Fig.4. Here’s the temperature profile of a step-cone core at 5% solid fraction.
数ӣब֡ О֣本 ֣ 。֣٢ӣچ温ਯ轮级
large thermal expansion of silica sand. Previous studies into the high temperature properties of silica sand have addressed the technical limitations metalcasters face while using silica sand molds or cores. As shown in Fig. 1 and Table 1, silica sand undergoes various phase transitions while being heated up to high temperatures. Once past the alpha-beta phase transition at approximately 1,063F (573C), silica sand experiences a steady contraction till the cristobalite phase transition at 2,678F (1,470C). Sand additives such as iron oxide or engineered sand addi-
tives are used in the metalcasting industry to either induce a tridymite transition which leads to a secondary expansion or induce the cristobalite transition at a lower temperature which causes a large secondary expansion. Tese additives caused large changes in the volume of bonded sand. Certain
子ਯ或型铸砂硅用҅֨Դ造铸，ӟ指९ूङਈ性温高砂 ՟过经要时温高ਙ热加֨砂硅。Ӳ限术技ךકث面要时 。ॐ۱ չ੮ ֣ײ，ՊबգЉय़ Ŝब ś过经Јچ温）℃ ℉（ 约֨砂硅旦一 ℉（ ℃ ֨ӱफ，ঢ়收定६੧进फ一砂硅，Պ 。止ОՊबਸ਼ी方过经Јچ温）
铸造ЏИѫ采用氧化铁或工३砂添加剂诱Շ鳞ीਸ਼转 ਸ਼ी方Շ诱й用Јچ温Ѻ较֨是或，胀膨次иਚح，Պ 转Պ，造成и次膨胀。这п添加剂҅得ডৈ砂ѽ॥Շ生 形并，ৈ烧ङ面੮ਯ砂进促לਈ剂加添定特。化Պם巨 成部ӣ融化ङ੮面。ंй烧ৈ੮面ড性增加，થ੮面ङ
Fig.5. Depicted is the silica with zircon blends thermal expansion results.
锆有配是ङ明પ֣本 ֣ ਸ਼砂混合物热膨胀ৈ果ङ 硅砂。
March 2017
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 47
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