Experimental Research On Compound Modification Of Sodium Silicate Sand For Foundry

Sodium silicate was the most promising non-polluted,environmental-friendly inorganic binder among many binders.It had the advantages of high temperature resistance and wide sources of raw materials.The sodium silicate sand prepared by sodium silicate could be applied to the production of various castings,and the quality and accuracy performance of the castings produced were also very superior.However,the bonded effect of sodium silicate was reduced after being placed for a long time,and the strength of sodium silicate sand could not be guaranteed,and its collapsibility was poor,which limited its application.In the paper,the problems were solved by modifying the sodium silicate.In this paper,organic ester was used as hardener to harden sodium silicate sand.The mass ratio of ceramic sand,sodium silicate and organic ester hardener was1000:30:3.Firstly,the sodium silicate was modified by disodium hydrogen phosphate,short carboxyl purified multi-walled carbon nanotubes combined with physical ultrasonic method,and the influence of modified sodium silicate on the properties of sodium silicate sand was studied.Secondly,the effect of the single Silica fume and a variety of powder hardeners Silica fume,Carboxymethylcellulose sodium and Bentonite as modifiers on the properties of sodium silicate was studied.Then,the effect of three organic modifiers polyethylene glycol 200,N,N dimethylacetamide and ?-Aminopropyl triethoxysilane on the properties of sodium silicate sand were studied.Finally,the SEM?EDS?XRD?DSC and FTIR were used to analyze the influence mechanism of modifier on the properties of sodium silicate sand.The experimental results showed that when the addition amount of disodium hydrogen phosphate and short carboxyl purified multi-walled carbon nanotubes were0.2% and 0.04% of the addition amount of sodium silicate,respectively,and the ultrasonic time was set to 10 min,the 1h strength of the sand sample was 0.142 MPa,the 4h strength was 0.381 MPa,the 24 h strength was 0.781 MPa,the 800°C residual strength was 2.786 MPa.Compared with the unmodified sand sample,the 1h strength,4h strength and 24 h strength of the modified sand sample increased by 34%,33% and30% respectively,and the 800°C residual strength decreased by 14%.The results showed that the modifiers combined with physical ultrasonic method had a certain improvement effect on the comprehensive performance of the sodium silicate sand.Under the condition of high temperature heating at 850°C,the gas evolution of the modified sodium silicate sand reached the maximum value of 6ml/g during 10-16 s and the gas evolution rate reached the maximum value of 1.9ml/g/s at 4s,which could meet the requirements of casting production.The surface of the bonded bridge of the modified 24 h strength sand sample was smoother,and the structure composed of sand particle-binder-sand particle was also denser.On the basis of modification of sodium silicate by disodium hydrogen phosphate,short carboxyl purified multi-walled carbon nanotubes and ultrasonic time.When the addition amount of the single Silica fume was 0.55 % of ceramic sand,the test has the best modification effect on the properties of sodium silicate sand.At the same time,on the basis of the single experiment,when the addition amount of Silica fume,Carboxymethylcellulose sodium and Bentonite were 0.55%,0.02%,0.3% of the ceramic sand,respectively,the room temperature strength and 800°C residual strength of the modified sand sample were better than those of the sand sample modified by the single test and the unmodified sand sample.The results showed that the modifier was filled in the small gaps between the sand grains and coated on the outer surface of the sand grains to keep the overall structure of the sand sample compact,thereby strengthening the 24 h strength of the sample.The continuity of bonded bridge of the sample was destroyed due to the presence of modifier under the condition of high temperature heating,thus improving the residual strength.On the basis of the above modified experiment,the 1% polyethylene glycol 200,0.6% N,N dimethylacetamide,0.2% ?-Aminopropyl triethoxysilane were further added to the sodium silicate.The 1h strength of the sodium silicate bond sand could reach0.302 MPa,the 4h strength could reach 0.689 MPa,the 24 h strength could reach1.278 MPa and the 800°C residual strength could reach 0.818 MPa.The organic modifiers could be adsorbed on the outer surface of gel colloidal particles by hydrogen bond to form a protective layer,thereby achieving the purpose of strengthening the properties of sodium silicate.At the same time,the organic modifiers volatilized gas in the sodium silicate system during the heating process,which destroyed the continuity of the bonded bridge,thereby modifying the collapsibility of the sand sample.The optimization scheme: the addition amount of disodium hydrogen phosphate,short carboxyl purified multi-walled carbon nanotubes were 0.2% and 0.04% of sodium silicate,and the ultrasonic time was set to 10 min.The addition amount of Silica fume,Carboxymethylcellulose sodium and Bentonite were 0.55%,0.02%,0.3% of the ceramic sand.The addition amount of polyethylene glycol 200,N,N dimethylacetamide and ?-Aminopropyl triethoxysilane were 1%,0.6%,0.2% of the sodium silicate.