| Casting sodium silicate has the advantages of clean and environmental protection,which is in line with the development concept of green manufacturing in China.However,the poor collapsibility of sodium silicate sand and the difficulty of recycling used sand have been restricting the application of sodium silicate.In this paper,the properties of sodium silicate sand are improved by developing modified sodium silicate and collapsing agent.In this paper,organic ester hardened sodium silicate sand(sodium silicate,organic ester added amount accounted for 3%and 0.3%of the sand weight,and kept unchanged),organic modifier(polyacrylamide,polyvinylpyrrolidone)and inorganic modifier(potassium tetraborate,lithium tetraborate,sodium pyrophosphate and disodium hydrogen phosphate)were used to modify high modulus sodium silicate.Collapsing agent was prepared from inorganic powder(Al2O3,SiC and BN).The effects of organic modifier,inorganic modifier and inorganic powder collapsing agent on the properties of sodium silicate sand were studied.The morphology and mechanical properties of sodium silicate sand were analyzed by means of SEM.EDS,XRD,DSC,room temperature strength test,residual strength test and gas emission test.The results showed that when potassium tetraborate,lithium tetraborate and polyacrylamide were added to sodium silicate,which accounted for 2.5%,1.5%,0.1%of its mass fraction.The retained strength at 1 hour,retained strength at 24 hours and the residual strength after 950? of the prepared sodium silicate sand sample were 0.261 MPa,0.72MPa and 7.2MPa.When the sample is heated at 950?,the maximum gas yield is 4.7ml/g at 24s,and the maximum gas yield is 0.6ml/g/s at 6s.Compared with the sodium silicate sand sample without added modifier,the strength of the 1h was increased by 32.5%.the strength of 24h was increased by 40.6%.and the residual strength of 950?was decreased by 8.9%.After the addition of the modifier,the sodium silicate binder unifonnly covers the surface of the sand,and the bondingbridge becomes dense,which improves the room temperature strength of the sodium silicate sand.When potassium tetraborate,lithium tetraborate and polyacrylamide were added.8%polyvinylpyrrolidone,0.2%sodium pyrophosphate and 0.2%disodium hydrogen phosphate were added into water glass.The retained strength at 1 hour,retained strength at 24 hours and the residual strength after 950? of the prepared sodium silicate sand sample were 0.283MPa,0.849MPa and 4.02MPa.It ensures that the sodium silicate sand has a high normal temperature strength and reduces its residual strength.Under the condition of heating at 950?,the sample gas reaches a maximum value of 5.4ml/g at 28s,and the gas generation rate reaches a maximum value of 0.5ml/g/s at 4s.The sample has a low gas generation rate and gas generation rate.It can avoid the blowhole defect caused by moulding sand.Adding modified sodium silicate(containing the above six modified substances such as potassium tetraborate)and inorganic powder collapsing agent of micron scale(10?50?m)into ceramic sand,the composition ratio of collapsing agent is Al2O30.4%cSiC,0.3%,BN 0.1%(all accounting for sand weight).The retained strength at 1 hour,retained strength at 24 hours and the residual strength after 950? of the prepared sodium silicate sand sample were 0.404MPa,0.854MPa and 1.25MPa.The collapsing agent accelerates the initial hardening rate of the sample.Under the hot concentrated alkali,the nitrogen-boron bond in BN is broken,and AIN is formed.During the cooling of the sample.Al2O3,SiC and AIN with small linear expansion coefficient split the bonded bridge.The effect is to.improve the collapsibility of the water glass sand.The composition of sodium silicate sand modifier is as follows:potassium tetraborate,lithium tetraborate,polyacrylamide,polyvinylpyrrolidone,sodium pyrophosphate and sodium hydrogen phosphate accounted for 2.5%,0.15%,0.1%,8%,0.2%,0.2%of sodium silicate,respectively.Al2O3,SiC and BN in collapsing agent accounted for 0.4%,0.3%and 0.1%of sand weight,respectively. |
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