Safety

Impact vs cone crushers: Which is more effective?

The post-primary crushing sector is largely divided into impact crushers for the processing of softer stone and cone crushers for the processing of harder, more abrasive stone. The advantages of both machines are well known.

The impact crusher, for example, has a higher co-efficient of reduction, produces crushed material with an optimal cubic shape for asphalts and concretes, allows faster and simpler maintenance, has a lower acquisition cost, gives continuous production curves with no irregularities or breaks between sizes (see Figure 1), permits bigger feed sizes and delivers higher production of small sizes. The cone crusher, on the other hand, has the advantage of fewer wear parts.

The vast majority of impact crushers have been conceived and designed to process relatively soft stone. Accordingly, their construction materials and components are strong enough to cope with this kind of material but are generally insufficiently robust to crush harder, more abrasive materials such as granite, flint, basalt and iron ore.

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However, what would happen if impact crushers could match cone crushers in terms of performance and wear costs? In emerging markets such as Russia, Africa, east Asia and South America among others, cone crushers are increasingly being replaced by impact crushers in granite and basalt quarries, providing an improvement in the quality of crushed material and a reduction in the cost per tonne, thereby increasing the competitiveness of some companies against their local rivals.

But how have impact crushers reached the wear parameters of cone crushers? In the past, the use of impact crushing for hard and abrasive stone was mostly limited to very small niche markets, especially in countries such as Spain and Germany. It was in markets such as these that the impact crusher evolved and matured for 50 years to become the trusted product it is today.

Based on innovation and experience, and an awareness of the advantages and disadvantages of impact crushers compared with cone crushers and the opportunities that this implies in overcoming the problem of wear, a few manufacturers have worked on two key areas: improving impact crusher efficiency and wear parts management; and developing the technology of the materials from which the parts are made.

{{image3-a:r-w:620}}The development of ceramic chrome alloys to increase the durability and abrasion resistance of wear parts, together with evolution in the management of these parts during use, has resulted in a significant reduction in the cost per tonne of material produced.

COMPETITIVENESS OF IMPACTORS

The smaller the output size, the more competitive impact crushers become because their percentage of finished product in the first pass is considerably higher than cone crushers. Combined with an upgrade to wear parts materials, this can allow impact crushers to reach a lower wear-cost ratio (per tonne) than cone crushers (see Table 1).

While it cannot be denied that the useful hours of impact crusher wear parts have not yet reached the useful hours of cone crusher wear parts in tertiary stage works, they have been upgraded enough to be a better option than cone crushers in some situations, allowing them to reach figures such as those shown in Table 1.

For secondary stage works, impact crushers have equalled cone crushers, overcoming all their disadvantages and matching their main advantage, the wear-cost ratio.

There is, however, an extra feature available when using a secondary stage impact crusher instead of a cone crusher.

Because of an impact crusher’s ability to deal with bigger feed sizes, the primary stage equipment can be smaller (ie lower purchase cost) or production through existing primary stage machines can be increased, because the jaw crusher will be able to work at a wider setting.

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Impact crushing is also more eco-friendly and can help save energy. A cone crusher will require the installation of a downstream VSI to achieve a similar cubic shape as that of an impact crusher, ie two machines instead of one and double the energy consumption.

Also, the friction-free movement and physical weight of the rotor and blow bars in an impact crusher help facilitate rotation, thereby drawing less power from the motor. This does not apply with cones because of the continuous friction involved in achieving the cone crushing action.

The reason impact crushing has not been developed in this way before is because most manufacturers produce both cone crushers and impact crushers, and each product is focused on its own market segment. Moreover, cone crushers are more expensive to purchase than impact crushers and provide greater returns for manufacturers. Most manufacturers, therefore, are not interested in developing their impact crushing lines out of the soft stone segment, and prefer to invest their R&D resources in upgrading their cone crusher lines. Only a small number of manufacturers, such as Spain’s ARJA Group, have focused their activity solely on manufacturing and developing impact crushing technology.


This story originally appeared in the September 2014 issue of Quarry Management UK and reappears in Quarry with kind permission.

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