Sprue in jewelry casting
A sprue is the channel that carries molten metal into a casting mould, and the metal stem that sets inside it. In lost-wax casting it starts as a wax or resin rod on the model and burns out with it. After casting, the sprue is cut off and the stub is filed and polished flush.
3D Jewelry Designer1 min read
How a sprue feeds the mould
In lost-wax casting, each model is fixed by one or more sprues to a central wax trunk. This builds a tree, set in a flask and encased in a plaster-like investment. After burnout in a kiln, each sprue leaves an open channel to the hollow its model left.
A sprue also feeds the piece as it cools. Metal shrinks as it sets, so the sprue is made thick enough to stay liquid longer than the piece and keep feeding it. The sprue is usually attached to the heaviest section, on a plain surface where the stub is easy to clean up. A sprue that is too thin, or fixed to a thin part, can leave the casting porous or incomplete.
Sprues and metal weight
The metal in the sprues, and in the button at the base of the tree, is poured but never reaches the finished piece. It counts as casting loss, and most of it is remelted or refined for reuse.
A CAD model usually holds only the piece, and the metal weight calculator weighs it as drawn, with no allowance for sprues. A model printed in castable resin is often sprued in CAD. To weigh a .3dm like that, keep its sprues on their own layer and hide that layer before saving: the calculator and the 3DM viewer leave hidden layers out.
To render the same file, see Rhino and MatrixGold rendering.
Related
- Lost-wax casting in jewelry making
Lost-wax casting turns a wax or 3D printed resin pattern into metal: the pattern is invested, burned out, and molten metal fills the hollow it leaves.
- Casting loss in jewelry manufacturing
Casting loss is the metal that never reaches the finished piece: sprues, flashing and polishing. It is why a cast ring weighs less than the metal poured.
- Gold Weight Calculator from a 3D Model
Drop an STL or 3DM file and get the gram weight in 9k to 24k gold, silver and platinum, gross and net of stones. Free.