With the in-depth study of the feed industry, more and more researchers and manufacturers are making feed processing technology an important way to improve product quality while improving raw material quality and optimizing formula. The particle hardness of pelleted feed is an important indicator of the appearance quality of pelleted feed. In the feeding process of some pig farms, it was also found that the particle hardness of pelleted feed had a certain influence on the performance of livestock and poultry. Therefore, how to regulate the particle hardness of pellet feed is an issue that some manufacturers and researchers are actively exploring. Throughout the whole process of the pellet feed processing technology, in addition to the feed formula, the processing techniques that affect the particle hardness of the pellet feed include: the crushing process of the raw materials; the expansion and expansion process of the raw materials; the mixing of raw materials, the addition of water, and the fuel injection process; Quenching and tempering process; selection of molds in the granulation process; post-maturing, post-spraying process; drying and cooling process.
1 Effect of crushing process on particle hardness
The factor that plays a decisive role in the hardness of the granulation process is the pulverization particle size of the raw material. Generally speaking, the finer the particle size of the raw material is, the more easily the starch is gelatinized during the quenching and tempering process, the stronger the bonding effect in the granular material, the less the particles are easily broken, the harder the hardness is. In actual production, according to different The production performance of the animal and the size of the ring mold pore size, the crushing particle size are required to be properly adjusted. The chicken and duck material requires coarser grain size, the average particle size of the crushed product is 800-900 μm, and the piglet material is required to be finer, and the average particle size of the crushed powder is 400～500μm, the average particle size of the fattening pig material is 600~700μm, and the particle size of the fish material and special aquatic material is more fine, generally below 250μm. In poultry feed, it is generally required that the pellets have a high hardness, a low powdering rate, and a reduced waste of feed. In order to improve the particle hardness of the pellet feed for poultry, the purpose of improving the hardness of the pellet can be achieved by adjusting the coarse, medium and fine proportions of the crushed particle size of the raw material. The coarse particles mean that the particle diameter is 900 μm or more and the requirement is not more than 15%, the medium particles are about 35% of the particle diameter of about 700 μm, and the fine particles mean that the particle diameter is 500 μm or less, and it is required to exceed 50%. Among them, the fine powder having a particle diameter of less than 250 μm is required to be not less than 25%. The starch in this part of the fine powder can be fully gelatinized during quenching and tempering, and plays an important role in the granulation process, and the coarse, medium and fine particle size particles are bonded together to become large particles, and the particles are improved. Hardness and reduced product pulverization rate. In the production of pig feed, the hardness of the granules is generally required to be moderate. Too hard will reduce the palatability and production performance of the product. Too brittle will increase the pulverization rate of the product, reduce the production performance and increase the waste. In the production of swine feed, it is generally required to pulverize more than 70% of the particle diameter between 700 and 500 μm, and the fine powder of 250 μm or less should exceed 20%. Such a particle size distribution facilitates pellet granulation and improves the appearance quality of the granules while ensuring proper hardness and low pulverization rate of the product. In the production of fish feed, on the one hand, the physiological characteristics of fish animals require that the raw material is pulverized to a particle size of not less than 85% below 250 μm; on the other hand, the small particle size is advantageous for the formation of particles and stability in water, fish The particle hardness of the material is relatively large, because the fish material is stable in water and the particles are dense. The fish materials currently produced are hard pellets and should be developed in the direction of soft pellets.
2 The impact of the expansion and expansion process of raw materials on the hardness of the particles
By the expansion and expansion treatment of the raw materials, the anti-nutritional factors in the raw materials can be destroyed, the toxins in the raw materials can be removed, the bacteria can be killed, the harmful substances can be eliminated, the proteins in the raw materials can be denatured, and the starch can be fully gelatinized. The effect of gelatinized starch on particle hardness is significant. At present, the expanded raw materials are mainly used for the production of high-grade suckling pigs and special aquatic materials. For special aquatic materials, after the raw materials are expanded, the degree of gelatinization of the starch increases, and the hardness of the particles after forming increases, which is beneficial to improve the stability of the particles in water. For suckling pigs, the granules are required to be crispy and not too hard, which is beneficial to the feeding of suckling pigs. However, since the expanded piglet pellets have a large degree of gelatinization of the starch, the hardness of the pellets is also large. The hardness of the particles should be reduced by other means.
