Section 2 - The Break System Flashcards
Where is the Break system
at the beginning of the milling process
Object of the earlier break system?
To shear open the wheat and scrape away the endosperm from the bran skin in large particles
Bran is left as large flat flakes
What is the object of the break system on later breaks
To scrape the remaining endosperm off the wheat skin as cleanly as possible, avoiding any cutting up of the bran
What affects the length of the break system
The types of wheat to be used, flour specifications, mill performance
How many break passages are used
used to be 4, with introduction of softer wheats, now 5 (soft is more difficult to clean)
What do break rolls do
Break open and scrape the wheat grains to release endosperm
How many break stages are used?
Between 3 and 9, in the UK 4 or 5
Do roll flutes get finer or coarser with each stage?
Finer
What are more finely fluted rolls known as
Scratch rolls
Where are bran finishers installed
After later break rolls
What is the aim of the break system
To achieve maximum release of endosperm particles as semolina and middlings without disintegration of wheat skin or bran
How is the most suitable flute configuration, roll diameters, speeds, differentials and grooving spirals determined
Experience!
Can bran powder be separated from flour?
No - wheat skins should be kept as whole as possible through the break system
What does the extent to which the endosperm is scraped off the bran depend on
Type of wheat
Condition of wheat
Flour extraction and product specification required
Design of fluting on rolls
Adjustment of rolls
How is break roll surface measured
mm/100kg of wheat ground/24 hours
What is the general surface allocation of break systems
4-6mm/100kg/24h
break roll surfaces on 1BK, 2BK, 3BK, 4BKC, 4BKF, 5BKF
1mm, 1mm, 1mm, 0.5mm, 0.5mm, 0.4mm (total 4.4mm)
What alternative to rollermills can be used in break or reduction passages
Disc milling
What is the main characteristic of disc milling
High productivity in relation to machines physical size and energy consumption
Advantages of disc milling
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
Disadvantages of disc milling
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
What is the standard diameter for break/reduction rolls
250mm
How long are the largest rolls and what breaks are they used on
1500mm, 1bk, 2bk, 3bk
What size rolls do 4th and more breaks, scratch and reduction systems use
1000mm
What are main rolls made of
Close-grained cast iron with hollow centre
How many flutes per roll on 1bk, 2bk, 3bk, 4bk, 5bk
250-325, 400-450, 500-550, 675-750, 800-850
What is the name of the flute profile that is most common
Saw tooth
What size is the land
0.3-1mm
What does the choice of flute profile depend on
Type of wheat to be ground
Mill flow sheet
Break release anticipated
Results required
How long is a flutes effective life
6-12months
Draw a saw tooth flute profile
What is the spiral on a break roll
1 in 50 (2%)
Label the spiral on 1bk 2bk 3bk 4bkc 4bkf
1:50, 1:50, 1:24, 1:24, 1:24
Which roll is run quicker?
The upper roll
What is the ratio of speeds of rolls called
Differential
How quick does the upper roll tend to go
550rpm
What is the usual differential
2.5 : 1
Draw the sharp sharp, sharp dull, dull sharp and dull dull arrangements
How is the amount of material released at each break passage limited?
Adjusting the grind to a predetermined percentage release
What do percentage release figures depend on
Length and type of system
The grist
Required spec of the finished products
What are the typical break releases for 76% extraction
1bk - 40%, 2bk - 36%, 3bk - 6%, 4bk - 1.8%, 5bk - 0.45%
What is the total release for 76% extraction
84.25%
What is Bran finishing
The process by which remaining endosperm particles are detached from the bran and recovered as flour
What is scalping
The separation of coarse overtails after any grinding operation, particularly the coarser bran fragments with endosperm still adhering after each break stage
What happens to throughs from scalping sieves
Graded on further sieves into coarse and fine semolinas and middlings
What happens to graded stocks
consigned to separate groups of purifiers according to particle size and quality
What happens to dunst stocks
graded off and sent direct to lower reduction rolls
What are all the separations from feed to flour?
coarse overtails
-Coarse semolina
-Medium semolina
- Fine semolina
- Coarse Middlings
- Fine middlings
- dunst
flour
What are the throughs of the first break rolls called
Break chop
Where are bran finishers used
On coarse bran before third break and 4thbkc rolls, can also be used as final clean up after 5bk scalper.
What affects efficiency of separation
Variations in flow or distortion of the range of particle size
What affects capacity of sieving equipment
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
In a pneumatic mill, what carries out the scalping, grading and dusting?
Plansifters
What does variation in covers for scalping and grading depend on
Length of break system
Whether coarse and fine stock are treated separately
flute disposition and profile
type of wheat to be milled
What are the two golden rules for covers on scalping and grading
Break stock should always be free of pure semolina
purifier stock should always be free from flour
What is a good guide for calculating how much surface the break stock requires
half the total surface
average sections for a 200 tonnes per day mill
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
