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Crushers or rock crushers are machines used to reduce the size of rocks and stones in aggregates production, construction material recycling applications, and in mining operations. Metso has designed, engineered and manufactured crushers for more than 100 years. Our offering covers different jaw crushers, gyratory crushers, cone crushers, and impact crushers – optimized for any size reduction need.
Efficient primary crushers.
High capacity primary crushers.
High uptime and consistent product quality in secondary, tertiary and quaternary applications.
Versatile and precise crushing in all stages of size reduction process.
Different types of crushers are optimal for distinct crushing needs
All rock crushers can be classified as falling into two main groups. Compressive crushers that press the material until it breaks, and impact crushers using the principle of quick impacts to crush the material. Jaw crushers, gyratory crushers, and cone operate according to the compression principle. Impact crushers, in turn, utilize the impact principle.
Jaw crushers are mainly used as primary crushers. Their main purpose is to reduce the material to a small enough size that it can be transported by conveyors to the next crushing stages.
As the name suggest, jaw crushers reduce rock and other materials between a fixed and a moving jaw. The moving jaw is mounted on a pitman that has a reciprocating motion, and the fixed jaw stays put. When the material runs between the two jaws, the jaws compress larger boulders into smaller pieces.
There are two basic types of jaw crushers: single toggle and double toggle. In the single toggle jaw crusher, an eccentric shaft is on the top of the crusher. Shaft rotation causes, along with the toggle plate, a compressive action.
A double toggle crusher has two shafts and two toggle plates. The first shaft is a pivoting shaft on the top of the crusher, while the other is an eccentric shaft that drives both toggle plates.
The chewing movement, which causes compression at both material intake and discharge, gives the single toggle jaw better capacity, compared to a double toggle jaw of similar size. Metso’s jaw crushers are all single toggle.
Gyratory crushers are frequently used in the primary crushing stage and a little less often in in the secondary stage.
Gyratory crushers have an oscillating shaft. The material is reduced in a crushing cavity, between an external fixed element (bowl liner) and an internal moving element (mantle) mounted on the oscillating shaft assembly.
The fragmentation of the material results from the continuous compression that takes place between the liners around the chamber. An additional crushing effect occurs between the compressed particles, resulting in less wear of the liners.
The gyratory crushers are equipped with a hydraulic setting adjustment system, which makes it possible to regulate the gradation of the crushed material.
Cone crushers resemble gyratory crushers from technological standpoint, but unlike gyratory crushers, cone crushers are popular in secondary, tertiary, and quaternary crushing stages. Sometimes, however, the grain size of the processed material is small enough by nature and the traditional primary crushing stage is not needed. In these cases, also cone crushers can carry out the first stage of the crushing process.
Cone crushers have an oscillating shaft, and the material is crushed in a crushing cavity, between an external fixed element (bowl liner) and an internal moving element (mantle) mounted on the oscillating shaft assembly.
An eccentric shaft rotated by a gear and pinion produces the oscillating movement of the main shaft. The eccentricity causes the cone head to oscillate between open side setting and closed side setting discharge opening.
The fragmentation of the material results from the continuous compression that takes place between the liners around the chamber. An additional crushing effect occurs between the compressed particles, resulting in less wear of the liners. This is called interparticular crushing also.
The cone crushers are equipped with a hydraulic setting adjustment system, which adjusts closed side setting and thus affects product gradation.
Depending on cone crusher, setting can be adjusted in two ways. The first way is for setting adjustment to be done by rotating the bowl against the threads so that the vertical position of the outer wear part (concave) is changed. One advantage of this adjustment type is that liners wear more evenly.
Another principle is that of setting adjustment by lifting or lowering the main shaft. An advantage of this is that adjustment can be done continuously under load.
To optimize operating costs and improve the product shape it is recommended that cone crushers are always be choke fed, meaning that the cavity should be as full of rock material as possible. This can be easily achieved by using a stockpile or a silo to regulate the inevitable fluctuation of feed material flow. Level monitoring devices detect the maximum and minimum levels of the material, starting and stopping the feed of material to the crusher, as needed.
Impact crushers are versatile crushing machines that can be used in any stage of the crushing process. However, the features and capabilities of different impact crusher types vary considerably.
