Simple Solutions That Work! Issue 11

D ue to a relatively low cost of test equipment and ease of operation, the Reduced Pressure Test (RPT) is the most widely used method of controlling hydrogen porosity in the aluminum foundry. However, with the RPT test method used at most foundries, both producing and analyzing the test sample is highly operator dependent yielding results which can vary from test to test. The inherent process variation and lack of repeatability has resulted in a negative view of the RPT test by many quality system managers and end customers. Fortunately, it is not difficult for the foundry to make changes in their RPT testing practices and test equipment to eliminate the process variation. With a few simple changes to foundry RPT procedures and equipment, RPT testing can be transformed from a qualitative test to a quantitative test, acceptable to even the most stringent quality systems. To eliminate process variation in RPT testing, the source of variation in each step of the process must be understood and controlled. The following Do’s and Don’ts will help you understand, control, and transform your RPT testing into a quantitative test. BRAD HOHENSTEIN Porosity Solutions www.PorositySolutions.com ARTICLE TAKEAWAYS: • Transform RPT testing from a qualitative to a quantitative test • Bring your RPT test in-line with today’s quality standards • Use density measurements to reduce costs and improve accuracy CONTROL POROSITY BY ELIMINATING VARIATION IN YOUR RPT TESTING 1. SAMPLE CUP Process variation can be caused by excessive influence of the sample cup on the solidification rate of the RPT sample. made, and ultimately making the final product more useful to the end user. 3D printed sand is not directed at a certain industry or a particular customer— this technology can be used by a wide range of customers from various backgrounds and industries of all levels. The sample cup can be made from either carbon steel or SS steel. To maintain a molten sample prior to placing in the vacuum chamber, the wall thickness should be approximately 1 to 1.5mm. Typically, two variations of sample cups are used, a disc shape (approximately 60mm diameter x 20mm height) and a plug shape (approximately 36mm diameter x 36mm height). Both types will work but one or the other should be selected and defined in your foundry RPT test procedure. To promote sample release from the cup and reduce heat transfer from the molten sample to the cup, coat the sample cup with a high temperature release agent or coating such as ZYP Boron Nitride Aerosol spray. 21 Continued on next page MAKING YOUR INSTALLATION ASUCCESS