of Bangni resin sand totally satisfied the requirements of the casting process, especially when the large core, weighing 70 metric tons was lifted; the core was strong and without any signs of cracking (Fig. 2). Sand strength in the ‘plum rain’ season in South
China—During the plum rain season, with a humidity of 98%, Bangni resin still has a satisfactory hardening rate and initial strength, overcoming the problem with water glass sand, which absorbs moisture and results in a slow hardening rate. The Tian Qian Industries Holdings Co. Ltd is located
on the bank of Taihu Lake where the maximum humid- ity reaches 90-98%; however, molds and cores still have good curability and strength. Good breakdown property—Bangni resin sand has
good shakeout characteristics, and large pieces of mold- ing sand can be seen falling off the casting during the shakeout process, which is welcomed by fettling opera- tors. The delegates who attended The National Confer- ence on Steel Casting Sand visited Wuxi foundry and were interested in the surface quality of steel castings after shot blasting. They were even more focused on the large pieces of molding sand seen falling off the castings (Fig. 3). Toughness of Bangni resin sand—Because Bangni
resin contains high molecular alkene genus carbon chains, after mold-making, the mold surface is tough and smooth; Bangni resin sand molds have good stripping characteristics and molds are not easily damaged dur- ing stripping. Also, when coating with a brush, the sand surface is not easily brushed off. Bangni resin sand and surface quality of steel cast-
ings—From a practical application, Bangni resin sand has two positive effects on the surface quality of castings. The first is similar to other resin-bonded sands.
Because resin undergoes a pyrolytic reaction after pouring, a reducing atmosphere forms at the interface between mold and metal. This protects the metal surface from oxidation. After shakeout, the casting surface has no sign of oxidation. Secondly, Bangni resin sand has appropriate
strength and the mold surface has good stability, thus the surface finish of the molds is improved and steel castings made with Bangni resin sand have a good surface quality. The castings for ships and large slag ladles produced by Wuxi Foundry for Japanese customers all received good comments. Steel castings produced for Sandvik (Fig. 4) by
other metalcasters using Bangni resin sand obtained recognition and praise from Swedish experts. A 160 metric ton, large rudder arm steel casting made
by Tian Qian Company with Bangni resin sand had a good surface quality. Te full production process of the steel casting was under the supervision of seven countries’ registries of shipping and was certified by each of them. Te casting was directly shot blasted after shakeout and its good surface quality can be seen in Figure 5.
时，强度很好，无任何裂纹，见图2。
（2）在南方梅雨季节时的型砂强度 邦尼树脂，在湿度高达98%的梅雨季节，仍保持一 定的硬化速度与初始强度，克服了过去水玻璃砂的吸 湿、硬化速度缓慢产生的问题。
地处于太湖边沿的天乾铸钢厂，湿度最大达到90% ～98%，但铸型和芯子仍有较好硬透性与强度。
（3）落砂性能好
邦尼树脂砂型浇注后脱箱时有良好的落砂性能，并 在脱箱时可看见铸型表面的大片型砂脱落，受到清理 工人的好评。2010年在无锡召开的全国铸钢型砂会议 期间，代表们在参观无锡铸造厂时，不仅对铸钢件抛 丸后的表面质量感到兴趣，对脱箱后铸件表面的型砂 大片脱落更为关注。图3为脱箱后铸钢件表面型砂大片 脱落的情况。
（4）邦尼树脂砂的柔韧性
由于邦尼树脂中含有高分子的烯属碳链，树脂砂 造型后砂型表面柔韧、光滑，工人普遍反映起模性能 好，起模时铸型不易损坏，上涂料时不易起砂，很受 操作者的欢迎。
5、邦尼树脂粘结砂与铸钢件的表面质量
从用邦尼树脂粘结砂生产铸钢件的实践中体会到： 邦尼树脂对铸件的表面质量有两种有利的作用。 一种作用与其他树脂相同，由于树脂在高温下热 解，在铸型与金属的界面处形成还原性气氛，从而避 免了金属表面的氧化。铸钢件脱箱后，即可明显地看 出铸件表面无氧化的现象。
其次是由于邦尼树脂型砂的强度适当，铸型表面 安定性好，促进了铸件表面粗糙度的细化。 因此，用邦尼树脂砂生产的铸钢件具有良好的表面 质量。无锡铸造厂生产的船用件及为日本用户生产的 大渣包等，都受到了用户的好评。
其它铸钢厂家，采用邦尼树脂砂为山德维克公司生 产的铸钢件（如图4所示），也得到了瑞典专家的肯定 与赞扬，。
天乾重工用邦尼树脂粘结砂制作的160吨大型挂舵 臂铸钢件，表面质量良好，经7个国家船级社对全过程 的监造，通过了7个船级社的认证，铸件落砂后直接抛 丸，表面质量良好，见图5。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION May 2013
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