Crushing is one of the important processes in the feed processing and production process (receiving and cleaning, pulverizing, compounding, mixing, granulating, and packaging of raw materials), which not only affects the production efficiency of the subsequent processes. It also has an impact on the nutritional value of the product, the processing cost, the animal's production performance and the air environment. The crushing size, crushing yield and processing cost of the feed together determine the choice of the crushing process. The size of the pulverized particle size of the feed material directly affects the pulverization process and animal growth performance. Within a certain range. The smaller the pulverization particle size, the more the animal's palatability and production performance can be improved. Therefore, when processing feed, according to the requirements of different varieties or different physiological stages of animal feed size, reasonable crushing equipment, optimal design of crushing process, and correct operation of crushing equipment to achieve the optimal nutritional effect. In this paper, the influence of crushing particle size on the crushing process is briefly described and analyzed.
1 The importance of crushing particle size on the crushing process
The feed pulverization particle size is used to indicate the average particle size after the feed is pulverized, reflecting the degree of pulverization of the feed. The particle size of the spherical pellet feed is its diameter, and the particle size of the non-spherical pellet feed has various representations such as the percentage residue on the sieve, the arithmetic mean particle diameter method, and the geometric mean particle diameter method. The current measurement method has two layers of sieves. The method, the four-layer sieve method, the eight-layer sieve method, the four-layer sieve method, and the fourteen-layer sieve method have very accurate results, but the measurement and calculation are troublesome and the workload is large. Therefore, studies have shown that the four-layer screening method can replace the fourteen-layer screening method within an acceptable range of accuracy.
In the process of feed pulverization, the pulverization particle size is controlled mainly by the hammer linear velocity, the hammer sieve gap, the thickness and number of the hammer, the sieve diameter, and the thickness of the sieve. Conversely, the difference in the pulverization granularity also affects the selection of these parameters and equipment. Similarly, the comminution granularity determines a range of facility equipment usage and operations, as well as process and method determination. It can be seen that determining the crushing size is the basis of the crushing process, and it is the cornerstone of the whole feed processing process, which plays a decisive role. This also makes the crushing link one of the essential and irreplaceable main links in the processing.
2 crushing particle size on the crushing process
2.1 The choice of pulverizer and the impact of the main structure
(1) With the advancement and development of science and technology. A pulverizer that adapts to various functional, regional and market needs has emerged. Different crushing sizes and different types of feed materials have different requirements for the crusher. The type of shredder selected is also different.
The pulverizer is generally classified into a jet mill, a mechanical pulverizer, a grinding pulverizer, and an ultra-low temperature pulverizer. In the production of the feed industry, a mechanical pulverizer is generally used. According to the crushing size of the feed, the crusher can be divided into coarse crusher, medium crusher, micro-grinder and ultrafine crusher. For the aquaculture feed with higher crushing particle size (grinding size <0.6), the micro-grinder or superfine should be selected. grinder. According to the mechanical structure features, it is divided into a hammer mill, a disc mill, a claw mill, a roller mill, a flattener and a chip breaking machine. Since the hammer mill is widely used because of its simple structure, strong adaptability and high production efficiency, in the livestock and poultry feed enterprises, the medium crusher type crusher is generally selected.
(2) The main structures of each type of pulverizer are different. Therefore, only the influence of the pulverization particle size on the various structures and parameters of the hammer mill is discussed in this paper.
The hammer is the main structure of the pulverized material, and the linear velocity at the end of the hammer directly affects the particle size. As early as the 1960s, experiments have shown that the higher the end velocity of the hammer, the smaller the particle size. For pulverizing raw materials with small particle size and high toughness, the optimum end line speed is 100-110 m/s. The thickness and number of hammers are also related to the pulverization particle size, according to the formula: (ε-hammer density factor; B-grinding chamber width, m; D-rotor diameter, m; Z-hammer number; δ-each hammer thickness , m) It can be seen that the smaller the particle size requirement is, the more the number of hammers is, the thinner the thickness is, but the more the number, the more the no-load energy consumption is increased, and the electricity output is reduced.
The hammer screen gap is also related to the crushing size. The small gap is not easy to block the mesh hole and has a good pulverizing effect. Generally, the ultra-fine pulverized hammer screen gap should be 5-6mm, usually about 12-15mm.
