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Digital Re-print - March | April 2010Feature title: Regulating granularity
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T
his being said, let us look at the
ramifications of the task that
faces the miller in reducing and,perhaps more importantly, control-
ling granularity of products throughout
the mill, rather than just controlling the
granularity of the end product.
First, let us consider the role which moisture
plays in the process.
Essentially there to hold bran particles
together when wheat passes through fluted
break rolls, the moisture enables the miller to set
his rollermills to scrape endosperm away from
the bran layers and allow him to then present a
coarse granule to the head reduction passages
via the purifiers and the middlings system, always
assuming the miller decides to incorporate puri-
fiers in the flow.
Roll flutingThe choice of fluting is all important to the
control of granularity and the flute pattern and
profile, spiral and disposition all play an impor-
tant part in preparing the semolinas for further
grinding and grading when they leave the break
system.
In semolina mills, we know now that the
number of facets we can cut on a granule of
semolina greatly influences the light reflectance
and hence the colour of the resultant pasta.
Rather like the number of facets that can be
ground on a diamond influences the sparkle by
reflecting the light which is shone upon it.
Much work has been done on roll fluting
and the effects that different flute forms have
upon granularity and release of semolina fromthe whole grain.
In the 1970s Henry Simons technical millers
put together a set of roll flutes which are now
almost universal in their use, albeit the spiral,
speed and disposition of these may vary from
engineer to engineer with each having their own
favoured forms dependent on the diagramme
being adopted and the cereal being ground,
hard, soft, durum, rye, maize, etc.
The various profiles define the lead in angle
and the fall away angle with a fixed amount
to land allow the engineer to fully describe
the parameters of the cutting surfaces without
having to list them each time when re-fluting
a roll chill.
The number of roll passages in the break
and reduction system varies from mill to mill and
the number of rollermills per passage also varies
from mill to mill.
The use of flake disrupters has reduced the
number of reduction rolls used since prior to
their use flakes generated through heavy grinding
were simply scalped off and lost to the coarse
reduction system.
Since their introduction in the late 1960s
and early 1970s, initially using entoleters, roll
numbers have decreased dramatically.
Heavier grinding has become common place
and because the concentration of grinding is
confined to just the area immediately around
the roll chills the whole frame of the machine,
irrespective of manufacturer, is lighter and with
much more simplified feed gate arrangements.
Hence the cost of manufacture has comedown proportionately and we see rollermills
being offered to the millers at very economical
prices.
Assessing the grindI recall when first starting out doing my mill
practice I had the job of assessing the grind at
each rollermill and adjusting it in line with the
instruction of the mill manager, who, using his
experience knew what was best for his mill
and how the rolls should be set to obtain
the most effective extraction at the best flour
colour.
He spent time with me going round t he rolls
and showing me the correct way to set rolls for
an effective grind.
Sadly, today there are few vacancies for mill-
ing apprentices and the age of millers is rapidly
advancing. We are not very likely to have mill
managers with sufficient time available to spend
with new starters in the industry, despite this
probably being a very effective strategy for main-
taining mill balance and affecting quality control
in months and years to come.
We now look to the milling schools to pro-
vide our future millers and I am in some doubt
whether the mill manager of today actually
spends enough time in his mill to allow him the
depth of knowledge of his facility that he should
have. Invariably tied up with bureaucracy and
paperwork he or she rarely get the opportunity
Regulating granularityby Jonathan Bradshaw
It has often been said that flour milling has more in common with the paint industry than it does
with the food industry. Whilst paint manufacturers and millers alike resent this comparison as a
slur on their skills, the proponents of this statement simply refer to the fact that f lour milling is
mainly a size reduction exercise where we seek to judiciously reduce a grain of wheat to its finer
components and separate out the bran. Rather like reducing pigments down to fine powder and
removing impurities and extraneous matter too large to be of any value in the paint industry.
Gn&feed mnG tenooGy14 | march - pril 2010
FeatureGranularity
to spend any concentrated length of time in the
mill setting rolls and examining mill samples.
Milling skills are hard to come by these days
but those who have the opportunity to learn
from the older generation will have a skill that
will last.
Fewer machines same outputAs the rollermill has advanced in use and
technology it has led to fewer machines being
used for the same or greater output. So too
have the sifter and the purifier moved along and
been matched to enhanced throughput.
Had this not been the case we would have
seen disproportionate machine balance and
some rather top-heavy buildings. The drawer
type plansifter took the place of the centrifugal
reel and it has subsequently been replaced by
the square sieve plansifter which has grown from
four sections initially of 16 sieves to anywhere
up to 12 sections of 30 sieves and capable of
matching the throughput and efficiency of any of
the rolls available today.
The rollermill has seen the superimposed
machine come into use on certain passages
and, in combination with the modular sifter
which can be used
in even the tight-
est of areas and
the newer range of
three deck purifier
with infinitely vari-
able angled deck
the mill of today
can be fitted into
a relatively small
space than in our
forefathers days.
Controlgranularity
To be in a posi-
tion, however, to
control granularity
in the mill properly,
we cannot simply
look at the infeed
and outfeed from
any one individual
machine.
The break roll
passages prepare
Gn&feed mnG tenooGy march - pril 2010 | 15
Feature Granularity
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The revised and upgraded range of purifiers
and sifters are also products of extensive field
trials and all are offered with a view to being
able to control granularity effectively throughout
the mill which subsequently enables machines
to be set most effectively in order to match
customers finished product specifications.
