Study On Influencing Factors Of Heat Transfer Process Between Intumescent Fire Retardant Coating And Steel Substrate

Steel structures are widely used in modern buildings,but they are prone to collapse when attacked by fire.Intumescent fire retardant coatings are widely used in fire protection of steel structures due to their good adhesion,excellent corrosion resistance and excellent fire performance.A series of physical and chemical reactions will occur in the coating in a high temperature fire environment,and the heat transfer process of the coating will change accordingly,and it will interact with its combustion process.Therefore,it is necessary to study the influencing factors of the heat transfer process between the intumescent fire retardant coating and the steel substrate.In this paper,two epoxy intumescent fire retardant coatings,IFR/TS and ADP/MPP were prepared by adding intumescent flame retardant（IFR）,tea saponin（TS）,aluminum diethyl hypophosphite（ADP）and melamine phenyl phosphonate（MPP）to epoxy resin（EP）,the combustion characteristics,heat transfer process and expansion behavior were analyzed by cone calorimeter,multi-channel data acquisition instrument,synchronous thermal analyzer and other instruments.The influence of the change of the substrate on the heat transfer process of the coating-steel plate was further analyzed.In addition,the thermal conductivity,specific heat capacity and other thermal properties of the IFR/TS epoxy intumescent fire retardant coating and the effective thermal conductivity of the intumescent char layer were further analyzed.The main research results are as follows:（1）The factors affecting the heat transfer process of IFR/TS epoxy intumescent fire retardant coatings prepared by IFR and TS as flame retardants were studied.The research results show that the combustion and heat transfer process of the coating affect each other,and the content of TS,incident heat flux and other factors affect the heat transfer process of the coating.The process of expansion into char and the structure of the char layer are related to the temperature change inside the coating.Through the analysis and comparison,it can be concluded that when the TS content is 4 wt%,the flame retardant effect is the best,the heating rate inside the coating is the slowest,and the expansion rate of 11.8 is achieved under the mass loss of 36.5 wt%,and the expansion effect is the best.（2）The influencing factors of the heat transfer process of ADP/MPP epoxy intumescent fire retardant coatings prepared by compounding ADP and synthetic MPP were studied.The research results show that the ratio of ADP and MPP,the expansion characteristics,and the structure of the char layer have different effects on the heat transfer inside the coating.The ability to expand into char and the structure of char layer are better than the intumescent fire retardant coatings prepared by using ADP and MPP alone.When the content ratio of ADP to MPP is 3:1,the flame retardant effect and thermal insulation ability are the best,and the expansion ratio reaches 10 when the mass loss is 47.1 wt%.（3）By studying the influence of changes in the material and thickness of the steel plate on the heat transfer between the coating and the steel plate,the results show that the difference in the material of the steel plate will basically not affect the temperature changes inside and outside the coating,and the content of carbon and alloying elements in the steel has a slight effect on the temperature field inside the steel plate.Thermal conditions at the steel-coating interface have a significant effect on the thermal response and degree of expansion of the fire retardant coating.（4）The correlation between the thermophysical parameters and the heat transfer process of the IFR/TS epoxy intumescent fire retardant coating was studied.The research results show that there is a correlation between the thermophysical parameters and the temperature of the coating.The addition of flame retardants changes the thermophysical parameters of EP,and their values vary with the content of TS.The thermal conductivity and specific heat capacity of oxy-resin composites decreased with the increase of TS content,while the thermal diffusivity was opposite.The calculation results of the effective thermal conductivity of the IFR/TS expanded char layer show that the difference in the internal structure of the expanded char layer causes the internal temperature of the char layer to be different,which leads to the change of the effective thermal conductivity.The effective thermal conductivity of the expanded char layer is between 0.047 and 0.104 W/（m·K）,and the effective thermal conductivity of the EP/IFR-TS-3 char layer is the smallest.The effective thermal conductivity has an effect.