Core Processes

Core Processes

Casting processes that employ cores are little if at all different from solid part manufacturing as core production is an operation performed separately. The pre-formed core is held in place with apparatus known as core prints or chaplets while molten metal is poured into the enclosed mold. Once the cavity has been filled, the material is cooled to promote solidification. The part is ejected from the mold and the core is in turn removed from the part. Shaking or breaking are commonly employed to remove the core and thus disposable or re-useable materials are popular in core processes as the item is used only once in many applications. While continuous use cores may be made of metals, ceramics or polymers; green or dry sand cores are popular in many applications as they are expendable and the materials are easily reclaimed for future use. Material considerations are important as each core must have adequate compression strength, permeability and refractoriness while maintaining a smooth surface that is easily broken down for removal or shakeout.

While the phrase core processes can be used to describe the casting methods of which they are an integral part, it may also apply to the manufacturing techniques used in the production of the core itself. While extrusion and injection molding may be used in some cases, casting is actually used to produce many of cores found in modern iron foundries. The first step is preparing the materials used to make the core. A continuous screw type mixer is used to combine sand and binders such as clay or pulverized coal to be used for the core. A special cast known as a core box is used to form the specific shape of core needed. The sandy slurry is either packed into and shaken out of a dump core box or injected into a split core box which opens for removal. The cores are then baked at variable temperatures which hardens them as needed for casting. If needed, multiple core segments can be joined with hot glue or other simple fasteners to create longer or larger cavities. As the use of sand may result in a rough surface, the core may be filed or grinded to smoother finish before use in grey iron casting. The method of core design and production varies based on the specific need and configuration of the part. Considerations for core processes and manufacturing include production rate and quantity, precision and surface finish.