EFFECT OF GATING SHAPE AND DIRECTION DURING CENTRIFUGAL CASTING OF ARTIFICIAL LUMBAR DISC MODEL OF CP-TI

Shape and direction of gating in centrifugal casting affected the microstructures and defects. The purpose of this research was to determine the effects of gating shape and direction in centrifugal casting toward porosity, density, roughness, and microstructures on the artificial lumbar disc model. The main shapes of gating were circular and rectangular cross-section.  The circular cross-section gating was used for two different directions of artificial lumbar discs; vertical, and horizontal. Furthermore, the rectangular cross-section design consisted of three different directions; oblique clockwise, oblique counter-clockwise and perpendicular towards the mold. The rotational mold was conducted at a speed of 60 rpm. The results showed that the rectangular cross-section gating with the oblique direction same with the rotation of the mold produced artificial lumbar disc model that had the smallest porosity area among the other directions. It was the best gating design among the others which had the smallest porosity area (0,68%), highest density (4,517 g/cm3), and smoothest roughness (8,76 µm). In the sub-surface, the microstructure of α-case was formed. The thickness and hardness of the α-case in this design were 50-100 µm and 760 VHN, respectively. Hence, the rectangular cross-section gating with the oblique direction same with the rotation of the mold was appropriate to be applied in the manufacture of an artificial lumbar disc model.