Shell thermal properties were estimated by running multiple computational fluid dynamic (CFD) simulation iterations, varying the thermal conductivity and heat capacity over a range of values in an effort to fit the calculated cooling curves to the experimental cooling curves for the shell and casting. Te inverse method takes much effort to achieve an
acceptable fit among the cooling curves. In this study, a method to correct the specimen thickness used in the laser flash method was introduced in order to obtain more accu- rate thermal property data. In a laser flash thermal diffusivity test, a small specimen is subjected to a high intensity, short duration radiant laser pulse after thermal equilibration at the test temperature. Te energy of the pulse is absorbed on the front surface of the specimen and the resulting rear face temperature rise is recorded by a noncontact infrared radiation thermometer. Te thermal diffusivity is calculated from specimen thickness and time required for the rear face temperature to reach 50% of its maximum value. In differential laser flash calorimetry, a reference specimen and the test specimen are mounted together under the same condition at the same temperature and irradiated uniformly with a homogenized laser beam. To ensure similar emissiv- ity, a graphite spray coating covers the front and rear faces of both the reference and test specimens. Te temperature rise of the reference with known specific heat capacity and the specimen are measured. If the density of the shell is known, then specific heat capacity can be calculated. Te laser flash method was designed for dense specimens, while measurement of highly porous materials has associated difficulties in defining the applicable specimen thickness. To evaluate the effective specimen thickness and density in this study, the researchers used a 3-D high resolution optical pro- filer to obtain the specimen surface topology (Fig. 1). Ten the effective thickness and density were determined and those data used to calculate thermal diffusivity and specific heat capacity. Specimens were taken separately from prime coats and
backup coats. For comparison, the rule of mixtures was used to estimate the thermal property of the entire shell based on the thickness ratio between the prime coats and backup coats. Tree runs of each type of specimen were conducted and the average values calculated. Te physically measured thermal property data was applied to the inverse method as the starting points to reduce a significant amount of computational time and avoid errors induced from extrapolation in the optimization algorithm.
Discussing the Results
Te specific heat capacities and thermal conductivity of the shell and insulating material as well as external heat transfer coefficient are the main parameters that influence the temperature curves of the casting and shell. Preliminary modeling showed that solidification time and the coordinate of the point where the shell reached the highest temperature were mainly influenced by the specific heat capacity and thermal conductivity of the shell. For higher specific heat capacity, more energy is needed to heat up the shell to a cer-
。چԼङս样正校法ذ照Ұ激дҵ引，据 热ӱ达Јچ温ડ测֨，率散扩热量测法ذ照Ұ激用 冲ਉҰ激ङ间时ि，چ强高Չ经需样ડֲش，ե੫平 接非用，Ї面੮ӹङ样ડӱ收吸ੴ量ਈङ冲ਉ。ذ辐 扩热。升Їچ温ङ面ਅ样ડ录ઓઋچ温ذ辐י红式ઇ ङқם最ҿӱ达چ温面੮եչچԼ样ડं是数系散 。算ઋ来间时ङ需۱％
样ડ测չս样ৰՀر，量热定测法ذ照Ұ激动差用
֮用并，起一֨装安Јў条ङգबչچ温ङգब֨ս Հ把，率ذՇङѷबґेдО。ذ照֪匀֮束Ұ激化 。त覆涂֕墨ी用都面Дե、ӹङս样ડ测չս样ৰ 样ৰՀ৲，ӟ测љՕ升Їچ温ङս样ડ测չս样ৰՀ 比Т那，ङऽ已是چإङד型果ײ，ऽ已容热比ङս 热容Օљઋ算得ӟ。 量测ङेত৲，ङઋગ本样چإ高О是法Ұ闪Ұ激 这֨ѳછдО。难֟ङ当ब有چԼङ样ડ料材性孔ך 维І用҅մы९ू，چإչچԼ效有ङ样ડИ९ू项 ） ֣（构ৈ۷拓面੮样ડ得ੂњ廓轮学Ұ率辨ӣ高 用据数п这ر并，定测੧进چإչچԼ效有ثե然。 йઋ算热扩散系数չ比热容。
比дО。样Ո开ӣד型كਅչד型ك面按本样ડ测 йׂ，өઁङ合混ङਈ性热ѽ整ד型ѳછй用适，较 样ડय़每算ઋ。比چԼङ间Фד型كਅչד型ك面 。қ֮平ङડ测次
҅用逆է方法，љ物理方法测得ङ热性ਈ数据О
ङન错Ҳ避љ法算化ѩ并间时算ઋصӗੋ显，点Շӟ 推断。
গ果的论૩ 数系热Ѯ部יչ率ح热、容热比ङ料材缘্չד型
੮型模步初。数Հ要Пङি曲چ温ד型չў铸ր影是 ד型是点标ֱङ时چ温高最ӱ达ד型չ间时֡凝，明 比ङ高较要需果ײ。প֜ր影要Пङ率ح热չ容热比 。چ温ङ定一ӱ热加ד型҅量ਈङך更要需就，容热 ङ液ً金҅ر率热حङ高更。िঢ়ر间时֡凝，样这 并，间时֡凝िঢ়Э这，放释֪速迅更ד型过通ਈ热 ડ测چ敏灵模建过通。量热ङچ温高最ङד型д加增 Ӓङў铸չד型ե化֡ր影要П数系热Ѯ部י明੮还 却速率。
进都ك一每ङד型ث，率隙孔չچإד型算ѳдО 。算ઋ法水排用率隙孔孔开չچإ॥容，测检੧
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION March 2016
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