The Dos and Don’ts of Sprueing
Professional casting begins with the right set up, and that begins with sprueing. When setting up your sprueing the main thing to remember is to attach a sprue to the heaviest part of the pattern. This will help control the progressive solidification. You might also consider a tri sprue. Keep in mind - some metals cool faster than others. Here are some helpful tips on the dos and don’ts of sprueing.
There are four functions of a sprue:
1
Secure patter in position.
2
Provide channel for the elimination of wax.
3
Provide channel for the introduction of metal into cavity.
4
Control progressive solidification of molten metal.
Things to remember when sprueing:
5
Location
Always attach at the heaviest part.
6
Diameter and Length
Diameter should be greater than the thickness of the pattern attached. Length should be as short as practical for removal of casting from button.
7
Placement
Make sure the center sprue, or tree, has adequate volume. Place sprues at approximately 45° angles with the smallest designs at the top and largest at the bottom.
8
Techniques
Here are a few techniques to use when sprueing:
Proper Spruing and Gating
Improper spruing is the leading cause of shrinkage porosity.
Don't use chock gates. They cut off the feed metal.
Place sprue (gates) at heaviest cross sections of the piece.
Use runners to heavy areas if they are separated by thin cross sections
Flair the gate at the connection to the piece. This will help reduce turbulence in the metal flow.
Don't put pieces too close together.
Smooth all surfaces to avoid sharp corners which may break off during casting (i.e. connections between main sprue and gates and gates and piece).
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