Process Monitoring/Evaluation And Numerical Simulation During Casting Explosive Solidification

Energetic materials (simply named explosives) casting is a widely used molded technique. In this way explosive is heated and melted with solid phase rate up to 40%-70%, then injected in mould using some treatment technology, and last solidified to cast products with some shape and dimension. It is mainly applied in TNT pure explosive or TNT liquid carrier mixed explosive.Explosive casting process involves many complicated physical changes, and phase change is the most important and attended change, which is liquid explosive solidification as temperature descends.This process can determine the casting quality characteristic at a large extent and accordingly affect the performance. For the complexity of crystallization, the understanding of explosive casting process mainly lies on the phase change and thermodynamics analysis.So it is urgent for on-line nondestructive test method to realize crystallization process and quality study. This paper studies test evaluation method of inner parameters and their distribution of explosive casting process based on ultrasonic and CT technique, and investigate the analysis method of abnormity through numerical simulation.The temperature distribution in the casting process was studied with thermocouple inner-laid method. The temperature change curves show that there is an association between phase change and temperature inflexion. The results indicate that the temperature at freezing point is held longer at closer center position for pure TNT while the holding time is very short for TNT/RDX mixed explosive and only obvious holding at center part during cooling process. The riser added will obviously affect the dynamic change of the temperature and the final solidification regions.The change rules of sound attenuation, sound velocity, and waveform character were obtained by on-line multichannel ultrasonic technique during explosive solidification process. Changes of waveform and sound velocity are related to solid and liquid phase interfacial character and solidification rate. And change of sound attenuation is related to explosive configuration such as pores and cracks and the density. The result shows that axis solidification rate is bigger than radius solidification rate of cylindrical casting explosive and solidification rate reduces with time. Acoustic data show that formation and growth of cracks induce ultrasonic amplitude rapid reduce then keeping stable, and shrinkages induce ultrasonic amplitude rapid reduce in TNT solidification process.The results show that acoustic characteristic has internal relation with explosive solidification characteristic and can online diagnose product quality.This paper studies cylindrical solidification structure of casting explosive with x-ray CT and obtains 3-D structure of crystallization in the melted TNT/RDX casting process.The results show that the solidification is from the outer to the inner along central axis line. Fine crystals and compact explosive are got near the wall of mould.Bulk crystals are formed along with solidification which induce many pores and porosity of casting products.Shrinkage rate is about 7% under heat preservation and no repair while density can be largely enhanced when RDX grain is added and isaxis crystal is formed.The density difference between upper and down is less than 2%.The crystallization tropism of pure TNT is relative with inner thermal stress and one is radial and another is axial. The shrinkage is less near mould wall and CT value is higher and density is bigger. The micro shrinkage is dense at central section. There are some pores produced during casting in TNT mixed explosive (RHT-902 or RHT-906) and longitudinal and transverse crack are brought at explosive pole. And the cracks are approved to be produced after entire solidification.The influence of temperature and viscosity and heat transfer on phase change of explosive casting is studied.Temperature and stress distribution and shrinkage etc. are simulated. The results show that reducing viscosity can decrease shrinkage and stress, and reducing heat transfer coefficient can make temperature change slower which reduced the area of shrinkage and thermal stress.Increasing mould temperature has no improvement effect on inner quality and the inflexion point of temperature change will cause time delay phenomena.The basic issues are discussed during explosive casting including crack, pore, shrinking hole based on above test.Casting mechanism and effect factor are analyzed and the infection of different techniques and RDX content for micro structure and quality are also studied.This can establish some theory basis for studying the relationship of structure and performance of TNT/RDX casting explosive.Above all, this paper provides an integrated measuring method of explosive casting and solidification process and studies mechanism of molded rules and inherent relation between different physical parameters. These provide important technology basis for explosive molded technology improvement and have important guiding significance.