Structural Analysis And Surface Strengthening On Flat-Die Of Pellet Mill

As the problem of energy crisis and environmental deterioration becoming serious, a cleaner and more efficient energy, biomass energy, has been paid more and more attention all over the world. Flat-die pellet mill is a common mechanical equipment for biomass compression. Development of biomass compression technology and equipment in China is far behind that in the developed countries. Low productivity, high energy-consumption and quick wearing for key components hinder the development of flat-die pellet mill. Operating principle of flat-die pellet mill and biomass compression feature are studied in ways of modeling and ANSYS simulation. Laser alloying other materials on the quick-wear parts of the flat-die surface is experimented to improve the mechanical properties.Mechanical models of compression region and material forming region are established to analyze stress distribution of biomass and flat-die. Grab angle and disposition effect are discussed. Biomass compression feature in forming region is further characterized. Influence of hybrid particles and the shear rheological phenomenon in the die holes are described. Compression region and forming region summed up to the first compression stage and the rebound and compression stage. Factors that influence compression ratio are discussed. A flat-die is designed according to the analysis.Plastic flow of biomass in compression region and forming region is simulated by ANSYS. Biomass stress distribution and strain distribution are investigated, the rebound and compression stage is further explained. Stress distribution of the flat-die surface and holes are discussed. The connect surface of the die holes and the parts around the tapered holes are regions with partial centralized stress, where are easy wearing and crushed. Friction coefficient and taper angle have a large effect on pellet quality and stress distribution. At last, the stress formulae of biomass in the straight hole are verified by ANSYS, and improvement project is proposed to strengthen the quick-wear surface.To improve micro hardness and wear resistance of the flat-die, the alloyed layer of NiCr-Al2O3 mixed in certain ratio was fabricated on 45 steel by laser surface alloying. Change the laser scanning speed and powder mixture ratio to observe the macro profile of the specimens, and the SEM analysis, XRD analysis, micro hardness and wear resistance tests are investigated. The results indicate that, uniform surface with high hardness and great wear resistance can be fabricated by laser alloying with NiCr+30% Al2O3 particles and 300mm/min-400mm/min laser scanning speed. The micro hardness of alloyed layer advances to 2.4 times, the wear resistance advances 5 times, which reaches the flat-die design property.Operating principle of flat-die pellet mill and biomass compression feature are further characterized. Granulating forming rule is researched from theory and simulation, laser alloying on the surface is experimented to strengthen the weak region, which are of great value for flat-die pellet mill design and development.