Simple Solutions That Work! Issue 11

A s casting geometries become thinner in design and more complex, the influences from resin selection will place a more crucial role in providing a solid casting. An aluminum foundry was experiencing issues with a dendritic type shrinkage defect that was related to a recent change in a resin package, resulting in higher scrap rates from the shrink defect. The only variable that changed and created the dendritic type shrink defect in this case was the resin. HA International designed an experiment to determine how PUCB resin percentages, and solvent packages used in urethane cold boxes affected the influence of shrink on this particular aluminum A316 casting during solidification. Evaluation occurred on a newly developmental phenolic urethane cold box and a modified version of this new system, utilizing the latest solvent packages found in HAI’s SigmaCure series of phenolic urethane cold box (PUCB). The experimental setup of the study included computer aided modeling, analytical testing, and actual casting tests to generate cooling curves. These results, in conjunction with the temperature dependent properties were used to create simulation model datasets for the cold box sand mix in order to simulate the actual sand mold physical properties and understand how it was creating the shrinkage defects. Between 1,500-2,000 design iterations were conducted in modeling software to obtain a dataset that matched the results from actual lab casting results. The specific heat capacity and density results required for the simulation datasets were measured directly using instrumentation on test molds. BRODIE BIERSNER Technical Sales Representative HA INTERNATIONAL ARTICLE TAKEAWAYS: • The amount of resin and resin types can change in the amount of energy re- quired to raise the temperature of the sand mold and solidification rate of the alloy. • A reduction in shrink related defects was immediately found. CASE STUDY: REDUCING SHRINKAGE IN ALUMINUM CASTINGS WITH RESIN SELECTION 27 INFLUENCE OF RESIN PERCENTAGE The first round of testing studied the influence of reducing the resin percentage. Previous research has documented that polymers have approximately 2 times higher heat capacity values than ceramics and metals. For the first experiment using the original PUCB package, a reduction of total resin percentage from 1.00% to 0.75% was studied. This reduction resulted in a measurable difference on heat from the liquid metal leaving and entering into the sand mold. More heat will transfer from the liquid metal and dissipate at a faster rate into the mold with the higher resin percentage, Figure 1. Reducing the resin percentage resulted in increasing the heat flow peak from 3.3 w/g to 3.6 w/g. Increasing the amount of energy required to increase the temperature of the sand mold. Figure 2 and Figure 3 display the temperature curves collected from the molding media. Thermocouples were placed in the molding media to understand effect and implement the results into modeling software. These curves were created by placing a thermocouple 1/8” away from the mold/ metal interface and ¼” from the mold metal interface in the molding media. The reduction in resin percentage of 25% revealed that less heat is absorbed into the sand mold. The results point out that the metal would remain in the fluid state longer. INFLUENCE OF RESIN SELECTION The second round of testing considered modifying one part of the resin package. An experimental part 2 was developed to understand how a change in the chemistry of the resin Continued on next page MAKING YOUR INSTALLATION ASUCCESS