Education of the republic of uzbekistan tashkent state technical university named after islam karimov

№3/2021 year. 
Technical science and innovation
250 
Types of impurities. The crop harvested by a combine is called a heap. In addition to 
grain, it contains three types of impurities: 

Cereals. These are underdeveloped, damaged, sprouted and spoiled by pests grains of 
the main crop. They are not harmful, but can affect the germination and shelf life of the product, 
as well as its nutritional value. 

Weed. These include rocks, dust, sand, insect debris, husks, straw, weeds and their seeds. 
They make up a large proportion of waste in the cleaning of grain and seeds of leguminous crops 
and have a negative effect on the quality of the crop.

Harmful. This category includes plants and their seeds that are hazardous to human and 
animal health. In addition to various impurities, the heap contains an excess amount of moisture, 
which must also be disposed of. The norms for the content of impurities and moisture are 
established by state standards for each type of grain, depending on the nature of their use. For 
example, for food wheat, the content of trash should be no more than 1%, and grain - no more 
than 3% [3]. 
The initial cleaning of grain and seeds of leguminous crops is carried out inside the 
combine, but this is not enough. To completely remove impurities, the heap must be processed in 
grain cleaning machines. Cleaning takes place in three stages:

Preliminary.This stage is carried out no later than one day after the harvest. If tightened 
with preliminary cleaning, then the moisture in the grain may increase and it will begin to 
germinate. In addition, the self-heating process quickly begins, which greatly impairs the food 
quality. During preliminary cleaning, the largest impurities are removed from the heap. 

Primary. For its implementation, the moisture content of the heap must be reduced to 
18%. At this stage, most of all types of impurities are removed from the heap, after which their 
amount should not exceed 3-4%. 

Secondary. This stage is needed for the final separation of impurities, as well as the 
separation of grain into fractions according to its value. At the end of this stage, the grain is 
divided into forage and seed. 
Sometimes a more detailed separation is carried out by dividing the seed grain into seed 
and food material. The grain can also contain various difficult-to-separate impurities that are 
difficult to remove by conventional methods. To sift them, one more stage of cleaning is needed 
using special equipment. For example, a magnetic grain separator is used to remove metal 
particles.
Modern grain cleaning machines can be divided into two types: simple and complex. 
Simple ones divide the heap into two fractions and are often aimed at isolating one type of 
impurities. Complex machines can divide the heap into several factions. Moreover, such models 
can be one machine, or a complex, where the grain passes from one simple separator to another. 
Classical separation most often involves the use of sieve, air and grader grain cleaning machines. 
An alternative to classical cleaning methods is the use of an aerodynamic separator. 
This technology has appeared relatively recently, however, it is already beginning to 
gradually replace the classical methods of cleaning. The equipment is a spacious chamber 
equipped with an impeller for air injection and sorting containers. After falling asleep a heap 
inside, it will fall into a powerful stream of air 
Technological processes. In the bunker of the combine, along with the grain, impurities 
are also supplied: pieces of straw, ears, seed heads, weed seeds, lumps of soil and small stones. 
The moisture content of the grain, as a rule, is higher than the conditioned one, therefore, it is 

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