Pengaruh Variasi Rasio Air Dan Jenis Gipsum Terhadap Sifat Mekanik Dan Morfologi Cetakan

Abstract

Mold quality is one of the factors that determines dimensional accuracy, surface condition, and the success of metal casting. Gypsum is attractive for small-scale casting because it is easy to shape, relatively economical, and has adequate thermal resistance. This study evaluates the effect of water content and gypsum type on the mechanical and morphological characteristics of gypsum molds. Two gypsum types were used, namely fire-resistant gypsum (A) and gypsum board material (B), with water additions of 50, 60, and 70 ml for every 100 g of gypsum powder. Six specimens were produced, dried in an oven at approximately 200 °C for 60 minutes, and then tested by compression at a crosshead speed of 2 mm/min. Microstructural observations were carried out using optical microscopy at 400× and 1000× magnification. The highest compressive strength was obtained by specimen B3 at 2.06 MPa, followed by A3 at 2.05 MPa, while the lowest value was 1.95 MPa for A2 and B2. The B-series specimens also showed much lower strain than the A-series. Microscopic observations indicate that differences in particle distribution, agglomeration, and air voids contribute to the variation in mechanical response. The results provide a practical basis for selecting gypsum-water composition for small-scale casting molds.

Keywords: gypsum, mechanical properties, morphology, mold, water ratio