I. Purpose and requirements of cleaning up In the raw materials entering the feed mill, it can be divided into plant raw materials, animal raw materials, mineral raw materials and other small varieties of additives. Among them, animal raw materials (such as fish meal, meat and bone meal), mineral raw materials (such as stone powder, calcium hydrogen phosphate) and vitamins, drugs, etc. have been cleaned up in the raw material production process, generally no longer cleaned. The main raw materials to be cleaned by the feed mill are grain raw materials and their processing by-products. Cleaning of liquid raw materials such as molasses and grease is carried out by placing a filter or the like on the pipe. The feed grain is often mixed with impurities such as sand, dander and straw. The presence of a small amount of impurities has a great influence on the quality of the finished feed. Because the finished feed has a wide limit on the impurities, the purpose of cleaning and removing the feed ingredients is not only to ensure that the impurities of the finished product are not excessive, but to ensure the safe production of the processing equipment, reduce equipment loss and improve the environment during processing. health. There are two common cleaning methods used in feed processing plants: Screening method: used to screen out large impurities and small impurities such as sediment and straw that are larger than or smaller than the feed. Magnetic separation method: used to separate various magnetic impurities. In addition, in the screening and other processing processes, it is often supplemented by suction and dust removal to improve the environmental sanitation of the workshop. Second, screening 1. The structure of the sieve surface Screening is an operation that separates materials based on their particle size. The material smaller than the sieve hole at the time of screening passes through the sieve hole as a pure material (the undersize material), and the impurities larger than the sieve hole cannot be cleaned out through the sieve hole (the sieve top), or vice versa. The screening equipment commonly used in feed mills has a cylindrical (or conical) primary cleaning screen, a powder primary screening screen and a flat rotary grading screen. (1) Grid screen, the grid screen located at the inlet (lower) material is the first line of defense for cleaning raw materials. Its main function is to initially clean the large impurities in the raw materials, and to protect the subsequent equipment and workers. The gap of the grid is based on the geometry of the material. Corn and other grain raw materials should be about 30mm, and oil cake should be about 40mm. At the same time, it should be ensured that the grid screen has a certain strength, usually welded with flat steel with a thickness of 3 mm and a width of 2 cm or a round steel of 10 mm. It should be fixed on the casting (lower) material port and ensure an inclination of 8 to 10° to facilitate the pouring of materials in the bag and reduce the labor intensity of workers. The grid screen for unloading of automobiles is made of steel plate with a thickness of 4 mm and a width of 5 cm. (2) Punching screen, also known as sieve plate, is usually made by punching out the mesh hole on a thin steel plate (black iron) or galvanized iron plate (white iron). The shape of the mesh hole is circular, round, long, triangular, etc., as shown in Figure 3-7. The thickness of the sieve surface generally depends on the size of the sieve hole, and the sieve surface having a small sieve opening is thinner, and the sieve surface having a large sieve opening or being severely worn should be appropriately thickened so that the sieve surface has sufficient strength. If the sieve surface is too thick, the sieve hole is easy to be blocked, and if it is too thin, the strength is not enough. Generally, the thickness of the sieve surface is 0.5 to 1.5 mm. (3) Weaving the screen surface, the woven screen surface can be woven from metal wire (such as steel wire, galvanized iron wire, etc.) and chemical synthetic wire. The sieve holes of the woven sieve are rectangular or square. The thickness of the wire used for weaving the screen surface depends on the size of the mesh hole. Generally, the diameter is between 0.5 and 1.5 mm, and both the powder and the pellet can be used. 2. Screening principle The sieving machine can be used to remove impurities from the feed, and the grading of the feed can also be carried out. The sieving is based on the difference in the shape, width and thickness of the material particles, so that part of them pass through the sieve surface to become the undersize, and the other part remains on the sieve surface to become the sieve, thereby separating the feed from the impurities and removing it. For the purpose of impurities, or for different sizes and shapes of feed to separate for classification. Use a round or square sieve to separate according to the width of the particles. The width of the feed granules or impurities is smaller than the diameter of the sieve hole. When sliding on the sieve surface, the particles with small width reach the pores, and the granules are erected, and the top end passes under the pores and passes through the sieve holes to become the undersize; the width is larger than the diameter of the sieve holes. The material becomes a sieve. The long hole sieve can be used for separation according to the particle thickness. The pellets or impurities having a thickness smaller than the thickness of the sieve hole, when sliding on the sieve surface, are tilted and turned over through the sieve hole to become a sieved object, and the thickness is greater than the thickness of the sieve hole and cannot pass through the sieve hole to become a sieve. For some special long rope heads, straw and other flexible impurities will hang on the screen hole during the screening, and it is generally removed by hand. From the analysis of the sieving condition of the material, the necessary conditions for the sieving are as follows: the granules should have relative sliding on the sieve surface; the sifted granules should have access to the sieve holes; if separated by the width, the granules must be The sifted granules stand upright into the mesh openings; if separated by thickness, the sifted granules must be stretched over the length of the mesh and passed sideways into the mesh. The above necessary conditions for sieving are attributed to three elements of sieving: 1 the material and the screen surface have relative motion; 2 the sieve and the screen surface are required to be contacted; 3 have the appropriate hole shape and size.
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Cleaning of feed ingredients