Design of combination sieve for hammer feed mill to improve crushing performance

The ring-sieve hammer feed mill is widely used, but the problems of low productivity, high energy consumption and circulation layer also exist. In order to improve the performance of ring-sieve hammer feed mill and crush materials with high efficiency and quality, a kind of combination sieve was designed for the CPS-280 hammer feed mill in this paper. First, according to the change of the attack angle of the material against the sieve, the influence of combination sieve on the crushing performance of the mill was analyzed. The air flow field of the mill with the circular flat sieve and the combination sieve (A3 sieve) were numerical simulated by computational fluid dynamics software (Fluent). Design parameters of A3 sieve are as follows: Equal division number is 3, Center angle of airfoil arc is 60º，Front arc radius of airfoil arc is 52 mm, Rear arc radius of airfoil arc is 196 mm, Equilateral angle is 120º，Center angle of equilateral angle is 16º，Center angle of arc is 37º. The velocity and pressure distribution of air flow field in crushing chamber were compared between the 2 sieves. Through the simulation analysis, it was found that the pressure of the air flow field gradually increased from the center of the rotor to the end of the hammer when the mill adopted the circular flat sieve. The maximum pressure reached 2 210 Pa at the end of the hammer. At the same time, the air flow formed a high-speed circulation layer in the interval between the hammer and the sieve. The maximum velocity was 60.9 m/s. When the hammer mill was operated with the combination sieve, the air flow field of the crushing chamber produced a violent vortex motion, which made the air flow disorderly and chaotic. In addition, this violent vortex movement constantly consumed energy, making the flow field of the crushing chamber pressure and velocity lower, and the maximum pressure was 542 Pa which was -1/4 of the circular flat sieve. The above results verified that the air flow field characteristics of the crushing chamber could be effectively improved by using the combination sieve. In order to verify the accuracy of the numerical simulation of the hammer feed mill airflow field, the velocity of the air flow field of the hammer feed mill with the circular flat sieve and the combination sieve (A3 sieve) was tested. Compared with the measurement results, the simulation results showed that the error was within 8.62%. In the same working condition, the hammer feed mill equipped with the circular flat sieve or combination sieve was used for crushing performance test, and the actual crushing effect of different sieves on the material particle of the corn was analyzed. Compared with the circular flat sieve, the productivity was increased by average 22.15% and electrical output per kW•h was increased by average 25.88%, respectively, and the temperature rise of the corn was decreased by 2.5 ℃ on average. This showed the use of a combination sieve could increase productivity and improve the quality of materials. The material crushing performance was better than the circular flat sieve, especially when the sieve equal division number was 4, the front arc radius of the airfoil arc was 26 mm, the rear arc radius of the airfoil arc was 200 mm, and the equilateral angle was 120°, respectively. The productivity and electrical output per kW•h were increased by 28.98% and 35.84%, respectively, and the temperature rise of the corn was decreased 2 ℃. The particle size of the corn was more uniform and the over crushing phenomenon was improved. The distribution variance was decreased by 40.62%. The theoretical analysis, numerical simulation and experimental results showed that the air flow field characteristics of the hammer feed mill using the combination sieve were better than the circular flat sieve, which was more conducive to improve the performance of the mill. This study provides theoretical basis and implementation method for the design of new sieves.