1 material factor
1.1 Material volume quality Generally speaking, the larger the material volume quality, the higher the granulation output. Therefore, when formulating materials, formulators should consider the bulk density of the materials in addition to the nutritional needs.
1.2 The material has fine particle size, large specific surface area and fast vapor absorption, which is beneficial to water regulation and high granulation yield. However, if the particle size is too fine, the particles are brittle and affect the quality of the particles; if the particle size is too large, the wear of the stamper and the press roll will increase, the energy consumption will increase, and the yield will decrease. Generally, the size of the pig material should pass through a 3 mm sieve. The grain size of the chicken should pass through a 3.5 mm sieve, at least 80% of which should pass through the 1.18 mm sieve.
1.3 The moisture content of the material moisture material is too high, which reduces the amount of steam added during granulation and affects the granulation temperature, thus affecting the yield and quality of pellet feed. At the same time, the moisture of the material is too high, the quenching and tempering is difficult, and the material is likely to slip between the inner wall of the ring mold and the pressure roller, resulting in blockage of the ring die hole. Generally, the moisture content of the material before quenching and tempering should be less than 13%.
1.4 Material composition
1.4.1 Protein material has high protein content. After heating, the material has high plasticity, increased viscosity and high granulation yield. However, when non-protein nitrogen (such as urea) is high, the granulation yield is lowered.
1.4.2 Starch Grains The starch content is high. It is easy to granulate under high temperature and high moisture, and the yield is also high. At this time, the tempering water is required to be between 16% and 18%, and the quenching and tempering temperature should be above 80 °C. Otherwise, the degree of gelatinization of the starch is poor to produce brittle particles, and it is impossible to form. If the grain is ripened before quenching (such as drying corn), the granulation yield will decrease. Therefore, it is better to choose not to dry when purchasing raw materials.
1.4.3 Adding a small amount of grease (0.5% to 1%) to the grease helps to reduce the wear of the machine components and allows the particles to pass through the die holes and increase the granulation yield. However, when the amount added exceeds 2%, the particles are loosened and it is difficult to form. Therefore, when adding high-dose oils, it is advisable to add 30% of the total amount at the mixer and 70% of the full amount of the granulator.
1.4.4 The appropriate crude fiber content (3% to 5%) of the crude fiber is beneficial to the bonding of the granular materials, reducing the powdering rate of the particles and increasing the granulation yield. However, when the crude fiber content exceeds 10%, the hardness and the forming ratio of the particles are affected due to poor adhesion, mechanical wear is increased, and granulation yield is lowered.
1.4.5 Minerals Inorganic feeds have almost no cohesive force and poor granulation performance, which affects granulation yield. Therefore, when the inorganic content is high, a small amount of a binder (such as molasses) is generally added to the material to improve the granulation performance and increase the yield.
1.4.6 Heat-sensitive feeds Lactose and whey powders increase the viscosity after heating, which is beneficial to increase the yield. However, when the temperature exceeds 60 °C, coking is likely to occur, and the pores are blocked, which affects the granulation yield. Therefore, warm water can be used for conditioning such feeds.
2 operational factors
2.1 After quenching and tempering moisture materials, the suitable moisture should be between 15.0% and 16.5%. It is advisable to use the hand to hold the dough and loosen the hands. When the tempering moisture exceeds 18%, the material easily slips between the inner wall of the ring mold and the pressure roller, and even the pellets are not pressed, thereby reducing the granulation yield. If the tempering moisture is less than 14%, the friction between the material and the machine is severe, and the granulation yield is reduced.
2.2 Roller and die spacing The gap between the press roll and the ring die has a great influence on the granulation quality. Generally, the gap should be between 0.05 and 0.3 mm. When the gap is larger than 0.3 mm, the material layer is too thick and unevenly distributed to reduce the granulation yield. When the clearance is less than 0.05 mm, the machine wears severely. Method for judging the distance between the rollers and the die: Generally, when the press roller is turned on, the roll is not turned or the hand is thrown into the granulator to hear the squeaking sound.
2.3 Mold hole finish The new ring mold has some iron filings, oxides, etc. attached to the inner wall of the die hole, and should be polished before use to smooth the inner wall of the die hole, reduce frictional resistance and increase granulation yield. The polishing treatment is carried out by: 1) cleaning the clogging of the mold hole by a drill having a diameter smaller than the hole diameter of the die hole. 2) Install the ring mold, apply a layer of grease on the feeding surface, and adjust the roller and mold spacing. 3) After mixing with 10% fine sand, 10% soybean meal and 70% rice bran, mix 10% fat and oil into abrasive, start to put abrasive, and treat for 20-40 min. With the improvement of mold hole smoothness, the particles will gradually loosen. According to this point, the degree of polishing is determined, and more than 90% of the die holes should be discharged.
