page_title: Linotype machine
section_title: Mold disk and crucible
hierarchical_section_title: Linotype machine / Design / Casting section / Mold disk and crucible
caption_attribution_description: Linotype mold disk, with a complete line of matrices and spacebands ready to be cast
context_page_description: The Linotype machine was a "line casting" machine used in printing sold by the Mergenthaler Linotype Company and related companies. It was a hot metal typesetting system that cast blocks of metal type for individual uses. Linotype became one of the mainstay methods to set type, especially small-size body text, for newspapers, magazines, and posters from the late 19th century to the 1970s and 1980s, when it was largely replaced by phototypesetting and computer typesetting. The name of the machine comes from the fact that it produces an entire line of metal type at once, hence a line-o'-type, a significant improvement over the previous industry standard, i.e., manual, letter-by-letter typesetting using a composing stick and shallow subdivided trays, called "cases".
  The linotype machine operator enters text on a 90-character keyboard. The machine assembles matrices, which are molds for the letter forms, in a line. The assembled line is then cast as a single piece, called a slug, from molten type metal in a process known as hot metal typesetting. The matrices are then returned to the type magazine from which they came, to be reused later.
context_section_description: The justification vise holds the assembled line against the face of the mold disk. The mold disk has rectangular openings which correspond to the line length and point thickness of the slugs (cast lines) to be made. Mold liners fit into these openings for specific slug dimensions. The maximum line length of the typical linecaster is 30 picas. A less common variant was fitted with 42 pica molds, though these are now rare to non-existent.
  Directly behind the mold disk is the crucible, which contains molten type metal at an optimal 535°. At the moment before casting, the mold disk moves forward on its slide. Studs in the mold disc engage with blocks on the vise so that the mold disc seats gently, yet tightly and squarely against the line of matrices held in the first elevator jaws and between the vise jaws. The vise jaws compress the line of matrices so molten metal is prevented from squeezing between the mats on cast. The crucible tilts forward, forcing the mouthpiece tightly against the back of the mold. The plunger in the well of the crucible quickly descends, forcing the molten metal up the crucible throat and injecting it into the mold cavity through the array of orifices in the mouthpiece. The jets of molten metal first contact against the casting face of the matrices, and then fills the mold cavity to provide a solid slug body. These have character shapes punched into them, so the result is a cast slug with the character shapes of the line on its top face. The mold disk is sometimes water-cooled, and often air-cooled with a blower, to carry away the heat of the molten type metal and allow the cast slugs to solidify quickly.
  When casting is complete, the plunger is drawn upward, pulling the metal back down the throat from the mouthpiece. The pot pulls backward away from the mold. The mold disk retracts from the vise studs which held it in perfect relation to the mold, thus breaking the slug away from the matrices. The mold disc then rotates counter-clockwise. In its travel, the slug base is trimmed by the back knife for height to paper (.918") and then returns to its neutral position in front of the ejector blades  and aligned with the knife block assembly a pair of honed knives with a fixed knife, and a knife which is set to the point thickness of the mold liners being cast with. The knives are set to dead parallel. The fixed knife on the left bears against the smooth side of the slug (the mold body face of the slug) as it brushes next to it, and the right knife trims the ribs on the slug (the mold cap face of the slug). The disk stops when the mold is vertical, on the right, directly in front of the ejector.
  The ejector is a stacked series of narrow blades that push the completed slug from the mold aperture in the mold disk. The blades are narrow enough to pass through a mold set to 6-points in thickness with .004" clearance between the fixed mold face and the left side of the blades. The blades are each 2 picas in width and the number of blades engaged on ejection are set based on the line length being cast. All blades are engaged for a 30 pica slug, fewer are engaged as the measure of the slug body is narrowed by the use of progressively longer mold liners. This prevents the ejector blades from striking the back of a mold liner on narrow slugs. As the slug is pushed from the mold, the slug passes a set of knife edges in the knife block, which trims off any small irregularities in the casting and produces a slug of exactly the desired point thickness. From there, the slug drops into the galley tray which holds the lines in the order in which they were cast.
caption: Linotype mold disk, with a complete line of matrices and spacebands ready to be cast
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