Creation of a Practice Guide for Flat Glass Manufacturers

Creation of a Practice Guide for Flat Glass Manufacturers

Project Summary

The UK window (flat) glass industry currently recycles approximately 10% of the estimated 500,000 tonnes of such glass entering the waste stream each year. The industry has the capacity to recycle more recovered glass (cullet), but is prohibited by the availability of good quality uncontaminated supplies. Contamination is a critical issue for all glass manufacturers as trace levels are sufficient to cause glass defects. The flat glass sector has particularly high optical quality requirements and a small number of defects can result in large production losses which can negate any advantage of recycling.

Currently no public specification exists for flat glass cullet used in flat glass manufacture nor is guidance given on its collection. Such guidance has been produced for container glass and has proven to be a useful tool. The main aim of this project was to help increase the volume of good quality flat cullet, by producing the following guidance documents:

  • A Specification for Flat Glass Cullet used in Flat Glass Manufacture
    This specification is a guide to the cullet processor as to the quality of cullet which will be acceptable to the glass manufacturer, subject to local agreement between both parties.
  • A good practice guide (GPG) for collection of flat glass for use in flat glass manufacture
    This good practice guide is aimed at window manufacturers who produce waste glass in the form of manufacturing off-cuts and rejected sealed units and who may also collect post consumer flat glass. The purpose of the guide is to explain the contamination issues and give advice on which glass types are permitted within the clear and mixed cullet streams. The guide also sets out good practice for collection, storage and transportation of recovered flat glass.

Both documents were produced following consultation with the UK flat glass manufacturers and cullet processors who attended steering group meetings throughout the project. Each glass manufacture provided their cullet specification for review and visits were made to the processors and glass manufacturers to discuss current practice and issues.

Samples were collected at each site to assess the quality of cullet currently available, and to assess the practicality of regular sampling as a method to assure quality. The samples taken subjected to a range of testing including: moisture, organic content, particle size, tinted glass, contamination and chemical composition. The data from this exercise in conjunction with the manufacturers own specifications were then used to produce the guide cullet specification.

The guide recognises the inherent difficulties in obtaining a representative sample from unprocessed flat glass waste. It concludes that, due to the nature of the material and the physical difficulties and time involved, standard sampling methods do not offer a practical basis on which to operate a routine quality control regime


GTS would like to thank all organisations that assisted with the production of this report and associated documents.

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