regulating granularity

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Grain & Feed Milling Technology is published six times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies,

the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis ofinformation published.Copyright 2010 Perendale Publishers L td. All rights reserved. No par t of this publication may be reproduced in any formor by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872

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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Designing bagginglinesto meetrequirements- Specifying and

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Germantechnologyconvincesin

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G lo ba l G ra in &Feedmarket report

Residue-freeconveyanceofgrain

RollerMillGrinders

Advantages,limitationsandhowrollermill

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