Poor mold strength can lead to cracking during handling or pouring.
砂型强度低可导致浇注时砂型破裂。
time when it experienced more than 25% tensile loss. In the case of the experiment, furan nobake achieved 25% tensile loss in 3 minutes, resulting in a 3-minute work time. Pheno- lic urethane and ester-cured nobake had longer work times of approximately 9 minutes (Fig. 2). Te results were compared with the results of a B scale
hardness gauge test run to determine the work time. Te commonly used readings of 45 or 60 for the B scale hardness gauge were used to determine work time. The interval and gauge tests gave conflicting results.
For instance, the gauge test indicated the amount of time before the tensile strength of the furan nobake binder would be too low was 14 minutes. However, the inter- val test indicated the sand mix produced with the same chemistry had just 3-6 minutes before tensile strength would be too low for proper core or moldmaking. Disparity of work times between the two tests occurred
for the other binders, as well. According to the experiment results, metalcasting facilities depending on nonscientific methods to determine work time, including the B scale hardness gauge, in particular, run the danger of attempting to produce molds and cores past their window for optimal tensile strength. Figure 3 shows a comparison of the percentage tensile loss in the interval test versus the B scale mold hardness gauge measurement for the furan nobake. Tis graph sug- gests that a much lower B scale gauge reading of 20-25 corresponds to a 25% loss in tensile strength.
的拉伸损失，导致它的可使用时间在3分钟以内。酚醛 尿烷和酯固化自硬粘结剂有较长可使用时间，大约9分 钟（图2）。
实验结果与B级硬度计测试结果确定可使用时间相比 较，通常地读数为B级硬度计45或60，适用于确定可使 用时间。
间隔测试和硬度计测试给了相互矛盾的结果。例如， 硬度计测试表明的呋喃自硬粘结剂抗拉强度太低的时间 量是14分钟。然而，间隔测试表明相同化学粘结剂混 砂，因抗拉强度太低而不能进行芯子或砂模制造的时间 只有3-6分钟。
其他粘结剂也发现，两种测试之间可使用时间的不一 致。根据实验结果，铸造厂依靠非科学的方法来确定可 使用时间，包括B级硬度计，特别是试图经过他的窗口 生产最佳拉伸强度的砂模和型芯是危险的。 图3示出了呋喃自硬粘结剂间隔测试拉伸强度损失 百分比和B级模型硬度计测量时间的比较。该曲线图表 明，B级模型硬度度数20-25对应于25％的拉伸强度损 失低得多。
在车间 仪表测试的优点是它的简单，它仍然可以在车间使
Fig. 1. Three core speci- mens produced with the major binders used in the U.S. were tested for ten- sile strength in the lab. In the test, a strip time of 20 minutes was used.
图1. 三种芯子样 本，在美国广泛使 用的粘合剂进行了 拉伸强度实的验室 测试。在测试中， 以 20分钟间隔。
February 2013
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