Simple Solutions That Work! Issue 11

DO'S • Ensure the melt is skimmed prior to sample collection • Ensure RPT vacuum is close to the melt and path is clear • Detail sample collection method in procedure to ensure sample cup is hot DONT'S • Don’t collect oxide layer or surface slag in sample cup • Don’t under-fill sample cup • Don’t use cold sample cup 3. PRODUCE RPT VACUUM SAMPLE Process variation during creation of the RPT vacuum sample is typically caused by a lack of vacuum system control. Typical target vacuum settings range from 25.5 Hg to 27.5 Hg. A good target vacuum number used by many foundries is 26.5 Hg. The key here is to be consistent. Results will vary widely if an operator sets the vacuum at 25 Hg for one test and 27 or 28 Hg for the next. This often happens when the operator walks away from the test prior to the vacuum gage reaching its working point. To a lesser extent, atmospheric conditions can also cause variation in test results. Foundries using vacuums with a mechanical gage have eliminated variation due to atmospheric pressure changes by incorporating a manometer into their RPT test calibration procedure. On a high or low pressure day, a manometer is attached to the dome and a vacuum is pulled to the target Hg per the manometer reading. When the dome vacuum is known, the mechanical gage is manually adjusted to match the manometer. The RPT test is then run per the DO'S • Define sample cup size and material in procedure • Define sample cup prep in procedure DONT'S • Don’t use ceramic cup or material other than steel • Don’t use a sample cup thicker than 1.5mm • Don’t use non-coated sample cup 2.COLLECT THE SAMPLE Process variation can be caused by a cup temperature that is too cold, surface slag or oxides in the sample, or not properly filling the sample cup. Prior to collecting the sample, the melt surface should be skimmed to remove the oxide layer immediately prior to collecting the sample. Once skimmed the sample cup should be filled with molten aluminum and held for at least 10 seconds. The molten aluminum is then poured back into the melt. Once emptied, the cup should be slightly glowing. Now the test sample can be collected by “back-dragging” the cup across the surface of the melt to push back the oxide surface layer. Then the sample is collected by filling the cup in the clean area. The cup should be full or nearly full and immediately placed under the vacuum dome within 30 seconds. 22 standard procedure. With this procedure, the same vacuum differential to atmospheric pressure is always pulled, no matter the weather 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. The operator must ensure the vacuum level reaches the correct setting, the vacuum runs for the proper time (typically 7 minutes), and no leaks are present in the dome seal. With a manually controlled RPT vacuum, it is critical that operators are well trained and process control forms are completed for each test. Periodic audits of the process should be performed to ensure compliance. Many foundries striving to satisfy ISO, TS, QS, and other quality systems, have turned to technology advancements in RPT test equipment to reduce potential operator variation in the vacuum process. Equipment like the Palmer PAS5000 automatically controls the test parameters, ensures a leak free test, while the eliminating influence of atmospheric variations. All testing parameters and test results are captured for integration into the quality system database. Both the Disc and Plug type RPT Sample are OK Automated systems control the vacuum and record the data