to process sand, gravel, minerals, rock, or other aggregate products and have not yet purchased or leased crushing equipment? There&#;s no question&#;you need to work with a capable and professional material handling equipment design and engineering company dedicated to selling, renting, and installing the best new crushers for your needs.

After all, our most recent Kemper Equipment success story illustrates what happens when an aggregate producer implements the wrong system design and material handling equipment!

However, if you&#;re new to the aggregate processing industry, you probably have a lot of questions about rock crushers. As foundational material handling equipment in all plants, crushers need to coordinate seamlessly with screens, conveyor systems, and washing equipment.

Today we&#;re breaking down everything you need to know about crushers to help you understand the questions you should ask as you search for the right material handling equipment for your operations.

Stages of Rock Crushing: Crushing Stations

It is common to use multiple crusher types within a project and set them up as stations in a circuit format to perform the necessary material reduction work. In many cases, primary, secondary, and tertiary, and quaternary stations are installed to reduce the rock to the desired size, shape, and consistency.

Of course, not all projects require all the stations or stages. Sometimes, primary crushing alone may offer enough reduction for your needs.

For instance, if the final size of your product only needs to be between 4 inches and 6 inches, a primary jaw or impact crusher can accomplish your goals. However, you will likely require a much finer product, and that means incorporating up to three&#;or even four&#;stations with a variety of crusher types.

1. Primary Crushing

As the first stage in a crushing circuit following extraction from a mine site, (or in the case of recycled asphalt production, delivery to the RAP processing plant via truck transport), primary crushing reduces material to a size and shape that can be handled by the secondary crusher.

Typically, the minimum setting on most primary crushers will be about 4 to 6 inches, as noted above. Compression-style jaw, cone, impact crushers, and gyratory crushers are most often appropriate as primary crushing equipment types, though there can be overlap between primary and secondary crushers as far as suitable types.

2. Secondary Crushing

In secondary crushing, reduction ratios become an essential consideration. Knowing just how fine you need your final output to be, along with the feed requirements of your tertiary or final reduction crushing station, will help you determine how much reduction needs to take place within this stage.

Cone crushers are often placed within the secondary crushing station because they are versatile in terms of feed, closed side setting, speed, and throw. With cone crushers, though, it is essential to operate them at consistent choked settings  to keep productivity up.

3. Tertiary/Quaternary/Final Reduction Crushing

The goal of the tertiary (third), quaternary (fourth) or final reduction stage of the crushing process is to size and shape rock or other material into a marketable product. Again, there may be overlap between stages in terms of which crusher styles work best.

Cone crushers, vertical shaft impactors (VSIs), horizontal impact crushers, or even high-pressure grinding roll crushers may be used in the final reduction position.

Types of Rock Determine the Crushers You Need

Sandstone, limestone, gravel, and granite are arguably the most common aggregates used in the construction industry today, but these rocks have very different hardness and abrasiveness characteristics.

The type of rock you plan to focus on processing in your operation will dictate the types of rock crushers you&#;ll need to include in your crushing circuit.

The more you know about the type of rock you wish to crush and what its end-use will be, the easier it is to choose the best equipment to achieve your project goals.

So, How Many Types of Rock Crushers Are There?

The question &#;how many types of rock crushers are there?&#; can be answered in a variety of ways depending on what the person asking is trying to learn about rock, sand, gravel, or mineral processing.

The answer might be three to four if you&#;re talking about setting up stations in a complete rock crushing plant. Those are the primary, secondary, and tertiary/quaternary/final reduction rock crushers, which we covered above.

Of course, there are also different styles of rock crushers. Compression-style jaw and cone crushers, for example, fit into the various stations in a crushing circuit (depending on factors like the sizes, varieties, and hardness of the rock you need to crush, as well as the necessary output).

The number of crusher types in terms of style and configuration can be more challenging to quantify, as there are lots of ways to customize rock crushers. However, you&#;ll find four basic designs&#;cone, jaw, gyratory, and impact crushers&#;operating within many crushing plants.

Jaw Crushers

In compression crushing, jaw crushers tend to be more of a blunt instrument compared to cone crushers, which is why they&#;re often used in the primary rock crushing circuit stage.

Jaw crushers are also known as &#;rock breakers&#; and are used to break up larger, harder materials into more manageable pieces. They tend to do well with many different types of materials and don&#;t display as much wear and tear as impact-style rock crushers. They also produce minimal fine materials and dust, though the finished product with this type of rock crusher almost always requires secondary crushing.

To learn more about jaw crushers, you&#;ll want to catch our previous blog post all about these tough pieces of material handling equipment and the most common questions operators have about jaw crushers.

Gyratory Crushers

Gyratory crushers feature a conical head and concave surface (often lined with manganese steel) and break apart material by compression through what is known as eccentric movement.

