Casting - Sprues
The sprue, or feed design is crucial for a successful casting. The laws of physics cannot be defied. The principles are quite simple. During the solidification period of any casting, it is vital that a constant and free flow of molten liquid metal can be supplied to the casting for at least as long as it takes for the casting to form to totally complete the solidification process. Once this process is understood the following is simple logic. The primary feed should always go into the largest mass/section of the casting form. The feed should always be round in section, and of a diameter that exceeds the greatest cross sections being filled. There are of course variations to this principle when multi feed points are needed, or the section is light weight and / or thin and the feed must be transformed from round to a shape that can be fitted to the object.
Often client models have feeds that have been, "necked", this habit should be avoided, as this will result in shrinkage porosity. At Hean Studio we often have to modify the feeds on client models, and we have skilled staff who are able to carry out this operation.
Feed material made of copper or brass should be avoided as this reacts with the sulphur in the rubber compound and as such the rubber sticks to these materials. Upon removal, the surface will be roughened, and is not helpful.
