Definition: Aluminum extrusion is a manufacturing process in which softened aluminum is forced through a shaped die, producing long, continuous mouldings or profiles with a consistent cross-sectional design. In picture framing, this method is used to create precision-shaped metal mouldings that can be cut and assembled into metal frames.

Overview

The extrusion process allows manufacturers to form aluminum into precise, repeatable shapes with tight tolerances. The resulting profiles can include decorative face details, functional channels for glazing and backing, and internal grooves for mechanical joining hardware. This flexibility is what makes extruded aluminum the standard for metal frames in the framing industry.

Applications in Picture Framing

Metal Frame Profiles: Extruded aluminum is cut into sections to form flat top, rounded, or beveled metal frame styles.
Functional Channels: Integrated channels accommodate glazing, artwork, mats, and backing boards.
Joining Hardware: Internal slots created during extrusion accept hardware such as spring clips, corner brackets, and tension systems.
Surface Finishes: After extrusion, profiles can be anodized, powder-coated, or painted to produce different aesthetic and protective finishes.

Manufacturing Process

Billet Preparation: Solid aluminum billets are preheated to a workable temperature.
Extrusion: The softened billet is pressed through a steel die shaped to the frame profile.
Cooling: The continuous length is cooled with air or water spray.
Stretching and Straightening: The extrusion is stretched to remove twists or warping.
Cutting: Long lengths are cut into stock sizes (commonly 6-12 feet for framing manufacturers).
Finishing: The extrusions are anodized or coated to improve durability and appearance.

Conservation and Archival Considerations

Extruded aluminum mouldings are generally considered dimensionally stable and resistant to warping. However, direct contact between raw aluminum and artwork is avoided in conservation practice, as aluminum can corrode or transfer metallic residues over time. Proper finishing and isolation layers (such as anodization or protective liners) are standard for professional use.

Comparison with Other Methods

Extruded Aluminum vs. Rolled Steel: Steel frames are stronger but heavier and prone to rust, while extruded aluminum is lighter, non-rusting, and easier to fabricate.
Extruded Aluminum vs. Wood Moulding: Wood offers traditional aesthetic variety, while aluminum excels in precision and modern, minimalist design.
Extruded vs. Cast Aluminum: Extrusion provides tighter tolerances and uniform shapes, whereas casting allows for thicker, heavier parts but with less dimensional precision.

Common Misconceptions

"Extruded aluminum frames are fragile." While lightweight, properly extruded aluminum profiles are strong enough to hold large-scale works when paired with appropriate hardware.
"All extrusions look the same." Extrusion dies can produce a wide variety of shapes, profiles, and decorative treatments, making aluminum frames versatile in both design and function.

Aluminum Extrusion