Maize Flour Mill

PROCESS DESCRIPTION

The maize Milling process is a Mechanical process and consists of cleaning , De germination, grinding and sieving operations. After each sieving operations, product of a particular quality is drawn and the residue is recycled for further grinding or Milling .

A maize mill can be broadly divided into three section, i.e.
a) Ceaning section.
b) Degermination section.
c) Milling section.

The Cleaning section

In this Section elaborate arrangement are made for through cleaning of the whole maize . The maize that is procured in bags contain numerous impurities such as sand and grit, metal pieces, mud limps, chaff, gunny pieces, full maize corns, husk and dirt. Old stocks of maize also contain other impurities such as insects and half eaten dead maize. The presence of the above impurities is harmful to human health. The whole of the cleaning section is devoted to the removal of these impurities and conditioning the maize to make it suitable for milling. The whole process of cleaning is an automatic process and consists of addition of water, primary sieving for removal of large sized impurities and dust particles, Removal of stones and mud ball by Destoner. Removal of metal impurities by passing the maize through a series of magnets. At the end of the cleaning operation, the clean maize suitable for the milling operation is stored in very large grain silos. The grain should be kept in the silos for several hours for conditioning before milling.

The Primary two objectives of conditioning are as follows :

a) To prepare the maize so that the milling process is most efficiently performed. This depends on the even distribution of moisture in maize.

b) To modify the Germ characteristic of maize

To elaborate on the first objective the following points should be mentioned:

I) The maize should be dry enough for :

• easy separation of endosperm from bran.,
• accurate and easy sifting on the plan sifter

II) The maize should be also be wet enough for:

• The bran to be sufficiently tough to avoid break in up.

The two conditions are contradictory to one another. But in practice it is not hard to make a compromise. Maize form different parts of the country vary considerably in physical condition and moisture content. Hence the maize must be brought to a physical state in which the endosperm can most efficiently be separated from the bran. For uniform distribution of moisture, it is stored.

Maize

0.1 CLEANING PROCESS

The bagged maize brought in Trucks will be stored in silos and will be conveyed to the cleaning of maize section of the plant by bucket elevators.

0.2 DRUM SIEVE

To start with the maize is FED into a hexagonal reel. As a Pre-cleaning machine the Drum sieve is very versatile and is used above all in the intake section It sieves to separate coarse impurities such as straw particles, string, paper pieces of wood, etc. in order to relieve down stream and conveyors.

A horizontal overhung sieve drum is rotated in an enclosed casing. The product (Maize) is fed via the inlet spout into the interior of the Drum and is revolved so that the fines drop through the sieve, where as the rolling motion causes the coarse impurities to move to the outlet channel below the inlet. The drum if divided into three sections having different size of perforated sieve on it. The first sieve has perforations slightly smaller than the average size of maize is to separate dust and fines. The other two sieve have perforations slightly larger than the average size of grain and it separate out the impurities larger in size like stones, string, wooden pieces.

0.3 SEPARATOR

From the Drum sieve machine the grain is fed into a separator. This machine basically consists of two perforated sieves. The top sieve having perforations Slightly bigger than the average size of the grain and lower sieve having perforations slightly smaller than the average size of the grain. The sieves are given an vibrating motion by two unbalanced vibro motors.

Material to be separated falls freely through the inlet onto the top coarse screen, which removes such coarse impurities as string, straw and stones. Troughs of the top sieve falls on the bottom sieve which can also be called as sand sieve which removes broken kernels, sand and other fine impurities. Tailings from the lower sieve layer consists of cleaned grain which pass to the outlet.

The vibrating movement of the sieves facilitates an increase of the capacity on a given sieve surface and also an increase of the sieve effect. At the discharge end the grains are subjected to aspiration by an aspiration chancel. The aspiration lifts with it light impurities such as chaff, husks, etc.

0.4 DRY STONER

This unit is used for the continuous removal of stones having the same size of grain from the stream of granular material. The function of this machine is based on a combination of micro projectile motion & wind sifter working on a vibro pneumatic principal. The product is gravity fed though an air shut off gate on to a preliminary separation screen maize,where it passes onto an inclined oscillating deck or table. This deck is designed as screen through which an upward current of air is passed fluidizing the product. Due to their different specific gravities, the heavy particles such as stones/metal go down while the lighter particles, supported by the caution of air float on top. The oscillating action of the screen causes the heavy particles to work their way to the upper end of the deck.

0.5 (INTENSIVE DAMPENING UNIT)

Maize, after being cleaned by different dry processes is fed to a intensive dampening. The maize is carried out into the machine in a stream of water and is rapidly sluiced around at high speed. As the maize is charged into the worm and conveyed through water heavier particles like stones, flints, etc. settle at the bottom of the through. Maize is conveyed by the worm in the trough to a whizzer which is a vertical rotating shaft at the centre with beaters. The beaters, while lifting the maize form the bottom to the top trash the maize on the surface of the drum to remove extra water sticking on to the maize, adhering dirt and some branny material. In this machine the maize is treated with water for conditioning before being taken for milling operation.

0.6 MAGENETS

Magnets are used in the process of maize conveying at different stages. The complete removal of iron is very important not only to avoid damaging the mill machinery but also to prevent any possibility of nail or metal washer striking a spark during later stager of the process and taus igniting a dust cloud, which is highly explosive.

