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IPPI > Size reduction of solids > Flashcards

Size reduction of solids Flashcards

1
Q

-usually carried out in order to increase the surface because, in most reactions involving solid particles, the rate is directly proportional to the area of contact with a second phase

A

Size Reduction

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2
Q
  • applicable mainly to that part of the process where new surface is being created and holds most accurately for fine grinding where the increase in surface per unit mass of material is large
  • energy required for size reduction is directly proportional to the increase in surface
A

Rittinger’s Law

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3
Q
  • more closely relates to the energy required to effect elastic deformation before fracture occurs and is more accurate than Rittinger’s Law for coarse crushing where the amount of surface produced is considerably less
  • energy required is directly related to the reduction ratio L1/L2
A

Kick’s Law

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4
Q

*2 DISTINCT METHODS OF FEEDING MATERIAL TO A CRUSHER

A
  1. Free Crushing

2. Choke Feeding

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5
Q

-involves feeding the material at a comparatively law rate so that the product can readily escape; its time of residence in the machine is therefore short and the production of appreciable quantities of undersize material is avoided

A

FREE CRUSHING

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6
Q
  • in this case, the machine is kept full of material and discharge of the product is impeded so that the material remains in the crusher for a longer period.
  • this method is therefore used only when a comparatively small amount of materials is to be crushed and when it is desired to complete the whole of the size reduction in one operation
A

CHOKE FEEDING

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7
Q

if the plant is operated, as in “choke feeding”, so that the material is passed only once through the equipment, the process is known as

A

Open Circuit Grinding

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8
Q

when the product contains material which is insufficiently crushed, it may be necessary to separate the product and return the oversize material for a second crushing. This system is generally to be preferred and is known as

A

Closed Circuit Grinding

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9
Q

*MOHR SCALE OF HARDNESS

A
  1. Tale
  2. Rock Salt or Gypsum
  3. Calcite
  4. Fluorspar
  5. Apatite
  6. Felspar
  7. Quartz
  8. Topaz
  9. Carborundum
  10. Diamond
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10
Q

*NATURE OF THE MATERIAL TO BE CRUSHED / PROPERTIES OF THE FEED

A
  • Hardness
  • Structure
  • Moisture Content
  • Crushing Strength
  • Friability
  • Stickiness
  • Soapiness
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11
Q

affects the power consumption and the wear on the machine

A

HARDNESS

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12
Q

normal granular materials such as coal, ores and rocks can be effectively crushed employing the normal forces of compression, impact, etc. with fibrous materials it is necessary to effect a tearing action

A

STRUCTURE

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13
Q

it is found that materials do not flow well if they contain between about 5 and 50 per cent of moisture; under these conditions the material tends to cake together in the form of balls

A

MOISTURE CONTENT

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14
Q

The power required for crushing is directly proportional to the crushing strength of the material

A

CRUSHING STRENGTH

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15
Q

material’s tendency to fracture during normal handling

A

FRIABILITY

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16
Q

a sticky material will tend to clog the grinding equipment and therefore it should be ground in plant that can be readily changed

A

STICKINESS

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17
Q

a measure of the coefficient of friction of the surface of the material.

A

SOAPINESS

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18
Q

must be ground wet or in the presence of an inert atmosphere

A

EXPLOSIVE MATERIALS 💣

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19
Q

*TYPE OF CRUSHING EQUIPMENT

Coarse Crushers

A
  • Blake Jaw Crusher
  • Dodge Jaw Crusher
  • Gyratory Jaw Crusher
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20
Q

*TYPE OF CRUSHING EQUIPMENT

Intermediate Crushers

A
  • Crushing rolls
  • Disc crusher
  • Edge runner mill
  • Conical crusher
  • Stamp battery
  • Hammer mill
  • Single roll crusher
  • Pin mill
  • Squirrel cage disintegrator
  • End runner mill
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21
Q

*TYPE OF CRUSHING EQUIPMENT

Fine Crushers

A
  • Buhrstone mill
  • Roller mill
  • Raymond mill
  • Griffin mill
  • Centrifugal ball mill
  • Ring roller mill
  • Ball mill
  • Tube mill
  • Hardinge mill
  • Lopulco mill
22
Q

has a fixed jaw and a moving jaw pivoted at the top. The crushing faces themselves are formed either of manganese steel or of chilled cast iron and must be carefully fitted because they re brittle

A

Blake Jaw Crusher

23
Q
  • the moving jaw is pivoted at the bottom. The minimum movement is thus at the bottom and a more uniform product is obtained, but the crusher is less widely used because of its tendency to choke
  • this crusher is usually made in smaller sizes than the Blake crusher, because of the high fluctuating stresses that are produced in the members of the machine
A

Dodge Jaw Crusher

24
Q

-employs a crushing head, in the form of a truncated cone, mounted on a shaft, the upper end of which is held in a flexible bearing, whilst the lower end is driven eccentrically so as to describe a circle

A

Gyratory Crusher

25
Q

a common form of _______________ consists of a large hollow cylinder with perforated walls.

