Progress in an Industrial Application of Fluidized Beds: Advances in the Sand Core Making Process

The flow of liquid droplets and solid particles in gas is important to numerous material processing and manufacturing techniques. The solid-gas flow is a very complex fluid mechanics problem. There are many experimental and theoretical approaches for modeling gas-solid fluidized beds. The work related to achieving an understanding of the hydrodynamics of aggregative fluidization (gas-solid two-phase flow), with special emphasis on the rheological aspects of the problem, was considered recently in our review paper. The metal casting industry is one of the areas where product quality directly relates to the fluidization of solid particles and liquid droplets. Spray casting, mixing, and tempering of foundry molding sand, filling of a molding box with sand in lost foam and vacuum castings, blast cleaning, and sand coremaking in a cold box process are just a few examples where proper fluidization of solid particles is a very important factor in process performance. In the effort to optimize the structure and properties of cast metals, a variety of casting techniques have evolved over the past few decades. This particular processing technique involves curing at room temperature of a resin-bonded sand core accelerated by a gas catalyst passed through the sand-binder mixture. In principle, the process has the typical relatively fast sand-blowing, gassing, purging, and stripping cycles, which are mainly affected by sand properties (density, grain size and distribution, shape, moisture content, close-packed volume fraction, and so on), type and amount of binders (ratios for binders systems of two or more parts), tolling design(blow tubes, sand magazine, input and exhaust piping and manifolds, vents, exhaust ports, core box, and so on), and gassing and purging performances (gas type, pressure, time, temperature, flow rate, and so on). Recently, we investigated experimentally the flow dynamics of a phenolicurethane-amine process in a core box of an inverted U configuration, using a commercial LAEMPE LI Core Shooter. The effects of reduction in the area of the vents were evaluated by manual reduction of the active vent areas. In addition, experimental data on the pressure decrease and friction factor for the vents were obtained as a function of the amounts of sand deposited in the vent area. The experimental data were compared with the predictions of the Blake - Kozeny - Ergun porous flow equations, and good agreement was found. An experimental study and a numerical analysis of high-pressure injection of sand air into sand core molds were performed by Snider and co-authors (1999). The high-speed photography showed complex filling patterns which are functions of the core shape, the blow tube, and vent locations. An Eulerian-Lagrangian numerical model was used for theoretical analysis. Particle collision frequency was resolved by mapping particle properties to the Eulerian grid, and then mapping the particle stress gradient back to the individual particles. Results from the calculations compare well with the experimental data. In this article, we present the results of numerical simulations and experimental measurements of process parameters during the PUA sand coremaking process.