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According to the feeding characteristics of different aquatic animals, such as river crabs and other benthic animals, they are used to finding food at the bottom of the water, and adopt a slower way of eating, so that the required feed particles cannot be too hard and too strong, and also try to reduce the loss caused by fine debris in the process of eating. From this point of view, the expanded and sunk feed is more suitable: the expanded and sunk pellet feed is easy to absorb water and soften, and is suitable for nibbling. It can also reduce the loss of debris generated during nibbling, reduce feed waste and water pollution. Moreover, the expanded feed has a long time of water resistance and a high degree of maturity. Double screw wet extruder is widely used to produce expanded feed. There are many factors influencing the material expansion, but they are closely related to the conditioning conditions, the operation conditions of the expander and the material properties. The floatability of extruded feed can be controlled by changing extrusion conditions.

1. The effect of conditioning is particularly important in the production of bulky feed. In the production of puffing and sinking feed, it is necessary to reduce the strong effect of extrusion and enhance the effect of conditioning. Water and steam are added during tempering, and sufficient tempering time is available to make the material fully soften and mature, so as to create conditions for the material to achieve better plasticity under the weaker conditions in the expansion chamber in the next step. In this way, the material will continue to mature without large expansion degree, so as to obtain the sinking feed. Sufficient conditioning has a good effect on improving feed digestibility, water resistance and extrusion stability, i.e. product homogeneity.

2. Low screw speed shall be adopted for expanding sinking feed, which can not only provide the required extrusion shear effect, but also avoid high pressure, avoid sharp increase of material energy, and it is not easy to become sinking feed due to excessive expansion after passing through the die hole.

3. Cavity temperature control is another important aspect of material energy control. In the feeding section of the extruder cavity, in order to ensure the good conveying performance of the materials, heating is not required; in the melting section of the cavity, heating is required, the temperature of the cavity is 120-125 ℃, which should not be too high. The screw and the cavity shear and knead the materials, so as to promote the maturation of the materials and improve the plasticity; in the homogenization section at the end of the cavity, cooling the cavity (the cavity temperature is 40-50 ℃), which has been reduced The energy of the cured plastic material can reduce the supersaturation state of the water in the material, so that when the material is extruded from the die hole into the atmosphere, it will not expand too much.

 4. The swelling degree of heavy feed is usually less than 1.3, which is different from that of floating feed and can reach more than 2 or 3. The pressure in the cavity is related to the screw configuration of the extruder, the material properties, the opening rate of the template and the feeding amount. The opening rate of the template affects the pressure of the material in the cavity. If the opening rate of the formwork is large, the discharge flow is large and it is not easy to accumulate high pressure at the formwork. During the trial production, the number of die holes can be changed according to the situation to get the suitable puffing and sinking feed.

Due to the low degree of maturity of the traditional hard granulated material, the problem was successfully solved by the expanded fish feed. In addition, the expanded and sunk fish feed has high stability in water, does not need to add artificial binder, does not break, does not disperse, so it has been widely used in fishery culture, and is gradually replacing the hard pellet feed.

Date: March 20, 2013 14:43:31