As one of the important processes in feed processing and production (raw material receiving and cleaning, crushing, batching, mixing, granulating and packaging), crushing not only affects the production efficiency of subsequent processes. It also affects the nutritional value of products, processing costs, animal production performance and air environment. The crushing granularity, crushing output and processing cost of feed all determine the choice of crushing technology. The crushing granularity of feed raw materials directly affects the crushing process and animal growth performance. Within a certain range. The smaller the particle size, the better the palatability and production performance of animals. Therefore, in feed processing, according to the requirements of different species or different physiological stages of animals for feed granularity, reasonable crushing equipment, optimized crushing process design and correct operation of crushing equipment are adopted to achieve the best nutritional effect. In this paper, the influence of crushing particle size on crushing process is briefly described, and analyzed and summarized.
Feed particle size is used to represent the average particle size of feed after crushing and reflect the degree of feed crushing. The particle size of spherical granular feed is its diameter, and the particle size of non-spherical granular feed can be expressed in many ways, such as percentage of residue on screen, arithmetic average particle size method, geometric average particle size method and so on. At present, there are two-layer sieve method, four-layer sieve method, eight-layer sieve method and fourteen-layer sieve method. Fourteen-layer sieve method is very accurate, but the measurement and calculation are more troublesome and the workload is large. Therefore, the research shows that the four-layer screening method can replace the fourteen-layer screening method within an acceptable accuracy range.
In the process of feed crushing, the crushing granularity is mainly controlled by the linear speed of hammer blades, the gap between hammer and screen, the thickness and number of hammer blades, the diameter and thickness of screen blades and other factors. Conversely, different crushing granularity also affects the selection of these parameters and equipment. Similarly, the crushing granularity determines the use and operation of a series of facilities and equipment, as well as the determination of process flow and method. It can be seen that the determination of crushing particle size is the basis of crushing and the cornerstone of the whole feed processing process, which plays a decisive role. This also makes the grinding link become one of the indispensable and irreplaceable main links in the machining process.
(1) With the development of science and technology. Crushers that meet the needs of different functions, regions and markets came into being. Different crushing granularity and different kinds of feed raw materials have different requirements for pulverizers. The type of pulverizer selected is also different.
Pulverizers are generally divided into airflow pulverizers, mechanical pulverizers, grinding pulverizers and ultra-low temperature pulverizers. In the production of feed industry, mechanical pulverizer is usually used. According to the particle size of feed, crushers can be divided into coarse crushers, medium crushers, micro crushers and ultra-fine crushers, which require high crushing granularity (crushing granularity)
(2) The main structure of each type of pulverizer is different. Therefore, this paper only discusses the influence of crushing particle size on the structure and parameters of hammer mill.
Hammer is the main structure of crushing materials, and the linear velocity at the end of hammer directly affects the particle size. As early as the 1960s, experiments showed that the higher the hammer tip speed, the smaller the particle size. For raw materials with small crushing granularity and high toughness, the optimal final linear velocity is100-110m/s. The thickness and number of hammer pieces are also related to crushing granularity. According to the formula: (ε-hammer piece density coefficient; B—— width of crushing chamber, m; D- rotor diameter, m; Z- the number of hammers; Δ-thickness of each hammer, m) It can be seen that the smaller the granularity requirement, the thinner the number of hammers, but the more the number, the greater the no-load energy consumption and the smaller the power output.
The gap between the hammer and the sieve is also related to the crushing particle size. The smaller gap is not easy to block the sieve holes, and the crushing effect is good. Generally, the clearance between the hammer and screen for superfine grinding should be 5-6mm, and it is about 12- 15mm.
Screen is the main grading component in the crushing process. It has different effects on crushing granularity, crushing quality and crushing effect. At present, sieve plate has been standardized, and different pore diameters have corresponding sieve plate thickness and opening rate. On the premise of sieve plate strength and crushing particle size, the larger the opening ratio, the better and the thinner the thickness. Once the particle size is determined, other parameters of the screen are also determined. Pore diameter is the core factor, and the relationship between sieve pore diameter and feed particle size is roughly as follows: average particle size (mm)=( 1/4- 1/3) sieve pore diameter (mm). There is a linear relationship between the geometric average particle size of feed and the pore size of screen with the same thickness, so the geometric average particle size of different raw materials can be roughly deduced, and the thickness and pore size of screen can be selected according to the required geometric average particle size of feed. The ratio of the aperture of the crushing screen to the geometric average particle size of the crushing material decreases with the decrease of the aperture of the screen.
