Ramming

Ramming refers to the compaction of granular materials (mold materials, but also refractory masses) using a ramming tool.

In hand or floor molding (open sand molding), bentonite-bonded or oil-bound mold sands (see Green sand mold, O.B.B. sand, Green sand molding process) are mainly compacted by hand ramming. The compaction by ramming should be as even as possible which is difficult to achieve with hand molding. Depending on the mold box height, several layers of mold sand are rammed onto each other. The following properties of the compacted mold must be ensured:

1. The mold must be sufficiently compacted and withstand the casting pressure, it must not change due to casting or solidification. In particular, swelling due to insufficient or uneven compaction needs to be avoided (Fig. 1).

2. The mold must have sufficient gas permeability so gases generated during casting can escape. A common method in hand molding is to create additional air holes (venting) by piercing.

For obtaining optimum compaction, different ramming tools are available to the molder for manual mold making. Pegging rammers and flat rammers (see Hand rammer) are used for small molds, and pneumatic rammers are used for large molds.

  • Fig. 1: 1: Correct compaction of mold material, casting is dimensionally accurate;2: Uneven or insufficient compaction: casting is “swollen”
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