Like jaw crushers, gyratory crushers are often utilized in primary crushing stations, though they may sometimes be used as secondary crushers, as well.

Cone Crushers

Similar to jaw and gyratory crushers, cone crushers work by compression, which means they reduce materials by squeezing them until they break apart.

There are also impact-style rock crushers&#;namely HSI and VSI equipment (more on those in a moment).

Cone crushers are built with a rotating mantle in a concave bowl lined with manganese&#;this is similar to gyratory crushers, but the crushing chamber in cone crushers is not as steeply angled.

Cone crushers can accept medium-hard to very hard and abrasive feeds that might be dry or wet, though not sticky (whereas gyratory crushers are better at handling softer, dryer feeds). Their output will be a relatively cubical product, with a reduction ratio of about 6-to-1 through 4-to-1.

Understanding the operating principle of cone crushing equipment is best illustrated in a visual format&#;check out this demonstration video from our Kemper Equipment YouTube channel.

Impact Crushers &#; VSIs and HSIs

Impact-style crushers include VSIs, as well as horizontal shaft impactors (HSIs), and are best used with less abrasive rock types, like limestone. These types of machines break apart material by the impacting forces of certain wear parts known as blow bars and impact plates or toggles.

Some operations also use impact-style crushers after they have already used a different type of rock crusher that produces a more elongated stone. This helps further shape the crushed material into a finer consistency with a more cubical nature.

Impact crushers tend to be less expensive than compression crushers (aka cone and jaw crushers, which we already covered) and have a higher reduction ratio. They can also break sedimentary deposit-type rocks&#;limestone and similar&#;along natural lines, which rounds off sharp angles and weak edges. This can produce a result that is more sand-like in nature.

Drawbacks of impact crushers include their tendency to produce an excess of fine materials if used with softer rocks. Impact rock crushers can also require frequent part changes and can create a large amount of dust that can be an issue on some worksites.

Portable vs. Stationary Crushing Plants

Depending on the length of your project and how mobile your crushing equipment needs to be, you can choose either stationary or portable/modular crushing plants.

Stationary plants have long been preferred because they feature a higher capacity and efficiency and lower production costs with easier maintenance. They also have historically featured a lower energy cost if you have on-site electricity, and no additional equipment is needed to move them from place to place.

The tides are beginning to change, though, and portable equipment has been technologically advancing to the point that it may be able to replace stationary plants in the future.

Want more information on Metal Crushing Solutions? Feel free to contact us.

It&#;s true that portable material handling equipment already offers unmatched production flexibility. For instance, if you need to move your crushing plant more than once a year to multiple job sites, you are likely better off investing in portable equipment.

These self-contained plants are better suited to smaller projects and can be moved from project to project as necessary. They are often still not quite as efficient and have less capacity than stationary plants, but they can be more cost-effective in the long run if you have multiple projects in different areas.

Kemper Equipment Has the Crushers You Need for Your Operation

Still have questions about crushers or any other aspects of aggregate processing and material handling?

Here at Kemper Equipment, we offer the best performing crushing equipment that will work hard to make any finished products you plan to produce&#;including sand, gravel, fertilizer, specialty mineral products, recycled asphalt, salt, coal, and slag&#;efficiently and affordably. Contact us today to discover how we can provide a custom-designed crushing circuit or retrofit a new rock crusher into your existing operation.

Crushers and Their Types

Crushers and Their Types

A crusher is a multi dimensional machine which is designed to reduce large size materials into smaller size materials. Crushers may be used to reduce the size, or change the form of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials (as in the case of ore), so that pieces of different composition can be differentiated for separation.

Crushers are normally low speed machines that are designed for breaking large lumps of ores and stones, even aving a size with a diameter of over one and half meter. The purpose of crusher is to reduce the size of the materials for making them usable in construction or industrial use, or for extraction of valuable minerals trapped within a ore matrix.

Crushing is the process of transferring a force amplified by mechanical advantage through a material made of molecules that bond together more strongly, and resist deformation more, than those in the material being crushed do. Crushing devices hold material between two parallel or tangent solid surfaces, and apply sufficient force to bring the surfaces together to generate enough energy within the material being crushed so that its molecules separate from (fracturing), or change alignment in relation to (deformation), each other.

There are four basic ways to reduce a material, namely (i) impact, (ii) attrition, (iii) shear, and (iv) compression. Most crushers employ a combination of all these crushing methods.

