| Castor is an important industrial oil crop that plays an important role in aerospace,pharmaceuticals,additives,lubricants,and cosmetics.The straight cylinder press is a classic single-shaft mechanical oil extraction method,producing castor oil with higher purity and preserving its own properties.The research on the mechanism of seed pressing in this field is insufficient,and the efficiency of oil extraction needs to be improved.Therefore,it is important to study oil yield and pressing mechanism under different working conditions.In this paper,hydrostatic tests were conducted on single castor seed and seed kernel by a texture analyzer apparatus,and the mechanical properties and structure-oil yield properties under each condition were analyzed in combination with in-situ observation.A universal testing machine combined with a straight uniaxial pressing device was used to study the oil yield of castor seed bulk,and the visualization of the device was used for process analysis.In addition,the oil output conditions were optimized by response surface method and the mathematical model of oil output was established.A coupled multi-physical field model of oil extraction was developed in COMSOL software to study the microscopic flow rates under different working conditions.This paper provides an in-depth analysis of the pressing state and mechanism in microscopic,macroscopic and visualization aspects,which can guide the research of extrusion type oil press.The main research results are shown as follows.(1)The static compression test on the outer seed coat showed the shell breaking force tended to increase with compression displacement,then slowly decreased and finally increased.This trend was related to the gap between the outer seed coat and the endosperm.In addition,the effect of compression speed on the shell breaking force was negligible.The temperature between 60℃-120℃ could effectively reduce the shell breaking force of the seeds.(2)The seed kernel static pressing test results showed the compression displacement increased and the peak compression force on the seed kernel increased exponentially with the oil yield.In addition,it was observed that the damage(cracks)in the seed kernels usually arose at the edges and extended toward the center.However,when the compression force is too high,the kernel will be compressed into two flaps due to the special structure of the "cavity" of the kernel.The higher the speed is,the oil yield will gradually decrease and stabilize.The effect of dwell time on the oil output is similar to the velocity part,and the effect decreases significantly when it exceeds 360 s.A decrease in peak force Fc will also decrease the oil output.The drying temperature affected the oil yield by changing the kernel moisture content.The higher the temperature,the lower the oil yield,but the peak compression force remained stable.(3)The stress-strain curve of castor bulk uniaxial pressing was analyzed,and the pressing process was expressed as four stages: elastic deformation,elasto-plastic deformation,oil dispersal stage,and compression consolidation stage.Stress,creep time,and temperature showed synergistic effects on oil yield,while speed showed antagonistic effects.The mathematical model of oil yield was established by Box-Behnken Design.The influence degree of each pressing condition on the oil yield was in the following order: stress,speed,temperature and creep time.The model predicted the optimal oil yield conditions and oil yield: 30 MPa,0.015 MPa/s,1420 s,90℃,and 42.91%.The model predicted the oil yield with an error of 5.31% from the test.(4)The results of the multi-physics field fluid-solid coupling model show that the Darcy velocity is mainly influenced by porosity and stress.The expression of oil yield was established by calculus idea.And the mathematical relationship of oil yield with time during the pressing process is established.The positive effect of material volume on oil output can be studied by changing the boundary condition parameters.And the trend of seepage velocity change under velocity and creep time is simulated by the model. |
