Cleaning of wheat flour milling machine
A. Wheat cleaning
- 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.
- Classification of impurities impurities in the wheat can be classified according to the chemical composition and physical properties.
(1) According to the chemical composition
①The inorganic impurities
inorganic impurities mixed with clay and sand, refers to the brick, metal and other inorganic substances in wheat.
②The 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.
（2）It can be divided into three categories according to physical property and particle size of impurity.
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.
（3）According to the specific gravity impurityies can be divided into two categories:
①Heavy impurities Refers to the wheat specific gravity is bigger than the impurities specific gravity.
②Light 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 equipment including vertical air duct and suction separator.
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 pre-cleaning screen.
(3) Using different grivatity 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..
(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..
- 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.
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.
B. wheat moisture regulation
The moisture regulation of wheat, is to add the water and give it a certain time for moisture, so that to re-adjust the moisture of wheat and improve its physical, biochemical and milling process performance, in order to obtain better milling process effect.
- Physical and biochemical changes after adding water, the corresponding physical and biochemical changes occur:
- the moisture content of wheatis more,the grain has a similar moisture content and similar water distribution by a certain
- The first layer of water swelling, aleurone layer and endosperm followed by water swelling. Due to the three are with different orders in water swelling,so, there is a slight displacement in the radial direction of the wheat grain , then the combination between the three Force is weakened. This is favorable in separation of the cortex and the endosperm,and the powder can scrap from the cortex down easily.
（3）Cortical after absorb the water, toughness increased ,
brittleness reduced, increasing its ability to resist mechanical damage. Therefore, in the grinding process this facilitate the preservation of bran slices and clean the bran film on the endosperm, to ensure the quality of flour and improve the extraction rate of flour. In addition, the integrity of the bran is also conducive to the sifting and bran brushing.
（4）the intensity of the endosperm is reduced. The starch and protein contained in the endosperm are crossed together. Protein water absorption capacity (large water absorption), slow water absorption; starch granules weak water absorption (small water absorption), fast water absorption. Because of the difference between the speed and ability of the two, the expansion of the different and the degree of difference, resulting in starch and protein particles displacement, so that the endosperm structure loose, reduced strength, easy to ground into powder, is conducive to reducing power consumption.
(5) The yield of wet gluten increases with the increase of wheat moisture, but the quality of wet gluten is weakened.
(6) proteolytic enzyme activity, free amino acid content, saccharification activity, sucrose and a variety of reducing sugar content has changed. But little effect on the milling process.
From the above changes can be seen, wheat moisture regulation, the milling process performance improved, can increase the rate of flour, improve the quality of finished flour, and reduce power consumption.
- The corresponding process effect of wheat by water regulation, should be the corresponding process effects are as follows:
(1) so that the grinding of wheat with the appropriate water to meet the requirements of the milling process to ensure the relatively stable process of milling, easy operation and management. This is very important to improve production efficiency, flour yield and product quality. Requiring moisture uniformity within 0.2%.
(2) to ensure that flour moisture in line with national standards. Wheat dryness will cause the flour moisture is too low, so that the powder plant suffered losses; the other hand, wheat overheating will cause flour moisture is too high, not only will affect the interests of consumers, will also affect the flour storage management.
(3) the wheat flour was suitable for milling. The wheat after moisture adjustment, cortex toughness increase, endosperm internal structure is loose, decreased the binding force between the cortex and the aleurone layer and endosperm, is conducive to the improvement of milling performance. However, the high moisture content of wheat will decrease the fluidity of work in process, cause the blockage of sieve and flow, and affect the normal production of flour milling. Therefore, considering the improvement of flour milling performance, there should be a suitable water content for wheat milling.
After adding water, the wheat must be mixed quickly, and the water will begin to penetrate into the water through a certain mechanical action, so that the wheat grain has certain water holding capacity. The water regulating equipment for wheat generally consists of two parts: the water adding device and the water feeding equipment. The wheat moisture regulation equipment generally has the cup water machine, the powerful water machine and the water mixer. At the same time, wheat after water, water from outside to inside infiltration requires a certain period of time, usually 16 to 24 hours, where wheat tempering time required by certain storage warehouse to ensure, called the tempering bin.
C. wheat cleaning process
- the development of wheat cleaning process based on
(1) grinding wheat quality standard net
①The buckwheat dust impurity not more than 0.02%, grain impurity does not exceed 0.5% (shelling of dissimilar grain at the present stage not included), should not contain metal impurities.
② the ash content of wheat should not be less than 0.06% after cleaning.
③The moisture content of the finished flour should be in line with the national standard.
(2) The quality of wheat
Wheat varieties and quality is not immutable and frozen, therefore, the designing of the cleaning section flow should take into account factors like the number of impurities in wheat,proportion of hard wheat and soft wheat, and the content of water, etc.It’s better to adopt good cleaning equipment and water conditioning equipment. In actual production, for wheat with little impurity and high moisture, can adjust the shunting device, not have to pass through every equipment.
Considering the wheat producing areas of China, wheat growing in south of China area normally have more buckwheat seeds and mud, less sand and high moisture. Usually not considering wheat washer, considering enhance threshing wheat, removing buckwheat and destone in dry way. Wheat growing in north of China normally contain more sand and marl, less buckwheat seeds and low moisture. To clean up this kind of wheat, should strengthen the suction, destone and wheat washing process, generally not consider buckwheat removing equipment. Wheat growing in Spring area have high moisture, more sand and wild grass seeds. To process this kind of wheat, should strengthen the screening, selection and destone process; low temperatures in winter, wheat should have procedure of preheating and moisture adjusting.
Wheat infected with smut, ergot and scab has a great influence on human health. Therefore, we must pay high attention to the cleaning. The infection of scab and smut of wheat, wheat should be strengthened, broken by a serious pest and weaken the wheat, and strengthen the screening and winnowing, in order to achieve effective cleaning. When wheat contains ergot, it can be cleaned effectively by gravity classifier.
Insect pests of wheat should be killed by the impact machine, and strengthen the screening and suction, remove insects and insects fragments. The grain length of wheat, such as wire worm disease, is shorter than that of normal wheat grain, but its width is similar. It is difficult to remove by screening, and it is more effective to remove with grain separator.
In China’s varieties kinds of wheat, soft wheat more than hard wheat, in the processing of hard wheat, need to add more water and moisture wheat time.
(3) factory size and type of milling flours
Under normal circumstances, the factory scale larger, the production of high precision flour higher, the relative clean-up process to be better. The small-scale processing factory have low precision of flour requirements , Suffer the investment conditions and plant space constraints limit, the relative clean-up process is simple, in this case, you can choose a compact, with a variety of functions and better combination of cleaning equipment , To ensure that the basic clean-up process and the necessary clean-up road.
2. Requirements for establishing wheat cleaning process
（1）Each process is complete, the number of cleaning equipment is appropriate, the process sequence is reasonable.
- In accordance with the “first easy after difficult, first inorganic after organic” principle to arrange the process sequence
- to the largeharm and much content impurity, such as sand, buckwheat seeds, wheat scab etc. should strengthen cleaning.
- The process should be flexible in order to adapt to the change of impuritiesin raw materials
- There should be perfect water regulation facilities to ensure the moisture content of the incoming wheat to meet the process requirements.
- There should be perfect wheat processing facilities, so that the quality index of wheat into the mill can basically meet the quality requirements ofthe finished flour.
- Serial, standardized, universal and efficient advanced cleaning equipment should be used as much as possible.
- In order to ensure environmental sanitation and improve the efficiency of impurity removal,thedesign ofair dust removal system should be reasonable
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