Riser (casting)

A riser, also known as a feeder,[1] is a reservoir built into a metal casting mold to prevent cavities due to shrinkage.

Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify.

Chvorinov's rule briefly states that the slowest cooling time is achieved with the greatest volume and the least surface area; geometrically speaking, this is a sphere.

The height to diameter ratio of the cylinder varies depending on the material, location of the riser, size of the flask, etc.

The casting must be designed to produce directional solidification, which sweeps from the extremities of the mold cavity toward the riser(s).

The connection is usually made short to take advantage of the heat of both the riser and the molding cavity, which will keep it hot throughout the process.

[3] A hot top, also known as a feeder head,[5] is a specialized riser, used to help counteract the formation of pipes when casting ingots.

Any time can be chosen but 25% longer is usually a safe choice, which is written as follows:[4] or Because all of the mold and material factors are the same for n. If a cylinder is chosen for the geometry of the riser and the height to diameter ratio is locked, then the equation can be solved for a diameter, which makes this method a simple way to calculate the minimum size for a riser.