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Crushers – an ABC primer

This is my first Classical Machines article for Q&M magazine and I thought I would ‘break the ice’ so to speak, by outlining the types of crushers commonly used, so here is a brief encapsulated history of how crushing came into being and advanced through the years. By Richard Campbell

Humans have been crushing rocks ever since they needed smaller sized ones!

With the advent of dynamite and the steam shovel, the size of material that could be obtained by utilisation of these methods of extraction increased, and so consequentially, methods of reducing large chunks to a more manageable size was required.

Traditionally, manual labour had been used to reduce rocks to the required size but with the increased size and volume of material now capable of being extracted, this method was now too time consuming and labour-intensive.

Water powered stamping mills, similar to those employed by gold miners were used for a time but proved to be largely ineffective on harder more abrasive rocks, causing frequent breakdowns.

In 1858, Eli Whitney-Blake was granted a US patent for a ‘stone crushing machine’. This contrivance was steam powered and quite effective, so much so that Whitney-Blake went on to form the Blake Rock Crusher Company.

The machine consisted of a pair of jaws, comprised of a stationary and movable jaw, that enabled the crusher’s operator simply to feed stones into the machine and the closing action of the jaws would crush stone to the desired size. Over 500 machines were in use by 1879.

Incidentally, Whitney-Blake was the nephew of the inventor of the cotton gin, Eli Whitney!

The aim of the job

In operation, raw material (rocks of various sizes) are delivered to the primary crusher by dump truck, conveyor, wheel loader or excavator. Primary crushing reduces the large pieces to a size which can be handled by the downstream machinery (other crushers) to produce the desired size of aggregate.

Types of crushers

As requirements for different sizes and grades of crushed material have expanded, so has the range and type of crushing equipment progressed.

All crushers can be classified as falling into two main groups – Compressive Crushers that press the rock until it breaks, and Impact Crushers which use the principle of quick impacts to crush the rocks.

The jaw crushers

Jaw crushers, gyratory crushers, and cone crushers all operate on the compression principle. Impact crushers, in line with their name, utilize the impact principle.

Jaw crushers are principally employed as primary crushers, their main purpose being to reduce the material to a small enough size that it can be sent to the next crushing stage(s) if required.

As their name suggests, jaw crushers reduce rock between a fixed and a moving jaw. The moving jaw has a reciprocating motion, while the other jaw is stationary. When the material runs between the two jaws, the jaws crush the rocks into smaller pieces.

Gyratory crushers are also commonly used as primary crushers stage and also as secondary crushers once the larger rocks have been reduced to a more manageable size.

Gyratory crushers work on the principle of a fixed bowl and an oscillating element called the mantle. Fragmentation occurs between the bowl liner and mantle as well as from other debris that is within the bowl. Setting adjustments allow control of the size of the material produced.

Cone crushers operate in a similar manner to gyratory crushers but are rarely used as the primary crushing source, being used in the production of progressively smaller sizes of aggregate. Cone crushers also have setting adjustments to allow control of the size of the material produced.

There is also equipment known as Ball Mills, but these pieces of equipment grind rather than crush and are outside the scope of this article (as are screeners).

The impact crushers

Impact crushers are usually split into two main types – horizontal shaft impact (HSI) crushers and vertical shaft impact (VSI) crushers. As the name implies, impact is the method in which they operate.

Horizontal shaft impact (HSI) crushers (sometimes known as “hammermills”) are used in primary, secondary or tertiary crushing and reduce the feed material by highly intensive impacts coming from the quick rotational movement of hammers or bars fixed to a rotor. The particles produced are then further fragmentated inside the crusher as they collide against crusher chamber and each other.

Vertical shaft impact (VSI) crushers, on the other hand, are most often used in the last stage of the crushing process, especially when the finished product must have a precise size.

Manufacturers – From the authors research, a great many makers have offered crushing equipment in the modern era (1920s to present), and while some manufacturers have gone completely out of business due to recessions and industry downturns, a number of others have been acquired by newer companies and rebranded.

More often than not, these re-brandings have been of very successful pieces of equipment which have received new metallurgy and improved and updated systems to make them more viable in modern times.

Some stellar names from the past and present would include: Allis-Chalmers, Cedarapids, Pioneer, Kue-Ken, Pegson, Sandvik, Metso, Nordberg, Williams, Terex-Findlay, Eagle, Superior, Symons, Extec, Kleemann, Rimac and these are only a few which were uncovered during research. There are no doubt many others which could be added. Note that some of these companies have been bought/merged with other manufacturers on this list.

One thing that did become apparent however, was the shift away from fixed crushing plant to more mobile pieces of equipment which can be moved easily and set up quickly where required. This trend appears likely to continue with the move towards more ‘focussed’ quarries and mines which do not cover vast expanses of land as they used to.

For the model collector

For those readers who are keen to obtain some items of crushing plant, you are very much in luck. Quite a number of manufacturers produce diecast models of crushing equipment, mostly to 1:50 scale. Due to the complexity of the models, they are not particularly cheap and most model shops per-se do not stock them due to their specialised nature. However specialist shops in the USA such as Buffalo Road Imports do have a selection of crushing equipment models from Kleemann, Sandvik and Nordberg which are well worth checking out

This list does not include screening plant which is a whole different ball game.




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