Jacket-core
The core which forms the space betwixt inner and outer shells of a jacketed casting, as a jacketed cylinder, etc. Sometimes these shells are joined together by studs at intervals, in which case the core must invariably be made in one piece, and vented at the top through holes purposely made in the casting for this purpose, but which are subsequently plugged. If a convenient branch, etc., offers the opportunity for making adequate vent connections, the labor of plugging is saved.
When the shells are joined by parallel webs the jacket-core is divided into as many segments as there are webs, and each core is vented separately. In the former case a cage or skeleton core-iron serves to construct the core; the latter needs only a centre web with protruding wings. For constructing a whole jacket-core the dummy-block is a cheap and effective device; a narrow core-box is all that is necessary for the web-jacket. See DUMMY-BLOCK; SKELETON; CORE-IRON; VENTING.