Feed Pellet Granulator

Product Details

Factors affecting the length of pellets in feed machinery and their control methods With the vigorous development of modern aquaculture and feed industry, the requirements for feed quality are getting higher and higher. For pellets produced by feed pellet granulator, pellet length is a very important quality assessment index. The length meets the requirements and is neat. Consistent pellets not only meet the sales needs of feed manufacturers, but also the actual breeding needs of users. Pellets that are too long, too short or uneven are not conducive to animal feeding. In actual production, the length of the granules produced by the granulating mechanism is generally required to be 2~3 times the diameter of the granules. For example, the length of granules with a diameter of Ñ„3mm is generally 6~9mm. Of course, according to actual user needs and differences,for the feed variety, the length requirement is not necessarily within this range. Therefore, in order to produce feed pellets with a length that meets the requirements or as close as possible to the requirements, we should discuss some factors that affect the pellet length of the feed pellet granulator, and find the corresponding control method to make it beneficial to the production needs. That is of great significance. Based on years of experience in granulator design and field commissioning, the author will discuss this issue from the following aspects.

The influence of the parameters of the feed pellet granulator itself

Suppose the output of the feed pellet 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 speed of the ring die is V (m/s), and the speed of the ring die is n (R/min), the hole diameter of the ring die is d (mm), the opening rate of the ring die is ψ, the number of openings is N (pieces), the length of the produced particles when they are not cut is L (mm), and the particle density Is ρ (kg/ m3)

â—† The impact of feed pellet granulator output

It can be seen from the formula that the particle length L is directly proportional to the output Q. With other parameters unchanged, the higher the output, the longer the particles, and vice versa. Therefore, in order to achieve a specific pellet length requirement, adjusting the output of the feed pellet granulator is a possible method of choice. In actual feed production, feed manufacturers do the same, and sometimes even sacrifice a lot of output to meet the pellet length requirement. , This issue will be mentioned later in the discussion.

â—† The influence of ring die linear speed or rotation speed

It can be seen from the formula that the particle length L is inversely proportional to the ring die linear velocity V or the ring die rotation speed n. Under the condition that the feed rate, that is, the output Q, remains unchanged, the faster the ring die speed, the more instantaneously extruded particles Shorter, vice versa, longer. For granulators of different sizes, the speed of the ring die varies greatly. Generally, the speed of small feed pellet granulator is high, and the speed of large granulators is low, but the linear speed of the ring die is controlled within an appropriate range, generally 6 m/s~9m/s to meet the needs of granulation. When the linear velocity of the ring die is low, the quality of the pellets produced is high, but the pellets produced may be longer than required, and at the same time, too small linear velocity will affect the output; when the linear velocity of the ring die is high, although it is beneficial to the output However, the pellets produced may be shorter than required, and the quality of pellets will become worse. This requires feed manufacturers to choose a suitable ring die line speed according to different feed varieties. The method can be adopted is changing the transmission ratio of the feed pellet granulator transmission system.

â—† The influence of ring die diameter and opening rate

The ring die aperture d does not directly affect the particle length L. It and the number of openings N together have an effect on the length L, that is, the size of the ring die aperture ratio ψ, because the aperture ratio ψ is proportional to the square of the ring die aperture d The product of the number of openings N. The greater the opening rate of the ring die, the shorter the particles produced, and vice versa. The opening rate of the ring die is different when it corresponds to different ring die diameters. For example, the opening rate of the ring die with the diameter of ф1.8mm is about 25%, and the opening rate of the ring die with the diameter of ф5mm is about 25%. About 38%, generally the larger the pore size, the higher the open porosity. In actual production, especially when producing small-diameter pellets, such as producing ф1.8mm shrimp feed, some users will complain that the pellets produced are too long because the corresponding ring die opening rate is low when the aperture is small. One of the solutions is to sacrifice a part of the output, or to increase the linear speed of the ring die discussed in the previous section. Another method is to adjust the cutter, etc.

â—† The influence of the inner diameter of the ring die, the effective width of the ring die and the particle density

For a feed pellet granulator, the inner diameter D of the ring die and the effective width W of the ring die are relatively fixed parameters. Generally, they will not change, and it is not easy for users to change them. Therefore, their influence will not be discussed here. The density of the pellets is related to the raw materials for pelleting, and also related to the compression ratio of the ring die. The larger the compression ratio, the stronger the pellets produced and the greater the density, but for general products, the density of the pellets is not much different. Therefore, the particle density is not a major influencing parameter, so I won’t discuss it too much here. In short, for the same granulation raw material, the greater the density of the produced particles, the shorter the length of the particles.

The impact of the cutter

★ The influence of the number of cutters

The number of cutters is usually determined by the number of press rollers of the feed pellet granulator. Generally, the granulator has 2 to 3 press rollers, and each press roller is equipped with a cutter. If each cutter is used, the ring Every time the mold rotates one round, a certain amount of incoming material is extruded and then cut by the cutter 2 or 3 times accordingly. Therefore, if the output is constant, the feed pellet granulator with three cutters is better than the granulator with two cutters. The granules produced by the mechanism are shorter, which means that the three-roll feed pellet granulator is more conducive to controlling the length of the granule than the two-roll granulator. This is also true in actual use, such as when producing small-sized aquatic materials. Due to the short length requirement, a three-roller granulator is usually used and three cutters are used for cutting.

