Resumo

MORIN, Gladys; HUNG, Xavier  e  MILLAN, Arnaldo. Lifespan and mechanism of deterioration of plaster molds used for slip casting of sanitary ware. Rev. Fac. Ing. UCV [online]. 2014, vol.29, n.4, pp.127-136. ISSN 0798-4065.

Gypsum plaster is a hydraulic binder used in the manufacturing of molds for slip casting. This process takes advantage of the workability of the mixing gypsum plaster/water and the high porosity of the molds manufactured. However, compared with these advantages, in most cases arises a constraint such as the low mechanical strength of the gypsum bodies, which is directly related to their own lifespan. It has been shown that the lifespan of the molds used for slip casting depends on the type or quality of the gypsum plaster. Therefore, in this paper we study the possible causes that produce this lifespan difference. Two brand plasters, one national and the other imported were selected for the manufacturing of molds for slip casting of sanitary ware, which allows campaigns on the order of 80 and 120 casts, respectively. To achieve the goal, we made studies of flexural strength (MOR), scanning electron microscopy (SEM), among others experiments, on samples built with different relationships plaster/water. The test samples whose ratio was 57/43 showed the highest resistance; being 3.2 MPa for national gypsum plaster and 4.0 MPa for imported gypsum plaster. Moreover, the observation of the fracture surfaces confirmed the presence of impurities and a strong porosity caused by air bubbles trapped in test samples made from national gypsum plaster. Based on these results, a theory was raised on the mechanism of deterioration of these plaster molds, which would explain the reason for their short duration.

Palavras-chave : Gypsum; Mold; Sanitary Ware; Slip Casting; Mechanical Strength; Porosity.

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