Attention has been paid by all engineers to
such items as roll cleaning mechanisms, purifier
brushes, feed gates, ball cleaners and sifter clean-
ing devices.
Without these operating correctly and effi-
ciently much is lost in terms of machine setting
control and the regularity of settings is lost.
In rollermills where auto key pad adjust-
ment is provided and where the ability to
recall previous settings is available, history has
shown that such setting storage has not been
as reliable as it could be, principally because ofpoor cleaner operation and variable springs
and air pressure support, often brought about
by climatic changes, humidity variance from
night to day, etc.
Fortunately, these items have been over-
come by attention to detail and the use of cen-
tralized control of the mill can now also be used
as an aid to controlling and regulating granularity.
The changes in mill control and the auto-
matic engagement and disengagement of roller-
mills as feed rates vary has been quite rapid and
developments seem to have been perfected
quickly. What we can expect in years to come
remains to be seen but I hope it reflects practical
experience rather than simply engineers trying
out new processes that have no relevance to
milling.
The daily walk-aroundControlling granularity within the mill and
maintaining mill balance is crucial to minimizing
power consumption in the mill and optimising
finished products physically as well as maintaining
starch damage, water absorption, etc.
That walk round every day is still one of
the most valuable tools a miller has at his
disposal and is an excellent tool to have.
After all, we wouldnt buy a new car and not
observe how it operates so we shouldnt buy
a new mill and not pay careful attention to
how it operates.
range of flour are produced there are still several
mills who utilise one or two sizings passages in
their flow.
Originally brought into use in Australia as the
sizings and protein shift diagram, the use of siz-
ing rolls was meant to influence the distribution
of protein within the mill. This sizings system
became more widely used to control and influ-
ence the particle size distribution patterns to the
head reduction rolls in European mills when the
use of purifiers lost favour in diagrams, partly as
a response to the perceived benefit of shorter
flow diagrams and the ability of rollermills to
handle much heavier loadings whilst purifier
throughputs remained relatively low.
Now the balance of capacity has been
restored in mill design we no longer see roller
floors larger than sifter floors, nor the top and
bottom floors jammed with peripheral equip-ment, and the aesthetic appearance of mills is
much improved.
The major engineers, especially Buhler have
now been able to turn their attention to the
mill flow and diagrammes once again are being
considered carefully.
The fact that Buhler regularly build complete
new mills, much more frequently than most of
the other engineers puts them in the fortunate
position of being able to evaluate changes in
flow sheet design in many areas of the world
and then build their knowledge based on the
results of mill surveys.
Power consumptions can be evaluated and
changes made to flows in s ubsequent mill proj-
ects for example and the very fact that so many
mills are built that handle such a wide variety
of wheat enables a depth of information to be
gathered and utilized and improved upon from
project to project. This is just one example of
the benefits of having a full and busy order book
with suitably trained millers in the field.
Optimising machine designAnother advantage of frequent orders is
that individual machine design can be optimised
and the Antares rollermill is a classic example
with many new innovative features, the feed
gate arrangement being an obvious one being a
simplified refinement from previous versions of
standard issue rollermills.
stock for the sifters to separate effectively into
component parts, always ensuring total com-
bined release is adequate to enable targeted
extraction rates to be met. Middlings sifters
should be clad to extract flour as early as pos-
sible in the flow when milling soft wheats but
should enable head reduction grinding to be
optimized in hard wheat mills in order to obtain
optimum starch damage and water absorption.
Purifiers are there to improve the feed to
the reduction rolls and can, and should, have the
greatest influence on granularity in a mill, espe-
cially semolina mills where it is the purifier that
is the final arbiter of finished products, coarse,
medium and fine.
Head reduction rolls are where the bulk of
the grinding is done and where water absorp-
tion and starch damage are influenced to the
greatest degree, but it is of no value if a widerange of particle sizes are presented to an indi-
vidual passage, in fact, it can ruin a mills output
if too wide a range is offered as only the coarse
fraction will be reduced down further and the
finer particles of semolina may pass between the
roll chills untouched.
The miller needs to present as fine and
narrow a particle range to all rollermills but
especially to the head reduction passages.
Feed gatesSimilarly, the presentation of an even feed
across the width of the roll is vital.
At one time when feed gates were made
up of several parts that supposedly spread the
feed across the nip it was often common to
see feeds running through just the centre of
the rolls with large gaps across the width of the
roll. This was obviously inefficient but reflected
the cautious attitude that mill operatives had to
their rollermills and they would open feed gates
more than necessary in order to avoid choke
conditions being created by inherent variances
in feed rate t o different rollermills.
With the advancements made in feed gate
design and the use of variable speed feed rolls
and level sensors that automatically instigate
increases and decreases in feed roll speed this
situation is now almost totally avoided and we
see excellently spread feeds across the feed rolls.
Where mixed grists are milled and a wide
ImagecourtesyofBuhler
Gn&feed mnG tenooGy16 | march - pril 2010
FeatureGranularity
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Regulatinggranularity
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Designing bagginglinesto meetrequirements- Specifying and
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Residue-freeconveyanceofgrain
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Advantages,limitationsandhowrollermill
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