Tis glass-like film also is difficult to wet with resin;
during mixing of reclaimed sand with added resin, it is dif- ficult to adhere the resin uniformly to the sand grain surface, and the readherence properties are not good. Terefore, the strength of self-hardening sand prepared from reclaimed sand is decreased significantly. At present, dry attrition reclamation is used widely for
resin sand and is effective for furan resin, resole phenolic resin and urethane resin bonded cores and molds. During the reclamation process, although the adhesive film on the sand surface cannot be totally removed, the residual, discontinuous resin film has no significant negative effect on the strength of rebonded sand. When using alkaline phenolic resin self-hardening sand,
the residual alkaline metal silicate film on the sand surface has a strong influence on rebonded sand. When using dry attrition reclamation, the strength of recycled sand is signifi- cantly reduced. At present, the worldwide recycling rate of reclaimed sand is below 80%. Some metalcasters have to use 100% new sand for facing. Although dry attrition reclamation is not effective, the cost
of combined thermal and dry attrition reclamation is high, and the results are not completely satisfactory. Because the resin is strongly alkaline, the discharge of waste sand must be carefully controlled.
Bangni Resin Bangni resin is a new type of resin, based on resole phe-
nolic resin and alkaline phenolic resin, and was developed to satisfy environmental protection and clean production requirements. In terms of molecular structure, it is a new type of modified resole phenolic resin. Bangni Chemical (Beijing) Co. Limited was established
in 2005. Te mission of Beijing Bangni was to study and develop environmentally friendly, modified phenolic resin based on the principle of sustainable development. In terms of the selection of raw materials, Bangni has two
principles: to ensure the products are based upon renewable resources; and to prevent harmful substances from entering the industry chain. Te aldehyde used for making resin is not the active, toxic
formaldehyde but selected aldehydes extracted from agri- cultural waste, which are chemically stable and have a high molecular weight. Te phenol used for making resin is not the highly toxic
phenol extracted from oil but selected phenols extracted from plants. In the molecular structure of the resin, there exists active phenolic hydroxyl (which has the properties of phenols) and alkene genus carbon chains; the resin has the toughness of aliphatic compounds after hardening. Under special conditions, various other substances are
added to modify the resin. Development commenced in 2005. After two years of
experimental study in the laboratory and pilot testing, the formulation of Bangni resin was finalized in 2007. From 2006 to 2008, production trials and tests were
carried out in seven metalcasting facilities, and good results were obtained in all cases.
酸盐。加热到510℃以上，碱金属盐转变为碱金属氧 化物，此种氧化物又可以与硅砂作用，在砂粒表面上 形成玻璃状碱金属复合硅酸盐薄膜。这种薄膜是碱金 属氧化物与硅砂砂粒作用而形成的，对砂粒的附着很 牢固，旧砂进行再生处理时，很难将其除去。 这种薄膜呈玻璃状，树脂不易将其润湿，再生砂中 加入树脂重新混砂时，树脂难以均匀地附着于砂粒表 面的薄膜上，因而再粘结的性能不佳，用以配制的自 硬砂的强度明显下降。
目前，广泛用于树脂自硬砂的干态摩擦再生方式， 对于以呋喃树脂、甲阶酚醛树脂、尿烷树脂等作粘结 剂的型砂、芯砂，都有很好的效果。在旧砂再生处理 的过程中，虽不能将砂粒表面的粘结膜完全脱除，但 是，再生后砂粒表面上残留少量不连续的树脂膜，对 再粘结的强度没有明显的负面影响。
采用碱性酚醛树脂自硬砂时，砂粒表面上残留的碱 金属硅酸盐薄膜对再粘结的影响很大，采用干态摩擦 再生方式时，再生砂的粘结强度显著降低。目前，世 界各国再生砂的回用量一般都不超过80％，有的铸造 厂甚至不得不全部用新砂配制面砂。
干态摩擦再生的效果不好，焙烧、摩擦联合再生的 费用很高，效果也还不能令人满意。 由于树脂的碱性很强，废弃砂的排放也必须审慎
处理。 二、邦尼树脂的基本情况
邦尼树脂，是以满足环保与清洁生产的要求为目 标，在甲阶酚醛树脂和碱性酚醛树脂的基础上研制而 成的，就其分子结构而言，是一种新型的“改性甲阶 酚醛树脂”（Modified Resole Phenolic Resin） 。
1、研制与应用过程的简介
北京邦尼公司成立于2005年，工作的目标是遵循 可持续发展的方针，研究、开发环保型改性酚醛树 脂。
在原材料的选用方面有两个原则：首先是立足于 可再生资源；其次是从源头上抑制有害物料进入产业 链。
制造树脂所用的醛，不用性质活泼、毒性很强的甲 醛。而选用自农产品下脚料提取的性质比较稳定、分 子量高的醛类。
制造树脂所用的酚，不用自石油中提取的、毒性 很强的苯酚，而选用自植物中提取的酚。其分子结构 中，有活泼的酚羟基，因而具有酚类的性质；也有高
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION February 2013
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