2.4 Feeding scraper For the granulator that has been used for a long time, the feeding scraper is seriously worn, so that the amount of feed entering the roll and the mold drawing range is reduced, thereby reducing the output of the granulator and increasing the powder content.
2.5 The clogging of the die hole is mainly caused by the fact that the material with poor granulation performance or the new mold is not polished or the oil material is not cleaned after granulation. It is found that the die hole is clogged, and the drill bit is used to open. For the case that is not easy to be opened, the ring die should be immersed in an iron box containing organic oil, and the iron box is heated, and can be directly used for granulation after hearing the click.
2.6 Coefficient of friction between material and roller and die The friction coefficient between the material and the inner surface of the pressure roller and ring die is small, and the material is easy to slip, thus reducing the output. When the friction coefficient between the material and the inner wall of the die hole is too large, the material will not be pressed out of the die hole, and the granulation yield is reduced. Factors affecting the coefficient of friction include formulation, tempering, and mechanical itself.
2.7 The feed amount is reduced, and even if the operator has a high level of quenching and tempering, it is impossible to increase the output.
2.8 The cooled pellet feed is not sufficiently cooled, the particles are loose, and the powder is increased after being lifted by the hoist. The powder is sieved and refluxed to reduce the granulation yield. This effect is particularly pronounced when the pellets need to be broken, which can be adjusted by adjusting the cooling air volume and cooling time. Generally, the temperature of the pellets after cooling cannot be higher than room temperature by 3 °C.
3 Machine installation and accessories selection factors
3.1 Opening rate The opening rate of the ring mold has a great influence on the production. In order to ensure the strength of the ring mold, the larger the hole diameter, the higher the opening rate and the higher the granulation output.
3.2 Mould hole shape Straight hole ring mold is suitable for processing compound feed, but for some grades of feed, because of its high crude fiber content, processing with straight hole ring mold will greatly reduce the output. At this time, the outer tapered hole ring mold can be used for processing.
3.3 The diameter of the die and the roll is larger than the diameter of the large ring die. The larger the diameter of the press roll, the smaller the angle between the material entering the pressing zone and the less likely the material is to be squeezed back, which is beneficial to increase the grain production. Generally, the roll and die diameter ratio needs to be greater than 0.4.
3.4 Scraper position feeding scraper is not installed properly, the material is pulled out of the ring mold, resulting in low output and many powder. The correct installation should be that the edge of the feeding scraper is 2 to 3 mm away from the ring die and the ring die cover, and the depth of the top of the scraper cannot exceed the die hole cutting groove.
3.5 Ring mold with large pore diameter and deep diameter ratio, the granulation yield is high, but the appropriate aspect ratio should also be selected. The die hole thickness is too large, the output is low, and the hardness is high; when the die hole thickness is small, the particle hardness is small, and the quality requirement is not achieved. Taking the 4.0 mm pore diameter as an example, the range of depth to diameter ratio is 9.5 to 12.5 for feeds with high grain content and 4.8 to 8.0 for heat sensitive materials. The large value should be selected when adding 1% to 2% grease.
3.6 Ring mold installation error Ring mold position installation error, will cause uneven excessive wear and uneven granulation, even ring mold turbulence, reduce granulation output.
3.7 The position of the cutter is too close to the ring mold, resulting in more powder and affecting the grain production. It should be adjusted during the granulation process, preferably with a ratio of particle length to particle diameter of 1 to 2:1.
4 other factors
4.1 Steam quality steam enters the pipeline with saturated steam at a given pressure of the boiler. During the transportation process, energy will be lost and the condensed water will become unsaturated and hot steam, which will adversely affect the quenching and tempering. Therefore, the condensed water should be discharged before quenching and tempered, and it can be turned into low-pressure dry heat steam through a pressure reducing valve to improve the quenching and tempering effect. After decompression, the steam pressure is not less than 0.2 MPa and the temperature is not lower than 120 °C.
4.2 The voltage, current, and stability of the feed have a significant impact on the granulation yield.
In short, the granulation process often encounters problems of insufficient yield, but as long as the granulator can find a solution according to the specific situation, the granulator can be operated efficiently.
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