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Crushers

A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust. 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 rock ore), so that pieces of different composition can be differentiated.

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. The earliest crushers were hand-held stones, where the weight of the stone provided a boost to muscle power, used against a stone anvil. Querns and mortars are types of these crushing devices.

In industry, crushers are machines which use a metal surface to break or compress materials. Mining operations use crushers, commonly classified by the degree to which they fragment the starting material, with primary and secondary crushers handling coarse materials, and tertiary and quaternary crushers reducing ore particles to finer gradations. Each crusher is designed to work with a certain maximum size of raw material, and often delivers its output to a screening machine which sorts and directs the product for further processing. Typically, crushing stages are followed by milling stages if the materials need to be further reduced. Crushers are used to reduce particle size enough so that the material can be processed into finer particles in a grinder. A typical circuit at a mine might consist of a crusher followed by a SAG mill followed by a ball mill. In this context, the SAG mill and ball mill are considered grinders rather than crushers.

In operation, the raw material (of various sizes) is usually delivered to the primary crusher's hopper by dump trucks, excavators or wheeled front-end loaders. A feeder device such as a conveyor or vibrating grid controls the rate at which this material enters the crusher, and often contains a preliminary screening device which allows smaller material to bypass the crusher itself, thus improving efficiency. Primary crushing reduces the large pieces to a size which can be handled by the downstream machinery.

Some crushers are mobile and can crush rocks (as large as 16 in), concrete and asphalt into material as it is driven over material on road surface, thus removing the method of hauling oversized material to a stationary crusher and back to road surface. They are used, for example in road constructions.

For the most part advances in crusher design have moved slowly. Jaw crushers have remained virtually unchanged for sixty years. More reliability and higher production have been added to basic cone crusher designs that have also remained largely unchanged. Increases in rotating speed, have provided the largest variation. For instance, a 48 inch cone crusher manufactured in 1960 may be able to produce 170 tons/h of crushed rock, whereas the same size cone manufactured today may produce 300 tons/h. These production improvements come from speed increases and better crushing chamber designs.

The largest advance in cone crusher reliability has been seen in the use of hydraulics to protect crushers from being damaged when uncrushable objects enter the crushing chamber. Foreign objects, such as steel, can cause extensive damage to a cone crusher, and additional costs in lost production. The advance of hydraulic relief systems has greatly reduced downtime and improved the life of these machines.

4. Answer the questions to the text:

1. What is a crusher?

2. Where are crushers primarily used?

3. What types of crushers do you know?

4. What is crushing?

5. What kind of crushers is most reliable in use?

6. What is the difference between the crushers and the mill?

7. What is crusher classification based on?

5. Match the words to make up possible word combinations:

6. Try to put these words in the right order and make a sentence:

1. A crusher is / to reduce / smaller rocks / a machine designed / into / large rocks.

2. Crushers are / material / particle size / used / to reduce.

3. Foreign objects / a crusher / can cause / damage to /extensive /.

4. Each crusher is /with /raw material /a certain maximum size of / designed to work.

5. The raw material / delivered to /by dump trucks /usually / is / the primary crusher's hopper.

6. Each crusher / of raw material / to work / a certain maximum size / is designed / with /.

7. Crushers / which / are machines / to break or compress / materials / use a metal surface /.

7. Say if the statement is true or false. If the statement is false give the correct answer:

8. Read the following text. Retell it to a partner:

Hydraulic Cone Crusher

HP Series of highly efficient Hydraulic Cone Crusher is a world-level cone crusher introduced with the up-to-the-minute technology of Germany. The cone crusher not only improves the production capacity and crushing efficiency, but also widens applying area, hardness range of materials from limestone to basalt. It has a great crushing performance in the work of medium-size crushing, fine crushing and super fine crushing.

The crusher is the improved type of spring cone crusher and can be used to replace ordinary hydraulic cone crusher in the field of mining and construction. It is the most ideal equipment for large stone crushing factory and mining industry.

The performance of ordinary hydraulic cone crusher acts as the reference for the performance of HP series of cone crusher. As a composing unit of the production line, its performance can be influenced by other units like feeder, belt conveyor, vibrating screen, motor, transmission part and hopper, etc.

9. Open the brackets choosing the correct form of the Participles. Translate the sentences into Ukrainian:

l. A positively (charging, charged) particle having the mass.

2. The scientist found that X-rays (producing, produced) were complex.

3. Oppositely (charging, charged) particles exert forces of attraction on one another.

4. The work (doing, done) by these research-workers resulted in many new discoveries.

5. The investigation (following, followed) by many experiments was of great importance.

6. The nuclei (forming, formed) in this reaction are unstable.

7. When (working, worked) in the lab the students carried out many experiments.

8. The student (translating, translated) the article knows English very well.

9. When (heating, having heated) this substance one should be very careful.

10. (Investigated, having investigated, Investigating) all the properties of new water, they could understand, the mystery of silvery clouds.

11. The (dissolving, dissolved, having dissolved) materials may be soluble solids, liquids or gases.

12. Later (using, used, having used) in steam boilers, should be free from substances that cause corrosion.

10. Use the following sentences in all the forms and tenses adding suitable adverbial modifiers where necessary:

1. People employ glass for many purposes.

2. Stainless steel is widely used in chemical machinery.

3. Pumps find many applications in the chemical process industries.

4. A crusher is a machine designed to reduce large rocks.

11. Translate into Ukrainian paying attention to the word "for":

1. Our age is called the age of atom, for we use the atom for various purposes.

2. For a long time scientists were not able to discover the secret of the atom.

3. Hydrogen is widely used for it contains a large amount of chemical energy.

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1. Pick up the key words from the text “Crushers”. Make up your own sentences with them.

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