Abstract: In the processing of pellet feed, there are many factors affecting the quality of pellets. The selection of components in the press chamber of the pelletizer and the operation on the production site are control details that cannot be ignored. Ring molds, press rolls, feeding scrapers, cutting knives and steam conditioning will have an impact on granulation efficiency and effectiveness. The system's selection of standards and operating standards for these parts is the basis for good pellet processing and product quality improvement.

Key words: granulation process; ring die; feeding scraper; cutter; steam conditioning

There are many factors that affect the quality of the pellets during the processing of pelleted feed. In addition to the quality standards similar to powdered feed, the pellet feed also has requirements for color, particle size, length, surface finish, hardness, powder content, and chalking rate. Through the analysis of the particle persistence (PDI) index, it is found that among the many factors determining the quality of pellet feed, the formula determines 40% (raw material composition and ratio), the pulverization particle size before granulation is determined by 20%, and the quenching and tempering decision 20 % (recipe composition and quenching length determine the quenching effect), mold hole parameters determine 15% (product and formulation determines the mold), cooling determines 5% (aperture and formulation composition determines cooling time). In addition to the above factors, the processing technology that affects the quality of the pellet feed includes the expansion and expansion process of the raw materials, the mixing of raw materials, the addition of water, the fuel injection process, the steam pre-conditioning process, the post-maturing, and the post-spraying process. This paper focuses on the influence of the granulator press chamber components and on-site operation on particle production from the perspective of production site regulation.

1 Effect of ring mold on granulation effect

The influence of the ring mold on the granulation effect is mainly reflected in the effective length of the die hole, the size of the hole, the roughness of the die hole, the die hole pitch, and the die hole shape.

1.1 Depth and aperture ratio of the die hole

The depth of the die hole is the length of the ring die for a certain thickness minus the release hole, and the size of the hole diameter forms a certain aperture ratio. The pore diameter ratio is small, the material is squeezed in the die hole for a short time, is easy to be extruded, has high production efficiency and low power consumption, but the produced particles are loose, which is easy to cause quality problems such as high powder content and irregular grain length; Conversely, the larger the aperture ratio, the longer the material is squeezed in the die hole, the lower the production efficiency, the more the power consumption, and the higher the hardness of the produced particles. As the effective pores of the die hole lengthen, the granulation yield is significantly reduced, and even the mold blocking phenomenon occurs. In order to obtain the best granulation performance, the yield and quality can be optimized, and the appropriate ring mode compression ratio is very high. important. Each formula will have a suitable range of compression ratio. When determining the compression ratio, it is necessary to refer to the composition of the raw materials of the formulation, the fineness of the pulverization, the characteristics of the raw materials, and the like. If the ring mold aperture ratio is not well suited to the formulation granulation requirements, it is more practical to moderately adjust the formulation composition and the proportion of the raw materials. In order to achieve the best granulation efficiency, the formula must be harmonious with the ring mold. Unite.

1.2 Roughness of the die hole

The lower the roughness of the die hole (ie, the higher the finish), the less friction the material receives in the die hole, the ease of extrusion, the high production efficiency, and the smooth surface of the formed particles is not easy to crack and the particle quality is good. It is therefore recommended to prioritize the use of stainless steel ring molds.

1.3 The spacing of the die holes

The spacing of the die holes is related to the properties of the pressed feed. For example, a feed with a small wear resistance can be used, and a ring die with a relatively close pitch can be used; a feed having a large wear resistance, such as a feed containing high minerals and a high fiber feed, can be used. Larger ring molds increase granulation efficiency and die life.

1.4 Shape of the die hole

The shape of the die hole mainly includes an inner tapered hole, an outer tapered hole, a stepped hole, a straight hole, and an outer tapered stepped hole. The inner tapered hole facilitates material entry, strong compression force, high particle hardness, low powdering rate, but low production efficiency, and short life of the ring die. The outer tapered hole facilitates the passage of the material, but is not conducive to the entry of the material into the die hole, the pressed particles are loose, and the powdering rate is high. Straight holes and stepped holes have moderate performance, high production efficiency and high particle forming rate, so they are most commonly used. The outer tapered stepped ring ring mold can exert a good effect in the application of livestock and poultry materials, and solves the problem that the granular material in the later use of the ring mold has high powder and loose texture, so that the ring mold is in the Throughout the production process, the produced particles have a uniform hardness and low power consumption.

2 Effect of die roll gap on granulation efficiency

2.1 The gap is too large

When the gap between the die rolls is too large, the layer of the granulated pressing zone will be thickened, the pressure in the pressing zone will increase, the current of the main motor will increase, the resistance of the press roller will increase, and the pressure roller slip and the granulator vibration phenomenon will occur. The granulation output is reduced, and sometimes it will not be granulated.

2.2 The gap is too small

When the gap of the die roll is too small, the die roll is directly contacted, causing mechanical wear, which seriously affects the service life. The ring die guide port will be deformed due to the mechanical wear of the press roll shell, which makes the die hole feeding difficult, and the granulation output gradually decreases. Lead to granulation difficulties, and even stop production.

2.3 normal die roll clearance

It should be adjusted to manually rotate the ring mold for one week, and 1/4 working surface can drive the roller shell to run, or intermittently, so that the gap can meet the granulation requirements.

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3 Effect of feeding scraper on granulation

3.1 The feeding scraper will gradually become smaller as the use time prolongs, and this wear is easily overlooked, often when the granulation capacity is found to be decreased, or the ring mold working surface is abnormally worn and the life is reduced. I want to check the wear of the feed scraper.

