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The Importance of Green MOR for Autoclave Cracking

During production trials using a new slurry system containing nylon fiber, a seemingly anomalous observation was made. While clearly lower in Green MOR than the standard fiber/polymer system being used, shells made with the new test slurry produced fewer autoclave cracked molds during the trial. An investigation was made to determine the reason for this observation. Tests of Green MOR were made using the standard technique, which is bars dry and the test preformed at room temperature. This was compared, using various slurry systems, to MOR tests that more closely simulate conditions in the autoclave and flash fire dewax processes. Results of these tests indicate possible explanations for why a shell system with substantially lower Green MOR produced fewer autoclave cracks.

Earlier this year, we at Buntrock, performed a plant trial using the Wex Chemicals Wexcoat binder system. This system contains Nylon fibers as the major additive to an otherwise normal or typical fused silica slurry. This “test” system was being compared to the customer’s “standard” shell system that is commercially available. The standard slurry contained an unknown type of fiber and substantial polymer additives. It is not the intent of this paper to present the details of that test, but the observations made during the test spawned research work that is important for the industry.

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