With the vigorous development of modern aquaculture and feed industry, the quality requirements of feed are getting higher and higher. For pellet feed produced by granulator, the length of the pellet is an important quality assessment index, and the length meets the requirements and is neat. Consistent pellets not only meet the needs of the feed manufacturer, but also the actual needs of the user. The pellets are too long, too short or uneven, which is not conducive to animal feeding. In actual production, the particle length of the granulation mechanism is generally required to be 2 to 3 times the diameter of the particles. For example, the production of pellets with a diameter of Ñ„3 mm is generally 6 to 9 mm in length, of course, depending on actual user needs and The feed variety, its length requirements are not necessarily within this range. Therefore, in order to produce feed pellets that meet the requirements or are as close as possible to the requirements, explore some factors that affect the pellet length of the pelletizer, and find a corresponding control method to make it beneficial to the production needs. Said that it is of great significance. Based on years of granulator design experience and on-site debugging experience, the author will discuss this issue from the following aspects.

1 The influence of the parameters of the granulator itself

The output of the granulator is Q (kg/h), the inner diameter of the ring die is D (mm), the effective width of the ring die is W (mm), the linear velocity of the ring die is V (m/s), and the rotational speed of the ring die is n. (r/min), the ring die aperture is d (mm), the ring die opening ratio is ψ, the number of openings is N (pieces), and the length of the produced particles when uncut is L (mm), particle density For ρ(kg/m3), the length of the pellets at the time of uncut can be calculated as:

For the above formula, it is not difficult to analyze the factors affecting the particle length L of the granulator:

1.1 Effect of granulator output

It can be seen from the formula that the particle length L is proportional to the yield Q. In the case where the other parameters are constant, the higher the yield, the longer the particles, and the shorter the particles. Therefore, in order to achieve specific particle length requirements, adjusting the output of the granulator is a possible method of choice. In actual feed production, feed manufacturers do the same, sometimes even sacrificing many yields to meet the particle length requirements. This issue will be mentioned later in the discussion.

1.2 Influence of ring mode line speed or speed

It can be seen from the formula that the particle length L is inversely proportional to the ring mode linear velocity V or the ring mode rotational speed n. In the case where the feed rate, ie, the yield Q, is constant, the faster the ring die is, the more the instantaneous extruded particles are. Short, and vice versa. For different sizes of granulators, the rotational speed of the ring mold is very different. Generally, the small granulator rotates at a high speed, and the large granulator rotates at a low speed, but the ring mold speed is controlled within a suitable range, generally at 6 Between m/s and 9m/s to meet the needs of granulation. When the linear velocity of the ring die is small, the quality of the produced pellets is high, but the produced pellets may be longer than required, and too small a line speed will affect the yield; when the loop mold speed is high, although it is advantageous for the yield The improvement, but the granules produced may be shorter than required, and the quality of the granules will be worse. This requires the feed manufacturer to choose the ring line speed suitable for itself according to different feed varieties. This is achieved by changing the gear ratio of the granulator drive system.

1.3 Influence of ring die aperture and opening ratio

The ring mode aperture d does not directly affect the particle length L. It has an effect on the length L together with the number of openings N, that is, the opening ratio of the ring die, because the opening ratio is proportional to the square of the ring mode aperture d. The product of the number of openings N. The larger the opening ratio of the ring mold, the shorter the produced particles, and the longer the particles. The opening ratio of the ring die is different for different ring die diameters, such as a ring die with a ring die diameter of Ñ„ 1.8 mm, an opening ratio of about 25%, a ring die with a ring die diameter of Ñ„ 5 mm, and an opening ratio. About 38%, generally the larger the pore size, the higher the open porosity. In actual production, especially when producing small-diameter pellets, such as the production of Ñ„1.8mm shrimp material, some users will complain that the produced pellets are too long, because the corresponding ring mold opening ratio is low when the pore size is small. One of the solutions is that it can be achieved by sacrificing a part of the output, or by increasing the linear velocity of the ring mold discussed in the previous section. Another method is to adjust the cutter, etc. Discussed in the following content.

1.4 Influence of inner diameter of ring mold, effective width of ring mold and particle density

For a granulator, the inner diameter D of the ring mold and the effective width W of the ring mold are relatively fixed parameters, generally do not change, and the user does not easily change, so their influence is not discussed here. The density of the particles is related to the raw material of the granulation and also to the compression ratio of the ring mold. The larger the compression ratio, the stronger the solid particles and the higher the density, but for the general product, the density of the particles is not much different. Therefore, particle density is not a major influence parameter, so there is no more discussion here. In summary, for the same granulation material, the greater the density of the granules produced, the shorter the granule length.