EACB Binders Results


T


esting showed a rapid decrease in tensile strength as the samples were heated. The most pronounced decrease in strength was seen at 212F (100C).


At this temperature, approximately 80% of the tensile strength and modulus were lost through heating the sample. This loss continued until 392F (200C), where a slight strengthening was observed. Similar to the PUCB, the EACB had a linear relationship between the tensile strength and the modulus of the samples tested at el- evated temperatures.


The Bottom Line


EACB systems have the quickest loss of strength due to temperature of the commercially available sand binders. This may cause thermal distortion in thin unsupported core sections.


Who Should Use Them? The EACB system has an almost unlimited bench life


and improved shakeout over the PUCB system due to rapid binder breakdown. Automotive metalcasters, for example, can benefit from these characteristics when shaking out engine cylinder head and block castings where cleanliness is critical.


comprised of cylinders 1.125 in. in diameter and 2 in. long. The bonded sand specimens were heated in a muffle furnace using a neutral atmosphere consisting of a 7 to 1 ratio of carbon dioxide and carbon monoxide. (This mixture replicates the mold gas atmosphere found in chemically bonded molds.) Three soak times of 15, 30 and 60 minutes were used to provide time dependent physi- cal properties. The test cores were removed after the desired soak times and immediately placed in a fixture for testing. The samples were compressed until fracture. Compression strengths and Young’s modulus calculations resulting from the deformation under load were compared to known values for bonded sands at room temperature. A second testing methodology


involved the use of a universal testing machine with integrated


MODERN CASTING / February 2010


How the Sands Were Tested C


ompression samples of phenolic urethane cold box (PUCB), epoxy acrylic cold box (EACB) and resin coated sand were produced using standard industry tooling and


extensometer. Fig. A illustrates the test setup using the exten- someter. The standard dog bone tensile specimen was modified for the 1-in. gage length necessary for strain measurement. The samples were produced using addition levels and ratios


provided by the manufacturers. The PUCB and EACB test samples were produced at a 1.2% binder level, while the resin coated sand was bonded by the manufacturer at a 1.9% resin level. Each of the samples was allowed to cure for a minimum of 24 hours in a low humid- ity environment before testing. High temperatures for the samples were provided with the muffle furnace. Samples were placed in aluminum foil and held in a nitrogen atmosphere for the required time at temperature. The three times were chosen to


Fig. A. A specimen is shown in a universal tester with an integrated extensometer.


give values corresponding to the temperatures involved in the casting process. Because sand is an insula- tor, the slow transfer of heat makes it difficult if not impossible to test the tensile stress and strain under casting conditions. A constant loading rate was used for all testing.


MC 41


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