Section 8 - Milling Machines

Question 1

What does the feeding device of a rollermill consist of

Answer 1

A pair of feed rolls and a balanced feedgate system

Question 2

What are the main types of fluting

Answer 2

Radiused groove, 1.5mm saw tooth, 3mm saw tooth, screw head

Question 3

What is automatic feed roll adjustment

Answer 3

A feedgate that automatically opens and closes using a pneumatic servo control that opens and closes depending on the level of stock in the roll sightglass

Question 4

What are the special features of a grind roll

Answer 4

Roll protection, roll gap adjustments, roll cleaning, discharge hopper, exhaust, control system

Question 5

Can a roller mill run without feed?

Answer 5

NO! this would damage the roll surfaces, and cause heat build up which could present a fire risk.

Question 6

What controls whether the grinding rolls are engaged

Answer 6

The pneumatic servo control - it disengages the rolls when there is no feed

Question 7

Why is there automatic roll gap adjustment

Answer 7

Removes operator inconsistencies and improves mill balance, consistency of mill performance and finished flour quality

Question 8

What cleans the rolls

Answer 8

Roll brushes and cleaners (scrapers)

Question 9

What is roll ringing?

Answer 9

When there is too much build up on the rolls - it can affect mill performance and product quality and an increase in temp

Question 10

What does a discharge hopper do

Answer 10

Collects the ground stock and directs

Question 11

When are rollermills connected to a central exhaust

Answer 11

In mills with bucket elevators

Question 12

What is perfect tram

Answer 12

Roll axes are in parallel

Question 13

What expands more, the ends or centre of a roll

Answer 13

Ends

Question 14

How do you combat roll expansion

Answer 14

A taper or camber

Question 15

What were the different types of plansifter

Answer 15

Reels, Centrifugals, Free-swinging

Question 16

Why are centrifugals better than plansifters

Answer 16

Simpler in design and more accessible
More effective way of dressing reduction stocks, particularly with soft wheats
A double collecting worm allowed complete freedom in division of stocks

Question 17

Advantages of Plansifters over centrifugals

Answer 17

Occupy less space
Use less power
Lower capital cost
Dressing surface is more effectively used
Gentle rotary motion makes the stock much cleaner
Covers are more easily changed
More stock separation can be achieved
Efficiency of throughs dressing is increased with pneumatic conveying

Question 18

What is the set up of a free swinging plansifter and a drawer type plansifter

Answer 18

Suspended from girders by 4 sets of canes
driven by a central vertical shaft
driven from either a motor mounted on steelwork above, or a motor built in the sifter frame

Question 19

What affects the ‘throw’ of a sifter

Answer 19

The balance weight adjustment

Question 20

What are the advantages of a buhler planostar type MPAD

Answer 20

Sieves and sieve frames may be individually removed
The flow partitions and channels may be quickly changed
Maintenance can be carried out by one person
Wear on sieve covers is reduced

Question 21

Why was the square sieve plansifter developed

Answer 21

To achieve higher capacities within one machine

Question 22

What advantages do square sieve plansifters have over free-swinging plansifters

Answer 22

Increased sieving efficiency so fewer sections required for each passage
A section can be taken down and cleaned in 1/4 of the time it takes to dismantle older machines
Flow is easily altered
Less time is lost on burst covers
Sieve cleaners are more efficient and less prone to sticking
Less spouting required
Easier to maintain
Greater flexibility due to more separation
take up less space

Question 23

Benefits of a square sieve plansifter

Answer 23

More sieve dressing area
Higher capacity
Greater flexibility to change internal stock flow

Question 24

How many nests, sections and sieves can be in a plansifter

Answer 24

2, 3, 4 or 5 nests
4, 6, 8 or 10 sections
up to 30 sieves

Question 25

What does a multi arm sieve cleaner do

Answer 25

Clean both the sieve cloth and sieve tray simultaneously which prevents stock build up on collection trays and aids flow of material

Question 26

Advantages of Henry Simon “QUADRO” Plansifter

Answer 26

Special chassis design and material for vibrating operations
Up to 30 sieves per deck
Easy cleaning and maintenance
High capacity in limited spaces

Question 27

Why has nylon or plated wire replaced silk on sieves

Answer 27

Nylon is stronger for the same size so thinner yarn can be used
Silk has a higher moisture absorption so it will swell more handling moist stocks
Nylon is less expensive

Question 28

What materials can be used when making sieves

Answer 28

Nylon, plated wire, polyester, stainless steel

Question 29

Why is stainless steel not widely used in milling

Answer 29

its more expensive than ordinary wire
It requires high tension
it dents easily which causes blinding
it may splinter when fatigued
it polishes off smooth quickly
it is brittle
it isnt more corrosion resistant than synthetics
it is not magnetic so cant be recovered

Question 30

What are the advantages of stainless steel wire

Answer 30

It is possible to get metal detectable wire
Developments mean easier stretching characteristics and increased life span

Question 31

How does a purifier work

Answer 31

Stock is spread across the feed gate
It flows down onto the top deck of the sieves
Air is drawn up through the sieve decks
Air flow controlled by main exhaust valve and individual air compartment valves
Vibration of sieve decks and air being drawn through them cause the stock to stratify
Light particles float and dense particle sink
The dense particles pass through the sieves and fall onto the next deck or the collection hopper
The sieves get finer with each deck below
Sieves are finer at the inlet than the outlet

Question 32

Purpose of purification

Answer 32

Purifiers clean and grade semolina released in break system before going to the reduction rolls to be ground to flour
Cleaner feeds, lower ash content, better colour

Question 33

Label the purifier diagram

Answer 33

Page 52

Question 34

What vibration speed is optimum for a purifier and what is the speed of a standard vibratory motor

Answer 34

500rpm and 750 rpm

Question 35

What does air allow in a purifier

Answer 35

Lifts the light bran off the sieves so only coarser semolina passes through and is graded

Question 36

Why use individual air compartment valves

Answer 36

If the air were not divided into compartments, it would take the path of least resistance and suck up through the sieve where the stock is thinnest not thickest

Question 37

What layers are stratisfied from top to bottom

Answer 37

Light bran and beeswing
Heavy bran
Large composite particles
Small composite particles
Large pure endosperm
Small pure endosperm

Question 38

What does a purifier split the feed into

Answer 38

Throughs - all endosperm stocks, collected in a hopper
Overtails - endosperm with adhering bran, endosperm and bran requiring retreatment, mainly bran
Aspirations - light beeswing and dust