A

Coal Breaker

26
Q
  • has been used extensively for moderately fine crushing in the past but it has now been very largely superseded by more efficient equipment.
  • it consists of a number of heavy stamps-up to 500-1000kg in weight-which are raised mechanically and allowed to fall under gravity on to the material to be crushed
A

STAMP BATTERY

27
Q

In this type, a heavy cast iron or granite wheel (muller), is mounted on a horizontal shaft which is rotated in a horizontal plane in a heavy pan; alternatively, the muller remains stationary and the pan is rotated

A

Edge Runner Mill

28
Q

usually made in small laboratory sizes and consists of a cast iron or porcelain mortar which is rotated so that grinding takes place against a cylindrical pestle mounted with its axis vertical

A

End Runner Mill

29
Q

an impact mill employing a high speed rotating disc, to which are fixed a number of hammer bars which are swung outwards by centrifugal force

A

Hammer Mill

30
Q

a form of pin mill and consists of two horizontal steel plates with vertical projections on their near faces

A

Kek Mill

31
Q
  • the upper disc is stationary whilst the lower disc is rotated at high speed.
  • the mill gives a fairly uniform fine product with little dust and is extensively used with chemicals, fertilisers and other materials that are non-abrasive and easily broken
A

Pin-type Mill

32
Q

similar in action but employs vertical discs with horizontal bars. It is used with friable materials, such as coal and limestone, and with fibrous materials

A

Squirrel Cage Disintegrator or Bar Mill

33
Q

consists of a toothed crushing roll which rotates close to a breaker plate. It is used extensively in crushing coal.

A

Single Roll Crusher

34
Q

they are similar in construction to the gyratory crusher, though they will not take such a coarse feed and give a very much finer product; they operate at rather higher speeds

A

Conical Crushers

35
Q

employs two saucer-shaped discs mounted on horizontal shafts, one of which is rotated and the other is mounted in an eccentric bearing so that the two crushing faces continuously approach and recede

A

Disc Crusher

36
Q
  • one of the oldest forms of fine crushing equipment though it has, very largely, been superseded now by roller mills
  • this equipment has been used in the past for the grinding of grain, pigments for paints, pharmaceuticals, cosmetics and printer’s ink but is now used only where the quantity of materials is very small
A

Buhrstone Mill

37
Q
  • consists of a pair of rollers that rotate at different speeds (e.g. 3:1 ratio) in opposite directions
  • now extensively used in the flour milling industry and for the manufacture of pigments for paints
A

Roller Mill

38
Q

-This mill consists of a series of pushers which cause heavy cast iron balls to rotate against a bull ring like a ball race, and the pressure of the balls on the bull ring is produced by pressure applied from above

A

Babcock Mill

39
Q

-these machines are being manufactured in large numbers at the present time for the production of industrial minerals such as limestone and gypsum

A

Lopulco Mill or Ring Roll Pulveriser

40
Q

slightly less economical in operation than the Lopulco mill, but will give a rather finer and more uniform product

A

Raymond Mill

41
Q

similar to the Raymond mill except that it employs only one grinding head and the separation of the product is effected using a screen

A

Griffin Mill

42
Q

In its simplest form, it consists of a rotating hollow cylinder, partially filled with balls, with its axis either horizontal or at a small angle to the horizontal

A

Ball Mill

43
Q

*FACTORS INFLUENCING THE SIZE OF THE PRODUCT

A
  1. Rate of feed
  2. Properties of the feed material
  3. Weight of balls
  4. Diameter of the balls
  5. Slope of the mill
  6. Discharge freedom
  7. Speed of rotation of mill
  8. Level of material in mill
44
Q

The minimum speed at which the balls are carried around in this manner

A

Critical Speed of the Mill

45
Q

-similar to the ball mill in construction and operation, but the ratio of length to the diameter is usually 3 or 4:1, as compared with 1 or 1.5 for the ball mill

A

Tube Mill

46
Q
  • High carbon steel rods about 50 mm diameter and extending the whole length of the mill are used in place of balls
  • this mill gives a very uniform fine product and power consumption is low, but it is not suitable for very tough materials and the feed should not exceed about 25 mm in size
A

Rod Mill

47
Q
  • the body of the machine is generally supported on powerful springs and caused to vibrate in a vertical direction; vibration frequencies of between 6 and 60 Hz are common.
  • has a very much higher capacity than a conventional mil of the same size and consequently either smaller equipment can be used or a much greater throughput obtained
A

Vibration Mill

48
Q

Colloidal suspensions, emulsions, and solid dispersions are produced by means of ________________

A

Colloid Mills or Suspension Mills

49
Q
  • another form of mill which does not give quite such a fine product.
  • the solid is pulverised in jets of high pressure superheated steam or compressed air, supplied at pressures up to 3.5 MN/m^2
A

Jet Pulveriser

50
Q

In this pulveriser, reduction is by bombardment of the particles against each other and classification is effected by arranging for the fluid to leave the circulating gas stream through vanes which are situated just downstream of the top of the loop and on the inner face of the loop, i.e. against the centrifugal force

A

Wheeler Fluid Energy Mill

IPPI (4 decks)

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