Cores (process)

The cores in the foundry process in the production of molds includes the core production for cast parts. Cores are mold components that cannot be technically reproduced with a natural model, with inner cores making the cavities and outer cores undercuts in the mold (on the casting) malleable. The ready-to-install cores are inserted or placed in the core marks (core storage) of the casting mold, then aligned or measured so that the liquid metal cannot flow into the core ventilation, the space between the core and core mark with dry sand or, if there is a risk of trickling through, with filling filled with molding material . Cores with core irons are installed in large casting molds in order to be able to fix them accordingly.

The core block process (or core molding process), in which the mold for the cast parts to be produced predominantly consists of individually manufactured cores, is used as a special molding process in foundries. In this way, cast parts with complex external shapes can be cast. The outer sides of the model are then practically only smooth surfaces and represent the core marks. The method is also necessary if, due to difficult core parts, the inner cores of the mold are assembled first and then the outer cores, which form the shell of the mold, follow. It can be worked without a box , ie without a molding box . Casting pits can be used to hold the outer and inner cores of large parts and at the same time serve as guides and bearings. The cores for this type of mold must be strong enough to withstand the casting pressures. Even if they start to disintegrate after casting, they must not allow metal breakthroughs.

There are core processes manually (normal bulk core box and molding material mixer) and mechanically (using core shooters - see core shooter ). The primary forming tools for this are core boxes, which are usually part of a foundry pattern facility.

Manual core manufacturing technology

In preparation, the mold surfaces of the core box are provided with a release agent. Depending on the casting geometry, one-piece or bulk core boxes, two-part or multi-part core boxes or half core boxes (if the mirror is the same) are used. For transport, as reinforcement and to guide the ventilation, core iron must be provided before the core molding material is filled . For larger cores, the core box is filled with model sand and backfill sand. After filling, the molding material is hardened . Since the hardening is promoted by free air access, the formwork of the cores should be done as early as possible. The cores are then processed by rubbing in radii and repairing damaged areas. Similar to the casting mold, the core surfaces that come into contact with the casting metal must be finished. After drying and checking, it is placed in the mold (core mark) and the attachment is closed.