3.2 Feeding scraper will also change the angle of guiding due to the blockage during production, accidental collision and other reasons when disassembling the ring die, and will also cause uneven feeding of the ring die working face, resulting in a decrease in output. Die life is reduced. The correct approach is to regularly inspect the granulator's consumables, including the feeding squeegee.

3.3 Feeding scraper wear or angle is not standard The effect on granulation: the feeding zone of the ring die and the press roll will be unevenly fed, and finally the wear of the ring die working face will be uneven (high and low), so that between the die rolls The gap is inconsistent, and the natural material layer is also thin and uneven. Where the gap is small, the material layer is thin, and the guide hole of the die hole is easy to wear and deform, which makes feeding difficult; although the feeding is normal, the material is normal, but because the material layer is too thick, the pressing force of the pressure roller on the material is reduced, so that the pressing force of the pressure roller on the material is reduced. Difficulty in discharging, the host current rises, and the production capacity is also reduced. At the same time, due to the uneven feeding of the working face of the ring mold, the wear of the die holes is inconsistent (large and small), and the thickness of the granular materials varies greatly.

4 Effect of feed amount on granulation

The main motor of each power is marked with the rated current value, the feed current will increase the current and the production capacity will be high. It should be adjusted according to the moisture content of the raw material, the nature of the formulation, the effect of quenching and tempering and the diameter of the particle. The amount of material, to achieve the best results. It should be noted that when adjusting the main motor current, its rated current value cannot be exceeded.

5 Effect of cutting knife on particle quality

When the cutter of the granulator is not sharp, the column material coming out of the ring die hole is broken, not cut, so the two ends of the granule are rough and the particles are arc-shaped, resulting in an increase in the powder content of the finished product. Particle quality. The adjustment of the cutter mainly affects the length of the particles. The length of the particles is generally 1.5 to 2.5 times the diameter of the material, and can also be appropriately adjusted according to the needs of the user. The method of adjusting the length of the particles is to adjust the distance between the cutter and the ring die. When the cutter exits, the distance between the knife edge and the ring die becomes larger, and the particles become longer, and conversely, the particles become shorter. It should be noted that the distance between the cutter and the ring die must be at least 3 mm, otherwise an accident will occur if the cutter head collides with the ring die. Take the special cutting knife for aquatic products as an example: the special cutting knife for aquatic material is an ultra-thin blade, generally with a thickness of 0.4-0.8mm. When adjusting, the knife edge should be close to the ring die, and the particle length is controlled by the feeding amount. As the amount of material increases, the particles become longer, and the amount of feed decreases to shorten the particles. This cutter is only suitable for pellets below 4.5mm.

6 Effect of steam on granulation

The use of steam to temper the feed can warm the material, gelatinize the starch, plasticize the protein and sugar, and increase the moisture of the feed. Because the water can act as a binder during granulation, it can not only improve The granulation quality, in turn, can lubricate the die holes, reducing the friction of the die holes on the feed, thereby increasing the granulation yield.

6.1 Effect of steam quality and steam intake control on particle quality and granulation efficiency

Steam must have the right pressure, temperature and moisture. The steam pressure is controlled by a pressure reducing valve, which is an important accessory in the steam line. The performance must be reliable and the outlet pressure fluctuations should be small. A steam filter (built-in 40 to 200 mesh screen) is installed in front of the pressure reducing valve to ensure that the pressure reducing valve is not blocked by suspended solids and impurities in the steam. The steam pressure should be guaranteed to be 0.2-0.4Mpa, and it is dry saturated steam without condensate, the temperature is 130-150 °C; when producing small-grain water-based material, the steam pressure is maintained at 0.1-0.2 Mpa, and the temperature is 115-130 °C. The most suitable for operation, can improve the quality of the particles; the higher the steam pressure, the higher the temperature, the temperature of the material after quenching and tempering is generally 65-85 ° C, and some feeds (such as aquatic products) need to reach above 90 ° C to meet the granulation. Claim. As the quenching and tempering temperature increases, the humidity is also increased accordingly. The most suitable moisture for granulation is 15.5%. The amount of steam added should be adjusted according to the formulation properties of various feeds and the configuration of the length-to-diameter ratio of the die. If the amount of steam is too much, the particles will be deformed, the temperature of the material will be too high, the nutrients such as additives will be destroyed, and even coking will occur during extrusion, which will affect the quality of the particles.

6.2 Correct control of steam usage in production

In the granulation process, as the feed amount changes, the amount of steam also changes accordingly, and the amount of steam that blocks the ring mold is 4% to 6% of the capacity of the granulator. For example, the water content of a certain formula is 13%, the granulating humidity is 15.5%, and the water should be added 2.5%. For every 1% increase in moisture, the temperature will increase by 11 °C, and the room temperature is 30 °C. The temperature was 2.5 x 11 ° C + 35 ° C = 62.5 ° C. For example, if the water content of a formula is 10% and the room temperature is 30 °C, the temperature of the feed after quenching and tempering is 5.5×11°C+35°C=95.5°C. This estimation method is only used for room temperature (20～30°C). Ordinary livestock and poultry and aquatic materials.

7 Generation and treatment of abnormal particles

Abnormal particles are often suppressed due to unsuitability between raw materials, formulations, processing techniques, and improper steam usage and pressure during conditioning (Table 1).

summary

The operation of the production site and the selection of the press chamber components have a great influence on the granulation production performance and product quality. When formulating and selecting raw materials, the actual situation of the granulation production process should be fully considered, and the formula, raw materials, process and Harmonization of equipment, maximizing quality requirements, and increasing production efficiency and reducing production costs.