Study On The Modification Of Slip Casting Ceramics Mould Gypsum

Because of the gypsum-model’s advantages like rich in raw material originate, lowcost, good water absorbing performance, dimension stability, clear outline and havingno pollution to environment, it has been extensively applied in sanitary ceramic industry.However, gypsum-mold also has a lot of disadvantages, such as: low strength, badcorrosion-resistance, bad abrasion-resistance and bad water-resistance, which shortenthe use life of the gypsum-mold. In China, the use times of gypsum-mold are sixty toninety commonly, which is far below the international average level. Therefore,improving the comprehensive property of mould gypsum has a very importanteconomic value and research significance.Molding is the basis of gypsum-mold use. Molding technology is the key factoraffecting the all-round performance of mould. The macro-performances andmicrostructure of gypsum-mold were discussed by changing molding process(water-gypsum ratio, stirring time and water temperature).Finally, the optimal moldingtechnology is: W/G1:1.6, stirring time2min, water temperature20℃.To improve the comprehensive property of gypsum-mold, the macro-performancesand microstructure of gypsum-mold were researched by the addition of water reducer,silicate sand, polypropylene fiber, glass fiber, Portland cement, aluminate cement andsulphoaluminate cement）. The mechanisms were analyzed by measurements ofSEM,DSC-TG,XRD and MIP. The result indicated that to reach the equal fluidity,mixing water of gypsum-mold was reduced greatly by content growing of water reducer.The porosity and average pore size of hardened gypsum were also decreased, whichenhanced the strength and corrosion-resistance remarkably. The optimum content ofwater reducer was0.15%. The continuity and toughness of gypsum-mold wasstrengthened evidently by the addition of fiber moderately. The fiber can hinder thegrowth of cracks and alleviate the stress concentration at crack tip. The flexural strengthof model-gypsum was increased by the content of fiber consequently. When the additionof the fiber was too large, the gypsum would produce bending and stress concentration.The performance of gypsum-mold was decreased by the content of fiber. GF was brittleand bad abrasion-resistance. The reinforced effect of PPF was better than GF.Therefore,the optimal fiber for gypsum-mold was PPF and the optimum content was0.04wt%. The most important reasons to enhance the performance of flexural strength and abrasion-resistance are the high hardness of silicate sand and the filling for pore ingypsum with small size. The optimum addition of silicate sand is10%.Theperformances of flexural strength, water-resistance and corrosion-resistance ofmodel-gypsum were enhanced significantly by the addition of Portland cement,aluminate cement and sulphoaluminate cement. Comparison of three kinds of cementson the comprehensive property of the gypsum-mold, the best cement for gypsum-moldis sulphoaluminate cement and the optimum addition is8%.The DH and AFt which areproduced by the addition of SAC are lapped to form a dense network structure. The porespace was filled with C-S-H and AH3closely to make the porosity and average pore sizeof the gypsum decreased. The structure stability and compactibility was strengthenedgreatly, consequently. The macro-performance of strength, water-resistance andcorrosion-resistance were improved obviously, too.In a word, the comprehensive property of gypsum-mold was strengthenedobviously at the W/G0.65,stirring time2min,water temperature20℃,waterreducer0.15%，PPF0.04wt%，silicate sand10%and SAC8%.