Study On The Effect Of Twin-screw Extender Die Structure And Extrusion Process On The Quality Of Fish Feed Pellets

Twin-screw extruder is the core equipment in the process of feed extrusion.The die structure design and extrusion process can make the extruder at the extruding feed more uniformly,improving the quality of aquatic feed products.Die is key component to control feed quality.The effect of changes in the parameters of the die structure on the feed flow characteristics is not clear.Therefore,this study conducted numerical simulations of material flow inside different die structures of the extruder,and investigated the effect of die structure on feed flow uniformity,the effect of extrusion process(screw speed,feed water,and die temperature)on the feed pellets quality.And analyzed the interaction between extrusion processes.It mainly contains the following aspects:Based on CFD numerical simulation,the effects of four different types of dies with different outlet numbers(12,13,14 and 15)on the feed flow uniformity was investigated.The results showed that extrusion outlet velocity was negatively related with outlet numbers.The extrusion viscosity was positively related with outlet numbers.The extrusion mass flow was negatively related with the outlet numbers.When the die outlet numbers were 15,the variance values of extrusion mass flow reached the minimum.When the die outlet numbers were 14,the variance values of extrusion velocity and viscosity reached the minimum.Therefore,when the number of die outlet numbers was 14,the feed flow at the die outlet was the most uniform.Based on CFD numerical simulations,the effects of six different types of dies with different Length/Diameter(L/D)ratio(1.25,1.5,1.75,2,2.25,2.5)on the feed flow uniformity was investigated.The results showed that the extrusion outlet velocity decreased,then increased and then decreased with increasing L/D ratio.The average extrusion viscosity decreased,and then increased with increasing L/D ratio.The average extrusion mass flow increased and then decreased with increasing L/D ratio.When the L/D ratio is 1.75,the variance values of extrusion velocity reached the minimum.When the L/D ratio is 1.25,the variance values of extrusion viscosity and mass flow reached the minimum.Therefore,when the L/D ratio is 1.25,the feed flow at the die outlet is the most uniform.The die was manufactured after the most optimal structure parameters were determined.The effects of different screw speed,moisture content and die temperature on the salmon feed pellets quality(bulk density,moisture,oil absorption,starch gelatinization degree,protein solubility,water absorption and water solubilization capacity)were investigated by singlefactor experiment and response surface optimization experiment.Quadratic multinomial regression models were developed based on the experimental results,and the interaction effects and significance between the three factors were analyzed.The analysis of the experimental results showed that the bulk density,moisture,oil absorption,starch gelatinization degree,protein solubility and water solubilization capacity all decreased with the increasing screw speed,and the water absorption increased with the increasing screw speed.The feed moisture,starch gelatinization degree and water solubilization capacity increased with the increasing moisture content.The oil absorption decreased with the increasing moisture content.The feed bulk density,protein solubility and water absorption showed a decreasing and then increasing trend with the increasing moisture content.The feed bulk density,moisture,starch gelatinization degree,protein solubility and water solubilization capacity increased with the increasing die temperature.The water absorption decreased with the increasing die temperature.The oil absorption decreased and then increased with the increasing die temperature.