8. Grinding

There is a wide variety of grinding equipment and systems to suit different materials and conditions in the requirements of many industries. Hammer mills ring-roll mills, tube mills and ball mills, each have their characteristic features and may be combined with various systems of powder■classification. Many difficult materials in the chemical process industries, such as agglomerates, filter cake, and centrifuged products can be ground and dried simultaneously, and cooling arrangements may be used when grinding heat-sensitive materials. Caleiners and machines for mixing and blending can be incorporated in a common system. Specialized plants are designed to meet the requirements for deducing metallic and non-metallic ores, phosphates, sulfur, barytes and other raw materials for the chemical and plastics industries. Sometimes/ , the final stage of crushing and the preliminary stage of// grinding are economically combined into one operation. "*

Impact crushers can be used to combine crushing and grin­ding, in one operation^^These machines offer the lowest capital cost of any grinding mill. Hammer speeds of 4,000ft/min. will suffice for a course product, but upwards of 15,000 ft/min, may be required for fine grinding. With different forms of

crushing chambers, grinding elements and discharge screens, they can be built to handle and reduce almost any material that is not too abrasive. They can be adapted for wet crushing and grinding to produce a slurry, in this way serving an additional purpose, but there is some loss of machine capacity and an increase in power consumption when the machine is used in wet operations. They are used for grinding and classifying non-mejallic minerals and dry chemicals to a fineness ranging from 800 to 35 microns with a high degree of uniformity.

I/Grinding is effected from the action of rollers running inside a horizontal stationary ring. The machine is used for grinding chalk clays, and slate, lime and limestone products; coal and graphites talc and resins, pigments, lead oxides, and so on. It lends itself for. grinding in a controlled atmosphere* For example, because sul-

28

29

fur is highly flammable, inert gas is introduced when grinding it. Again, when grinding phenol-formaldehyde resins, refrigerated air la introduced to prevent softening of the resin.

Commentary

отвечая

1. ... in the requirements of many industries требованиям многих отраслей промышленности

2. ft/min (feet per minute) - футов в минуту

3. ranging from... to - в пределах от ... до

14. slurry -суспензия, пульпа

15. power consumption - потребление энергии 16.- fineness - мелкозернистость, тонкость 17.uniformity - однородность

18. roller - валец, ролик, валок

19. ring - кольцо, обод, хомут, обойма

20. clay - глина

21. slate - сланец

22. lime - известь

23. resin - смола

24. to lend itself - быть пригодным

25. sulfur - сера •

26. softening - размягчение

Answer the following questions

Words and word combinations :

1. to grind - дробить, молоть grinder - дробилка

grinding - дробление, измельчение

2. to suit - подходить, годиться

3. mill - мельница, дробилка hammer mill - молотковая мельница ring-roll mill - кольцевая роликовая мельница tube mill - трубная мельница

ball mill - шаровая мельница roller mill -вальцевая мельница

4. filter cake - осадок после фильтрования ■

5. heat-sensitive -термочувствительный

6. calciner - обжигательная печь

7. mixing = blending - смешивание

8. to meet the requirements - отвечать требованиям

9. to reduce -уменьшать, измельчать

10. crushing -дробление, раздавливание, измельчение crusher - мялка,дробилка

11. upwards - больше, выше, свьшіе

12. chamber - камера

13. discharge screen - выпускной грохот

1. What types of mills do you know?

1. What materials in the chemical process industries can be ground and dried simultaneously?

2. What materials can be reduced at specialized plants?

3. Can crushing and grinding be combined into one operation? 5. Can impact crushers be used in wet operations?

6. What are roller mills used for?

7. What parts does a roller mill consist of?

8. What materials can be ground by means of в roller mill?

Exercises

I. Open the brackets choosing the correct form of the Parti-Spies. Translate the sentences into Russian:

l.A positively {charging, cbarged) particle having the mass.

30

31

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.

II. 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.

III. Translate into Russian 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.