Drain Sow Molds Explained: Purpose, Design Features and How to Specify the Right One

Drain sow molds are a specialised subset of sow molds, designed specifically to receive and solidify the residual aluminium metal drained from a furnace during relining, maintenance, or alloy changeover operations.

While standard sow molds are used in the continuous casting cycle, drain sow molds serve a different function — capturing an irregular, often high-volume pour in a controlled and safe manner.

Why Drain Sow Molds Are a Separate Category

When a furnace is drained, the operator has limited control over pour rate and metal temperature. The residual heel metal may have been sitting at high temperature for an extended period, and the drain rate is determined by the furnace geometry rather than a controlled launder system.

This creates different demands on the mold:

• Higher thermal shock — the mold may receive a high-temperature metal pour with little or no pre-heating time
• Larger volume per event — a single furnace drain may fill multiple large-format molds in rapid succession
• Irregular use pattern — drain sow molds may sit unused for weeks between furnace maintenance cycles, then be pressed into service with minimal preparation time

Standard casting sow molds are optimised for a consistent, repeatable cycle. Drain sow molds must tolerate an irregular and more demanding thermal event.

Key Design Features

Large Format Capacity

Drain sow molds are typically manufactured in larger capacities than standard sow molds — commonly 500 kg, 750 kg, or 1,000 kg per mold — to minimise the number of molds required to receive a full furnace heel.

Heavier Wall Section

To absorb the higher thermal mass of a large, rapid pour, drain sow molds use thicker wall sections than equivalent standard sow molds. This slows heat transfer to the mold body and reduces peak thermal stress.

Robust Flange and Lifting Lug Design

Drain sow molds need to be positioned quickly and must be safe to move when partially or fully loaded. Lifting lug design and flange integrity are critical safety specifications.

Material Recommendation

Ductile iron is strongly recommended over grey iron for drain sow molds due to the impact and thermal shock conditions involved. Alloy steel is used in the most demanding applications.

Sizing and Specification: What Information You Need

When specifying drain sow molds, the key inputs are:

• Maximum furnace heel volume — determines minimum total mold capacity required
• Drain rate — faster drains require more molds to be positioned in advance
• Metal temperature at drain — higher temperatures require heavier wall sections
• Handling equipment available — crane capacity and bay geometry determine maximum single mold weight

SMI manufactures drain sow molds to customer-specific dimensions. Standard and custom capacities from 200 kg to 1,200 kg per mold are available in grey iron, ductile iron, and alloy steel.

Contact our engineering team for sizing support and a quotation based on your furnace specifications.