Section 8 - Milling Machines Flashcards
What does the feeding device of a rollermill consist of
A pair of feed rolls and a balanced feedgate system
What are the main types of fluting
Radiused groove, 1.5mm saw tooth, 3mm saw tooth, screw head
What is automatic feed roll adjustment
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
What are the special features of a grind roll
Roll protection, roll gap adjustments, roll cleaning, discharge hopper, exhaust, control system
Can a roller mill run without feed?
NO! this would damage the roll surfaces, and cause heat build up which could present a fire risk.
What controls whether the grinding rolls are engaged
The pneumatic servo control - it disengages the rolls when there is no feed
Why is there automatic roll gap adjustment
Removes operator inconsistencies and improves mill balance, consistency of mill performance and finished flour quality
What cleans the rolls
Roll brushes and cleaners (scrapers)
What is roll ringing?
When there is too much build up on the rolls - it can affect mill performance and product quality and an increase in temp
What does a discharge hopper do
Collects the ground stock and directs
When are rollermills connected to a central exhaust
In mills with bucket elevators
What is perfect tram
Roll axes are in parallel
What expands more, the ends or centre of a roll
Ends
How do you combat roll expansion
A taper or camber
What were the different types of plansifter
Reels, Centrifugals, Free-swinging
Why are centrifugals better than plansifters
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
Advantages of Plansifters over centrifugals
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
What is the set up of a free swinging plansifter and a drawer type plansifter
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
What affects the ‘throw’ of a sifter
The balance weight adjustment
What are the advantages of a buhler planostar type MPAD
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
Why was the square sieve plansifter developed
To achieve higher capacities within one machine
What advantages do square sieve plansifters have over free-swinging plansifters
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
Benefits of a square sieve plansifter
More sieve dressing area
Higher capacity
Greater flexibility to change internal stock flow
How many nests, sections and sieves can be in a plansifter
2, 3, 4 or 5 nests
4, 6, 8 or 10 sections
up to 30 sieves
What does a multi arm sieve cleaner do
Clean both the sieve cloth and sieve tray simultaneously which prevents stock build up on collection trays and aids flow of material
Advantages of Henry Simon “QUADRO” Plansifter
Special chassis design and material for vibrating operations
Up to 30 sieves per deck
Easy cleaning and maintenance
High capacity in limited spaces
Why has nylon or plated wire replaced silk on sieves
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
What materials can be used when making sieves
Nylon, plated wire, polyester, stainless steel
Why is stainless steel not widely used in milling
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
What are the advantages of stainless steel wire
It is possible to get metal detectable wire
Developments mean easier stretching characteristics and increased life span
How does a purifier work
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
Purpose of purification
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
Label the purifier diagram
Page 52
What vibration speed is optimum for a purifier and what is the speed of a standard vibratory motor
500rpm and 750 rpm
What does air allow in a purifier
Lifts the light bran off the sieves so only coarser semolina passes through and is graded
Why use individual air compartment valves
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
What layers are stratisfied from top to bottom
Light bran and beeswing
Heavy bran
Large composite particles
Small composite particles
Large pure endosperm
Small pure endosperm
What does a purifier split the feed into
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
