Study On The Technology And Device For Separating And Extracting Molten-metal Drops At The Fire Scene

Collecting the evidence at the scene is essential to investigate the cause of fire.And it will directly affect the accuracy of fire identification and evidence analysis.In the fire scene,which is based on electrical appliances,the molten-metal drops are always extracted because of its relatively stable properties.Nowadays the evidence collected from fire scene is carried out by hand picking,which is power consuming and low accuracy.In order to solve the practical problem about the molten-metal drops at the fire scene are difficult to be separated,this study introduce eddy-current separation technology into the field of fire evidence collection.And we attempt to develop a small device used at the fire scene,which separates the molten-metal drops with the diameter from 0.5 to 2 mm.This study is conductive to the development of the technology of fine evidence extraction in our country.And it is also helpful to improve the efficiency and accuracy of fire identification.The development of the eddy-current separator provides portable and efficient equipment for the field of fire protection.The method of determine optimal parameters and optimization design of the new structure,which were proposed in this study provide theoretical reference for the development of the eddy-current separator.In many kinds of the eddy-current separator,in this study we used belt eddy-current separator whose structure is simple.To extract the molten-metal drops with the diameter from 0.5 mm to 2 mm from the mixture of metal and non-metallic debris at the fire scene,in this study we firstly simulated the magnetic field of magnetic roll.The magnetic strength was used for the calculation of the eddy-current force of the metal particles.Based the trajectories of particles,we analyzed by the force.Secondly,the horizontal dropping distance and the separation distance can be obtained.Then the optimal parameters which can guide the design of the eddy-current device can be determined.After that we analyzed the separation efficiency of separation experiments under the optimum parameters.Finally we proposed a new type of eddy-current separator through optimizing and improving the device.This new eddy-current separation device was more suitable for extracting molten-metal drops at the fire scene,which was called the vertical eddy-current separator.The main conclusions of this study were as follows:(1)When the magnetic roll was rotating,the magnetic field on the magnetic roll surface was approximately uniform,and the magnetic flux density was between 2×10-3 and 0.49 T.(2)The optimal parameters of designed separator for separating the molten-metal drops with the diameter from 0.5 mm to 2 mm at the fire scene was the speed of conveyor is 0.6 m/s,the speed of magnetic roll is 350 rpm.At the optimal parameters,all the separation efficiency for the molten-metal drops with the diameter fewer than 2 mm was above 95%.In order to completely extract the molten-metal drops from the mixture at the fire scene,we screened the mixture of materials firstly and then separate repeatedly.(3)At the respect of the optimization and improvement,to improve the performance of the belt eddy-current separator,we adjusted the horizontal position of the metal material receiver to 100-115 mm,and sited a baffle at the boundary between metal and non-metal receiver.The height of the baffle was from 10 to 30 mm,and the angle of the baffle was from 53 to 56 degrees.After optimizing the structure of belt eddy-current separation device,the vertical eddy-current separator was expected to not only solve the problem of material sticking and conveyor wearing,but also to improve the separation efficiency at certain extent.