Study On Properties Of Slip Casting Plaster Mould In Sanitary Ceramics

China is a major sanitary producing country, the output has led the world for many years.Plaster mould has many advantages, such as good water absorbing performance, convenientmaking, low cost, rapid response to market changes and so on, so it is widely used as the mainslip casting mould in sanitary ceramic industry. Plaster, as a slight soluble material, also hasmany disadvantages, such as bad water resistance, bad corrosion resistance to electrolyte(Na2SiO3、Na2CO3) from slip. So the absorption slip performance of plaster mould is poor inthe use later and the working life of plaster mould is short, generally60-80times. Toenterprise, there is an important subject to save cost and resources by continually improvingusing life of plaster mould.In this paper, we first conduct a series of experiments about process factors to analyzethe inherent mutability of plaster mould. The results show that: water temperature10-20℃isan instable region of plaster performance, while water temperature5℃and25-35℃is thestable regions. To maintain a steady production of plaster mould, we choose30℃as the bestwater temperature. Finally, the optimal combination of process factors is obtained:plaster-water ratio1.25:1, water temperature30℃, stirring speed500r/min, stirring time3min, soaking time3min.To reduce or prevent plaster corrosion effectively, we choose three good film-formingmacromolecule materials, CMC, PVA, methyl-sodium silicate, as modified additives ofplaster. Good water resistance PVA/TEOS composite films were obtained through the reactionbetween TEOS and PVA when the mass ratio of PVA and TEOS is2:1. The experiments showthat:3%CMC solution,3%PVA solution, CMC/PVA mixed solution, modified PVA/TEOSsolution and methyl-sodium silicate have fine film-forming property. As plaster additives,they can all reduce plaster corrosion ratio, and increase plaster strength, but the influencemechanisms are different. The addition of CMC can change growth habit of dihydrate gypsumcrystal, make its morphology transform from needle-shaped to short columnar and evenclastic, while the addition of PVA, PVA/TEOS, methyl-sodium silicate almost have noinfluence to morphology of gypsum crystal and inner pore distribution, but they can increasecontact angle between dihydrate gypsum crystal and water, so as to decrease capillary suction of the whole plaster mould, display low water absorption, all of these provide a basis forimproving corrosion resistance of plaster mould. From the point of reducing plaster corrosionand maintaining working performance of plaster mould, the experimental results show thatthe best addition of3%CMC solution and3%PVA solution is1%and0.5%respectively,methyl-sodium silicate is0.075%.