Explosion Mitigation Of Aluminum Alloy Polishing Waste Dust By Ultrafine Soild Inerting Agent

The demand for aluminum alloy products is recently increasing rapidly in our country.Explosion accidents occasionally occur in the polishing process of aluminum alloy workpiece.In order to take appropriate measures to reduce the hidden risk of explosion in the relevant workplace,investigation of explosion sensitivity deactivation and flame propagation mitigation for aluminum alloy polishing waste dust/air mixtures were carried out in the international standard 1.2L Hartmann tube and a square device by addition of ultrafine solid inertants.In the meanwhile,comparative study was performed through high-purity aluminum powders with similar mean diameter.In addition,a typical production scene has carried on the concrete application,through to the polishing dust removal pipe with the addition of the ultrafine inerting agent.It provides detailed and reliable data support and practical basis for taking reasonable measures to prevent and control combustible dust/air mixture explosion in industrial production process.The main conclusions are listed as followed:（1）The explosive characteristics and flame propagation of high-purity aluminum powder and aluminum alloy polishing waste dust were studied in Hartmann tube and square device respectively.The lower limit of explosion of high-purity aluminum powder is 80g/m³,within the range of 40-45m J.The lower explosive limit of polishing dust of aluminum alloy is 150g/m³,and the minimum ignition energy is between 500-550m J.The explosion limit of aluminum alloy shot blasting dust is 150g/m³,and the minimum ignition energy is between 700-750m J.In addition,the explosive flame of high-purity aluminum powder,aluminum alloy polishing waste dust propagated upward first,then slowed down,and finally reached the top of the pipe installation.Compared with high-purity aluminum powder,the explosive flame of aluminum polishing dust propagates to the top of the device for a longer time,while the propagation process and explosive effect of aluminum shot blasting dust are worse than those of the other two kinds of dust.（2）The influence of the amount of inerting agent on the flame propagation process of high-purity aluminum powder and aluminum alloy polishing waste dust/air mixture was studied experimentally.The results show that the amount of inerting agent has a significant effect on the flame propagation process of high-purity aluminum powder and aluminum alloy polishing waste dust/air mixture,and the time required for the flame to spread to 380mm above the ignition electrode and reach the peak propagation velocity is prolonged with the increase of the mass fraction of inerting agent.The corresponding peak flame propagation velocity decreases with the increase of the mass fraction of inerting agent.（3）The influence of the type of inerting agent on the flame propagation process of high-purity aluminum powder and aluminum alloy polishing waste dust/air mixture was studied.The inerting effect of two kinds of ultrafine powder inerting agents on high-purity aluminum powder and aluminum alloy polishing waste dust explosion is as follows:ultrafine CaCO₃>ultrafine Al（OH）₃,mainly showing as:the minimum ignition energy and the lower limit of explosion of high-purity aluminum powder and aluminum alloy polishing waste dust increase with the increase of the mass fraction of ultrafine inert agent in the combustible powder.When ultrafine CaCO₃ is added,the increase range is obviously higher than that of ultrafine Al（OH）₃.When ultrafine CaCO₃ is applied as inerting agent,the passivation effect of explosion sensitivity parameters represented by minimum ignition energy and lower limit of explosion is more obvious,that is,the inerting effect of ultrafine CaCO₃ on high-purity aluminum powder and aluminum alloy polishing waste dust is better.（4）In typical production applications,it is found that the initial ignition position of the dust cloud of aluminum alloy polishing waste is random.When no superfine inerting agent is applied,the number of independent luminous point flame is large in the initial stage of explosion,and the flame front is continuous smooth in the growth stage.When superfine inerting agent is applied,the number of independent luminescent point flame is significantly reduced,and the flame is more discrete in the growth stage,and the flame propagation process is significantly delayed.After mixing ultrafine CaCO₃ powder,on the one hand,the local concentration of combustible dust is reduced;on the other hand,inert ultrafine powder is easy to suspend in the air due to its small particle size,and a large number of ultrafine CaCO₃ powder can be adsorbed on the dust particles of aluminum alloy polishing waste,preventing combustible dust from contacting with the air and reducing its contact area with oxygen.