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any foundries have experienced costly outbreaks of high reject rates due to


inclusions in castings. An inclusion defect may arise from a single clearly defined cause or might be a result of a combination of factors, so the necessary preventive measures are initially unclear. However, to prevent recurrence it is necessary to correctly identify the inclu- sion before troubleshooting the process to find the root cause of the defect. To correctly diagnose inclusion


casting defects, metalcasters have to: a) fully examine the general character- istics and occurrence of the inclusion and describe in detail its size, distribu- tion, and appearance; b) document the defect’s location with photographs; and c) understand the casting process. Attempting a corrective action without knowing the type of the inclusion may prove very expensive. Once a correc- tive action is found, it must be imple- mented, monitored and re-evaluated. Typically, foundries use four techniques to evaluate casting


Inclusions! M


Determining the Best Cost Saving Approach


This is the first of a two-part series providing a guideline to better understand the interrelated aspects between oxides, inclusions, dross, fluxes and molten metal quality. RAFAEL GALLO, PYROTEK INC. (AURORA, OHIO)


inclusion defects: • Simple visual evaluation (“educated guess”).


• Optical microscope and/or stereo- microscope.


• Optical microscope coupled with computer and image analysis.


• SEM analysis. Nearly everyone who casts aluminum


alloys, regardless of sophistication, has at some time experienced an issue with inclusions from molten aluminum. Even the molten aluminum being used for sheet ingot and beverage cans, which is considered the cleanest molten alumi- num, will have inclusions to some extent (smaller sizes and lower concentrations of them). Tus, various types of inclu- sions such as oxides, nitrides, carbides, fluorides, borides, chlorides and salts may be present in molten aluminum alloys. During the last 50 years, several


techniques have been developed and used for assessing the cleanliness of molten aluminum casting alloys. Tese include qualitative, quantitative, and analytical laboratory procedures, as well as on-line and off-line techniques.


Better understanding of the cleanli-


ness level of the molten metal being delivered by the melting department and the additional influence that other casting process factors may have on the molten metal quality level would help aluminum foundries implement feasible, practical and robust controls during the molten metal treatment and handling operations to minimize inclusion defects. However, implemen- tation alone would not be sufficient to guarantee success if melting and/or casting operational changes are made, intentional or unintentional. Typical common process changes


and deviations related to the treatment and handling of liquid aluminum that would negatively impact the quality of the molten metal are: • Accepting raw materials of lower quality.


• Charging dirtier returns/scrap (i.e., contaminated with oil, and grease due to poor foundry equipment maintenance).


• Operating equipment which has inoperative and malfunctioning


August 2017 MODERN CASTING | 31


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