Research On Key Technology And Device For The Harvesting Of Mud Snails(Bullacta Exarata) In Mudflats

Mud snail(Bullacta exarate)is an important economic shellfish in the coastal areas of China,and harvesting is a key link to the cultivation of mud snails in the mudflat.At present,due to the lack of available machines,manual picking is still adopted,which has some problems such as low work efficiency,high operation intensity,and easy damage to mud snails.Based on the technical requirements of harvesting and the research on biomechanical characteristic parameters of mud snails,the brush-screen collaborative mud snail harvesting device was designed,conducted theoretical analysis on the key technology of flexible brush collection.Using EDEM discrete element simulation software,response surface testing,and bench tests to determine the reasonable structure and working parameters of the harvesting device.The results of research on biomechanical characteristics of mud snails showed that the morphology and size of mud snails obeyed normal distribution,and the shell length,shell width,shell height,and body length were 14～22mm,13～17mm,9～13mm,and 24～36mm respectively.The average weight of mud snail was 1.93 g.The stacking angles of mud snails on stainless steel plates,PVC plates,and plexiglass plates were 3.67 °,4.85 °,and 4.07 ° respectively.The average values of the static sliding friction coefficient of mud snails on stainless steel plate,PVC plate,and plexiglass plate were 0.30,0.70 and 0.52 respectively.The breaking force test of mud snail measured that the breaking force of mud snail was 1.38～3.85 N,and the significant effect on the breaking force of mud snail was that the direction of loading > the size of the mud snails > the loading speed.The design of the mud snail harvesting device was completed.According to the technical requirements of mud snail harvesting,this study adopts the brush-screen synergistic mechanical harvesting technology.To reduce the damage and leakage of mud snails in the process of harvesting,the leakage area,the movement state,and the force of mud snails were analyzed,the collecting mechanism and screen-shovel mechanism of the harvesting device were analyzed and calculated,and the width of the rolling brush operation was determined to be 1000 mm.The bristle’s row number is 10 rows and arranged in a straight line on the roller;The spacing between the screen bars of the sifting-shovel mechanism is 10 mm,and the Angle of penetration is 25°.The power of the whole machine is calculated and the diesel engine was selected to drive the whole machine.A simulation study was conducted on the harvesting of mud snails.A discrete element interaction model of brush rolling,screen-shovel,mud snail and mudflat sediment was established.The effects of different rolling brush speeds,brush bristle lengths,and forward speeds on mud snail harvesting rate and breaking rate were investigated by single factor and response surface tests.The test results showed that the order of significant effects on mud snail harvesting rate was rolling brush speed>forward speed>brush bristle length.The order of significant impact on the breaking rate of mud snail harvesting is roller brush speed>brush bristle length>forward speed.When the roller brush speed,brush bristle length,and forward speed are 40r/min,175 mm,and 0.8m/s respectively,the highest mud snail harvesting rate was 94%;the lowest breaking rate was 2.13%.Bench tests on the effects of different brush speeds and forward speeds on the harvesting rate and breaking rate of snails were completed.The results show that the harvesting rate increases with the increase in brush speed and the breaking rate also showed an increasing trend.The mud snail harvesting rate increases as the forward speed increases and breaking takes the lead in decreasing and then increasing.When the rolling speed and rolling speed are 40r/min and 0.8m/s,respectively,the harvesting rate and breaking rate are 90% and 2.22%,respectively.The error between the simulation prediction results and the bench test results under the optimal parameter combination is less than 5%.This research developed a brush-screen collaborative harvesting device for mud snails in the mudflat.Through simulation and experimental research,the influence of the structural parameters and working parameters of the brush screen collaborative harvesting device on the harvesting performance was analyzed,and the reasonable parameters of the harvesting device were determined,which provided a reference for the research on the mechanized harvesting technology of mudflat mud snail.