★ The influence of cutter structure and adjustment

Cutters are generally divided into hard blade type and thin blade type. Hard blades have good wear resistance and poor toughness, and are suitable for large particle size livestock and poultry materials; thin blades have good toughness and poor wear resistance, and are suitable for small diameter aquatic materials. When adjusting, the hard blade should generally be adjusted so that the blade is about 5mm away from the outer surface of the ring die. If the distance is too small, the powder will increase, and the blade may be damaged. If it is too large, the length of the particles will not be consistent, and long particles may appear. As the distance increases, the bending moment of the knife edge on the particles increases, and the particles may break off the surface of the ring die. Because of its elasticity, the thin blade can be adjusted to a position close to the outer surface of the ring mold, so that the cut particles are neat and consistent, which is especially suitable for small-particle aquatic materials such as shrimp pellets. In actual production, the adjustment of the cutter is very flexible, and one, two or three cutters can be used for cutting as needed. Another situation is that in theory, when two or three cutters are used at the same time, the cutting edge should be adjusted to a position equal to the distance from the outer surface of the ring die, so that the cut particles are neat, but the actual situation is not In this way, due to the distribution defects of the feed pellet granulator when feeding, the amount of feed distributed to each pressure roller cannot be guaranteed to be completely consistent, so that the length of the pellets extruded in each squeeze zone is different , some extruded particles in the extrusion zone are longer, and some extruded in the extrusion zone are shorter, but they are basically the same in an extrusion zone. In this case, each cutter should be adjusted separately position, so that the cutter at the press roller with less feed distribution is closer to the surface of the ring die, and the cutter at the press roller with more feed distribution is farther away from the surface of the ring die, in order to make the whole The length of the particles produced on the above is the same.

Influence of ring die hole structure

There are two commonly used ring die hole structures, straight cylindrical holes (Figure a) and stepped cylindrical holes (Figure b).

The length of the particles produced by straight cylindrical holes is more uniform (as shown in Figure a), while the particles produced by stepped cylindrical holes often have individual long particles (as shown in Figure b). Its formation mechanism is: The reason for using stepped cylindrical holes is that the actual pelletizing requires relatively small compression, and the ring die cannot be made too thin in thickness due to the need for strength. Only the section that passes through the cylindrical hole can only be used. The method of expanding the hole to achieve the goal not only guarantees the compression ratio of the ring die, but also meets the strength requirements. However, the consequence of such a compromise is that the cutter is cutting because the cutting point is away from the particle bending point. When the cutter is not sharp enough, the particles may break off the junction of the stepped holes and become longer than ordinary particles. This situation is even worse when the outer stepped holes are drilled deeper. The solution is to change the feed formula, use a larger compression ratio as much as possible, do not use step holes or make it as short as possible; or use a sharper cutter, and try to be as close to the ring die as possible; or adjust the feed moisture to be larger to make the extrusion The brittleness of the particles is reduced, and the texture becomes soft and not easy to break.

The influence of the outer surface structure of the pressure roller

The structure of the outer surface of the pressure roller mainly includes the tooth groove type, the tooth groove type with sealing edge and the honeycomb type. The tooth groove type pressure roller has good coil performance and is widely used in livestock and poultry feed factories. However, because the feed slides in the tooth groove, the pressure roller and ring die wear unevenly, and they wear at both ends of the pressure roller and ring die. For a long time, the two ends of the ring die are difficult to discharge, and the produced particles are shorter than the middle part of the ring die. The tooth groove type pressure roller with sealing edge is mainly suitable for the production of aquatic material. The aquatic material is easy to slide when squeezed. Because the tooth groove is sealed on both sides, it is not easy to slide to both sides when the feed is squeezed, and the distribution of the feed is limited. It is more uniform, and the wear of the pressure roller and the ring die is also more uniform, so that the length of the particles produced is more consistent. The advantages of the honeycomb press roll are that the ring die is uniformly worn and the length of the produced particles is relatively consistent, but the performance of the coil is poor, which affects the output of the feed pellet granulator, and it is not as common as the tooth groove type in actual production.

The impact of the screening system after granulation

The granulated granules must be sieved to remove unnecessary large particles, small particles and powders to obtain qualified products with uniform length. Feed pellet granulator generally use rotary sizing screens or vibrating sizing screens for particle screening. The grading screen is generally equipped with upper and lower screens, the upper screen is the longer particles or large impurities, the lower screen is the finished material, and the lower screen is the smaller length Therefore, for an existing grading screen, how to configure the screen reasonably is the key to affecting the uniformity of the length of the finished material. If the feed manufacturer requires a higher uniformity of the length of the finished material, it must remove more large and small particles, and get less finished materials. On the contrary, more finished materials are obtained, which depends on each production. The manufacturer controls it by himself.

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