| Micro-nano powder micro-delivery of milligram size refers to the micro-nano-sized micro-nano-sized powder particles transported by external force.It is the core technology and key link in the fields of laser cladding and high-efficiency API preparation.It is suitable for forming precision,performance and efficiency of parts.The ratio of raw material medicine and the effect of sustained release play a decisive role.In recent years,although researchers at home and abroad have developed a variety of powder micro-transport methods such as pneumatic method,electrostatic method,mechanical method and ultrasonic vibration method,they have not fundamentally solved the problem of adhesion due to powder arching and powder particles.The powder conveying result caused by agglomeration is not high and the conveying process is unstable.In order to solve this problem,this paper proposes to introduce the ultrasonic standing wave field at the exit of the micro nozzle,and use the acoustic radiation force of the standing wave field to break the powder particles,break up the powder particles,explore its transport mechanism and conduct experimental research.Firstly,theoretical analysis and numerical simulation are used to explore the feasibility of using acoustic radiation force to carry out micro-nano-scale powder stable transportation.Through the analysis of the physical properties of micro-nano-sized powder particles,the underlying causes that affect the micro-transport precision and the instability of the transport process are the arching characteristics caused by factors such as powder shape,scale difference,nozzle size and interparticle viscosity.A physics-coupled model of pressure acoustics and particle tracking was established in Comsol.The results show that the acoustic radiation force has a dissipative effect on the densely packed phase powder of the angular metal powder and the whisker-like non-metal powder,which can fundamentally eliminate the phenomenon of agglomeration caused by clogging.Secondly,the ultrasonic micro-transport experimental study of angular chromium powder and angular titanium alloy powder commonly used in laser cladding technology is carried out.The results show that during the micro-transport of angular powder particles,the irregular movement of the particles due to the irregular shape of the particles and the random and frequent collisions between the particles are beneficial to the scattering of the densely packed phase powder,and finally the acoustic radiation force and gravity.The micro-nozzles are delivered under the action of a combined force.The controllable range of single-pulse transport quality of 300 mesh angle chrome powder is 0.4?16mg and the controllable range of continuous transport rate is 6.0?65mg/s;the coefficient of variation of pulse transport quality is greatly reduced(less than 2%)with the increase of nozzle size.The coefficient of variation of continuous delivery rate is less than 6%.Finally,the ultrasonic micro-transport method and micro-transport characteristics of the viscous lactose powder commonly used in the preparation of high-efficiency APIs were studied.The introduction of pulse inertial force during the experiment solved the problem that the viscous powder could not move to the micro-nozzle outlet under the action of its own gravity.The minimum average delivery volumes of Respitose SV003 and Granulac 230 powders were 0.6 mg/s and 0.5 mg/s,respectively,and the average delivery range was 0.6-58.0 mg/s and 2-40 mg/s,respectively;when simultaneous application of acoustic radiation and pulses At the time of inertial force,continuous delivery of the above two powders was achieved,with minimum delivery rates of 0.4 mg/s and 0.5 mg/s,respectively,and minimum relative standard deviations(RSDs)of up to 0.022. |
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