ASK Chemicals produced dog bone core specimens and tested them over intervals to determine how quickly tensile strength deteriorated.


ASK 化学制作了不同厚度样 本，测试他们按时间间隔，如 何快速失去拉抻强度。


Unfortunately, many mold and casting problems also


can be attributed to other issues in the casting process, so exceeding the worktime may not be recognized as the root cause. Telltale signs that your facility is compacting its molds too late after curing include weak molds and the penetration defect, as well as stiff sand during compaction. A good molder will notice when the sand is starting to stiffen up, indicating it is curing too fast and the catalyst should be reduced.


Measuring Work Time In the sand lab at ASK Chemicals, Dublin, Ohio,


researchers developed an interval testing method to deter- mine work time. After the sand was mixed with the binder, laboratory core specimens were produced at 3-minute inter- vals until the cores were too weak to hold. Each specimen was tested for tensile strength and compared (Fig. 1). Te experiment was performed with the three most com-


mon nobake binders used in the North American metal- casting industry—1% furan nobake, 1% phenolic urethane nobake and 1.25% ester-cured phenolic. Tese systems were run with catalyst or coreactants to provide the same 20-min- ute strip time for each binder chemistry. Tensile strengths of the specimens at each interval were recorded and the percentage of tensile loss calculated. It was determined that a binder had exceeded its work


可能会无法识别超过可使用时间是缺陷根源。能说明问 题的是您的设备正在压紧由于固化后太迟造成的脆弱的 砂模和粘砂缺陷，以及在压实过程中极度硬化的型砂。 一个好的模型工应注意到当型砂开始变硬时，如它的固 化速度过快，应减少催化剂的用量。


测量可使用时间


在美国俄亥俄州都柏林，ASK化学型沙实验室，研究 人员开发出一种的间隔测试方法，以确定可使用时间。 型砂与粘结剂混合后，实验室芯子标本以3分钟的间隔 产生，直到芯子太弱而无法握住。每个测试试样的拉伸 强度和比较（图1）。


实验选用三种在北美铸造业最常见的自硬粘结剂—1 ％呋喃自硬粘结剂，1％ 酚醛尿烷自硬粘结剂，和1.25 ％酯固化碱性酚醛。这些系统与催化剂或共反应物一起 运行，为每个化学粘结剂提供同为20分钟的脱模时间。 每个试样的抗拉强度和拉伸损失的百分比计算被按时间 间隔记录。实验可以确定的是，当它的拉伸损失超过25 ％时，粘结剂已经超过 了其可使用时间。就实 验来说，呋喃自硬粘结 剂在3分钟内达到25％


Making a mold or core past its work time can lead to penetration defects in the casting due to poor density in the mold.


制作砂模或芯子超过可使 用时间，将导致铸件粘砂 缺陷和密度差。


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


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