Research And Design Of Large Air Classifier For High Impurity Raw Grain

In recent years, with the increase of grains crops’ total production year by year in ourcountry, the mechanized level of harvesting grains improved gradually; the raw grains alsocontain more and more impurities. As the processing scale of food processing plant isincreasing, grains’ cleaning has become the bottleneck of grain processing plant development.The removal of impurities can be divided into three processes for the principle ofunprocessed grains separation: preliminary cleaning; cleaning; choiceness. And preliminarycleaning is the premise of subsequent processing. The existing equipments of preliminarycleaning have small processing capacity; the impurities cleaning effect is also unsatisfactory.They can’t meet the actual needs of grain storages and grains processing plants. So theresearch and development of series air classifiers with big processing capacity andsatisfactory impurity cleaning effect is very significant.This paper makes an investigation on the technology of raw grain cleaning and currentsituation of the development of preliminary cleaning equipments at home and abroad,analyzes the basic principle of sifting and the application of sifting technology, pointes outthe influential factors of sifting, introduces the existing sifting equipments and their commonstructures. On the basis of investigation and research, the large capacity air separationequipment of the high impurity of gross grain will be developed. After the design of airclassifier, the prototype trial-production and experimental test will be made.This development of air separation equipment (raw grain air classifier) mainly includessix parts: sifting room, device of separating and removing dust, air source, feeding device,frame, steering walk mechanism. Sifting room is the key to air classifier for performance andstructure. The design of air duct and the trend of air will directly have an effect on processingcapacity and the impurity cleaning. The device of separating and removing dust is also a veryimportant structure. Vertical wind which come through the material flow can make thematerial and impurity separated, the vertical section can implied material and a totalseparation of impurities, impurity air flow into the sedimentation chambers to subside theimpurity and dust. So it need reasonable device of removing dust，four cyclones. The feedused gravity gate control flow, the feed roll material. In addition, there is steering walkmechanism on the air classifier, which can make the air classifier swerved and walked conveniently.When the design of air classifier be finished，prototype trial-production will come outfinally. The problem of design and processing technology will be found and solved throughthe prototype trial-production. The design will become perfect with some necessaryimprovements finished, and then the air classifier will enter into massive production.When the completion of prototype trial-production accomplished, we will make anexperimental test, the test contains the wind speed of air duct and impurities removal port,and the air pressure of inlet and outlet. The tests indicate that, in the air duct, wind speed isgreater than the suspension velocity of light suspended impurities and slower than thesuspension velocity of grain material, the grain material will fall with gravity into the outlet,the impurities are been flown away by the air; in the near area of impurity outlet, wind speedis greater than the suspension velocity of dust speed and slower than the suspension velocityof light impurities, impurities can be smoothly into the outlet and discharged out from lightimpurities screw conveyor, meanwhile the dust with the flowing air flowed into the cyclonefor settlement.The research and design of air classifier can promote the development of large-scaleequipment of grain trade. It also plays a oriental role in the discussion of its function andprinciple，and on improvement of air classifier structure.