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我国铸造覆膜砂的生产、应用与展望
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作者 蔡教战 《柳州科技》 2003年第4期7-14,共8页
在造型、制芯前砂粒表面上已覆有一层固态树脂膜的型砂、芯砂称为覆膜砂,也称壳型(芯)砂。它最早是一种热固性树脂砂,由德国克罗宁(CRONING)博士于1944年发明。其工艺过程是将粉状的热固性酚醛树脂与原砂机械混合,加热时固化。现已... 在造型、制芯前砂粒表面上已覆有一层固态树脂膜的型砂、芯砂称为覆膜砂,也称壳型(芯)砂。它最早是一种热固性树脂砂,由德国克罗宁(CRONING)博士于1944年发明。其工艺过程是将粉状的热固性酚醛树脂与原砂机械混合,加热时固化。现已发展成用热塑性酚醛树脂加潜伏性固化剂(如乌洛托品)与润滑剂(如硬脂酸钙)通过一定的覆膜工艺配制成膜砂,覆膜砂受热时包覆在砂粒表面的树脂熔融,在乌洛托品分解出的亚甲基的作用下,熔融的树脂由线性结构迅速转变成不熔体的体型结构,从而使覆膜砂固化成型。覆膜砂一般为干态颗粒状,近年来我国已有厂家开发出湿态和粘稠状覆膜砂。 展开更多
关键词 覆膜砂 型砂 热固性树脂砂 流动性 存放性 骨料 混制工艺 硬化时间 结壳时间 铸造业
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A possible mechanism for the formation of annual growth lines in bivalve shells 被引量:1
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作者 LIU XiaoJun YAN ZhenGuang +4 位作者 ZHENG GuiLan ZHANG GuiYou WANG HongZhong XIE LiPing ZHANG RongQing 《Science China(Life Sciences)》 SCIE CAS 2011年第2期175-180,共6页
We report a unique shell margin that differed from the usual shell structure of Pinctada fucata.We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin.Al... We report a unique shell margin that differed from the usual shell structure of Pinctada fucata.We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin.All the characteristics of the growing margin indicated that the shell was growing rapidly.To explain this anomaly,we propose the concept of "jumping development".During jumping development,the center of growth in the bivalve shell jumps forward over a short time interval when the position of the mantle changes.Jumping development explains the unusual structure of the anomalous shell and the development of annual growth lines in typical shells.Annual growth lines are the result of a discontinuity in the shell microstructure induced by jumping development. 展开更多
关键词 bivalves shell microstructure internal growth bands the prismatic layer the nacreous layer
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