Shell Mould Strength of Rice Husk Ash (RHA) and Bentonite Clays in Investment Casting

Abstract

Investment casting process (IC) plays a major role in the modern manufacturing process in providing an economical means of mass production components with intricate shape and complex geometry as demand in various crucial applications including aerospace, automotive, military, biomedical and others. This casting technique, develop shell mould fabrication by coating the required pattern with a refractory mixture which offers the complex geometrical shape and sizes parts to be cast. However, the modern IC approach in shell mould production suffers from zircon's cost and supply instability as it is the main material to be used. Zircon uses as refractory filler for slurry production, and also in the form of sand used as stucco particles, is favoured by the investment casting facilities and industries as it exhibits the most versatile properties such as low thermal expansion and low reactivity to the metal to be cast. During the period of zircon supply shortage, many facilities introduce several alternatives. Currently, the step taken to reduce the cost of primary slurry material is by using some alternate refractory material like, alumina, silica, to be used with zircon for shell mould production. In relation to that, several researches continue to search for alternatives approach for shell mould materials. This research introduces the alternative method in fabricating investment casting shell mould as recognized from investment casting industry located in Sungai Puar of Bukittingi Padang Indonesia. This industry employs several local resources to fabricate the shell mould. These materials consist of rice husk ash (RHA), and two types of bentonite clays. The bentonite clays were obtained nearly from Kota Payakumbuh in the western provinces. However, this industry suffers from weak shell mould strength and need to be investigated and consulted. In this paper, the investigation on shell mould strength made from rice husk ash (RHA), and bentonite clays were conducted. The strength was measured by its modulus of rupture (MOR) performed in 3 points flexural bending test. The green and fired shell mould strength was determined from five type of slurry composition. The results revealed that the highest green and fired strength obtained were 0.157 MPa and 0.361 MPa from shell mould sample C of RHA (46%) and bentonite (54%) of its composition.

Toughening of Ceramic Shell Mould with Rice Husk Fiber (CSm-RH) to Improve Strength Property and Mould Performance

“…Meanwhile, the existence of SiO2 phase generated from RH ash able to harden and strengthen the fired reinforced mould [32]. In fact, a study has proved the addition of fly ash RH to slurry composition makes the slurry more hardened [4,21]. Indeed, highest MOR value indicates the possibility of SiO2 bonding in the fired CSm structure as supported by [24], proved that the existence of RHs fiber are not only purposely as reinforced agent in green body but existed SiO2 is indirectly influence the properties of fired CSm.…”

“…Usually, cracking mechanism easily occurred in CSm structure during the autoclave wax removal, which can be avoided via fiber-matrix incorporation. Inasmuch, green CSm strength also increases [4,11,12,19]. High permeability also affectedly by the fibers addition, due to porosity networks from the fiber burned out.…”

“…die casting, sand casting, forging etc. [1][2][3][4][5]. Generally, a good CSm requirement involved an adequate strength and mould permeability to be operating at higher casting temperatures [2,4,[6][7][8].…”

“…[1][2][3][4][5]. Generally, a good CSm requirement involved an adequate strength and mould permeability to be operating at higher casting temperatures [2,4,[6][7][8]. Ceramic material applications are limited due to their inherent brittle nature that simply induces the catastrophic failure, particularly during the handling and processing stage [9].…”

“…The most promising approach in strengthening and improving the fracture toughness of brittle CSm is forming a ceramic-matrix composite by introducing the toughening phase; particles [10], whiskers and fibers [11][12][13] to the base material. Fiber is the most recognized as a promising reinforcement with large aspect ratio respected to their versatile toughening mechanisms [4,[14][15][16][17][18] by introducing energy dissipating phenomena.…”