Sam Ramrattan

Wet to Dry—Refractory Coating Control for Precision PUCB Sands

This research project was supported by the American Foundry Society (AFS) and the American Metalcasting Consortium (AMC). As the industry moves to tighter dimensional controls of castings, stricter coating controls are required. Baumé as a singular refractory measure does not suffice. An out-of-spec Baumé measure does not suggest the corrective wet chemistry adjustment. In addition, coating solids, surface tension, and viscosity must be monitored to determine the proper corrective action.The effect of refractory coating thickness on thermal distortion was studied. Coatings were prepared using different levels of surfactant. Additionally, dip time was examined. Disc-shaped phenolic urethane coldbox binder (PUCB) sand specimens were robotically dipped into the refractory coating mixture and then dried. During these processes, wet and dry weights of the applied coating were measured. The coating thickness was measured and compared to permeability and elevated temperature testing.To control the depth of coating penetration without altering coating solids, the level of surfactant in the coating was varied. Three different surfactant levels, 0.15, 0.25 and 0.35%, were studied. Increasing the level of surfactant decreased the surface tension of the coating, increased the low shear viscosity of the coating, and increased the thixotropy of the coating. The lower surface tension coatings wetted the PUCB sand samples more readily. The wet coat weight thickness was not influenced by dip time at the highest level of surfactant addition but was strongly influenced at the other two levels. At the highest surfactant level, complete wetting occurred at all dip times, resulting in equal wet coating weights. Wet coat weights and dry coat weights showed the same trends. Depth of penetration increased with surfactant level. The higher the surfactant level, the greater the influence of dip time on the depth of penetration. The results indicate a relationship between capillary pressure and surface tension forces. The lower the surface tension of the coating (higher surfactant level), the more readily the coating wets the sand specimen. The thickness of the refractory coating layer correlated well to permeability.The distortion of the coated PUCB disc specimens was measured at 1000C (1832F). The thermal distortion curves (TDC) and mass changes are provided. The results from TDC for the different thicknesses of refractory coating on PUCB sand systems showed differences. The surface tension influenced the wetting and penetration of the coating. Coatings that wetted more readily had a thicker subsurface coating thickness and thinner proud layer coating thickness. The underlying sand distribution also affected coating thickness. The refractory coating prevented sand/binder losses but offered expansion at the hot surface/specimen interface. The level of distortion depended on coating thickness.

Adapting More Progressive Refractory Coating Measurement Controls

The Baume test to control the dilution of refractory coatings adds variability to the % solids of the coating. Increasing the variability in the % solids translates to changes in the refractory dry deposit on the core’s surface and molds which ultimately results in an increased number of casting defects and changes to the dimensions of the casting. The foundry industry is in need of more progressive refractory coating measurement controls for reducing application variability. In this study, a set of standard test methods used to characterize the flow and leveling properties of paper coatings were used to characterize the properties of foundry coatings. The solids of the coatings were varied and the Baume number of each coating measured.Several new testing techniques for the foundry industry has been identified through testing on a generic refractory coating that can be used on chemically bonded cores and molds.

Qualification of Chemically Bonded Sand Systems Using a Casting Trial for Quantifying Interfacial Defects

Chemically bonded sand cores and molds are an important part of metal casting technology and their interaction with metal (mold–metal interface) is of great interest. Currently, the metal casting industry places a strong emphasis on near-net-shape and thin wall castings, while simultaneously maintaining increasingly stringent dimensional reproducibility requirements. To efficiently and cost effectively accomplish this task, it becomes crucial to ensure or “qualify” high-quality performance at the mold–metal interface. The thermal distortion test (TDT) was used in published American Foundry Society (AFS) studies as a laboratory technique to determine the presence of anomalies and for measuring distortions in chemically bonded sand binder systems. However, these laboratory tests focus purely on sand binder system behavior, without considering the effects of actual mold–metal interfaces. While the TDT provides valuable insight, it is unable to ensure castings will be free (or contain an acceptable amount) of specific defects. Therefore, to maximize casting quality and efficiency, it becomes imperative to incorporate casting trials into a foundry’s quality control system. This will allow the occurrence of potential casting defects to be observed at the mold–metal interface. This paper presents a casting trial technique that provides three specific benefits to foundry quality control systems. First, these trials will qualify sand binder systems against a specific casting surface defect(s), such as surface roughness, veins, penetration, cuts, washes, and erosion. Second, these casting trials are implemented under constant casting, mold, process, and design parameters. This allows the casting trial(s) to provide diagnostic information (i.e., if a specific defect occurs when using a qualified sand binder system, the cause cannot be related to the sand binder system). Third, the casting trial technique provides new opportunities for data analysis and deeper system understanding. Specifically, results in this paper identify the possibility of a potential relation between TDT data (e.g., anomalies and distortions) and actual casting trial data (e.g., defects).

Shell V-Process

The current V-Process casting methods used in today’s industry are time intensive and energy inefficient. This project consisted of modifying two existing casting techniques in order to formulate a new patentable process. This new Shell V-Process will utilize both shell sand and a high temperature infrared (IR) heater to rapidly cure the sand around a pattern. Testing is important to determine the best cure rates, maximum height of curable sand, flask size, optimal sand binder levels, and thickness of plastic used in the process. The hope is to have this process automated for use in industry.