The Typographic Hub

Metals for slug casting

18th September 2012

The metals for Linotype and Intertype machines were the same

The metals for Linotype and Intertype machines were the same. Their casting conditions demanded a fluid and mobile metal with a short freezing range. The metal was injected into the mould via a horizontal mouthpiece; after the slug had solidified metal remaining in the mouthpiece had to flow back freely. To get speed of casting the metal had to solidify quickly after entering the mould. Rapid solidification of the large body necessitated using an alloy that could be cast at comparatively low temperatures. These requirements meant using alloys close to the eutectic composition. The tin content could vary between 2.5% and 5%; the antimony not less than 11% or more than 12% otherwise there was difficulty in casting. There was a tendency for the antimony content to rise with repeated re-melting. The alloys most generally used were 3% tin, 11% antimony 86% lead, and 4% tin, 11% antimony, 85% lead. The higher tin content of the second specification helped towards a finer face on the slug. The casting condition of slug machines necessitated using an alloy that was not so hard as other metals. Some compensation was obtained from the support provided by the long slug. For slugs that had to withstand the pressure of moulding, solidity was more important than the hardness of the metal.