The document outlines the importance of cleaning wheat before milling to remove impurities that impact flour quality and safety. It classifies impurities based on chemical composition and physical properties, detailing methods of wheat cleaning including wind selection, screening, gravity separation, selection, impact, magnetic separation, and grinding. Additionally, it mentions other less common methods like photoelectric sorting and provides contact information for further inquiries.

1. Cleaning section technology of wheat flour milling machine
Wheat cleaning
1. The purpose of wheat cleaning, due to the current technical constraints, wheat growth,
harvest, storage, transportation and other processes will have impurities mixed. In the growing
season, the wheat which is germinated and moldy because of too much rain and the wheat
which is attacked by insects and diseases is the impurity in wheat, and the mixing of these wheat
will affect the quality and odor of wheat flour.Therefore, in the milling wheat must be cleaned
before, all kinds of impurities in wheat completely clean, so as to ensure the quality of flour, to
meet the needs of the food industry and people's lives, to ensure people's health, and achieve
the purpose of safe production.
2. Classification of impurities impurities in the wheat can be classified according to the chemical
composition and physical properties.

2. (1) According to the chemical composition
The inorganic impurities inorganic impurities mixed with clay and sand, refers to the brick,
metal and other inorganic substances in wheat.
The organic impurities organic impurities is mixed with wheat roots, stems, leaves, grass seed,
shell, grain and edible dissimilar value buds, spots, metamorphic and other organic substances of
wheat.
It can be divided into three categories according to physical property and particle size of
impurity.

3. ①large impurities Refers to the impurity retained in Diameter of 4.5 mm sieve screen surface.
②Side by side impurities Refers to the impurities through the diameter of 4.5 mm sieve
screen surface, retained in the diameter of 1.5 to 2.0 mm sieve screen surface impurities.
③Small impurities Refer to pass through the diameter of 1.5 ~ 2.0 mm sieve screen surface
impurities.
According to the specific gravity impurities can be divided into two categories:
① Heavy impurities Refers to the wheat specific gravity is bigger than the impurities
specific gravity.
② Light impurities Refers to wheat specific gravity is smaller than the impurities specific
gravity.
3. Common methods of wheat cleaning
(1)wind selection method
The method of cleaning the air dynamics properties of wheat and impurities is called wind
selection method.The aerodynamic properties are generally expressed as suspended
velocities.wind selection method needs participation of air media.Commonly used air - selection

4. equipment including vertical air duct and suction separator.
(2)Screening method
The method of cleaning with different size of wheat and impurity is called screening
method.Grain size is generally based on the thickness and width of wheat and impurities.The
screening method needs to be equipped with a suitable screen for the movement of the sieve,
and the relative motion of the sieve and the wheat is used to stratify the wheat.Small size and
heavy flour would be pass through the sieve.
The commonly used screening equipment has vibrating screen, rotary flat sieve and per-cleaning
screen.
(3)Using different gratuity of wheat and impurity to separate them.It is called gravity separation
method. The gravity separation method needs the participation of the medium, and the medium
can be air and water. The use of air as a medium is called dry gravity separation; the use of water
as a medium is called wet gravity separation. The proportion of dry separation equipment
commonly used gravity destoner, gravity separation, gravity separation equipment commonly
used in wet stone wheat washing machine etc..

5. (4) selection method using impurities and wheat geometry and different length of cleaning
method called selection method. It is necessary to use the inclined plane and the spiral surface to
separate the wheat and the spherical impurity by the different geometric shapes. The common
buckwheat seed throwing vehicles and other equipment. The use of different lengths for cleaning
requires a rotating surface with a pocket. The short grain embedded bag holes are taken away,
and the long grains remain outside the bag holes and are not taken away, so as to achieve the
purpose of separation. Commonly used equipment has drum selection machine, disc selection
machine, disc roller selection machine, etc..
(5) impact method by the impurity and wheat of different intensity cleaning method called
impact method. Germination, moldy, diseases and insect pests of wheat, wheat and soil surface
adhesion of dust, the adhesion strength is lower than that of wheat, the impact of the high-speed
rotating component, broken off, the use of suitable mesh separating it, so as to achieve the
purpose of cleaning. The impact of equipment commonly used are beating machine, impact
machine, wheat brush machine etc..
(6) magnetic separation method using wheat and impurity ferromagnetic different cleaning
method called magnetic separation method. Wheat is a non-magnetic material, in the magnetic
field is not magnetized, thus cannot be absorbed by the magnets; and some metal impurities
(such as iron nails, nuts, etc.) is a magnetic material in a magnetic field will be magnetized by the
magnet adsorption, which is separated from wheat. Permanent magnetic drum, magnetic steel
and permanent magnetic box are commonly used in magnetic separation.

6. (7）Grinding method;
To clean up wheat surface dust or grind wheat straw by the use of rotating rough surfaces
(such as sand grain) is known as the grinding method. It is widely used for peeling and milling.
Through the grinding of the surface of a few sand rolls can partially separate the wheat flour,
which can shorten the powder path and make it easier to pulverize. The commonly used
equipment is like peeling machine etc.
In addition to the above methods, there are other methods,such as the one according to the
color of the photoelectric sorting method, the equipment is color selection machine. The current
application is not yet widespread as the equipment is very expensive.
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