The Experimental Study On Rheology Of Fresh Herbage Materials In The Process Of The Compression

The experimental study took the typical fresh herbage, forage crop and crop stalk as the study object, the grass piece which was compressed by one feeding as the research unit, the 'no-bottom die' compression as the experimental basis. It studied the rheologic characteristic of fresh herbage during the whole high density compression process under the actual operating conditions of a baler by using LABVIEW data collection system and MATLAB data analysis system, production technology of fresh high density grass products and the nutrition retention mechanism of the products in the procedure of storage and transportation. On the basis of this kind of researches, the following new conclusions have been drawn from the study. 1. When the fresh herbage was compressed every time, the force on the piston and grass piece was in four stages of rising up fast, descending down sharply, descending down slowly and descending down fast. The value of descending down sharply was related to the form of fresh herbage and the position of grass piece in compression chamber and the stage of descending down slowly was a typical stress relaxation period. The maximum compression pressure was only related to the form of fresh herbage and the structure of compression chamber and had no direct relation to the power supplied by the baler. During the whole compression process, the characteristic of maximum compression pressure and minimum distortion restitution force of grass piece in the different position of compression chamber had distinct difference. Though the above two forces occurred in every compression process, however, they had the essential difference. 2. The experimental study has brought a viewpoint that there were one density point and three density zones of the density change during the compression process. Taking three different forms of fresh herbage as the research object, the distorted restitution was tested and analyzed on one density point and three density zones of the density change during the compression process and a corresponding rheologic equations was set up to analyze comprehensively on the forming cause. The quantification analysis on the inutility power consumption caused by distorted restitution was made and the main cause that affected power consumption has been confirmed. The viewpoint that the compression chamber length should be determined according to the position of the stable zone of density has been put forward. 3. That there were three stress relaxations when the fresh herbage was compressed has been found out under the actual working condition of the baler. A viewpoint of taking the stress relaxation rate as the basis of choosing the compression frequency of the baler has been put forward. After the comprehensive analysis on the various factors having been made, the choice scope of reasonable compression frequency value and compression chamber length have been put forward, which has supplied reference to determine the productivity and structure parameters of a baler. 4. The test and study on three-dimensional stress of high density baler have been made and the rule of stress change in the direction of Z and Y in different position during the whole compression process has been found out. The viewpoint that the rheologic change would occur in the direction of Z and Y during the whole compression process has been brought forward and the conclusion that stable zone of high density was the maximum distorted restitution stress zone of the grass piece in the direction of Z and Y and the zone of producing main fraction has been gained. 5. Through the test and analysis, the conclusion that deducting the outlet height of the baler would exert great influence on the whole compression process has been gained and the affecting rule on the compression pressure, power consumption and stress relaxation has been gained too. So, it is not economical to raise the compression density simply by reducing the outlet size. 6. Through the test and analysis on the bale durability, the changing rule of distorted restituti...