Dissertation
Measurement of air entrainment during pouring of metal castings
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2020
DOI: 10.17077/etd.005671
Abstract
Understanding and reducing air entrainment in liquid metals is important for improving casting filling systems and liquid metal transfer processes. Air entrainment generates oxide inclusions that reduce mechanical performance of metals. This study presents air entrainment measurements for a jet of liquid aluminum alloy A356 plunging into a pool and examines the results of similar experiments performed with ASTM 216 WCB steel alloy. Measurements are performed in argon and air atmospheres for a range of jet fall heights. The volume ratio measured of entrained gas to liquid aluminum poured in the argon atmosphere is 0.43 for an average jet impact velocity of about 3.8 m/s. This ratio is of a similar magnitude as water under the same jet parameters. For the corresponding aluminum experiments in air, the measured volumetric ratio is only 0.16. It was not possible to measure the volume of air entrained by a plunging jet of liquid steel. The expansion of the gas due to thermal radiation of the steel jet greatly affected the volume of air entrained measurements for the experiments with steel. It is found that nearly 50% of the volume of oxygen entrained is consumed by oxidation when pouring A356, but this alone does not account for the difference between the volume ratio measurements in inert and oxidizing atmospheres for A356. Instead, the ratio air is so low because during some portion of the experiment no air was entrained. In contrast, all the oxygen in the entrained air is consumed by oxidation when pouring a steel alloy.
The onset velocity for gas entrainment for a plunging jet of liquid A356 in an air atmosphere is found to be 3.9 m/s and is 3.4 m/s in argon, with the difference attributed to the effect of the oxide film on the jet surface in air. The onset velocity for gas entrainment for a plunging jet of liquid WCB steel is found to be 3.8 m/s in both air and argon environments. These are about three times greater than the onset velocity previously measured for water.
Details
- Title: Subtitle
- Measurement of air entrainment during pouring of metal castings
- Creators
- Lucas Andrew Archer
- Contributors
- Christoph Beckermann (Advisor)H S Uday Kumar (Committee Member)Pablo M. Carrica (Committee Member)Albert Ratner (Committee Member)Ricardo Mantilla (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Mechanical Engineering
- Date degree season
- Autumn 2020
- DOI
- 10.17077/etd.005671
- Publisher
- University of Iowa
- Number of pages
- ix, 78 pages
- Copyright
- Copyright 2020 Lucas Andrew Archer
- Language
- English
- Description illustrations
- illustrations (chiefly color)
- Description bibliographic
- Includes bibliographical references (pages 76-78).
- Public Abstract (ETD)
Metal castings are used in many different industries, including the automobile and aerospace industries. Solid metals, like steel and aluminum are heated past their melting point and poured into a mold where they solidify into the cast part. One of the most frequently reported defects in this manufacturing process are oxide inclusions. In aluminum, for example, the molten aluminum reacts with the oxygen in the air to form aluminum oxide (Al2O3). These and other oxide inclusions flow with the bulk of the liquid metal until they become frozen somewhere inside the cast part. Inside the cast part these inclusions weaken the mechanical properties and can require repair or complete rejection of the part.
Air entrainment is a major source of oxide inclusion during the pouring of metal castings. A common example of air entrainment occurs when a glass of water is filled from a pitcher, as the stream impacts onto the pool of water, air bubbles are pulled into the pool. These bubbles are considered the entrained air. This exact same phenomenon occurs when liquid metals are poured into molds; however, unlike water, oxide inclusions are generated as the metal jet entrains air and pulled into the mold cavity with the bulk flow. Therefore it is important to know the amount or volume of air entrained by a jet of liquid metal in order to understand oxide inclusion generation. While air entrainment is well understood for water, no experiments have ever been conducted to measure the volume of air entrained by a plunging jet of metal. In this study a system is developed to measure the volume of air entrained by a jet of liquid metal plunging to a pool.
The system was first tested with water, then experiments are conducted with liquid aluminum and steel.
- Academic Unit
- Mechanical Engineering
- Record Identifier
- 9984036790402771
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