Q:  We will be selecting a different furan binder system, and among other selection criteria we need to make certain that the new binder will not cause any warpage in the cores and molds. What laboratory testing can estimate the warpage associated with the use of furan binders?

A:  Warpage testing depends on numerous variables, including sand type, binder type and level, type and level of catalyst, mixing cycle, humidity, sand temperature, mold dimension, span of the warpage bar, and amount of load and time lapse after strip time.

To make certain that the resin systems chosen to replace an existing system will not result in increased warping of cores and molds after stripping from the pattern, a new laboratory method for warpage estimates suitable for furan binder systems needs to be applied.

Warpage samples should be prepared with a minimum of three different binders with the same catalyst, and:
•  The same level of binder should be used for all the systems;
•  The type and amount of catalyst should remain the same for all the samples; and
•  A typical 4X4X18-in. mold can be used for the warpage test.

For each of the systems, approximately 10,000 g of sand mixed with the binder and the catalyst should be transferred in to the mold immediately after the mix. The sand should be packed tightly by ramming inside the mold. Work time and strip time should simultaneously be measured with the rest of the sand transferred in the picture frame mold.

For the measurement of warping the test specimen is supposed to be taken out of the mold immediately after the strip time and be placed on supports spanning 16 inches (about 41 cm) soon after strip time is achieved and an approximately 5.1 kg mass should be placed at the center.

The test specimen of a 4x4x8-in. rectangular block weighs about 7.4 kg when made with furan no-bake bonded sand. The deflection of the bar at the center point measured at intervals of 1 min., 5 min, 10 min and 15 min is the indicator for warping of the specimens. The amount of deflection with time is considered as the warpage of the samples. Sand temperature also should be monitored during the test.

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