How Casting Residues May Form in Die Casting and How They are Eliminated

Die casting companies apply a surface finish on the casting in order to enhance the aesthetics and the durability of the component. However, prior to using techniques such as powder coating or anodizing for that, the material on the part has to be removed completely in order to apply the extra layer of coating on the final part.

The residue material stuck on the metal casting can be seen in any of the systems as explained below. If you are new to the die cast mold making process, it is a casting process that forces the molten metal into the mold cavity using high-pressure.

Spruce and Runners

In the molding phase, spruces and runners are formed when the molten metal reaches the mold cavity. Spruces are large-diameter channels, which streamline the molten metal into the mold cavity. On other hand, runners are small-diameter channels that serve the same purpose via an individual part. The part wherein the metal goes through and starts to enter the mold cavity is known as the ‘Gate’.


A flash may form on the mold when the molten metal enters the mold cavity through seam lines and leaves a wafer-thin material when ejected from the mold. However, the flashes are preventable in co-design systems wherein a software is employed to design the mold in such a way as to make sure the flash won’t affect the function of the finished part. Foundries often integrate a designing team comprising of engineers and a tool and maintenance unit for that.

Ejector Pins

Ejector pins are protrusions of spruce, runners, and flashing systems used in combination and an integral component of many of the castings. In fact, these small pins in the inner portion of the mold are often used to remove the casting once the molten metal cools. They are used in die cast mold making since many of the castings are tough to eject, and in order to enhance the speed of the process. However, when the small pints are stuck in the mold, it may leave a small yet noticeable imperfection on the surface of the part like a flash. Surface finishing would become mandatory in such cases for the die casting companies.