0.7 CONVEYING

Conveying of maize is done with the help of bucket elevators. The belt bucket elevator is the ideal type of conveyor for vertical handling or granular materials. The entire housing is made of steel shee

OBJECT OF MILLING

The objective in the milling of Grit are:
To separate, as completely as possible, the endosperm, which is required for the Grit , from the bran and germ, which are rejected, so that the Grit shall be free form Germ & bran specks, and of good colour, and so that the palatability and digestibility of the product shall be improved

To reduce the, Minimum amount of endosperm to flour fineness, thereby obtaining the maximum extraction of Grit from the maize.

The reduced endosperm is known as Grit , flour, and residual adhering germ are obtained as a by product, used primarily in animal feeding.

PROCESS OF MILLING

In order to separate the endosperm form the bran and germ and reduce the endosperm to Gritt fineness, a particular from of grinding has been developed which is combination of shearing scraping and crushing, achieved by roller mills, and which exploits the differences in mechanical properties between the endosperm, bran and germ. It is essential to minimise the production of fine particles of bran, and this basic requirement is responsible for the complex arrangement of the modern flour milling system and for the particular design of the specialised machinery used in it.

GRADUL REDUCTION PROCESS

The modern roller milling process for making flour is described as a “gradual reduction process” because the grain and its parts are broken down in a secession of relatively gentle grinding stage so that only the required amount of endosperm fragmentation and bran occurs at each stage.

MILLING OPERATIONS IN BRIEF

After the maize has been conditioned ,Degerminated a succession of grinding stages, using roller mills in each is used to open the whole grain in the first stages, and in subsequent stages preceding grindings.

An individual grinding stage may be light or heavy, according to the character of its feed, in general, feeds consisting of relatively pure endosperm can be heavily ground, whereas these containing much bran must be lightly ground.
Each grinding stage yields a “grind” consisting of a mixture of coarse, medium, and fine particles, including a portion of flour. The differentiated particles are sorted by shifting, a shifting stage therefore follows each grinding stage. Some of the coarse particles are potentially Grit yielding, these are conveyed to subsequent grinding stage, others can yield no useful Grit , these are removed from the milling system and contribute to the milling by-products.

Particles deferring widely in size (in the grind from any one stage of roller milling) also differ in composition. Particles of endosperm, which tend to be friable, are generally smaller than particles of bran, , which tend to be tough and leathery. The process of sieving, besides sorting the particles according to size, thus to some extent separates particles of differing composition from each other, e.g. endosperm from bran.

The BREAK SYSTEM consists generally of Two “ breaks” on roller mill grinding stages, each followed by a sieving stage. The system is fed with the whole grain in the first break, and with the break stock in subsequent stages. The objective in the first break to open the whole grain, and in subsequent break to scrape off the endosperm from the bran coat which owing to their fibrous structure and tough nature, remain relatively large pieces.

BREAK ROLLER MILLS

Each of the break roller mills is equipped with a pair of rolls, usually 10” (25.4 cm) in diameter and up to 40” (101.6 cm) long mounted diagonally in parallel alignment along heir whole length. The narrow gap, or “nip” between the aligned rolls can adjusted to allow precision grinding. The rolls rotate in opposite directions so that the surfaces of both rolls are entering the nip on the same direction. One of the rolls rotation at a faster speed than the other, the speed differential between the two generally being 2 ½, 1 for break roller-mills. The break rolls are corrugated or grooved over their entire surfaces, the corrugations (or ‘flutes’) running along the length of the roll, but disposed at a slight angle to their axes this angle being known as the ‘spiral’.

The effect of the speed differential between the to rolls and the spiral arrangement of the flutes is to cause the flutes of the fast roll to move across those of the slow roll at the point of contract, simulating the action of scissors.
The first break grind thus consist of a mixture of particles which differ in size and composition. The largest are the bran.

SIEVING

Screening or bolting cloth is made of woven wire, silk or nylon, for dressing, dusting and grading, although wire may also be used for these purpose to be sieved is fed in at the top and falls from sieve to sieve by gravity. A single plan sifter may incorporate sieves of four or five different mesh sizes thereby delivering five or six fractions of differing particle size. A certain depth of stock on the sieving cloth is required to obtain a satisfactory sieving effect. Owing to the movement of the sieve, the stock resting on it becomes stratified, the finest particles work down until they are adjacent to the cloth, whilst the largest ride up to the surface of the stock. The overlying layers of medium and coarse particles thus tend to keep the finest particles in contact with the sieve cloth and assist their passage through the sieve spertures.

PURIFYING

A purifier consists of an oscillacing sieve set at a slight angle to the horizontal and enclosed by a hood or cover. The sieve comprises four sections which become progressively coarser in size of mash from head to tail. The good, divided into sections to correspond to the sieve sections, is connected by trunking to the section, side of a fan so that air, controlled by valves, is drawn up through each sieve section. Stock to be purified is fed into the head end of the sieve and is moved down by the oscillating motion towards the tail or coarse sieve section. Particles of endosperm, decreasing in purify from head to tail sieve sections fall through the respective sieves, against the direction of the air current (being relatively) dense and having high terminal velocity, and are collected in hoppers, light particles of free bran and bees-wing are lifted by the air current, and are collected in trays (tins) suspended above the sieves. Particles intermediate in density and terminal velocity, consisting of bran loaded with endosperm, are not lifted, more do they fall through the sieves, but remain floating on the sieve, and are eventually discharged as overtails. The required percentage of suji, Rava is taken out here and the balance directed to Reduction system.

LIST OF EQUIPMENT

Production Capacity : 20 TPD

RAW MATERIAL

MAIZE        50 TPD

PRODUCT

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