Cavitation: A Brief Review of the Literature
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Transcript of Cavitation: A Brief Review of the Literature
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Cavitation:A Brief Review of the Literature
Stephen P. MidsonThe Midson Group, Inc.
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NADCA Technical PaperFrom 1981
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• Cavitation means literal generation of cavities in a fluid» Occurs when the local pressure falls
below the vapor pressure of the fluid» Whenever bubble nuclei are available
• In zinc die casting, cavitation bubbles can be formed in the cavity, the gooseneck or the nozzle
Definition of Cavitation:Davis & Murray
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Mechanism of Cavitation Erosion
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• Bubbles in the liquid can impact surfaces at speeds of 130 m/sec (300 miles/hr)
• Peak surface stresses of 900 MPa (130 ksi) have been measured
Damage from Cavitation
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• Cavitation bubbles are produced in places where low pressures occur» Bends» Changes in cross-section» Junctions between runners» Protrusions, such as ejector pins
• Bubbles carried downstream & can collapse on die surfaces
Effect of Flow System Geometry on Erosion
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Examples of Cavitation
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Examples of Cavitation
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• “I talk often about cavitation because it is one of the most common failures of dies”
• “During my course on runner design, I discuss cavitation due to ejector pins standing into the flow (or back from the die) & bad runner design (i.e. square bends)”
Morris Murray
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• SAE paper from 2000
• Reported cavitation erosion data for selected aluminum alloys used with squeeze & semi-solid casting
• Results show that type of casting process, surface finish & alloy chemistry influence erosion wear
DasGupta & KillingsworthSPX Corp.
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Flow 3-D
• Most recent version of Flow 3-D has potential to simulate cavitation and identify areas vulnerable to cavitation damage
• The cavitation model can be turned on or off by the user for a filling analysis.
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End of FillingCavitation Potential Found Mostly on One Side of the Cavity
Metal colored by cavitation potential (red is bad)
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• Kado, Hasuno & Asada
» Ryobi Limited
• Simulation test of die erosion in die casting with acoustic cavitation
2008 Japanese Die Casting Association Congress