Measuring And Simulating Analysis On Material-Sieving Properties For A New Hammer Mill

Feed hammer mill is widely used in grinding feed for poultry and animals due to its advantages of good suitability for materials, reliability, simplicity, high productivity, ease of maintenance, as well as low manufacturing cost. However, the conventional hammer mill exists the material circular layer which results in the problems of low seveing efficiency, high energy consumption, material over milled and material heated. In order to solve this problem, a new type of hammer mill has been developed by our research group in recent years. This dissertation aims at studying its sieving efficiency and factors affecting on it by means of simulation and measurement. The results will provide a basis on improving the productive efficiency and optimized designing for the new type of hammer mill.(1) The 3-D air flows in the new type of hammer mill at different rotating speeds were simulated and analyzed using CFD (computational fluid dynamics) software FLUENT, and the fundamental characteristics about the air field were gained. Comparing simulation results with experimental ones showed that it is feasible to simulate the actual air flow in the feed mill in FLUENT. Moreover, it has been proved that the subpressure in the chamber of feed mill has an influence on pressure in the central material-returning pipe, the flow pattern in the sieving setup is not only related to the curvature of the curving part of the sieving setup but also the structure of transition part between the chamber and the sieving setup.(2) The air-material two phase flow in the sieving setup was simulated by the Mixture model in software FLUENT6.3, and the tests on distribution of materials in the sieving set-up was performed as well. The material distribution pattern in the sieving set-up under different conditions was obtained, which has a good agreement between simulation and test, showing that the simulation on air-material two phase flow is reliable. The results prove that the subpressure at outlet of the material-returing pipe has a great effect on the sieving of the material, too high or too low subpressure will make the materials accumulate, lowered the material sieving efficency. The sedimentation of bigger-size particles was observed apparently in the curved part of pipe, they have difficulties in passing the inlet area of material returning pipe and unfavorable to material sieving. The material speed at inlet of sieving set-up is important for the convey of materials, and an appropriate speed range is existed for the sieving of materials. The curvature of curved part of sieving set-up has a great influence on material sieving efficency, decrease of the curvature will reduce the resistance of material flow by pipe wall thus improve the sieving efficiency.(3) The multi-factor orthogonal experiments on performance of the new model hammer mill were carrired out. The result shows that the subpressure in the outlet of central material-returning pipe has the greatest effect on material sieving efficency compared to other factors, so it is necessary to study the properties of the subpressure in the central material-returning pipe for improving the sieving efficiency of this new hammer mill.