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Module 3 - Mill Processes and Performance > Section 2 - The Break System > Flashcards

Section 2 - The Break System Flashcards

1
Q

Where is the Break system

A

at the beginning of the milling process

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2
Q

Object of the earlier break system?

A

To shear open the wheat and scrape away the endosperm from the bran skin in large particles
Bran is left as large flat flakes

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3
Q

What is the object of the break system on later breaks

A

To scrape the remaining endosperm off the wheat skin as cleanly as possible, avoiding any cutting up of the bran

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4
Q

What affects the length of the break system

A

The types of wheat to be used, flour specifications, mill performance

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5
Q

How many break passages are used

A

used to be 4, with introduction of softer wheats, now 5 (soft is more difficult to clean)

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6
Q

What do break rolls do

A

Break open and scrape the wheat grains to release endosperm

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7
Q

How many break stages are used?

A

Between 3 and 9, in the UK 4 or 5

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8
Q

Do roll flutes get finer or coarser with each stage?

A

Finer

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9
Q

What are more finely fluted rolls known as

A

Scratch rolls

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10
Q

Where are bran finishers installed

A

After later break rolls

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11
Q

What is the aim of the break system

A

To achieve maximum release of endosperm particles as semolina and middlings without disintegration of wheat skin or bran

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12
Q

How is the most suitable flute configuration, roll diameters, speeds, differentials and grooving spirals determined

A

Experience!

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13
Q

Can bran powder be separated from flour?

A

No - wheat skins should be kept as whole as possible through the break system

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14
Q

What does the extent to which the endosperm is scraped off the bran depend on

A

Type of wheat
Condition of wheat
Flour extraction and product specification required
Design of fluting on rolls
Adjustment of rolls

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15
Q

How is break roll surface measured

A

mm/100kg of wheat ground/24 hours

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16
Q

What is the general surface allocation of break systems

A

4-6mm/100kg/24h

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17
Q

break roll surfaces on 1BK, 2BK, 3BK, 4BKC, 4BKF, 5BKF

A

1mm, 1mm, 1mm, 0.5mm, 0.5mm, 0.4mm (total 4.4mm)

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18
Q

What alternative to rollermills can be used in break or reduction passages

A

Disc milling

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19
Q

What is the main characteristic of disc milling

A

High productivity in relation to machines physical size and energy consumption

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20
Q

Advantages of disc milling

A

compact
easily accessible and durable wearing parts
rapid disc and element replacement
accurate handwheel adjustment of grinding gap
large grinding surface gives high capacity and lower power consumption

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21
Q

Disadvantages of disc milling

A

Higher temp of flour produced may damage flour enzymes
possible degradation in proteins of whole wheat flour
high temp of released particles reduces sieving efficiency
increased maintenance requirements caused by sweating in sifter sections

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22
Q

What is the standard diameter for break/reduction rolls

A

250mm

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23
Q

How long are the largest rolls and what breaks are they used on

A

1500mm, 1bk, 2bk, 3bk

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24
Q

What size rolls do 4th and more breaks, scratch and reduction systems use

A

1000mm

25
Q

What are main rolls made of

A

Close-grained cast iron with hollow centre

26
Q

How many flutes per roll on 1bk, 2bk, 3bk, 4bk, 5bk

A

250-325, 400-450, 500-550, 675-750, 800-850

27
Q

What is the name of the flute profile that is most common

A

Saw tooth

28
Q

What size is the land

A

0.3-1mm

29
Q

What does the choice of flute profile depend on

A

Type of wheat to be ground
Mill flow sheet
Break release anticipated
Results required

30
Q

How long is a flutes effective life

A

6-12months

31
Q

Draw a saw tooth flute profile

A
32
Q

What is the spiral on a break roll

A

1 in 50 (2%)

33
Q

Label the spiral on 1bk 2bk 3bk 4bkc 4bkf

A

1:50, 1:50, 1:24, 1:24, 1:24

34
Q

Which roll is run quicker?

A

The upper roll

35
Q

What is the ratio of speeds of rolls called

A

Differential

36
Q

How quick does the upper roll tend to go

A

550rpm

37
Q

What is the usual differential

A

2.5 : 1

38
Q

Draw the sharp sharp, sharp dull, dull sharp and dull dull arrangements

A
39
Q

How is the amount of material released at each break passage limited?

A

Adjusting the grind to a predetermined percentage release

40
Q

What do percentage release figures depend on

A

Length and type of system
The grist
Required spec of the finished products

41
Q

What are the typical break releases for 76% extraction

A

1bk - 40%, 2bk - 36%, 3bk - 6%, 4bk - 1.8%, 5bk - 0.45%

42
Q

What is the total release for 76% extraction

A

84.25%

43
Q

What is Bran finishing

A

The process by which remaining endosperm particles are detached from the bran and recovered as flour

44
Q

What is scalping

A

The separation of coarse overtails after any grinding operation, particularly the coarser bran fragments with endosperm still adhering after each break stage

45
Q

What happens to throughs from scalping sieves

A

Graded on further sieves into coarse and fine semolinas and middlings

46
Q

What happens to graded stocks

A

consigned to separate groups of purifiers according to particle size and quality

47
Q

What happens to dunst stocks

A

graded off and sent direct to lower reduction rolls

48
Q

What are all the separations from feed to flour?

A

coarse overtails
-Coarse semolina
-Medium semolina
- Fine semolina
- Coarse Middlings
- Fine middlings
- dunst
flour

49
Q

What are the throughs of the first break rolls called

A

Break chop

50
Q

Where are bran finishers used

A

On coarse bran before third break and 4thbkc rolls, can also be used as final clean up after 5bk scalper.

51
Q

What affects efficiency of separation

A

Variations in flow or distortion of the range of particle size

52
Q

What affects capacity of sieving equipment

A

Moisture content of stocks - damp stocks do not flow well, sieving capacity is reduced and blockages can occur, too dry stocks have poor product quality

53
Q

In a pneumatic mill, what carries out the scalping, grading and dusting?

A

Plansifters

54
Q

What does variation in covers for scalping and grading depend on

A

Length of break system
Whether coarse and fine stock are treated separately
flute disposition and profile
type of wheat to be milled

55
Q

What are the two golden rules for covers on scalping and grading

A

Break stock should always be free of pure semolina
purifier stock should always be free from flour

56
Q

What is a good guide for calculating how much surface the break stock requires

A

half the total surface

57
Q

average sections for a 200 tonnes per day mill

A

1bk - 2 section
2bk - 2 sections
1&2 md - 1.5 sections
3bk - 2 sections
3md - 1 section
4bk - 2 sections
5bk - 1 section
X - 0.5 sections
reduction - 12 sections

58
Q
A
59
Q
A

Module 3 - Mill Processes and Performance (11 decks)

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