Impact crushers are traditionally classified to two main types: horizontal shaft impact (HSI) crushers and vertical shaft impact (VSI) crushers. These different types of impact crushers share the crushing principle, impact, to reduce the material to smaller sizes, but features, capacities and optimal applications are far from each other.
Horizontal shaft impact (HSI) crushers are used in primary, secondary or tertiary crushing stage. HSI crushers reduce the feed material by highly intensive impacts originating in the quick rotational movement of hammers or bars fixed to the rotor. The particles produced are then further fragmentated inside the crusher as they collide against crusher chamber and each other, producing a finer, better-shaped product.
Vertical shaft impact (VSI) crushers, on the other hand, are used in the last stage of the crushing process, especially when its required that the end product has a precise cubical shape.
VSI crusher can be considered a ‘stone pump’ that operates like a centrifugal pump. The material is fed through the center of the rotor, where it is accelerated to high speed before being discharged through openings in the rotor periphery. The material is crushed as it hits of the outer body at high speed and due to rocks colliding against each other.
Crushing equipment selection
How to select an optimal crusher?
Selecting optimal crushing equipment can be difficult. Luckily there are tools and software available that simplify weighting different options and help in making decisions. The backbone of all these analyzes are careful calculations that take into account the capabilities and constraints of different crushers and operational requirements.
Every crushing site and operation is different, and the optimal results are normally obtained by combining theoretical conclusions with practical experience of different materials, operational conditions, maintenance needs, and economic aspects of various alternatives.
Below are some key issues listed according to crushing stages in brief. While defining the best technical solution for your requirements, it’s good to remember that many crushers are available not only as stationary but also as mobile or portable versions – in case you prefer to move or transport your crusher at the production site or between sites regularly.
If you are interested in more detailed analyzes tailored just for your crushing operations, please contact Metso experts. We have practical experience of thousands of different crushing applications around the world, and we are happy to help in finding the equipment that best fits your needs.
Primary crushing with different types of crusher
The main purpose of a primary crusher is to reduce the material to a size that allows its transportation on a conveyor belt. In most crushing installations a jaw crusher takes care of primary crushing. Plants with very high capacities that are common in mining and less popular in aggregates production, normally use a primary gyratory crusher. When the processed material is easy to crush and not very abrasive, an impact crusher may be the best choice for primary crushing.
One of the most important characteristics of a primary crusher is its capacity for accepting feed material without bridging. A large primary crusher is, naturally, more expensive than a smaller one. Therefore, the investment cost calculations for primary crushers are compared together against the total costs of primary stages, including quarry face clearing, blasting, and drilling costs. In many cases, dump trucks transport the rock to a stationary primary crusher. This may be an expensive solution. Amortization, fuel, tires, and maintenance costs can be included when the vehicles are in high demand. In modern aggregates operations, the use of mobile primary crushers that can move alongside the rock face is, in many cases, the most economical solution.
Primary crushing with jaw crushers
In terms of the size of the feed opening, the client gets a better return on investment when the primary crusher is a jaw crusher. That means less drilling and blasting because the crusher accepts larger boulders. The disadvantage of this type of crusher, when high capacity is required, is the relatively small discharge width, limiting the capacity as compared with the discharge circuit of a gyratory crusher. Jaw crushers are mainly used in plants producing up to approximately 1600 t/h.
Primary crushing with gyratory crushers
The primary gyratory crusher offers high capacity thanks to its generously dimensioned circular discharge opening (which provides a much larger area than that of the jaw crusher) and the continuous operation principle (while the reciprocating motion of the jaw crusher produces a batch crushing action). The gyratory crusher has no rival in large plants with capacities starting from 1200 t/h and above. To have a feed opening corresponding to that of a jaw crusher, the primary gyratory crusher must be much taller and heavier. Also, primary gyratories require quite a massive foundation.
Primary crushing with impact crushers
The primary impact crusher offers high capacity and is designed to accept large feed sizes. The primary impact crushers are used to process from 200 t/h up to 1900 t/h and feed sizes of up to 1830 mm (71") in the largest model. Primary impact crushers are generally used in nonabrasive applications and where the production of fines is not a problem. Of all primary crushers, the impactor is the crusher that gives the best cubical product.
Intermediate crushing with different types of crushers
The purpose of intermediate crushing is to produce several coarse-grade products – for example, road base aggregates – or to prepare material for final recrushing.
