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with elevated temperature, the heat transferred causes thermomechani- cal movement and thermochemical reactions resulting in dimensional changes at the mold-metal interface. At any given temperature, these dimensional changes or thermal distortions are attributable to simul- taneous changes in the sand and binder. Depending on the binder type and temperature at any point in the sand plane, thermally induced reactions occur simultaneously with sand expansion, leading to significant distortions in the composite shape. Te original thermal distortion tes-


ter (TDT) uses disc-shaped specimens to compare chemically bonded sand systems but has certain limitations as a laboratory testing device: • The disc-shaped specimen thick- ness is limited to 0.3 in. (8 mm)


• It is unable to represent the variable head-pressure during mold fill


• There is no radial measurement of displacement


• There are no real time measures for heat transfer in the specimen. Researchers at Western Michigan


Univ. designed and built a prototype device to study the effects of heat and pressure on sand binder systems. Tis next generation machine, referred to as the TDTng, has the capability to rep-


Fig. 1. Thermal distortion tester stresses on a specimen are illustrated here. Table 1. Thermo-Mechanical Properties of PUCB Samples


PUCB Sample


% Binder DE


0.9 1.4


Results of Thermal Distortion Testing at 3.25N for 90 seconds


Longitudinal (mm)


0.069 0.051


DP


Longitudinal (mm)


0.113 0.107


TD


Total longitudinal distribution (mm)


0.182 0.158


DR Radial


distribution (mm)


0.22 0.234


Observation During Elevated Temperature Testing


% Change in mass


8.7 1.5


Cracks and Fractures


Faint Large


resent the heat and pressures that sand binder systems will experience from molten metal filling and solidification in the mold. Operating conditions of the TDT


device are like those where a mass of molten metal is pressing against the mold wall in a pseudo-static state. Te load (metallostatic head pressure) on


the specimen is held constant. Te specimen can move into or out of the face of the hot surface depending on whether the specimen is expanding or plastically deforming (Fig. 1). Hold- ing the temperature of the hot surface constant during testing simulates the mass of molten metal.


Testing Procedure Te testing procedure consists of


three major steps: 1) preparation of the disc-shaped specimens, 2) TDTng testing and 3) observations of physical and mass changes. In a test to verify the TDTng instru-


ment, researchers’ produced polyure- thane coldbox (PUCB) specimens in a three-cavity corebox. To operate the


MEDIA RESOURCE Fig. 2. Shown is the overall machine setup for the TDT.


Using the Actable App, scan this page to see video of the next generation thermal distortion tester. For instructions on how to use the app, go to page 16. To watch online, go to www.metalcastingtv.com.


July 2013 MODERN CASTING | 33


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