Editing Metal casting (section)

===Filling{{anchor|Filling}}===
[[File:Low pressure permanent mold casting schematic.svg|class=skin-invert-image|thumb|300px|upright|Schematic of the low-pressure permanent mold casting process]]
{{Expand section|date=February 2010}}

There are a few common methods for filling the mold cavity: ''gravity'', ''low-pressure'', ''high-pressure'', and ''vacuum''.<ref name="degarmo319"/>

Vacuum filling, also known as ''counter-gravity'' filling, is more metal efficient than gravity pouring because less material solidifies in the gating system. Gravity pouring only has a 15 to 50% metal yield as compared to 60 to 95% for vacuum pouring. There is also less turbulence, so the gating system can be simplified since it does not have to control turbulence. Plus, because the metal is drawn from below the top of the pool the metal is free from [[dross]] and slag, as these are lower density (lighter) and float to the top of the pool. The pressure differential helps the metal flow into every intricacy of the mold. Finally, lower temperatures can be used, which improves the grain structure.<ref name="degarmo319">{{harvnb|Degarmo|Black|Kohser|2003|pp=319–320}}.</ref> The first patented vacuum casting machine and process dates to 1879.<ref>{{Citation | last = [[Iron and Steel Institute]] | title = Journal of the Iron and Steel Institute | page = 547 | publisher = Iron and Steel Institute | year = 1912 | volume = 86 | url = https://books.google.com/books?id=Bz8ZAQAAIAAJ&pg=RA2-PA547 | postscript =.}}</ref>

Low-pressure filling uses 5 to 15&nbsp;psig (35 to 100&nbsp;kPag) of air pressure to force liquid metal up a feed tube into the mold cavity. This eliminates turbulence found in gravity casting and increases density, repeatability, tolerances, and grain uniformity. After the casting has solidified the pressure is released and any remaining liquid returns to the crucible, which increases yield.<ref>{{Citation | last = Lesko | first = Jim | title = Industrial design | page = 39 | publisher = John Wiley and Sons | year = 2007 | edition = 2nd | url = https://books.google.com/books?id=1_3snz7LgiMC&pg=PA39 | isbn = 978-0-470-05538-0 | postscript =.}}</ref>

====Tilt filling{{Anchor|Tilt casting}}====
''Tilt filling'', also known as ''tilt casting'', is an uncommon filling technique where the crucible is attached to the gating system and both are slowly rotated so that the metal enters the mold cavity with little turbulence. The goal is to reduce porosity and inclusions by limiting turbulence. For most uses tilt filling is not feasible because the following inherent problem: if the system is rotated slow enough to not induce turbulence, the front of the metal stream begins to solidify, which results in mis-runs. If the system is rotated faster it induces turbulence, which defeats the purpose. [[Durville (metallurgist)|Durville]] of France was the first to try tilt casting, in the 1800s. He tried to use it to reduce surface defects when casting coinage from [[aluminium bronze]].<ref>{{Citation | last = Campbell | first = John | title = Castings practice: the 10 rules of castings | pages = 69–71 | publisher = Butterworth-Heinemann | year = 2004 | url = https://books.google.com/books?id=MS-JFA04n0QC&pg=PA69 | isbn = 978-0-7506-4791-5 | postscript =.}}</ref>