Chapter 3:
Basic Components of a Slot Die

External Components

A slot die consists of key external parts that ensure structural integrity and precise operation:

1. Die Body: The main housing, typically made from stainless steel for rigidity and corrosion resistance. It includes an upper and lower body, with multilayer dies adding wedges for additional layers (e.g., one wedge for dual-layer, two for triple-layer). The body provides support and contains the internal flow paths.

2. Lip: The edges where fluid exits, controlling the coating interface with the substrate. Lips are precision-ground to ensure smooth extrusion.

3. Slot/Lip Gap: Located between the upper and lower lips, this gap determines coating thickness and must be precisely machined to avoid defects like streaking.

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​Additional external features include:

• Die Hinges: For opening the die during maintenance, allowing access without full disassembly.

• Body Offset Block and Shim: Adjust die position relative to the substrate for optimal alignment, influencing shear and bead stability.

• Feed Adapter: Connects to the fluid supply, ensuring seamless integration with pumps.

• Die Alignment Key: Ensures component alignment during assembly, preventing misalignment that could cause uneven coatings.

• Turning Bar: Guides the substrate for smooth movement, reducing tension variations.

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Internal Components

Internal parts manage fluid flow for uniform distribution:

1. Inlet: Entry point for the coating material, connected to the manifold via the throat. Design impacts initial flow rate.

2. Throat: Distributes fluid evenly across the die width, preventing pressure drops.

3. Lip Land: Ensures even flow and high-quality finishes; custom designs optimize for specific viscosities and reduce defects.

4. Manifold: The chamber that spreads fluid uniformly, available in shapes like T-shaped or coat-hanger for better distribution. Coat-hanger manifolds are preferred for wide coatings to minimize edge effects.

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Material and Maintenance Considerations

Components must be compatible with fluids to avoid corrosion—e.g., using Hastelloy for aggressive chemicals. Precision machining is vital for defect-free coatings, and regular cleaning prevents clogs from dried residues or particles. Understanding these parts is foundational for effective slot die operation, as misalignment or wear can lead to issues like non-uniform thickness.

Chapter 2: History of Slot Die Coating

Chapter 4: How Slot Dies Work