3 The effect of mixing, adding water and fuel injection on the hardness of the
The mixing of raw materials can improve the uniformity of various particle size components, and is beneficial to maintain the particle hardness substantially consistent and improve product quality. The water adding process in the mixer is still a problem that is being actively explored. In the production of hard pellet feed, adding 1% to 2% of water in the mixer is beneficial to improve the stability and hardness of the pellets. However, due to the increase in moisture, it has a negative effect on the drying and cooling of the particles. Also unfavorable for the storage of the product. In the production of wet pellet feed, up to 20% to 30% of water can be added to the powder, and about 10% of water is added during the mixing process, which is easier to add during the quenching and tempering process. The particles formed by the high moisture material have small hardness, softness and good palatability, and can improve the production performance of livestock and poultry. This wet pellet feed can be used in large aquaculture companies. Wet granules are generally not stored, and are generally required to be fed immediately. The addition of grease during the mixing process is a grease addition process commonly used in feed production plants. The addition of 1% to 2% of the oil reduces the hardness of the particles to be insignificant, and the addition of 3% to 4% of the oil can significantly reduce the hardness of the particles.
4 Effect of steam quenching and tempering process on particle hardness
Steam quenching and tempering is the key process in the processing of pellet feed. The quenching and tempering effect directly affects the internal structure and appearance quality of the pellet. Steam quality and quenching and tempering time are two important factors that affect the quenching and tempering effect. High-quality dry saturated steam can provide more heat to increase the temperature of the material, and gelatinize the starch. The longer the conditioning time, the higher the starch gelatinization degree. The denser the granular structure after forming, the better the stability and the hardness. The bigger. For the general livestock and poultry, by adjusting the amount of steam added, the quenching and tempering temperature is maintained at 70-80 ° C, and the quenching and tempering time is controlled by about 30 seconds by changing the length of the conditioner, the blade angle and the rotation speed. For fish stocks, there are generally double or multi-layer jackets to improve the quenching temperature and prolong the conditioning time. It is more conducive to improving the stability of the fish granules in water, and the hardness of the granules is correspondingly increased.
5 Effect of granulating mold on particle hardness
The technical parameters such as the pore size and compression ratio of the ring die of the granulator can significantly affect the hardness of the particles. The hardness of the particles formed by the ring die with the same pore diameter and different compression ratios increases with the increase of the compression ratio. By selecting a suitable compression ratio ring mold, it is possible to produce particles of suitable hardness. The length of the particles has a significant effect on the pressure bearing capacity of the particles. In the case of particles of the same diameter, the longer the particle length, the greater the hardness measured. Adjusting the position of the cutter and maintaining the proper particle length keeps the hardness of the particles substantially the same. The cross-sectional shape of the particle diameter also has a certain influence on the hardness of the particle. The 8-shaped cross-section has a stronger pressure bearing capacity than the circular cross-section, and the hardness value measured is also larger. In addition, the material of the ring mold also has a certain influence on the appearance quality and hardness of the particles. There is a significant difference between the ordinary steel ring mold and the stainless steel ring mold.
6 post-maturing, post-spraying process on the hardness of the particles
The post-maturing and post-spraying processes are used less in the livestock and poultry feed production process, and the fish and special aquatic materials production processes are widely used. Post-aging can fully gelatinize the starch inside the particles, make the internal structure of the particles more dense, prevent the infiltration of water, and is beneficial to the stability of the water-producing feed particles in water, and also improve the hardness of the particles. Post-spraying process In the hot pellet feed spraying technology, the sprayed grease or other sprayed material will penetrate into the interior of the granules to loosen the internal structure and reduce the hardness of the granules, but prevent the immersion of water and improve the stability of the granules in water.
7 Effect of drying and cooling process on particle hardness
In order to prolong the storage time of the feed product and ensure the quality of the product within a certain period of time, the feed granules need to be dried and cooled as necessary. In the test for determining the hardness of the particles, the hardness of the particles was determined by the cooling of the same product for 5 minutes, 10 minutes, and 15 minutes, respectively. The hardness of the particles with low hardness was not significantly affected by the cooling time, but the hardness was less. Large particles decrease in particle hardness as the cooling time is lengthened. This may be because as the water inside the particles is lost, the brittleness of the particles increases, affecting the hardness of the particles. At the same time, the particles were subjected to rapid cooling (full cooling of the damper) (cooling time of 3 minutes) and small air volume (the damper was closed to one third) and slowly cooled (cooling time of 20 minutes). The hardness is reduced and the surface crack of the particles is increased. In addition, it is worth mentioning that the large hard particles are broken, and the large particles become small particles, which can significantly reduce the hardness of the particles. In the processing of pellet feed, the factors affecting the hardness of the pellet are far more than these. With more and more researchers who are enthusiastic about feed processing technology, more and more methods to control the hardness of the pellet have been adopted. Mastered, I believe that in the near future, we can process a variety of animal feed pellets.
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