Examining new processes, sand traits.

This year's 29 molding presentations, including six panel sessions, provided a program packed with information on improving current molding processes, including studies on sand characteristics and foundry innovations that might influence processes beyond 2000. Presentation topics included investment casting tooling dimensions and defect elimination; heat treatment effects; metal, binder and green sand-related defects; emission characteristics of sand supplements; sand preparation; and improving coldbox core processes.

In their presentation (046), T. Okamura, Toyota Motor Corp., and M. Naito, Sintokogio, Ltd., discussed how Toyota is meeting the challenges of environmental compliance with a new production line in its Japanese cast iron cylinder block plants.

A key system to the line is the automated molding equipment, which utilizes an airflow squeeze process that assures dimensional accuracy and strength. At the start of the four-stage molding process, the sand fills the mold space left by the pattern plate, flask and filling frame. Next the machine table lifts and presses the pattern, flask and filling frame against the molding chamber so that the whole space is hermetically sealed and an airflow valve forces compressed air into the molding chamber to compact the sand. Then, the mold is squeezed again from above with hydraulic segment squeezing system. Last, the mold is stripped from the flask by lowering the machine table.

One goal of the new line was to increase productivity to make it cost competitive with aluminum lines and increase the number of castings per mold to four. Also, it created a well-lighted and spacious working area by installing part of the mold conveying and cooling system below ground level, reduced dust and noise levels, and achieved ISO 14000 certification.

The initial cost of the line was prohibitive, and the authors stressed that Toyota adopted synthetic high-purity mullite crystals as the molding sand for its entire plant to reduce costs from scrapped castings.

In their presentation (099), M.J. Keil, J. Rodriguez and S.N. Ramrattan, Western Michigan Univ., investigated the thermal properties of chemically bonded sands. Tests were performed using a dedicated thermal distortion tester, and sand/binder mixtures were selected to demonstrate the capability of the tester in dealing with diverse binder systems. The specially designed tester can apply simultaneous heat and pressure loads in the absence of combustion, and both loads can be selected independently.

Tests were performed on two shell sands and two unbonded (silica and chromite) sands using disc-shaped specimens with a diameter of 1.97 in. and a thickness of 0.315 in. Each disc was subjected to the AFS standard scratch hardness and transverse strength tests at room temperature and a distortion test at 1400F (760C) - the pouring temperature for aluminum. Different samples were used for each test because the tests were destructive, and the average and standard deviation weights were recorded for each batch of 15 discs. The maximum thermal distortion was determined during a 3 min test cycle.

Shell sands that had been predicted to crack showed no such tendency, according to the authors. Shell sands were found to be very stable at high temperature when compared to the nobake systems. The thermal distortion data was compared to room temperature test data for scratch hardness and transverse strength, but no correlation was found.

The tester developed for the study was proven to aid in predicting the behavior of core and mold material in thermomechanical applications for dimensional control.

In their presentation (030), T.A. Dorn, Neenab Foundry Co., M.D. Rothwell, Grede Foundries, Inc.-Reedsburg, and R.W. Heine, Univ. of Wisconsin, discussed particle and agglomerate size distributions and their relationship to clay and fines in reused green sand.

The authors compared sieve analysis results from two foundries, accumulating data from a core sand sieve analysis, an AFS sieve analysis without clay plus the percent AFS clay totaling 100% by weight, and a dried agglomeration sieve analysis. Molding was accomplished with a vertically parted automated machine. They found that:

* the base silica sand sieve analysis from cores or new sand additions prevails in agglomerate formation;

* higher AFS clay from higher methylene blue (MB) clay are the major contributors to the extent of agglomeration. A higher percentage of AFS clay leads to a greater percentage change in agglomerates;

* AFS grain fineness, sieve analysis and its surface area exert a dominant effect on agglomerate formation;

* the number of particles and agglomerates varies much more than the total surface area of washed molding sand sieve analysis (WMS), unwashed molding sand sieve analysis (UWMS) and base silica sand sieve analysis (CS) of a green sand;

* divergence of WMS, UWMS and CS particles or agglomerates begins at 70,100 or 140 sieve sizes, increasing with AFS grain fineness number.