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題名 | 消失模型鑄造法之模型熱分解現象及其對球墨鑄鐵顯微組織之影響=The Thermal Degradation of the Polystyrene Patterns and Its Effect on the Microstructures of Ductle Irons |
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作者 | 廖高宇; 蘇昭源; 潘永寧; | 書刊名 | 鑄工 |
卷期 | 23:3=94 1997.09[民86.09] |
頁次 | 頁53-71 |
分類號 | 472.2 |
關鍵詞 | 消失模鑄造; 熱分解現象; 燒失量; 球墨鑄鐵; EPC; Thermal degradation energy; L.O.I.; Ductile iron; |
語文 | 中文(Chinese) |
中文摘要 | 本研究探討保利龍模型之熱分解現象,由聚苯乙烯在熱分解過程中質量平衡之觀 點,計算苯乙烯單體與分解產物之間原子鍵結能之變化量。計算結果顯示模型熱分解所吸收 之熱量隨分解溫度之增高而增加,且類似焦碳的殘留物量亦會增加。比較鑄鐵及鋁合金溶液 澆鑄後在塗層及模砂中所分析之燒失量(L.O.I.)獲知,燒失量隨著澆鑄溫度之增高以及熔 液與模型接觸時間之增長而增加。故,鑄鐵之燒失量較鋁合金多,且側澆之燒失量較頂澆多。 此外,澆鑄鑄鐵後以SEM可以觀察到塗層內含有大量類似石墨之鬚狀物,顯示模型熱分解 產物中含有頗多量之焦炭。 本研究也較球墨鑄鐵在不同鑄模及鑄造條件之下凝固冷卻速率,結果顯示凝固冷卻速率 以未抽氣消失模最快,抽氣消失模次之,而CO 模最慢。由於保利龍模型的熱分解吸熱作 用,消失模不論抽氣與否均有過冷現象發生,且由於抽氣有助於熱分解產物之迅速逸出,因 此其過冷度較未抽氣者小,而CO 模則無過冷現象。 本研究亦深入分析消失模球墨鑄鐵條件與CO 模鑄件在金相組織上之差異,結果指出, 以頂澆充模時,由於紊流之流動特性,因此熔液前緣並未有保利龍分解吸熱所產生的冷激效 應。此外,當斷面厚度在約7mm以下時,由於單位截面的保利龍量太少,因此相較於模砂 的吸熱效應,保利龍模型的分解吸熱效應對於鑄件顯微組織之影響並不顯著。但是採用側澆 充模且斷面厚度在7mm以上時,則熔液流動前緣的冷激現象頗為明顯,因此未抽氣之消失 模具有較高的球墨數目,且碳化物所析出的傾向也較高。 |
英文摘要 | This study evaluated the thermal degradation of the polystyrene patterns. The energy required for pattern dissociation at various temperatures were determined based upon the changes in total bonding energies between the polystyrene monomer and the degradation products. The calculated results indicate that the dissociation heat of EPS patterns increases with increasing degradation temperature. Also, detailed analyses of L. O. I. (a value corresponds roughly to the amount of carbon residue in the substrates being analyzed) of the sample taken from molding sands and coatings at various locations were conducted, with the results showing that the L. O. I. Values increase with increasing casting temperature and with longer contact time between the liquid metal and the EPS dissociation products. Microstructure analyses by using SEM revealed graphite whiskers coral-like graphite particles in the coatings being cast with iron melts. Due to the endothermic reaction involved in the EPS degradation, the melt front experienced a chilling effect and therefore the solidification cooling rate and the microstructure of the casting produced are affected to a certain extent. The present results on ductile iron cast irons indicate that the solidification cooling rates are highest for EPC without vacuum, followed by EPC with vacuum, while CO molds have lowest solidification rates among these three casting processes. In addition, the solidification of non-vacuumed EPC experienced a marked undercooling phenomenon. However, no undercooling has been observed for the CO process. |
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