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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