• Impact &#; In crushing terminology, impact refers to the sharp, instantaneous collision of one moving object against another. Both objects may be moving, or one object may be motionless. There are two variations of impact, namely (i) gravity impact, and (ii) dynamic impact. Material dropped onto a hard surface such as a steel plate is an example of gravity impact. Gravity impact is most often used when it is necessary to separate two materials which have relatively different friability. The more friable material is broken, while the less friable material remains unbroken. Separation can then be done by screening. Material dropping in front of a moving hammer (both objects in motion), illustrates dynamic impact. When crushed by gravity impact, the free-falling material is momentarily stopped by the stationary object. But when crushed by dynamic impact, the material is unsupported and the force of impact accelerates movement of the reduced particles toward breaker blocks and/or other hammers. Dynamic impact has definite advantages for the reduction of many materials.
• Attrition &#; It is a term applied to the reduction of materials by scrubbing it between two hard surfaces. Hammer mills operate with close clearances between the hammers and the screen bars and materials reduce by attrition combined with shear and impact reduction. Though attrition consumes more power and exacts heavier wear on hammers and screen bars, it is practical method for crushing the less abrasive materials such as limestone and coal.
• Shear &#; It consists of a trimming or cleaving action rather than the rubbing action associated with attrition. Shear is usually combined with other methods. For example, single roll crushers employ shear together with impact and compression. Shear crushing is normally called for under the conditions when material is somewhat friable or when a relatively coarse product is desired. It is usually employed for primary crushing with a reduction ratio of 6 to 1.
• Compression &#; As the name implies, crushing by compression is done between two surfaces, with the work being done by one or both surfaces. Jaw crushers using this method of compression are suitable for reducing extremely hard and abrasive materials. However, some jaw crushers employ attrition as well as compression and are not as suitable for abrasive materials since the rubbing action accentuates the wear on crushing surfaces. As a mechanical reduction method, compression is to be used if the material is hard and tough, if the material is abrasive, if the material is not sticky, and where the finished product is to be relatively coarse.

The above four methods for the size reduction of materials are shown in Fig 1.

Fig 1 Methods for size reduction of materials

 The reduction of size of the material when it pass through a crusher is expressed as reduction ratio. The reduction ratio is the ratio of the crusher feed size to product size. The sizes are usually defined as the 80 % passing size of the cumulative size distribution.

 Types of crushers

Crushers are classified into three types  based upon the stage of crushing they accomplish. These are (i) primary crusher, (ii) secondary crusher, and (iii) tertiary crusher. The primary crusher receives material directly from run of mine (ROM) after blasting and produces the first reduction in size. The output of the primary crusher is fed to a secondary crusher, which further reduces the size of the material. Similarly the output of secondary crusher is fed to the tertiary crusher which reduces the material size further. Some of the materials may pass through four or more of the crushing stages before it is reduced to the desired size. The degree of crushing is spread over several stages as a means of closely controlling product size and limiting waste material.

Crushers are also classified by their method of mechanically transmitted fracturing energy to the material. Jaw, gyratory and roll crushers work by applying compressive forces while impact crushers such as hammer crusher apply high speed impact force to accomplish fracturing.

There are several types of crushers which are used in various industries. These are given below.

Jaw crusher

 Jaw crusher is used as primary crusher. It uses compressive force for breaking the material. This mechanical pressure is achieved by the two jaws of the crusher. Reduction ratio is usually 6:1. The jaw crusher is consisting of two vertical jaws installed to a V form, where the top of the jaws are further away from each other than the bottom.

One jaw is kept stationary and is called a fixed jaw while the other jaw, called a swing jaw, moves back and forth relative to it, by a cam or pitman mechanism. The volume or cavity between the two jaws is called the crushing chamber. The movement of the swing jaw can be quite small, since complete crushing is not performed in one stroke. The inertia required to crush the material is provided by a weighted flywheel that moves a shaft creating an eccentric motion that causes the closing of the gap.

Feed is entering to crusher from the top and lumps are crushed between jaws. Jaw crushers are heavy duty machines and hence need to be robustly constructed. The outer frame is generally made of cast iron or steel. The jaws themselves are usually constructed from cast steel. They are fitted with replaceable liners which are made of manganese steel, or Ni-hard (a Ni-Cr alloyed cast iron).Usually both jaws are covered with replaceable liners. Also in some types, the liners can be turned upside down after a while, extending the replacement time.

Gyratory crusher

A gyratory crusher is similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head with both the surfaces are typically lined with manganese steel liners. The inner cone has a slight circular movement, but it does not rotate. The movement is generated by an eccentric arrangement. The crushing action is caused by the closing of the gap between the mantle line (movable) mounted on the central vertical spindle and the concave liners (fixed) mounted on the main frame of the crusher. The gap is opened and closed by an eccentric on the bottom of the spindle that causes the central vertical spindle to gyrate. The vertical spindle is free to rotate around its own axis.

The material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces. A gyratory crusher is used both for primary or secondary crushing.

 Cone crusher

 Cone crusher is consisting of a crushing chamber, a crushing cone and a operating mechanism. The cone is built in to a vertical shaft, which is supported from the top with a bowl-shaped bearing and from the other end to an eccentric operating mechanism.

