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Determining Your Binder Work Time


A common nobake binder work time testing procedure may not be as accurate as you think. GREG STURTZ AND JEAN SZABO, ASK CHEMICALS, DUBLIN, OHIO


确定你的粘结剂可使用时间


通常的自硬化粘结剂的工作时间测试程序也许不如你想象的准确。 GreG Sturtz and Jean Szabo, aSK ChemiCalS, dublin, ohio, u.S.


I


f you work in the nobake molding department of your metalcasting facility, it is likely you are using the B scale mold hardness gauge method to determine the work time of your binder. Te test, which was originally designed to measure green sand hardness and now is used for nobake molds, is one of several common tests used across the metalcasting industry offered by the AFS Mold and Core Test Handbook. However, few of the tests are scientific ways of measuring work time. In nobake molding, sand is mixed with the binders and


then packed into a pattern. Tis step must be finished quickly before the binders start to react, resulting in stiff sand, poor mold strength and, eventually, flawed castings. Determining how long the molder has to pack the pattern before the sand mix loses its optimal molding properties is necessary to keep molds or cores from breaking or producing defective castings.


Work Time Defects Te consequences of exceeding the work time of your


binders are costly. Compacting the sand too long after curing begins could result in: • Reduced strength. • Mold breakage during handling.


• Mold cracking or core failure at casting.


• Poor mold and core density. • Penetration defects and poor surface finish in the casting.


果你工作在铸造厂自硬砂造型车间,也许 你正用B级模型硬度法决定粘结剂的可使用 时间。这种测试,最初是设计用在潮模砂硬度测量, 现在被用于自硬砂模型,也是几种通常被用于铸造业 测量粘结剂工作时间的方法之一,由AFS造型和制芯 测试手册提出,这些测试方法几乎没有科学的测量可 使用时间。





自硬砂造型,砂子与粘结剂混合然后放入模型。这一 步必须完成的非常快,早于树脂起化学反应前,


可使用时间缺陷


超过粘结剂的可使用时间所带来的后果是严重的。固 化太长时间后压实砂模,可能会导致: •强度降低。


•砂模处理过程中的破损。 •浇注时砂模破裂或砂芯破坏。


•低的砂模和砂芯密度。 •粘砂缺陷和铸件的表面光洁 度差。


遗憾的是,许多模型和铸 造的问题也可以归结为铸造 工艺中的其他问题,因此,


Many metalcasting facilities rely on these tools to determine work time.


许多铸造厂依靠这些工具确定可 使用时间。


February 2013 FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 37


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