Generally the goal of secondary, tertiary, and quaternary crushing is to obtain the best possible size reduction at the lowest cost.
If the intermediate crushing is done with the purpose of producing railway ballast, the quality of the product is important. In other cases, there normally are no quality requirements, except that the product be suitable for fine crushing.
Cone crushers are often used for intermediate crushing, due to their high capacity and low operating costs.
Fine crushing with different types of crushers
Fine crushing with cone crushers
Due to their design, cone crushers are generally a more expensive investment than impactors are. However, when correctly used, a cone crusher offers lower operating costs than a conventional impact crusher. Therefore, clients crushing hard or abrasive materials are advised to install cone crushers for the final crushing and cubicising stage.
Cone crushers can in most cases also give a good cubic shape to fine grades. They can be adapted to different applications. This is an important factor, as client-specific needs often change during a crusher’s lifetime.
For cone crushers there are few rules to be followed of optimum cubical shape. These ‘Ten Golden Rules’ are:
- Full crushing chamber. This means that cone head must be covered by rock.
- Stable and continuous feed.
- Material below setting in the feed 10-30% (but no filler and fines 0-4 mm normally).
- Maximum feed size. Reduction ratio must be limited to 3 (-4). Recommended max feed size is 50 mm.
- Correct feed distribution. Feed distribution should be non segregated and evenly distributed around crushing cavity.
- Setting closer to required product
- Correct choke point. This means the right selection of cavities for feed in question.
- Crusher itself. New generation cones will produce considerably better shape than so called old generation. This is due to improved crusher kinematics and shape of cavity.
- Closed circuit. This improves shape by attrition, gives constant feed curve and recrushing of flaky product. In secondary stages closed circuit calibrates feed to tertiaries.
- Flow sheet in general. Important, especially in production of very high quality (shape) aggregate is that selective circuits are used, meaning that secondary and tertiary products are not mixed.
Fine crushing with impact crushers
The impactor family consists of two main types of impact crushers.
The conventional type has horizontal shaft configuration, known as HSI. The other type consists of a centrifugal crusher with vertical shaft, generally known as VSI. Impactor operation is based on the principle of rapid transfer of impact energy to the rock material. Impactors produce cubic products, and they can offer high reduction ratios as long as the feed material is not too fine. This means that in certain cases it is possible to use a single impact crusher to carry out a task normally done in several crushing stages using compressing crushers (i.e., jaw, gyratory, and/or cone crushers). Impactors are mostly used for nonabrasive materials.
The two main types of impactors can be further subdivided, into various groups.
Conventional horizontal-shaft impact crushers are available in various sizes and models, from high-capacity primary crushers for large limestone quarries to specially designed machines for the crushing of materials such as slag.
There are two main categories of VSI crushers – machines with impact wear parts around the body and machines that use a layer of accumulated material. The first type is in many respects similar to the conventional impactor with horizontal shaft and rotor. The second type became quite popular in the past decade and is known as the Barmac crusher. The difference between a conventional impactor and a VSI of the Barmac type is that the latter offers lower operating costs, but its reduction ratio is lower also. In a Barmac VSI, the material undergoes an intense rock-on-rock crushing process. In the other crushers, most of the reduction is done by the impact of stone against metal.
Customers operating old, rebuilt, or expanded plants often have problems with the shape of the product. In these cases, the addition of a Barmac VSI in the final crushing stage offers a solution to product shape problems.
The same applies to many mobile crushing units. As the number of crushing stages is normally small with this type of plant, it is almost impossible to obtain a good product shape unless the rock is relatively soft and thus more suited for the production of cubic product. A centrifugal crusher in the final stage can help to solve the problem.
The plant’s capacity and the size of the feed material are the main factors in selection of a primary crusher. To ensure good performance of the primary plant and prevent production losses, it is necessary to have an adequate correlation between the size of the feed material and the dimensions of the crusher feed opening. This means that the maximum size of feed material should be in the range of 60 to 80% of the crusher intake opening’s size. Factors that may have an effect on the choice include the type of feeder used, material flow to the crusher, and the availability of the necessary means (like breakers) to remove large-sized boulders in the event of bridging at the material intake opening. In cases where capacity requirements are very high, the natural choice is a primary gyratory crusher.
Naturally, a large intake opening is always an advantage. However, in practice, the limit is set by the capacity of the plant and the budgeted investment.
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