Simple Solutions That Work! Issue 14

Continued on next page ADVANCED MANUFACTURING SOLUTIONS 27 R educed Pressure Testing (RPT) is the most commonly used method of controlling hydrogen in the melt and eliminating porosity in aluminum castings. BRAD HOHENSTEIN President Porosity Solutions ARTICLE TAKEAWAYS: • Variation in RPT testing causes inaccurate results • Environment, man, and machine are all sources of RPT test variation • Advances in RPT equipment technology can eliminate the variation ADVANCES IN EQUIPMENT TECHNOLOGY ELIMINATE VARIATION IN RPT TESTING However, the manual RPT process is highly operator dependent and fraught with variation leading many foundries to distrust the results. As a Foundry Consultant, I hate to see this loss of confidence in RPT testing because when performed correctly, the RPT test is one of the least expensive, quickest, and most accurate methods for controlling hydrogen porosity in aluminum. The key to eliminating RPT test variation is understanding the source of the variation and controlling it. This sounds easy, however RPT process variation can be caused by both operator and equipment. Fortunately, recent technological advances in Reduced Pressure Testing equipment eliminate most, if not all, of the variation in the RPT test. Not only do the equipment advances help the foundry control their casting process, but they also transform RPT testing into a robust, repeatable process meeting the strict quality requirements of the foundry customer. Let’s take a look at where process variation can occur in RPT testing and how advances in RPT testing equipment, eliminates RPT test variation. 1. Vacuum Setting Hg Lack of vacuum control is a common cause of variation in RPT testing. Typical target vacuum settings range from 25.5 Hg to 27.5 Hg. The key here is to be consistent. If your target vacuum setting is 26 Hg, use 26 Hg for each and every test. Results will vary widely if an operator sets the vacuum at 26 Hg for one test and 27 the next. When using a vacuum system with a mechanical gage and hand- controlled vacuum valve, the foundry is reliant upon the operator to run the vacuum per the test procedure and to properly record the data. Even when the operator does everything to the procedure, it is difficult to get much better than a +/- 0.5 Hg variation using a mechanical gauge and a hand operated valve. With automated RPT equipment, the vacuum is precisely controlled by the computer. In advanced units, the vacuum parameters are set by the quality engineer and cannot be changed by the operator. This ensures the vacuum is the same for every test. In addition, these RPT The automated system ensures the test vacuum is accurate and repeatable.