Ever wondered how those tough, cylindrical rolls in steel mills are made? The secret often lies in their casting moulds—and these aren’t one-size-fits-all. Let’s break down how a roll’s structure, purpose, and size all factor into crafting the perfect mould.

Part 1: Structure Matters Most—Integral vs. Composite Rolls

Let’s start with the basics: a roll’s structure. It’s like choosing between a solid wooden dowel and a layered cake—each needs a different “mould” to turn out right.

Integral rolls are the “solid dowel” of the bunch. From their thick middle (the roll body) to the narrower ends (roll necks), they’re made of a single material—think cast iron or cast steel. So, their moulds are straightforward: a single sand cavity that mirrors the roll’s shape.

• For cast iron rolls, simple green sand or resin self-hardening sand works. These sands set quickly and handle the moderate heat of molten iron.

• Cast steel rolls need tougher stuff. Their molten metal reaches 1500-1600°C, so moulds use high-heat-resistant sand (like zircon) to avoid melting or sticking.

These moulds focus on two things: staying rigid enough to resist the molten metal’s pressure and having a simple “feeding” system (gates and risers) to fill in gaps as the metal cools.

Composite rolls are the “layered cake” version. They have a hard, wear-resistant outer layer (say, high-chromium cast iron) and a tough, shock-absorbing core (like ductile iron). This means double the mould work:

• First, the outer layer is cast in a spinning metal mould (called a centrifugal mould). It spins super fast (1000-3000rpm) to ensure the molten metal spreads evenly, creating a smooth, uniform layer.

• Once that cools, the core is poured into a second mould—this time, the already-cooled outer layer acts like a built-in “wall” to contain the core metal. The two moulds fit snugly (gap ≤1mm) to prevent leaks.

The key takeaway? Integral rolls need one sturdy sand mould, while composites need a dynamic duo of spinning and static moulds. Structure sets the stage for everything else.