Research On The Pyrolysis Characteristics And Mechanism Of Typical Foams Of Lost Foam Casting

The Lost Foam Casting has the advantage of producing casting with complex structure and parting difficultly.However,the form pattern will absorb heat from the liquid metal with high temperature and pyrolyze during the pouring.A large number of products are formed,which tends to form a multi-phase turbulent zone to hinder the filling and change the front metal component,which brings in the casting defects.In order to understand the influence of foam pyrolysis on the casting filling process,it is necessary to grasp the pyrolysis characteristics and reaction mechanism of the foam pattern.In this paper,the pyrolysis thermodynamics and kinetics of typical foam EPS and St-MMA copolymer were studied using a series of experiments and theoretical calculations,and the reaction mechanism of foam pyrolysis was investigated.Firstly,the pyrolysis thermodynamic characteristics of the foam patterns were studied.The evolution of foam morphology under thermal action was observed,it was found that both of the two foams contracted and collapsed,and their melting temperatures were different.The multi-state endothermic mechanism of foam was studied by using differential scanning calorimetry(DSC).It was found that the EPS pyrolysis gasification temperature was higher than St-MMA,and the thermal absorption heat of EPS and St-MMA foam was 706.71 J/g and 605.28 J/g,respectively.Secondly,the pyrolysis kinetic characteristics of the foam patterns were studied.It was found that the decomposition behaviores of the two foam materials in non-oxidation and oxidation atmospheres were different.The non-oxidation environment would inhibit the initial decomposition of EPS foam and promote the initial decomposition of St-MMA foam.The kinetics of pyrolysis and thermo-oxidative degradation for two foam patterns were analyzed by using iso-conversional method and model-fitting method,and the kinetic models of the two foams in different environmental atmospheres were constructed.The kinetic equations were also reconstructed by using Runge-Kutta numerical integration method,and the reconstruction equations were be in good agreement with the experimental results.Finally,the related research on the pyrolysis volatile products and pyrolysis mechanism of foam materials was carried out.It was found that the volatile products of EPS pyrolysis were mainly styrene,toluene,dimer,α-methylstyrene,1,2-diphenylethylene,etc.The products of St-MMA were mainly methyl methacrylate,styrene,α-methyl styrene,benzene,methanol,and the like.In addition,according to the composition of volatile products,it was found that the pyrolysis reactions of foam might include chain-end fracture,random fracture within the chain,hydrogen transfer,β-cleavage,side-chain cleavage and so on.And the pyrolysis mechanisms of different foam materials were determined.