Glass Cullet Metal Removal: Managing Caps and Closures
In a May 13, 2026 position paper, the European Container Glass Federation (FEVE) emphasized the importance of improving cullet quality and supporting stable markets for recycled glass. The message is relevant well beyond Europe: collecting more bottles is useful only when processors can turn the incoming material into cullet that meets a buyer's specifications.
One persistent obstacle is metal. Used bottles and mixed glass streams may contain steel crown caps, aluminum screw closures, rings and other fragments. These items are not glass, and they should be treated as a separate contamination problem before cullet is supplied for remelting.
Identify the Metal in Incoming Glass
The challenge changes with the source of the feed. Source-separated bottle glass may carry closures that were not removed during collection. Glass recovered from mixed recycling can also contain loose steel fragments, aluminum pieces, paper and plastic. Crushing makes the material easier to handle, but can create small metal pieces that are harder to detect and separate.
Operators should distinguish magnetic steel from conductive non-ferrous metals, then measure the size distribution of both contaminants. It also matters whether closures are free or still attached to bottle necks. Separation equipment cannot reliably remove a metal piece that is physically trapped inside a larger composite object without suitable preparation.
Remove Steel with Magnetic Separation
A magnetic separator can extract ferromagnetic steel closures and iron fragments from a suitably presented glass stream. This is a practical first metal-removal stage because steel can be captured without relying on the appearance or color of the surrounding glass.
However, capture depends on installation distance, material depth and particle size. Fine steel buried beneath a deep bed of cullet may be harder to remove. Wet residue and abrasive glass can also affect equipment selection, cleaning intervals and wear. Magnetic separation does not remove aluminum screw caps, and not every stainless-steel fragment is strongly magnetic.
CurrenTek lists glass recycling among the applications for its magnetic separation equipment. The correct arrangement should be selected from representative feed samples rather than a universal removal percentage.
Recover Aluminum Closures with Eddy Currents
After ferrous removal, an eddy current separator can target exposed conductive non-ferrous pieces, including suitable aluminum caps and fragments. Its rapidly changing magnetic field induces currents in conductive material, changing the discharge trajectory relative to many non-conductive glass particles.
This is not optical glass sorting. An eddy current separator does not identify glass color, remove ceramic fragments by appearance, or determine aluminum alloy grade. Thin closure fragments, very small particles, uneven feeding and attached materials may all complicate the separation. The discharge split and feed presentation should be tested on the actual cullet fraction.
Where size variation is extreme, screening or other preparation may be useful, but adding a trommel is not automatically necessary for every glass plant. Abrasive fines and the risk of losing saleable cullet into metal rejects must be considered.
Verify Cullet Quality and Reject Losses
A February 20, 2026 article from the Glass Manufacturing Industry Council identified ferrous and non-ferrous metals among the contaminants that can undermine cullet quality. Its discussion of furnace risks concerns glass manufacturing generally; it is not a test of CurrenTek equipment.
A plant trial should therefore measure residual steel and aluminum in the glass product, glass carried into metal rejects, feed stability and maintenance requirements. Sampling should cover changes in collection source and moisture rather than one carefully prepared batch.
Removing metal addresses only part of the quality specification. Ceramics, heat-resistant glass, organics and color mixing may require other processes. The practical value of a staged metal-removal system is cleaner, more consistent cullet and fewer avoidable losses, with results demonstrated against the buyer's requirements.