The crushing particle size is directly or indirectly related to many parts or working parameters of the pulverizer. Understanding their relationship can better serve production, optimize equipment and solve practical problems. Crushing particle size will affect animal protein digestibility, feed conversion rate, daily gain, slaughter rate and other economic indicators, which is the fundamental reason for enterprises to obtain economic benefits in the industry, thus driving economic development in all directions, and the development of pulverizers also benefits from this.
At present, the pulverizer will be equipped with a reasonable air suction system, which can increase the output 10%-30% and reduce the temperature of pulverized materials. Song Yongxin used a sieve with the same particle size to optimize the parameters of the air suction system of ordinary pulverizer and superfine pulverizer. The results show that the air volume of superfine pulverizer is less than that of ordinary pulverizer, but the air pressure is greater than that of ordinary pulverizer. Therefore, when choosing to produce products with small particle size, the air volume should be appropriately reduced, but the air pressure should not be low and must be high. After the raw materials are crushed, it is necessary to transport the crushed materials to the batching bin. The main discharging modes of hammer crusher are pneumatic conveying and mechanical conveying plus auxiliary air suction (screw conveyor and hoist). The suction system of mechanical transportation makes the crushing chamber become negative pressure, which improves the efficiency to a certain extent. When the particle size of the crushed finished product is small, choosing pneumatic conveying system is the most suitable way to ensure the continuous conveying of materials with small particle size, and it is not easy to cause pollution. Generally speaking, pneumatic conveying has high energy consumption, high noise and high water loss, which is slightly higher than the fixed cost of the following feed. However, many researchers have studied the problems caused by pneumatic conveying. It provides a basis for future improvement.
The batching process is closely related to the crushing process. In the process of feed processing, two technological processes are derived: first crushing and then batching, and first batching and then crushing. The best crushing efficiency can be obtained by the process of crushing first and then batching, and it is convenient to control the particle size. The process of crushing first and then batching has strong adaptability and does not need a large number of batching bins. The floor space is saved, and the feed granularity is uniform. These two processes have their own advantages, but if the particle size of the products produced is relatively small. If the content of grain raw materials is low and the content of protein is high, which is easy to bulge (such as some aquatic feeds), the process of mixing first and then crushing can be given priority.
The technological process of crushing stage can be divided into primary crushing and secondary crushing. The primary crushing process equipment is simple. Investment cost is low, but power consumption is high. The secondary crushing process can make up for the deficiency of primary crushing. The power consumption is reduced by more than 22% and the output is increased by more than 25%, but the equipment investment cost is high. When producing small-particle feed (aquatic feed), the secondary crushing process should be selected, and the materials should be classified before or after crushing, and those that meet the particle size requirements will enter the next process. Otherwise, return to the crusher to continue crushing. Until the requirements are met. In addition, small feed mills should adopt a one-time crushing process to save the investment in processing equipment. However, in the production process, special attention should be paid to whether the crusher breaks the net to ensure the qualified rate. However, at present, feed mills are becoming larger and larger, and the primary process is gradually replaced by the secondary crushing process.
To sum up, the crushing granularity has a certain relationship with the whole crushing process. According to the appropriate crushing particle size, first select the crusher and set the parameters, and then determine the technological process of the crushing section and the technological process of the crushing batching section. In order to design a correct and reasonable crushing process, it is necessary to know the best crushing granularity of different physiological stages and different kinds of animals, and design a reasonable technological process based on the characteristics of the selected crusher. Maximize production benefits. At present. The crushing stage is still the most power-consuming and noisy part in feed processing. When designing and selecting the technological process of feed factory, we should consider the cost, energy consumption and benefit as much as possible, and do a good job in environmental evaluation.
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