. American foundry practice . he four handles of the bottom plate. When ram-ming this sand, care must be used, as it is not like rammingVi]) a plain vertical loam mould. The pounding of the ram-mer should be lighter the higher up it is used ; in fact, theupper parts do not require hard ramming. The lower part of the mould should be rammed solid andhard, as there is considerable strain there ; but for the top,if the sand is firmly tramped and the plate solidly beddeddown, it will require but very light ramming. For running kettles moulded in this way a num])er ofsmall grates are in general set
. American foundry practice . he four handles of the bottom plate. When ram-ming this sand, care must be used, as it is not like rammingVi]) a plain vertical loam mould. The pounding of the ram-mer should be lighter the higher up it is used ; in fact, theupper parts do not require hard ramming. The lower part of the mould should be rammed solid andhard, as there is considerable strain there ; but for the top,if the sand is firmly tramped and the plate solidly beddeddown, it will require but very light ramming. For running kettles moulded in this way a num])er ofsmall grates are in general set around the top, one beingshown at E. If run from the bottom, such castings arelikely not to be solid, because the iron gets dull before itreaches the top, and also because the dirt has a betterchance to gather in lumps or streaks, thereby makingspongy iron. Even when the casting is poured from the • top there will be more or less dirt, but it will not be so bad ? as when run from the bottom. MOULDING KETTLES IN^ LOAM- 151. r — ? • ? /.i nKVICE FOE MOULDING KETTLES IN LOAM, 152 LOAM MOULDING. It is very important in casting kettles to properly carry offthe vent from the inside of the core. Not many years ago an accident happened to a moulder,an acquaintance of the author, that came near costing himhis life and setting fire to the shop, by the blowing up of themould when being cast. When the mould was nearly fullof iron, there was an explosion that threw out the most ofthe iron in the mould. The trouble was in making no pro-vision for vent except one small tube or pipe, and the mouldbeing poured fast, gas was generated rapidly, producingwhat is sometimes called fire-damj). There being only onepipe and lighted with shavings, the gas took fire, and runningdownwards to the gas inside the brick mould, it instantlyexploded. In moulds that have a confined air space, when the gas ofthe mould is driven by the heat of the melted iron it exertsa pressure. This pressure, if given a go
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