Improving mold integrity. (Molding Methods & Material).

The 13 presentations and one panel for the Molding Methods and Materials Div. all had one thing in common: help foundrymen improve mold quality to produce higher quality castings. Whether the focus was on the binders, mold-metal interaction or gating, the key is to translate that information into production-related solutions.

In their presentation "Expansion Control Method for Sand Cores (03023)," S. Baker and J. Werling, International Truck and Engine, discussed a new method developed by their firm to reduce the expansion of silica and lake sand while also reducing cost. The new method involves the addition of red iron oxide to commercially available anti-vein agents in the production of phenolic urethane coldbox cores.

The combination of red iron oxide and the anti-vein agent allows for a reduction in usage of the agent by up to 70% and a reduction of resin by up to 0.1%. Since the cost of red iron oxide is 33% that of the typical anti-vein agent, this new method equates to approximately a $15/ton savings on prepared core sand cost.

In performance, this new method allows silica sand to work as well as lake sand in expansion control. If lake sand is used, this new method improves expansion characteristics as well.

The result may not be exact for all applications," said Baker and Werling, "but the fact remains that the addition of red iron oxide allows for the reduction in the amount of expansion control agent used." While this testing was done on a phenolic urethane system, the type of expansion control agent tested is used in many resin systems. Since the mechanism of veining prevention is the same from core to core, the same result of expansion control agent reduction should be achieved using any resin system.

In another presentation "Effects of Aluminum Fill Temperatures on the Distortion of Chemically Bonded Sand Systems" (03-154), S. Ramrattan, S. Cheah and S. Zandarski, Western Michigan Univ., detailed work to accurately assess the thermal distortion differences found in various chemically bonded sand systems. With today's increased emphasis on thin-wall castings, these distortion differences are critical to ensure that castings are produced within specification.

The research determined that all chemically bonded sand systems tested showed the same relative amount of thermal distortion where the pressure was 1.2 psi during mold filling at typical aluminum fill temperatures. Even when the fill temperatures were raised by 400F, the difference did not cause a significant change in thermal distortion.

However, there was a significant mass change and surface cracks on hot box and phenolic urethane specimens tested at higher fill temperatures. As a result, the research determined that the aluminum fill temperature must be closely controlled with these two systems to ensure against unbonded sand at the mold-metal interface and expansion defects.

In their presentation "Thermal Expansion of Investment Casting Pattern Wax (03-040)," V. Richards and S. Mascreen, Univ. of Missouri-Rolla, outlined research on two common pattern waxes for investment casting, focusing on how pattern injection flow orientation, reclamation and injection pressure can affect the pattern's thermal expansion during autoclaving. The research also took a look at the effect of the glossy and crystalline components of wax structure.

The conclusions drawn from the research thus far are:

* the thermal expansion of most user pattern waxes suggests the presence of both a glossy and crystalline component;

* the thermal expansion shows a relaxation of volume in the glassy component and an abrupt increase in volume as the crystalline component melts;

* the relocation temperature of pattern waxes increases as the heating rate increases;

* recycling procedure changes can change the relative amounts of the crystalline and glassy components of pattern waxes;

* changing the injection shear rate can change the relative amount of glassy and crystalline component in pattern waxes.

Based on this research, the recommended further work on this topic includes:

* examining relaxation in quenched waxes relative to non-quenched waxes;

* obtaining relaxation data on additional heating rates so the activation enthalpies (fitting constants) can be obtained.