Editing Sand casting (section)

====Patterns====
From the design, provided by a designer, a skilled ''pattern maker'' builds a ''pattern'' of the object to be produced, using wood, metal, or a plastic such as expanded polystyrene. Sand can be ground, swept or [[Wiktionary:strickle|strickle]]d into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as ''contraction allowance''. Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others. Patterns also have core prints that create registers within the molds into which are placed sand [[core (manufacturing)|cores]]. Such cores, sometimes reinforced by wires, are used to create under-cut profiles and cavities which cannot be molded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks.

Paths for the entrance of metal into the mold cavity constitute the runner system and include the [[sprue (casting)|sprue]], various feeders which maintain a good metal 'feed', and in-gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via [[Riser (casting)|risers]],{{#tag:ref|'Riser' (UK) is a term for an up-runner, in which the poured metal ''rises'' from the casting. In US practice, a riser is another term for a feeder to the top of a casting.<ref>{{Cite book
  |title=Castings
  |last=Campbell  |first=John
  |year=1993
  |publisher=[[Butterworth-Heinemann]]
  |isbn=0-7506-1696-2
  |page=49
}}</ref>|group=note}} which are added either in the pattern itself, or as separate pieces.