Cone crusher is similar in operation to a gyratory crusher, with less steepness in the crushing chamber and more of a parallel zone between crushing zones. A cone crusher breaks material by squeezing the material between an eccentrically gyrating spindle, which is covered by a wear resistant mantle, and the enclosing concave hopper, covered by a manganese concave or a bowl liner. As the material  enters the top of the cone crusher, it becomes wedged and squeezed between the mantle and the bowl liner or concave. Large pieces of the material are broken once, and then fall to a lower position (because they are now smaller) where they are broken again. This process continues until the pieces are small enough to fall through the narrow opening at the bottom of the crusher.

A cone crusher is suitable for crushing a variety of mid-hard and above mid-hard materials. Feed is dropped to the crusher from the top and it is crushed between the crushing chamber and the slowly rotating cone.

Cone crushers are mostly used for the large scale crushing in the mining industry. It has the advantage of reliable construction, high productivity, easy adjustment and lower operational costs. The spring release system of a cone crusher acts as an overload protection that allows tramp to pass through the crushing chamber without damage to the crusher.

Roller crusher

Roller crusher is  a crusher that breaks material by squeezing it between two revolving metal cylinders, with axes parallel to each other and separated by a space equal to the desired maximum size of the finished product. It consists essentially of two opposite directions driven cylinders that are mounted on horizontal shafts. The other shaft is mounted permanently in the frame and is leaning on robust springs. The gap between cylinders can be adjusted, so the size of crushed product is easily adjustable. Usually both cylinders are covered with manganese steel liners. Crushing ratio is usually lower than in other crushers. Roll crusher is suitable for fine crushing. The roll crusher uses compression to crush materials. Reduction ratio is 2 to 2.5 to 1. Roller crushers are not recommended for abrasive materials.

Hammer crusher

Hammer crusher consists  of a high-speed, usually horizontally shaft rotor turning inside a cylindrical casing. The crusher contains a certain amount of hammers that are pinned to the rotor disk and the hammers are swinging to the edges because of centrifugal force. Feed is dropped to the crusher from the top of the casing and it is crushed between the casing and the hammers. After crushing the material falls through from the opening in the bottom.

Impact crusher

Impact crushers make use of impact rather than compression to crush material. The material is contained within a cage, with openings of the desired size at the bottom, end, or side to allow crushed material to escape. There are two types of impact crushers namely (i) horizontal shaft impact crusher, and (ii) vertical shaft impact crusher.

Impact crushers are often used with materials, which are soft or which are easily cleaving from the surface. The crusher consists of a fast spinning rotor and beaters attached to the rotor. Feed is entering to the crusher from the top and crushing starts immediately when the feed is impacted with beaters towards the crusher&#;s inner surface. Impact crusher can also be equipped with a bottom screen, which prevents material leaving the crusher until it is fine enough to pass through the screen. This type of crusher is usually used for soft and non abrasive materials.

 Mineral sizers

The basic concept of the mineral sizer is the use of two rotors with large teeth, on small diameter shafts, driven at a low speed by a direct high torque drive system. This design produces three major principles which all interact when breaking materials using sizer technology. The unique principles are the three-stage breaking action, the rotating screen effect, and the deep scroll tooth pattern.

• The three-stage breaking action &#; Initially, the material is gripped by the leading faces of opposed rotor teeth. These subject the material to multiple point loading, inducing stress into the material to exploit any natural weaknesses. At the second stage, material is broken in tension by being subjected to a three point loading, applied between the front tooth faces on one rotor, and rear tooth faces on the other rotor. Any lumps of material that still remain oversize, are broken as the rotors chop through the fixed teeth of the breaker bar, thereby achieving a three dimensional controlled product size.
• The rotating screen effect &#; The interlaced toothed rotor design allows free flowing undersize material to pass through the continuously changing gaps generated by the relatively slow moving shafts.
• The deep scroll tooth pattern &#; The deep scroll conveys the larger material to one end of the machine and helps to spread the feed across the full length of the rotors. This feature can also be used to reject oversize material from the machine.

Criteria for selection of crusher

 The following are the criteria used in the selection of the right type of a crusher for crushing a material.

• Production requirement &#; It includes output size and shape, and the required capacity.
• Ore characteristics &#; Include material specification, feed (input) size, material friability, and material abrasiveness.
• Operational considerations &#; It includes power demand, equipment availability (hours/annum), availability and cost of replaceable parts, reduction ratio, maintenance requirements, needed manpower, approachability of parts for maintenance, availability of spares, safety and environment.
• Equipment ruggedness &#; Can the crusher pass uncrushable debris without damage to the crusher.
• Capital cost of the crusher and the total cost of the crusher station




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