Effect Of Composite Fiber Content On Properties Of Silicon Sol Slurry And Shell Reinforced By Fiber For Investment Casting

Investment casting is one of the major forming technologies of complex aerospace precision castings. Silica sol shell molding is widely used in shell process, which high temperature strength is higher, and the environment pollution is lower, but there are restrictive relation among strength and breathability of shell. By adding composite fibers in silica sol slurry can be enhanced shell strength and permeability at the same time. To study the effect laws of fiber content on properties of silicon sol slurry and shell, there is a certain theoretical basis and practical application value to prepare high quality shell for investment casting.In this paper, ceramic and nylon composite fibers at different content was mixed into silica sol slurry to reinforce shell, composite fibers were dispersed by ultrasonic action and hydroxypropyl methyl cellulose(HPMC) in silica sol slurry, the effect laws of composite fiber content on the properties of slurry and fiber-reinforced shell were studied, the strengthening mechanism of composite fiber on investment casting shell was analyzed. Meanwhile, the best composite fiber content and baking process parameters of fiber-reinforced shell were optimized. The experiment results indicate that the ultrasonic action and HPMC dispersant are all efficient to improve the dispersion of composite fibers in silica sol slurry, when ultrasonic power is 900 W, HPMC content is between 0.2%~0.3%, the dispersion of composite fiber is more evenly. When composite fiber content increasing from 0 to 0.75%, the movement viscosity of slurry is increased gradually, the thickness of smearing shell in each direction are increased accordingly, and the shell thickness of corner line direction is increased remarkable, the quality of moistening slurry and composite fiber content are increased in an exponential form. With the increase of composite fiber content, the permeability of shell is increased gradually, and the green strength and fired strength of fiber-reinforced shell are firstly increased and then decreased. When composite fiber content is 0.6%, the green strength and fired strength all reached maximum, which respectively are 3.64 MPa and 4.94 MPa. And the relation on composite fiber content, firing temperature and fired strength of shell is established, the fired strength is firstly increased and then decreased with increasing of composite fiber content and firing temperature, when composite fiber content is 0.6% and firing temperature is 1050℃, the fired strength reached maximum.Composite fibers were dispersed by ultrasonic action and HPMC dispersant in silica sol slurry, and composite fiber content on coating performance of silica sol slurry was studied, the influence law of the composite fiber content on the shell property was obtained. It can provide theoretical guidance and technological support for high melting point complex structure integral investment casting.