The main fractionation part of the sieve in the pulverization process. The pulverization particle size, pulverization quality and pulverization effect have different degrees of influence. Nowadays, the sieves have been standardized. Different apertures have corresponding sieve thickness and opening ratio. Under the premise of sieve strength and pulverization particle size, the larger the opening ratio of the sieve, the better the thickness and the thinner the better. Once the particle size is determined, the other parameters of the sieve are also determined. The pore size is the core factor, and the relationship between the mesh diameter and the feed particle size is generally: average particle size (mm) = (1/4 - 1/3) mesh diameter (mm). The geometric mean particle size of the feed has a linear relationship with the sieve aperture of the same thickness, so that the geometric mean particle size of different raw materials can be roughly derived, and the thickness and pore size of the sieve can be selected according to the required geometric mean particle size of the feed. The ratio of the pore size of the comminuted sieve to the geometric mean particle size of the pulverized material decreases as the pore size of the sieve decreases.
The comminution particle size is directly or indirectly linked to the various components or operating parameters of the pulverizer, and by understanding the relationship between them, it is better to serve the production, optimize the equipment and solve practical problems. The crushing particle size will affect the animal's protein digestibility, feed conversion rate, daily gain, slaughter rate and other economic indicators, and this is the fundamental reason for the company to gain economic benefits in the industry, thus driving the relevant economic direction. Development, the development of pulverizers is also benefiting from this.
2.2 Impact on suction system and conveying device
The current pulverizers are equipped with a reasonable suction system, which can increase the output by 10%-30% and reduce the temperature of the pulverized material. Song Yongxin used the same size sieve to optimize the parameters of the ordinary pulverizer and the ultrafine pulverizer suction system. The results show that the air volume of the ultrafine pulverizer is smaller than that of the ordinary pulverizer, but the wind pressure is greater than the latter. Therefore, when selecting a product with a small crushing size, the air volume should be appropriately reduced, but the wind pressure cannot be low and must be high. After the raw materials are pulverized, the pulverized material needs to be transported into the batching bin. The discharging method of the hammer pulverizer mainly includes pneumatic conveying and mechanical conveying plus auxiliary suction (screw conveyor and hoist), and the mechanical conveying suction system makes the smashing indoor Negative pressure improves efficiency to a certain extent. When the particle size of the pulverized product is small, the selection of the pneumatic conveying system is the most appropriate way to ensure the continuous conveying of the material when the pulverizing particle size is small, and it is not easy to cause pollution. In general, pneumatic transmission has high energy consumption, high noise, and high water loss, which is slightly higher than the fixed cost of the latter feed. However, many researchers have studied the problems caused by pneumatic transport. Provide a basis for future improvements.
2.3 The impact of the crushing and compounding process
The batching process and the pulverizing process are closely related. In the process of feed processing, two kinds of technological processes are derived: firstly pulverizing the ingredients and pulverizing the ingredients first. After the pulverization and batching process, the best pulverization efficiency can be obtained, and the control of the particle size is convenient. The granulation process is strong after the first batching, and a large number of batching bins are not required. Saves floor space and is conducive to feed particle size uniformity. Both processes have their own points, but if the product produced is relatively small in size. The raw material content of cereals is low, the protein content is high, and it is easy to be arched (such as some aquatic feeds).
2.4 Impact on the crushing process
The process of the pulverization stage can be divided into primary pulverization and secondary pulverization. The pulverization process equipment is simple. The investment cost is low, but the power consumption is high. The secondary pulverization process can compensate for the shortcomings of one pulverization. Moreover, the power consumption is reduced by about 22%, and the output is increased by more than 25%, but the equipment investment cost is high. In the production of small-sized feed (aquatic feed), the secondary pulverization process should be selected, and the materials should be classified before or after pulverization, and the next step should be carried out in accordance with the particle size requirements. Otherwise go back to the shredder and continue to smash. Until the requirements are met. In addition, small feed mills should use a one-time crushing process to save investment in processing equipment. However, in the production process, special attention should be paid to whether the crusher is broken or not, and the pass rate is guaranteed. However, at present, the feed mill is becoming more and more large-scale, and the primary process is gradually replaced by the secondary pulverization process.
3 Summary
In summary, the pulverization particle size has a certain relationship with the entire pulverization process. The pulverizer selection and parameter setting are first performed according to the appropriate pulverization particle size, and then the process flow of the pulverization section and the process flow of the pulverization and batching section are determined. . To carry out the correct and reasonable pulverization process design, it is necessary to understand the optimal pulverization granularity of different physiological stages and different kinds of animals, and to design a reasonable process flow in combination with the characteristics of the selected pulverizer. Maximize production efficiency. Currently. The crushing stage is still the most energy-consuming and noisy part of the feed processing process. When designing and selecting the feed plant process, it is necessary to consider the issues of cost, energy consumption and efficiency, and do environmental assessment work.
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