How to choose the best crusher?

Choosing the best crushing equipment can be difficult. Fortunately, there are tools and software that can simplify the process of weighing different options and help make decisions. All of this analysis is based on careful calculations that take into account the capabilities and limitations of different crushers as well as operational requirements.Every crushing site and operation is different, and the best results are usually obtained by combining theoretical conclusions with practical experience of different materials, operating conditions, maintenance needs and the economic aspects of various alternatives.

Here is a brief list of some of the key issues according to the crushing stage. When determining the best technical solution for your needs, keep in mind that many crusaders are not only available in stationary, but also in mobile or portable versions – if you wish to move or transport the crusher regularly between production sites or sites.

If you are interested in a more detailed analysis tailored to your crushing operation, please contact us. With practical experience in thousands of different crushing applications worldwide, we are happy to help you find the equipment that best suits your needs.

Primary Crushing

Fine crushing with different types of crushers

The primary purpose of the primary crusher is to reduce the material to a size that allows it to be transported on a conveyor belt. In most crushing equipment, the jaw crusher is responsible for the primary crushing. High capacity plants, common in the mining industry but less popular in aggregate production, often use primary rotary crushers. When the processing material is easy to break and the abrasive property is not strong, the impact crusher may be the best choice for primary crushing.

One of the most important features of the primary crusher is its ability to receive feed without bridging. Large primary crushers are naturally more expensive than small crushers. Therefore, the investment cost calculation of the primary crusher is compared with the total cost of the primary stage, including the quarry surface cleaning, blasting and drilling costs. In many cases, dump trucks transport the rock to a stationary primary crusher. This can be an expensive solution. When vehicles are in high demand, amortization, fuel, tires and maintenance costs may be included. In modern aggregate operations, the use of a mobile primary crusher that can be moved along the rock surface is in many cases the most economical solution.

Initial crushing is performed using a jaw crusher

In terms of feed port size, customers get a higher return on investment when the main crusher is a jaw crusher. This means less drilling and blasting, as the crusher can accept larger boulders. When high capacity is required, the disadvantage of this crusher is that the discharge width is relatively small, and its capacity is limited compared to the discharge circuit of the rotary crusher. The jaw crusher is mainly used in factories with production capacity up to about 1600 tons/hour.

Initial crushing is performed using a rotary crusher

The primary rotary crusher has a high capacity, thanks to its large circular discharge port (much larger area than the jaw crusher) and continuous operation principle (while the reciprocating motion of the jaw crusher produces a batch crushing effect). Rotary crushers are unmatched in large plants with capacity from 1200 tons/hour and above. To have an inlet comparable to a jaw crusher, a primary rotary crusher must be taller and heavier. In addition, primary rotary crushers require a fairly strong foundation.

Initial crushing with impact crusher

The primary impact crusher has a high capacity and is designed to receive large feed sizes. The primary impact crusher has a processing speed of 200 t/h to 1900 t/h, with feed sizes up to 1830 mm (71 in) for the largest models. Primary impact crushers are typically used in non-abrasive applications, and the production of fine powder is not a problem. Of all the primary crushers, impact crushers are the ones that offer the best cube products.

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:

  1. Full crushing chamber. This means that cone head must be covered by rock.
  2. Stable and continuous feed.
  3. Material below setting in the feed 10-30% (but no filler and fines 0-4 mm normally).
  4. Maximum feed size. Reduction ratio must be limited to 3 (-4). Recommended max feed size is 50 mm.
  5. Correct feed distribution. Feed distribution should be non segregated and evenly distributed around crushing cavity.
  6. Setting closer to required product
  7. Correct choke point. This means the right selection of cavities for feed in question.
  8. 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. 
  9. 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.
  10. 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.