The granulator parameters affecting the pellet feed PDI mainly include the output, the ring mold line speed, the ring mold working area, the die roll gap and the ring mode compression ratio.
In the case where the other parameters of the granulator are unchanged, the higher the yield, the looser the granules produced and the more the powder. This is because when the output is high, the time for being squeezed in the die hole is short, the power consumed per unit of production is less, and the compaction of the particles is insufficient. Therefore, in order to control the PDI of the particles, the granulator should be selected. Feed speed, control production.
When the line speed or rotation speed of the ring mold is high, the feed does not easily form a proper thickness of the layer in the extrusion zone and the feed is difficult to enter the die hole, which causes the relative sliding of the pressure roller and the ring die to even block the machine, affecting the quality of the particles, and simultaneously producing The particles are scooped out by a large centrifugal force, and the particles are easily broken and have many surface cracks. The suitable ring-shaped line speed is 6~9 m/s (Li Haibing et al., 2005). Generally, the raw materials which are difficult to be granulated are selected at a lower speed, and the raw materials which are easy to be granulated are selected at a higher speed.
Under the same yield, the larger the working area of ​​the ring mold, the more the number of die holes, the longer the feed stays in the die hole, the longer the time of extrusion, the denser the structure of the particles, and thus the pellet PDI produced. The higher.
The granulator can work normally when the die roll gap is set between 0.1 and 0.5 mm. In this range, the larger the gap, the more power the pellet machine consumes at the same output, and the higher the pellet PDI produced, the higher the This is because there is a pre-compression force in the material in the feed layer of the press roll in the pressing zone. For ring molds with different die hole diameters, smaller gaps are generally used for pressing small diameter particles, and larger gaps are used for pressing larger diameter particles.
The ring mode compression ratio refers to the ratio of the effective length of the ring die hole to the die hole diameter. For a ring mold of the same pore size, the larger the compression ratio, the thicker the effective thickness of the ring mold, the greater the frictional resistance of the feed when it is extruded in the die hole, and the stronger the extruded particles, so in order to obtain A higher particle PDI can increase the compression ratio of the ring mold as appropriate. Different pellet feed varieties have different requirements for PDI. Generally, the requirements for aquafeeds are higher than those for livestock feeds. This is because high PDI can increase the stability of pellet feed in water and reduce water pollution and feed waste. The ring mode compression ratio is not as large as possible, because the high compression ratio means high energy consumption and low output, and must be reasonably selected according to the formulation characteristics. The specific selection method will not be discussed.
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