Study On The Mechanism And Key Technology Of Rotary Extrusion Forming Of Feed Powder

As the main technology in the international granulation field,the ring-die granulation forming technology(rotary extrusion forming technology),is widely used in the feed industry,renewable biomass energy industry and pharmaceutical industry and other fields.The pellet quality and cost are heavily dependent on the ring-die pellet mill,which is one of the most important processing machines used for feed production directly.China has been the largest animal feed producing country,however,the fundamental researches of rotary extrusion forming are still relatively deficient,and there still exists huge technology gaps from foreign integrated technical level.In order to improve the production efficiency and pellet quality,and extend the service life of ring-die,the pelletization process and mechanism,modeling of pellet quality and energy consumption,and wear mechanism of ring-die were studied through theoretical analysis and experimental investigation.The main research works in this dissertation include the following contents:The basic principle of rotary extrusion forming and the change rule of material between ring-die and roller were analyzed,and the productivity model was established based on the grab condition of material.The extrusion forming mechanism in the die-hole was investigated and two pressure models were respectively deduced based on continuum mechanics and discrete theory,and the related factors were also analyzed.The rotary extrusion forming process was divided into a compression deformation zone and an extrusion forming zone.Based on the mechanical analysis of the material in these two zone,the torque model and energy consumption model were established,and the effects of critical parameters on torque and energy consumption were analyzed.The above research provides an effective reference and theoretical basis for the optimization of the structure and process of the ring-die pellet mill,and also lays a theoretical foundation for further research on the extrusion forming mechanism.The problems and shortcomings of the single pellet press in the simulation process of pelletization were analyzed.Based on the demand analysis of simulation process of pelletization,a multi-hole device was designed and the test platform was established to investigate the influence rules of critical parameters such as the ratio of length to diameter,material moisture content,die temperature,on the compression force.According to the analysis of compression force-time curve,the extrusion forming mechanism was discussed.Based on the compression pressure obtained with the multi-hole test platform,the driving torque of the ring-die pellet mill with the corresponding process parameters was calculated and verified.The experimental results provide an effective reference for the process optimization of the ring-die pellet mill.The influence of pelleting process factors,such as feedstock moisture content,feedstock particle size,die temperature and compression speed,on the compression force and pellet properties were investigated experimentally based on RSM and MPD.According to the experimental results,the mechanical model describing compression force and quality evaluation models describing pellet density,pellet moisture content and pellet tensile strength were established.Experimental verification results showed that the prediction errors of compression force,pellet density,pellet moisture content and pellet tensile strength models were 3.60%,1.54%,2.19%,and 6.0%,respectively.The establishments of compression force model and particle quality models provide an effective reference for improving the pellet quality and equipment property.To investigate the wear mechanism of ring-die,a wear experiment was carried out under the practical production condition.The surface morphology was observed firstly.The abrasion depth of ring-die wall and die-hole wall was measured by LK-G10 laser displacement sensor,and the test results showed that the abrasion depth of die-hole wall decreased with the depth of die-hole exponentially,consistent with the law of the pressure in the die-hole.The hardness of the wearing surface was measured with HR-1500DT electric Rockwell apparatus,the microscopic wear morphologies of the wearing surfaces such as the inner wall of ring-die,the chamfer and the inner wall of the die-hole,were analyzed based on the observation results scanned by JSM-6300 scanning electron microscope(SEM).The wear mechanisms of different wearing surfaces were studied from both macroscopic and microscopic aspects.The research results showed that the wear mechanisms of ring-die include polishing wear,abrasive wear and fatigue wear,and different wear mechanism plays a leading role in different wear position.Some improvement programs were proposed to extend the service life based on the wear mechanism analysis above.Based on the above research,some improvements were proposed and the performance tests were carried.The test results showed that the output of the improved pellet mill has increased by 15.77%,and the specific energy consumption has decreased by 10.13%.The forming rate,durability,tensile strength and bulk density of the pellet products have increased by 6.07%,4.06%,3.81%and 4.45%,respectively.