Different aquatic animals have different feeding characteristics. Take river crab and other benthonic animals for example, they are used to seek food underwater; and they often chew with slower speed. Too hard or too firm feed pellets are not suitable for them. It also should to reduce the small fragments waste during their feeding process. So, the sinking extruded feed are beneficial for them. The sinking extruded feed has many advantages: easy to soften after absorbing water, suitable for chewing, decreasing the small fragments waste, decreasing the water pollution, long water resistant time and high aging degrees.
Twin screw wet extruders are widely used in extruded feed processing. The material extrusion situation is affected by many factors. It mainly connects with the conditioning conditions, operation of the extruder and the material character. The extrusion feed buoyancy can be controlled by changing the extrusion conditions.
1.The conditioning effect is important in processing sinking extruded feed. During the process, it needs to decrease the extrusion effect and increase the conditioning effect. Moisture adding, steam adding and enough conditioning time can make the raw materials soften and cure fully. Thus the materials can achieve better plasticity under weaker conditions in the extrusion chamber. The materials can cure continually and won’t generate bigger puffing degree. We can get the sinking extruded feed at last. Fully conditioning can improve the feed digestibility, water resistance ability and stability.
2.Processing sinking extruded feed pellets should adopts lower screw rotation speed. It can provides the effect of shear and squeeze and won’t generate over-high pressure. At last, the materials through the die holes won’t be over-extruded.
3.Chamber temperature is another important factor for material energy control. In the chamber feeding section, it’s no need to heat to ensure good delivery performance. In fusion section, you must heat to ensure the chamber temperature reach 120~150℃. It can promote the material’s curing degree and plasticity. In the end homogenize section, the chamber temperature is cooled to 40~50℃. It can decrease the cured material’s energy and the supersaturation of the moisture in materials, thus the materials can be extruded out the die holes and not over-extruded.
4.Sinking feed extrusion degree is lower than 1.3 and floating feed can achieve higher than 2-3. The pressure inside the chamber are connected with the screw configuration, material character, porosity of the die and feeding quantity. The die porosity affects the pressure of the materials inside the chamber. If the die has higher porosity, the discharging flow is bigger. We can change the quantity of die holes according to our requirements to get suitable sinking extruded feed.
Traditional hard pelleted feed has low curing degree and sinking extruded fish feed doesn’t have the problem. Extruded feed has high stability in water and no need to add binder. Extruded feeds are widely used in aquaculture instead of hard feed pellets.
